01807nas a2200181 4500008004100000022001400041245003600055210003500091260001400126490000600140520134200146100001501488700002301503700001701526700002401543700002101567856003701588 2024 eng d a2691-339900aClifford-Deformed Surface Codes0 aCliffordDeformed Surface Codes c3/19/20240 v53 a

Various realizations of Kitaev's surface code perform surprisingly well for biased Pauli noise. Attracted by these potential gains, we study the performance of Clifford-deformed surface codes (CDSCs) obtained from the surface code by applying single-qubit Clifford operators. We first analyze CDSCs on the 3×3 square lattice and find that, depending on the noise bias, their logical error rates can differ by orders of magnitude. To explain the observed behavior, we introduce the effective distance d′, which reduces to the standard distance for unbiased noise. To study CDSC performance in the thermodynamic limit, we focus on random CDSCs. Using the statistical mechanical mapping for quantum codes, we uncover a phase diagram that describes random CDSC families with 50% threshold at infinite bias. In the high-threshold region, we further demonstrate that typical code realizations outperform the thresholds and subthreshold logical error rates, at finite bias, of the best-known translationally invariant codes. We demonstrate the practical relevance of these random CDSC families by constructing a translation-invariant CDSC belonging to a high-performance random CDSC family. We also show that our translation-invariant CDSC outperforms well-known translation-invariant CDSCs such as the XZZX and XY codes.

1 aDua, Arpit1 aKubica, Aleksander1 aJiang, Liang1 aFlammia, Steven, T.1 aGullans, Michael uhttps://arxiv.org/abs/2201.0780202447nas a2200169 4500008004100000245005000041210004900091260001300140520194800153100002002101700003302121700002102154700002802175700001702203700002002220856003702240 2024 eng d00aComplexity-constrained quantum thermodynamics0 aComplexityconstrained quantum thermodynamics c3/7/20243 a

Quantum complexity measures the difficulty of realizing a quantum process, such as preparing a state or implementing a unitary. We present an approach to quantifying the thermodynamic resources required to implement a process if the process's complexity is restricted. We focus on the prototypical task of information erasure, or Landauer erasure, wherein an n-qubit memory is reset to the all-zero state. We show that the minimum thermodynamic work required to reset an arbitrary state, via a complexity-constrained process, is quantified by the state's complexity entropy. The complexity entropy therefore quantifies a trade-off between the work cost and complexity cost of resetting a state. If the qubits have a nontrivial (but product) Hamiltonian, the optimal work cost is determined by the complexity relative entropy. The complexity entropy quantifies the amount of randomness a system appears to have to a computationally limited observer. Similarly, the complexity relative entropy quantifies such an observer's ability to distinguish two states. We prove elementary properties of the complexity (relative) entropy and determine the complexity entropy's behavior under random circuits. Also, we identify information-theoretic applications of the complexity entropy. The complexity entropy quantifies the resources required for data compression if the compression algorithm must use a restricted number of gates. We further introduce a complexity conditional entropy, which arises naturally in a complexity-constrained variant of information-theoretic decoupling. Assuming that this entropy obeys a conjectured chain rule, we show that the entropy bounds the number of qubits that one can decouple from a reference system, as judged by a computationally bounded referee. Overall, our framework extends the resource-theoretic approach to thermodynamics to integrate a notion of time, as quantified by complexity.

1 aMunson, Anthony1 aKothakonda, Naga, Bhavya Tej1 aHaferkamp, Jonas1 aHalpern, Nicole, Yunger1 aEisert, Jens1 aFaist, Philippe uhttps://arxiv.org/abs/2403.0482802447nas a2200169 4500008004100000245005000041210004900091260001300140520194800153100002002101700003302121700002102154700002802175700001702203700002002220856003702240 2024 eng d00aComplexity-constrained quantum thermodynamics0 aComplexityconstrained quantum thermodynamics c3/7/20243 a

Quantum complexity measures the difficulty of realizing a quantum process, such as preparing a state or implementing a unitary. We present an approach to quantifying the thermodynamic resources required to implement a process if the process's complexity is restricted. We focus on the prototypical task of information erasure, or Landauer erasure, wherein an n-qubit memory is reset to the all-zero state. We show that the minimum thermodynamic work required to reset an arbitrary state, via a complexity-constrained process, is quantified by the state's complexity entropy. The complexity entropy therefore quantifies a trade-off between the work cost and complexity cost of resetting a state. If the qubits have a nontrivial (but product) Hamiltonian, the optimal work cost is determined by the complexity relative entropy. The complexity entropy quantifies the amount of randomness a system appears to have to a computationally limited observer. Similarly, the complexity relative entropy quantifies such an observer's ability to distinguish two states. We prove elementary properties of the complexity (relative) entropy and determine the complexity entropy's behavior under random circuits. Also, we identify information-theoretic applications of the complexity entropy. The complexity entropy quantifies the resources required for data compression if the compression algorithm must use a restricted number of gates. We further introduce a complexity conditional entropy, which arises naturally in a complexity-constrained variant of information-theoretic decoupling. Assuming that this entropy obeys a conjectured chain rule, we show that the entropy bounds the number of qubits that one can decouple from a reference system, as judged by a computationally bounded referee. Overall, our framework extends the resource-theoretic approach to thermodynamics to integrate a notion of time, as quantified by complexity.

1 aMunson, Anthony1 aKothakonda, Naga, Bhavya Tej1 aHaferkamp, Jonas1 aHalpern, Nicole, Yunger1 aEisert, Jens1 aFaist, Philippe uhttps://arxiv.org/abs/2403.0482801355nas a2200181 4500008004100000245008400041210006900125260001400194520077500208100001800983700002301001700002401024700001601048700002401064700002501088700002301113856003701136 2024 eng d00aEfficiently verifiable quantum advantage on near-term analog quantum simulators0 aEfficiently verifiable quantum advantage on nearterm analog quan c3/13/20243 a

Existing schemes for demonstrating quantum computational advantage are subject to various practical restrictions, including the hardness of verification and challenges in experimental implementation. Meanwhile, analog quantum simulators have been realized in many experiments to study novel physics. In this work, we propose a quantum advantage protocol based on single-step Feynman-Kitaev verification of an analog quantum simulation, in which the verifier need only run an O(λ2)-time classical computation, and the prover need only prepare O(1) samples of a history state and perform O(λ2) single-qubit measurements, for a security parameter λ. We also propose a near-term feasible strategy for honest provers and discuss potential experimental realizations.

1 aLiu, Zhenning1 aDevulapalli, Dhruv1 aHangleiter, Dominik1 aLiu, Yi-Kai1 aKollár, Alicia, J.1 aGorshkov, Alexey, V.1 aChilds, Andrew, M. uhttps://arxiv.org/abs/2403.0819502367nas a2200181 4500008004100000022001400041245004800055210004800103260001400151300000900165490000600174520189200180100001802072700001802090700001802108700002002126856003902146 2024 eng d a2521-327X00aFast simulation of planar Clifford circuits0 aFast simulation of planar Clifford circuits c2/12/2024 a12510 v83 a

A general quantum circuit can be simulated classically in exponential time. If it has a planar layout, then a tensor-network contraction algorithm due to Markov and Shi has a runtime exponential in the square root of its size, or more generally exponential in the treewidth of the underlying graph. Separately, Gottesman and Knill showed that if all gates are restricted to be Clifford, then there is a polynomial time simulation. We combine these two ideas and show that treewidth and planarity can be exploited to improve Clifford circuit simulation. Our main result is a classical algorithm with runtime scaling asymptotically as nω/2<n1.19 which samples from the output distribution obtained by measuring all n qubits of a planar graph state in given Pauli bases. Here ω is the matrix multiplication exponent. We also provide a classical algorithm with the same asymptotic runtime which samples from the output distribution of any constant-depth Clifford circuit in a planar geometry. Our work improves known classical algorithms with cubic runtime. A key ingredient is a mapping which, given a tree decomposition of some graph G, produces a Clifford circuit with a structure that mirrors the tree decomposition and which emulates measurement of the corresponding graph state. We provide a classical simulation of this circuit with the runtime stated above for planar graphs and otherwise ntω−1 where t is the width of the tree decomposition. Our algorithm incorporates two subroutines which may be of independent interest. The first is a matrix-multiplication-time version of the Gottesman-Knill simulation of multi-qubit measurement on stabilizer states. The second is a new classical algorithm for solving symmetric linear systems over F2 in a planar geometry, extending previous works which only applied to non-singular linear systems in the analogous setting.

1 aGosset, David1 aGrier, Daniel1 aKerzner, Alex1 aSchaeffer, Luke uhttps://arxiv.org/abs/2009.03218v300787nas a2200121 4500008004100000245005500041210005200096260001300148520042900161100002000590700001800610856003700628 2024 eng d00aFree Quantum Codes from Twisted Unitary $t$-groups0 aFree Quantum Codes from Twisted Unitary tgroups c2/2/20243 a

We introduce twisted unitary t-groups, a generalization of unitary t-groups under a twisting by an irreducible representation. We then apply representation theoretic methods to the Knill-Laflamme error correction conditions to show that twisted unitary t-groups automatically correspond to quantum codes with distance d=t+1. By construction these codes have many transversal gates, which are naturally fault tolerant.

1 aKubischta, Eric1 aTeixeira, Ian uhttps://arxiv.org/abs/2402.0163801285nas a2200121 4500008004100000245009700041210006900138260001400207520087200221100001901093700001401112856003701126 2024 eng d00aA Quantum "Lifting Theorem" for Constructions of Pseudorandom Generators from Random Oracles0 aQuantum Lifting Theorem for Constructions of Pseudorandom Genera c1/30/20243 a

We study the (quantum) security of pseudorandom generators (PRGs) constructed from random oracles. We prove a "lifting theorem" showing, roughly, that if such a PRG is unconditionally secure against classical adversaries making polynomially many queries to the random oracle, then it is also (unconditionally) secure against quantum adversaries in the same sense. As a result of independent interest, we also show that any pseudo-deterministic quantum-oracle algorithm (i.e., a quantum algorithm that with high probability returns the same value on repeated executions) can be simulated by a computationally unbounded but query bounded classical-oracle algorithm with only a polynomial blowup in the number of queries. This implies as a corollary that our lifting theorem holds even for PRGs that themselves make quantum queries to the random oracle.

1 aKatz, Jonathan1 aSela, Ben uhttps://arxiv.org/abs/2401.1431901538nas a2200169 4500008004100000022001400041245006400055210006400119260001400183300000900197490000600206520105300212100002201265700002401287700002001311856003701331 2024 eng d a2521-327X00aRandomized measurement protocols for lattice gauge theories0 aRandomized measurement protocols for lattice gauge theories c3/20/2024 a13000 v83 a

Randomized measurement protocols, including classical shadows, entanglement tomography, and randomized benchmarking are powerful techniques to estimate observables, perform state tomography, or extract the entanglement properties of quantum states. While unraveling the intricate structure of quantum states is generally difficult and resource-intensive, quantum systems in nature are often tightly constrained by symmetries. This can be leveraged by the symmetry-conscious randomized measurement schemes we propose, yielding clear advantages over symmetry-blind randomization such as reducing measurement costs, enabling symmetry-based error mitigation in experiments, allowing differentiated measurement of (lattice) gauge theory entanglement structure, and, potentially, the verification of topologically ordered states in existing and near-term experiments. Crucially, unlike symmetry-blind randomized measurement protocols, these latter tasks can be performed without relearning symmetries via full reconstruction of the density matrix.

1 aBringewatt, Jacob1 aKunjummen, Jonathan1 aMueller, Niklas uhttps://arxiv.org/abs/2303.1551902111nas a2200133 4500008004100000245009200041210006900133260001300202520166000215100002001875700002201895700002301917856003701940 2024 eng d00aScattering wave packets of hadrons in gauge theories: Preparation on a quantum computer0 aScattering wave packets of hadrons in gauge theories Preparation c2/1/20243 a

Quantum simulation holds promise of enabling a complete description of high-energy scattering processes rooted in gauge theories of the Standard Model. A first step in such simulations is preparation of interacting hadronic wave packets. To create the wave packets, one typically resorts to adiabatic evolution to bridge between wave packets in the free theory and those in the interacting theory, rendering the simulation resource intensive. In this work, we construct a wave-packet creation operator directly in the interacting theory to circumvent adiabatic evolution, taking advantage of resource-efficient schemes for ground-state preparation, such as variational quantum eigensolvers. By means of an ansatz for bound mesonic excitations in confining gauge theories, which is subsequently optimized using classical or quantum methods, we show that interacting mesonic wave packets can be created efficiently and accurately using digital quantum algorithms that we develop. Specifically, we obtain high-fidelity mesonic wave packets in the Z2 and U(1) lattice gauge theories coupled to fermionic matter in 1+1 dimensions. Our method is applicable to both perturbative and non-perturbative regimes of couplings. The wave-packet creation circuit for the case of the Z2 lattice gauge theory is built and implemented on the Quantinuum H1-1 trapped-ion quantum computer using 13 qubits and up to 308 entangling gates. The fidelities agree well with classical benchmark calculations after employing a simple symmetry-based noise-mitigation technique. This work serves as a step toward quantum computing scattering processes in quantum chromodynamics.

1 aDavoudi, Zohreh1 aHsieh, Chung-Chun1 aKadam, Saurabh, V. uhttps://arxiv.org/abs/2402.0084002266nas a2200265 4500008004100000245005900041210005900100260001400159520150200173100002901675700001801704700002501722700002001747700002501767700001901792700002001811700001201831700001601843700002201859700001301881700002401894700002001918700002501938856003701963 2024 eng d00aSimulating Meson Scattering on Spin Quantum Simulators0 aSimulating Meson Scattering on Spin Quantum Simulators c3/11/20243 a

Studying high-energy collisions of composite particles, such as hadrons and nuclei, is an outstanding goal for quantum simulators. However, preparation of hadronic wave packets has posed a significant challenge, due to the complexity of hadrons and the precise structure of wave packets. This has limited demonstrations of hadron scattering on quantum simulators to date. Observations of confinement and composite excitations in quantum spin systems have opened up the possibility to explore scattering dynamics in spin models. In this article, we develop two methods to create entangled spin states corresponding to wave packets of composite particles in analog quantum simulators of Ising spin Hamiltonians. One wave-packet preparation method uses the blockade effect enabled by beyond-nearest-neighbor Ising spin interactions. The other method utilizes a quantum-bus-mediated exchange, such as the native spin-phonon coupling in trapped-ion arrays. With a focus on trapped-ion simulators, we numerically benchmark both methods and show that high-fidelity wave packets can be achieved in near-term experiments. We numerically study scattering of wave packets for experimentally realizable parameters in the Ising model and find inelastic-scattering regimes, corresponding to particle production in the scattering event, with prominent and distinct experimental signals. Our proposal, therefore, demonstrates the potential of observing inelastic scattering in near-term quantum simulators.

1 aBennewitz, Elizabeth, R.1 aWare, Brayden1 aSchuckert, Alexander1 aLerose, Alessio1 aSurace, Federica, M.1 aBelyansky, Ron1 aMorong, William1 aLuo, De1 aDe, Arinjoy1 aCollins, Kate, S.1 aKatz, Or1 aMonroe, Christopher1 aDavoudi, Zohreh1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2403.0706101595nas a2200145 4500008004100000245005500041210005500096260001300151520116600164100002301330700002001353700002201373700001701395856003701412 2024 eng d00aTopology and entanglement of molecular phase space0 aTopology and entanglement of molecular phase space c3/7/20243 a

We formulate a quantum phase space for molecular rotational and nuclear-spin states. Taking in molecular geometry and nuclear-spin data, our framework yields admissible position and momentum states, inter-convertible via a generalized Fourier transform. We classify molecules into three types -- asymmetric, rotationally symmetric, and perrotationally symmetric -- with the last type having no macroscopic analogue due to nuclear-spin statistics constraints. We identify two features in perrotationally symmetric state spaces that are Hamiltonian-independent and induced solely by symmetry and spin statistics. First, many molecular species are intrinsically rotation-spin entangled in a way that cannot be broken without transitioning to another species or breaking symmetry. Second, each molecular position state houses an internal pseudo-spin or "fiber" degree of freedom, and the fiber's Berry phase or matrix after adiabatic changes in position yields naturally robust operations, akin to braiding anyonic quasiparticles or realizing fault-tolerant quantum gates. We outline scenarios where these features can be experimentally probed.

1 aAlbert, Victor, V.1 aKubischta, Eric1 aLemeshko, Mikhail1 aLiu, Lee, R. uhttps://arxiv.org/abs/2403.0457202465nas a2200517 4500008004100000245011600041210006900157260001400226520098200240100001701222700001701239700002501256700002001281700002401301700002201325700001601347700001901363700001901382700001801401700001901419700002001438700001901458700002101477700003101498700001801529700001901547700001601566700001601582700001601598700002001614700001901634700002101653700001901674700002201693700001801715700002401733700002301757700001801780700002001798700001801818700002301836700001901859700002001878700001201898856003701910 2023 eng d00aAccelerating Progress Towards Practical Quantum Advantage: The Quantum Technology Demonstration Project Roadmap0 aAccelerating Progress Towards Practical Quantum Advantage The Qu c3/20/20233 a

Quantum information science and technology (QIST) is a critical and emerging technology with the potential for enormous world impact and is currently invested in by over 40 nations. To bring these large-scale investments to fruition and bridge the lower technology readiness levels (TRLs) of fundamental research at universities to the high TRLs necessary to realize the promise of practical quantum advantage accessible to industry and the public, we present a roadmap for Quantum Technology Demonstration Projects (QTDPs). Such QTDPs, focused on intermediate TRLs, are large-scale public-private partnerships with a high probability of translation from laboratory to practice. They create technology demonstrating a clear 'quantum advantage' for science breakthroughs that are user-motivated and will provide access to a broad and diverse community of scientific users. Successful implementation of a program of QTDPs will have large positive economic impacts.

1 aAlsing, Paul1 aBattle, Phil1 aBienfang, Joshua, C.1 aBorders, Tammie1 aBrower-Thomas, Tina1 aCarr, Lincoln, D.1 aChong, Fred1 aDadras, Siamak1 aDeMarco, Brian1 aDeutsch, Ivan1 aFigueroa, Eden1 aFreedman, Danna1 aEveritt, Henry1 aGauthier, Daniel1 aJohnston-Halperin, Ezekiel1 aKim, Jungsang1 aKira, Mackillo1 aKumar, Prem1 aKwiat, Paul1 aLekki, John1 aLoiacono, Anjul1 aLončar, Marko1 aLowell, John, R.1 aLukin, Mikhail1 aMerzbacher, Celia1 aMiller, Aaron1 aMonroe, Christopher1 aPollanen, Johannes1 aPappas, David1 aRaymer, Michael1 aReano, Ronald1 aRodenburg, Brandon1 aSavage, Martin1 aSearles, Thomas1 aYe, Jun uhttps://arxiv.org/abs/2210.1475702420nas a2200157 4500008004100000245006400041210006400105260001500169520193300184100001702117700002802134700002502162700001602187700002202203856003702225 2023 eng d00aAccurate and Honest Approximation of Correlated Qubit Noise0 aAccurate and Honest Approximation of Correlated Qubit Noise c11/15/20233 a

Accurate modeling of noise in realistic quantum processors is critical for constructing fault-tolerant quantum computers. While a full simulation of actual noisy quantum circuits provides information about correlated noise among all qubits and is therefore accurate, it is, however, computationally expensive as it requires resources that grow exponentially with the number of qubits. In this paper, we propose an efficient systematic construction of approximate noise channels, where their accuracy can be enhanced by incorporating noise components with higher qubit-qubit correlation degree. To formulate such approximate channels, we first present a method, dubbed the cluster expansion approach, to decompose the Lindbladian generator of an actual Markovian noise channel into components based on interqubit correlation degree. We then generate a k-th order approximate noise channel by truncating the cluster expansion and incorporating noise components with correlations up to the k-th degree. We require that the approximate noise channels must be accurate and also "honest", i.e., the actual errors are not underestimated in our physical models. As an example application, we apply our method to model noise in a three-qubit quantum processor that stabilizes a [[2,0,0]] codeword, which is one of the four Bell states. We find that, for realistic noise strength typical for fixed-frequency superconducting qubits coupled via always-on static interactions, correlated noise beyond two-qubit correlation can significantly affect the code simulation accuracy. Since our approach provides a systematic noise characterization, it enables the potential for accurate, honest and scalable approximation to simulate large numbers of qubits from full modeling or experimental characterizations of small enough quantum subsystems, which are efficient but still retain essential noise features of the entire device.

1 aSetiawan, F.1 aGramolin, Alexander, V.1 aMatekole, Elisha, S.1 aKrovi, Hari1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2311.0930501846nas a2200337 4500008004100000245008100041210006900122260001500191520083900206100002401045700002201069700001801091700001801109700002001127700002301147700002301170700002301193700002301216700002301239700002101262700001801283700002201301700002401323700001701347700002501364700002101389700002301410700002101433700001701454856003701471 2023 eng d00aData Needs and Challenges of Quantum Dot Devices Automation: Workshop Report0 aData Needs and Challenges of Quantum Dot Devices Automation Work c12/21/20233 a

Gate-defined quantum dots are a promising candidate system to realize scalable, coupled qubit systems and serve as a fundamental building block for quantum computers. However, present-day quantum dot devices suffer from imperfections that must be accounted for, which hinders the characterization, tuning, and operation process. Moreover, with an increasing number of quantum dot qubits, the relevant parameter space grows sufficiently to make heuristic control infeasible. Thus, it is imperative that reliable and scalable autonomous tuning approaches are developed. In this report, we outline current challenges in automating quantum dot device tuning and operation with a particular focus on datasets, benchmarking, and standardization. We also present ideas put forward by the quantum dot community on how to overcome them.

1 aZwolak, Justyna, P.1 aTaylor, Jacob, M.1 aAndrews, Reed1 aBenson, Jared1 aBryant, Garnett1 aButerakos, Donovan1 aChatterjee, Anasua1 aSarma, Sankar, Das1 aEriksson, Mark, A.1 aGreplová, Eliška1 aGullans, Michael1 aHader, Fabian1 aKovach, Tyler, J.1 aMundada, Pranav, S.1 aRamsey, Mick1 aRasmussen, Torbjoern1 aSeverin, Brandon1 aSigillito, Anthony1 aUndseth, Brennan1 aWeber, Brian uhttps://arxiv.org/abs/2312.1432200422nas a2200133 4500008004100000245006200041210006100103260001400164490000800178100002400186700001900210700002200229856003700251 2023 eng d00aDecoherence from Long-Range Forces in Atom Interferometry0 aDecoherence from LongRange Forces in Atom Interferometry c3/17/20230 v1071 aKunjummen, Jonathan1 aCarney, Daniel1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2205.0300601726nas a2200253 4500008004100000022001400041245005000055210005000105260001500155490000600170520104100176100002201217700002201239700001801261700002101279700001601300700001301316700002901329700001801358700002401376700001901400700001601419856003701435 2023 eng d a2375-254800aDigital quantum simulation of NMR experiments0 aDigital quantum simulation of NMR experiments c11/29/20230 v93 a

Simulations of nuclear magnetic resonance (NMR) experiments can be an important tool for extracting information about molecular structure and optimizing experimental protocols but are often intractable on classical computers for large molecules such as proteins and for protocols such as zero-field NMR. We demonstrate the first quantum simulation of an NMR spectrum, computing the zero-field spectrum of the methyl group of acetonitrile using four qubits of a trapped-ion quantum computer. We reduce the sampling cost of the quantum simulation by an order of magnitude using compressed sensing techniques. We show how the intrinsic decoherence of NMR systems may enable the zero-field simulation of classically hard molecules on relatively near-term quantum hardware and discuss how the experimentally demonstrated quantum algorithm can be used to efficiently simulate scientifically and technologically relevant solid-state NMR experiments on more mature devices. Our work opens a practical application for quantum computation.

1 aSeetharam, Kushal1 aBiswas, Debopriyo1 aNoel, Crystal1 aRisinger, Andrew1 aZhu, Daiwei1 aKatz, Or1 aChattopadhyay, Sambuddha1 aCetina, Marko1 aMonroe, Christopher1 aDemler, Eugene1 aSels, Dries uhttps://arxiv.org/abs/2109.1329801506nas a2200157 4500008004100000245005800041210005700099260001400156520104400170100002001214700001801234700002101252700002001273700001801293856003701311 2023 eng d00aEffect of non-unital noise on random circuit sampling0 aEffect of nonunital noise on random circuit sampling c6/28/20233 a

In this work, drawing inspiration from the type of noise present in real hardware, we study the output distribution of random quantum circuits under practical non-unital noise sources with constant noise rates. We show that even in the presence of unital sources like the depolarizing channel, the distribution, under the combined noise channel, never resembles a maximally entropic distribution at any depth. To show this, we prove that the output distribution of such circuits never anticoncentrates — meaning it is never too "flat" — regardless of the depth of the circuit. This is in stark contrast to the behavior of noiseless random quantum circuits or those with only unital noise, both of which anticoncentrate at sufficiently large depths. As consequences, our results have interesting algorithmic implications on both the hardness and easiness of noisy random circuit sampling, since anticoncentration is a critical property exploited by both state-of-the-art classical hardness and easiness results.

1 aFefferman, Bill1 aGhosh, Soumik1 aGullans, Michael1 aKuroiwa, Kohdai1 aSharma, Kunal uhttps://arxiv.org/abs/2306.1665901881nas a2200193 4500008004100000245007300041210006900114260001400183490000600197520129800203100002001501700002201521700002101543700001601564700001801580700002401598700002801622856003701650 2023 eng d00aExperimental Observation of Thermalization with Noncommuting Charges0 aExperimental Observation of Thermalization with Noncommuting Cha c4/28/20230 v43 a

Quantum simulators have recently enabled experimental observations of quantum many-body systems' internal thermalization. Often, the global energy and particle number are conserved, and the system is prepared with a well-defined particle number - in a microcanonical subspace. However, quantum evolution can also conserve quantities, or charges, that fail to commute with each other. Noncommuting charges have recently emerged as a subfield at the intersection of quantum thermodynamics and quantum information. Until now, this subfield has remained theoretical. We initiate the experimental testing of its predictions, with a trapped-ion simulator. We prepare 6-21 spins in an approximate microcanonical subspace, a generalization of the microcanonical subspace for accommodating noncommuting charges, which cannot necessarily have well-defined nontrivial values simultaneously. We simulate a Heisenberg evolution using laser-induced entangling interactions and collective spin rotations. The noncommuting charges are the three spin components. We find that small subsystems equilibrate to near a recently predicted non-Abelian thermal state. This work bridges quantum many-body simulators to the quantum thermodynamics of noncommuting charges, whose predictions can now be tested.

1 aKranzl, Florian1 aLasek, Aleksander1 aJoshi, Manoj, K.1 aKalev, Amir1 aBlatt, Rainer1 aRoos, Christian, F.1 aHalpern, Nicole, Yunger uhttps://arxiv.org/abs/2202.0465200804nas a2200121 4500008004100000245006000041210005800101260001400159520043400173100002000607700001800627856003700645 2023 eng d00aA Family of Quantum Codes with Exotic Transversal Gates0 aFamily of Quantum Codes with Exotic Transversal Gates c5/11/20233 a

Recently it has been shown that the binary icosahedral group 2I together with a certain involution forms the most efficient single-qubit universal gate set. In order for this to be viable, one must construct a quantum code with transversal gate group 2I, however, no such code has ever been demonstrated explicitly. We fill this void by constructing a novel family of quantum codes that all have transversal gate group 2I.

1 aKubischta, Eric1 aTeixeira, Ian uhttps://arxiv.org/abs/2305.0702302121nas a2200181 4500008004100000245006900041210006800110260001400178520156100192100001901753700002201772700001901794700001901813700002401832700002501856700002101881856003701902 2023 eng d00aFault-tolerant hyperbolic Floquet quantum error correcting codes0 aFaulttolerant hyperbolic Floquet quantum error correcting codes c9/18/20233 a

A central goal in quantum error correction is to reduce the overhead of fault-tolerant quantum computing by increasing noise thresholds and reducing the number of physical qubits required to sustain a logical qubit. We introduce a potential path towards this goal based on a family of dynamically generated quantum error correcting codes that we call "hyperbolic Floquet codes." These codes are defined by a specific sequence of non-commuting two-body measurements arranged periodically in time that stabilize a topological code on a hyperbolic manifold with negative curvature. We focus on a family of lattices for n qubits that, according to our prescription that defines the code, provably achieve a finite encoding rate (1/8+2/n) and have a depth-3 syndrome extraction circuit. Similar to hyperbolic surface codes, the distance of the code at each time-step scales at most logarithmically in n. The family of lattices we choose indicates that this scaling is achievable in practice. We develop and benchmark an efficient matching-based decoder that provides evidence of a threshold near 0.1% in a phenomenological noise model. Utilizing weight-two check operators and a qubit connectivity of 3, one of our hyperbolic Floquet codes uses 400 physical qubits to encode 52 logical qubits with a code distance of 8, i.e., it is a [[400,52,8]] code. At small error rates, comparable logical error suppression to this code requires 5x as many physical qubits (1924) when using the honeycomb Floquet code with the same noise model and decoder.

1 aFahimniya, Ali1 aDehghani, Hossein1 aBharti, Kishor1 aMathew, Sheryl1 aKollár, Alicia, J.1 aGorshkov, Alexey, V.1 aGullans, Michael uhttps://arxiv.org/abs/2309.1003301740nas a2200145 4500008004100000245008100041210006900122260001400191520125300205100003001458700002401488700002301512700002201535856003701557 2023 eng d00aFeasibility of a trapped atom interferometer with accelerating optical traps0 aFeasibility of a trapped atom interferometer with accelerating o c8/23/20233 a

In order to increase the measured phase of an atom interferometer and improve its sensitivity, researchers attempt to increase the enclosed space-time area using two methods: creating larger separations between the interferometer arms and having longer evolution times. However, increasing the evolution time reduces the bandwidth that can be sampled, whereas decreasing the evolution time worsens the sensitivity. In this paper, we attempt to address this by proposing a setup for high-bandwidth applications, with improved overall sensitivity. This is realized by accelerating and holding the atoms using optical dipole traps. We find that accelerations of up to 103-105 m/s2 can be achieved using acousto-optic deflectors (AODs) to move the traps. By comparing the sensitivity of our approach to acceleration as a baseline to traditional atom interferometry, we find a substantial improvement to the state of the art. In the limit of appropriate beam and optics stabilization, sensitivities approaching 10−14 (m/s2)/Hz−−−√ may be achievable at 1 Hz, while detection at 1 kHz with a sensitivity an order of magnitude better than traditional free-fall atom interferometers is possible with today's systems.

1 aPremawardhana, Gayathrini1 aKunjummen, Jonathan1 aSubhankar, Sarthak1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2308.1224601778nas a2200157 4500008004100000245006400041210006300105260001400168520129800182100001301480700002201493700001901515700002401534700002501558856003701583 2023 eng d00aImproved Digital Quantum Simulation by Non-Unitary Channels0 aImproved Digital Quantum Simulation by NonUnitary Channels c7/24/20233 a

Simulating quantum systems is one of the most promising avenues to harness the computational power of quantum computers. However, hardware errors in noisy near-term devices remain a major obstacle for applications. Ideas based on the randomization of Suzuki-Trotter product formulas have been shown to be a powerful approach to reducing the errors of quantum simulation and lowering the gate count. In this paper, we study the performance of non-unitary simulation channels and consider the error structure of channels constructed from a weighted average of unitary circuits. We show that averaging over just a few simulation circuits can significantly reduce the Trotterization error for both single-step short-time and multi-step long-time simulations. We focus our analysis on two approaches for constructing circuit ensembles for averaging: (i) permuting the order of the terms in the Hamiltonian and (ii) applying a set of global symmetry transformations. We compare our analytical error bounds to empirical performance and show that empirical error reduction surpasses our analytical estimates in most cases. Finally, we test our method on an IonQ trapped-ion quantum computer accessed via the Amazon Braket cloud platform, and benchmark the performance of the averaging approach.

1 aGong, W.1 aKharkov, Yaroslav1 aTran, Minh, C.1 aBienias, Przemyslaw1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2307.1302801026nas a2200349 4500008004100000022001400041245006600055210006600121260001400187100002100201700002200222700002400244700001900268700001800287700001800305700001800323700001800341700002300359700002400382700002800406700002000434700001500454700001300469700002800482700002300510700002200533700002100555700002000576700002000596700002300616856003700639 2023 eng d a1476-468700aLogical quantum processor based on reconfigurable atom arrays0 aLogical quantum processor based on reconfigurable atom arrays c12/7/20231 aBluvstein, Dolev1 aEvered, Simon, J.1 aGeim, Alexandra, A.1 aLi, Sophie, H.1 aZhou, Hengyun1 aManovitz, Tom1 aEbadi, Sepehr1 aCain, Madelyn1 aKalinowski, Marcin1 aHangleiter, Dominik1 aAtaides, Pablo, Bonilla1 aMaskara, Nishad1 aCong, Iris1 aGao, Xun1 aRodriguez, Pedro, Sales1 aKarolyshyn, Thomas1 aSemeghini, Giulia1 aGullans, Michael1 aGreiner, Markus1 aVuletic, Vladan1 aLukin, Mikhail, D. uhttps://arxiv.org/abs/2312.0398202618nas a2200229 4500008004100000245007500041210006900116260001500185520193200200100001902132700002002151700002602171700001702197700001802214700001802232700002302250700002202273700001502295700001802310700002302328856003702351 2023 eng d00aMicrowave signal processing using an analog quantum reservoir computer0 aMicrowave signal processing using an analog quantum reservoir co c12/26/20233 a

Quantum reservoir computing (QRC) has been proposed as a paradigm for performing machine learning with quantum processors where the training is efficient in the number of required runs of the quantum processor and takes place in the classical domain, avoiding the issue of barren plateaus in parameterized-circuit quantum neural networks. It is natural to consider using a quantum processor based on superconducting circuits to classify microwave signals that are analog -- continuous in time. However, while theoretical proposals of analog QRC exist, to date QRC has been implemented using circuit-model quantum systems -- imposing a discretization of the incoming signal in time, with each time point input by executing a gate operation. In this paper we show how a quantum superconducting circuit comprising an oscillator coupled to a qubit can be used as an analog quantum reservoir for a variety of classification tasks, achieving high accuracy on all of them. Our quantum system was operated without artificially discretizing the input data, directly taking in microwave signals. Our work does not attempt to address the question of whether QRCs could provide a quantum computational advantage in classifying pre-recorded classical signals. However, beyond illustrating that sophisticated tasks can be performed with a modest-size quantum system and inexpensive training, our work opens up the possibility of achieving a different kind of advantage than a purely computational advantage: superconducting circuits can act as extremely sensitive detectors of microwave photons; our work demonstrates processing of ultra-low-power microwave signals in our superconducting circuit, and by combining sensitive detection with QRC processing within the same system, one could achieve a quantum sensing-computational advantage, i.e., an advantage in the overall analysis of microwave signals comprising just a few photons.

1 aSenanian, Alen1 aPrabhu, Sridhar1 aKremenetski, Vladimir1 aRoy, Saswata1 aCao, Yingkang1 aKline, Jeremy1 aOnodera, Tatsuhiro1 aWright, Logan, G.1 aWu, Xiaodi1 aFatemi, Valla1 aMcMahon, Peter, L. uhttps://arxiv.org/abs/2312.1616601518nas a2200169 4500008004100000245007200041210006900113260001300182520098500195100001901180700002501199700002201224700002101246700001601267700002801283856003701311 2023 eng d00aNoncommuting conserved charges in quantum thermodynamics and beyond0 aNoncommuting conserved charges in quantum thermodynamics and bey c9/7/20233 a

Thermodynamic systems typically conserve quantities ("charges") such as energy and particle number. The charges are often assumed implicitly to commute with each other. Yet quantum phenomena such as uncertainty relations rely on observables' failure to commute. How do noncommuting charges affect thermodynamic phenomena? This question, upon arising at the intersection of quantum information theory and thermodynamics, spread recently across many-body physics. Charges' noncommutation has been found to invalidate derivations of the thermal state's form, decrease entropy production, conflict with the eigenstate thermalization hypothesis, and more. This Perspective surveys key results in, opportunities for, and work adjacent to the quantum thermodynamics of noncommuting charges. Open problems include a conceptual puzzle: Evidence suggests that noncommuting charges may hinder thermalization in some ways while enhancing thermalization in others.

1 aMajidy, Shayan1 aBraasch, William, F.1 aLasek, Aleksander1 aUpadhyaya, Twesh1 aKalev, Amir1 aHalpern, Nicole, Yunger uhttps://arxiv.org/abs/2306.0005402080nas a2200193 4500008004100000245009100041210006900132260001500201520147600216100002501692700001301717700001401730700001901744700001601763700002101779700002501800700002401825856003701849 2023 eng d00aObservation of a finite-energy phase transition in a one-dimensional quantum simulator0 aObservation of a finiteenergy phase transition in a onedimension c10/30/20233 a

One of the most striking many-body phenomena in nature is the sudden change of macroscopic properties as the temperature or energy reaches a critical value. Such equilibrium transitions have been predicted and observed in two and three spatial dimensions, but have long been thought not to exist in one-dimensional (1D) systems. Fifty years ago, Dyson and Thouless pointed out that a phase transition in 1D can occur in the presence of long-range interactions, but an experimental realization has so far not been achieved due to the requirement to both prepare equilibrium states and realize sufficiently long-range interactions. Here we report on the first experimental demonstration of a finite-energy phase transition in 1D. We use the simple observation that finite-energy states can be prepared by time-evolving product initial states and letting them thermalize under the dynamics of a many-body Hamiltonian. By preparing initial states with different energies in a 1D trapped-ion quantum simulator, we study the finite-energy phase diagram of a long-range interacting quantum system. We observe a ferromagnetic equilibrium phase transition as well as a crossover from a low-energy polarized paramagnet to a high-energy unpolarized paramagnet in a system of up to 23 spins, in excellent agreement with numerical simulations. Our work demonstrates the ability of quantum simulators to realize and study previously inaccessible phases at finite energy density.

1 aSchuckert, Alexander1 aKatz, Or1 aFeng, Lei1 aCrane, Eleanor1 aDe, Arinjoy1 aHafezi, Mohammad1 aGorshkov, Alexey, V.1 aMonroe, Christopher uhttps://arxiv.org/abs/2310.1986901818nas a2200169 4500008004100000020002200041245005100063210005100114300001600165490000800181520131000189100002301499700002101522700002501543700002401568856005601592 2023 eng d a978-3-95977-263-100aQuantum Algorithms and the Power of Forgetting0 aQuantum Algorithms and the Power of Forgetting a37:1--37:220 v2513 a

The so-called welded tree problem provides an example of a black-box problem that can be solved exponentially faster by a quantum walk than by any classical algorithm [Andrew M. Childs et al., 2003]. Given the name of a special entrance vertex, a quantum walk can find another distinguished exit vertex using polynomially many queries, though without finding any particular path from entrance to exit. It has been an open problem for twenty years whether there is an efficient quantum algorithm for finding such a path, or if the path-finding problem is hard even for quantum computers. We show that a natural class of efficient quantum algorithms provably cannot find a path from entrance to exit. Specifically, we consider algorithms that, within each branch of their superposition, always store a set of vertex labels that form a connected subgraph including the entrance, and that only provide these vertex labels as inputs to the oracle. While this does not rule out the possibility of a quantum algorithm that efficiently finds a path, it is unclear how an algorithm could benefit by deviating from this behavior. Our no-go result suggests that, for some problems, quantum algorithms must necessarily forget the path they take to reach a solution in order to outperform classical computation.

1 aChilds, Andrew, M.1 aCoudron, Matthew1 aGilani, Amin, Shiraz1 aKalai, Yael, Tauman uhttps://drops.dagstuhl.de/opus/volltexte/2023/1754001590nas a2200217 4500008004100000245004000041210004000081260001400121520100000135100002101135700001601156700001501172700002201187700002001209700001901229700001901248700002101267700002201288700002501310856003701335 2023 eng d00aQuantum Sensing with Erasure Qubits0 aQuantum Sensing with Erasure Qubits c10/2/20233 a

The dominant noise in an "erasure qubit" is an erasure -- a type of error whose occurrence and location can be detected. Erasure qubits have potential to reduce the overhead associated with fault tolerance. To date, research on erasure qubits has primarily focused on quantum computing and quantum networking applications. Here, we consider the applicability of erasure qubits to quantum sensing and metrology. We show theoretically that, for the same level of noise, an erasure qubit acts as a more precise sensor or clock compared to its non-erasure counterpart. We experimentally demonstrate this by artificially injecting either erasure errors (in the form of atom loss) or dephasing errors into a differential optical lattice clock comparison, and observe enhanced precision in the case of erasure errors for the same injected error rate. Similar benefits of erasure qubits to sensing can be realized in other quantum platforms like Rydberg atoms and superconducting qubits

1 aNiroula, Pradeep1 aDolde, Jack1 aZheng, Xin1 aBringewatt, Jacob1 aEhrenberg, Adam1 aCox, Kevin, C.1 aThompson, Jeff1 aGullans, Michael1 aKolkowitz, Shimon1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2310.0151201207nas a2200181 4500008004100000022001400041245005100055210005000106260001300156300001400169490000600183520071300189100002500902700002000927700001800947700002300965856003700988 2023 eng d a2522-582000aQuantum Simulating Nature's Fundamental Fields0 aQuantum Simulating Natures Fundamental Fields c4/9/2024 a420–4320 v53 a

Simulating key static and dynamic properties of matter -- from creation in the Big Bang to evolution into sub-atomic and astrophysical environments -- arising from the underlying fundamental quantum fields of the Standard Model and their effective descriptions, lies beyond the capabilities of classical computation alone. Advances in quantum technologies have improved control over quantum entanglement and coherence to the point where robust simulations are anticipated to be possible in the foreseeable future. We discuss the emerging area of quantum simulations of Standard-Model physics, challenges that lie ahead, and opportunities for progress in the context of nuclear and high-energy physics.

1 aBauer, Christian, W.1 aDavoudi, Zohreh1 aKlco, Natalie1 aSavage, Martin, J. uhttps://arxiv.org/abs/2404.0629805435nas a2201621 4500008004100000245010800041210006900149260001500218520094500233100001801178700002301196700001601219700002801235700002001263700002001283700001601303700002001319700002101339700002401360700001901384700001901403700002601422700001801448700002301466700002101489700001601510700001701526700002101543700002301564700002101587700001601608700001701624700003101641700003401672700001801706700001801724700002101742700001801763700002401781700001801805700002001823700003501843700002201878700001601900700002001916700001901936700001701955700001901972700002301991700001802014700002402032700002302056700002302079700001802102700001702120700001902137700002602156700002002182700001902202700001902221700002302240700001802263700002202281700001802303700001902321700002802340700002402368700001902392700002002411700002002431700002702451700001202478700001702490700001502507700002102522700001802543700001902561700003202580700002402612700002202636700003102658700001702689700002302706700002402729700002002753700001902773700001902792700001602811700001702827700001802844700001802862700002002880700001902900700002302919700001902942700001702961700002602978700001603004700002003020700001603040700001803056700002803074700002103102700001803123700002403141700001403165700002303179700002003202700002103222700002003243700001803263700001803281700002103299700002103320700002303341700001803364700001803382700001403400700001903414700001603433700001503449700002003464700002103484700002103505700001703526700002803543700002203571700002303593700002603616700001503642700001703657700002303674700002403697700001803721700001703739700002003756856003703776 2023 eng d00aQuantum-centric Supercomputing for Materials Science: A Perspective on Challenges and Future Directions0 aQuantumcentric Supercomputing for Materials Science A Perspectiv c12/14/20233 a

Computational models are an essential tool for the design, characterization, and discovery of novel materials. Hard computational tasks in materials science stretch the limits of existing high-performance supercomputing centers, consuming much of their simulation, analysis, and data resources. Quantum computing, on the other hand, is an emerging technology with the potential to accelerate many of the computational tasks needed for materials science. In order to do that, the quantum technology must interact with conventional high-performance computing in several ways: approximate results validation, identification of hard problems, and synergies in quantum-centric supercomputing. In this paper, we provide a perspective on how quantum-centric supercomputing can help address critical computational problems in materials science, the challenges to face in order to solve representative use cases, and new suggested directions.

1 aAlexeev, Yuri1 aAmsler, Maximilian1 aBaity, Paul1 aBarroca, Marco, Antonio1 aBassini, Sanzio1 aBattelle, Torey1 aCamps, Daan1 aCasanova, David1 aChoi, Young, jai1 aChong, Frederic, T.1 aChung, Charles1 aCodella, Chris1 aCorcoles, Antonio, D.1 aCruise, James1 aDi Meglio, Alberto1 aDubois, Jonathan1 aDuran, Ivan1 aEckl, Thomas1 aEconomou, Sophia1 aEidenbenz, Stephan1 aElmegreen, Bruce1 aFare, Clyde1 aFaro, Ismael1 aFernández, Cristina, Sanz1 aFerreira, Rodrigo, Neumann Ba1 aFuji, Keisuke1 aFuller, Bryce1 aGagliardi, Laura1 aGalli, Giulia1 aGlick, Jennifer, R.1 aGobbi, Isacco1 aGokhale, Pranav1 aGonzalez, Salvador, de la Puen1 aGreiner, Johannes1 aGropp, Bill1 aGrossi, Michele1 aGull, Emmanuel1 aHealy, Burns1 aHuang, Benchen1 aHumble, Travis, S.1 aIto, Nobuyasu1 aIzmaylov, Artur, F.1 aJavadi-Abhari, Ali1 aJennewein, Douglas1 aJha, Shantenu1 aJiang, Liang1 aJones, Barbara1 ade Jong, Wibe, Albert1 aJurcevic, Petar1 aKirby, William1 aKister, Stefan1 aKitagawa, Masahiro1 aKlassen, Joel1 aKlymko, Katherine1 aKoh, Kwangwon1 aKondo, Masaaki1 aKurkcuoglu, Doga, Murat1 aKurowski, Krzysztof1 aLaino, Teodoro1 aLandfield, Ryan1 aLeininger, Matt1 aLeyton-Ortega, Vicente1 aLi, Ang1 aLin, Meifeng1 aLiu, Junyu1 aLorente, Nicolas1 aLuckow, Andre1 aMartiel, Simon1 aMartin-Fernandez, Francisco1 aMartonosi, Margaret1 aMarvinney, Claire1 aMedina, Arcesio, Castaneda1 aMerten, Dirk1 aMezzacapo, Antonio1 aMichielsen, Kristel1 aMitra, Abhishek1 aMittal, Tushar1 aMoon, Kyungsun1 aMoore, Joel1 aMotta, Mario1 aNa, Young-Hye1 aNam, Yunseong1 aNarang, Prineha1 aOhnishi, Yu-ya1 aOttaviani, Daniele1 aOtten, Matthew1 aPakin, Scott1 aPascuzzi, Vincent, R.1 aPenault, Ed1 aPiontek, Tomasz1 aPitera, Jed1 aRall, Patrick1 aRavi, Gokul, Subramania1 aRobertson, Niall1 aRossi, Matteo1 aRydlichowski, Piotr1 aRyu, Hoon1 aSamsonidze, Georgy1 aSato, Mitsuhisa1 aSaurabh, Nishant1 aSharma, Vidushi1 aSharma, Kunal1 aShin, Soyoung1 aSlessman, George1 aSteiner, Mathias1 aSitdikov, Iskandar1 aSuh, In-Saeng1 aSwitzer, Eric1 aTang, Wei1 aThompson, Joel1 aTodo, Synge1 aTran, Minh1 aTrenev, Dimitar1 aTrott, Christian1 aTseng, Huan-Hsin1 aTureci, Esin1 aValinas, David, García1 aVallecorsa, Sofia1 aWever, Christopher1 aWojciechowski, Konrad1 aWu, Xiaodi1 aYoo, Shinjae1 aYoshioka, Nobuyuki1 aYu, Victor, Wen-zhe1 aYunoki, Seiji1 aZhuk, Sergiy1 aZubarev, Dmitry uhttps://arxiv.org/abs/2312.0973301765nas a2200169 4500008004100000245008000041210006900121260001400190300001100204490000600215520126900221100001401490700001501504700001601519700002301535856003701558 2023 eng d00aQubit-Oscillator Concatenated Codes: Decoding Formalism and Code Comparison0 aQubitOscillator Concatenated Codes Decoding Formalism and Code C c6/14/2023 a0203420 v43 a

Concatenating bosonic error-correcting codes with qubit codes can substantially boost the error-correcting power of the original qubit codes. It is not clear how to concatenate optimally, given that there are several bosonic codes and concatenation schemes to choose from, including the recently discovered Gottesman-Kitaev-Preskill (GKP) – stabilizer codes [Phys. Rev. Lett. 125, 080503 (2020)] that allow protection of a logical bosonic mode from fluctuations of the conjugate variables of the mode. We develop efficient maximum-likelihood decoders for and analyze the performance of three different concatenations of codes taken from the following set: qubit stabilizer codes, analog or Gaussian stabilizer codes, GKP codes, and GKP-stabilizer codes. We benchmark decoder performance against additive Gaussian white noise, corroborating our numerics with analytical calculations. We observe that the concatenation involving GKP-stabilizer codes outperforms the more conventional concatenation of a qubit stabilizer code with a GKP code in some cases. We also propose a GKP-stabilizer code that suppresses fluctuations in both conjugate variables without extra quadrature squeezing and formulate qudit versions of GKP-stabilizer codes.

1 aXu, Yijia1 aWang, Yixu1 aKuo, En-Jui1 aAlbert, Victor, V. uhttps://arxiv.org/abs/2209.0457301560nas a2200181 4500008004100000245006500041210005800106260001500164520103400179100001701213700002101230700002201251700002301273700002001296700001801316700002301334856002101357 2023 eng d00aOn the Rational Degree of Boolean Functions and Applications0 aRational Degree of Boolean Functions and Applications c10/12/20233 a

We study a natural complexity measure of Boolean functions known as the (exact) rational degree. For total functions f, it is conjectured that rdeg(f) is polynomially related to deg(f), where deg(f) is the Fourier degree. Towards this conjecture, we show that symmetric functions have rational degree at least deg(f)/2 and monotone functions have rational degree at least deg(f)−−−−−√. We observe that both of these lower bounds are tight. In addition, we show that all read-once depth-d Boolean formulae have rational degree at least Ω(deg(f)1/d). Furthermore, we show that almost every Boolean function on n variables has rational degree at least n/2−O(n−−√).
In contrast to total functions, we exhibit partial functions that witness unbounded separations between rational and approximate degree, in both directions. As a consequence, we show that for quantum computers, post-selection and bounded-error are incomparable resources in the black-box model.

1 aIyer, Vishnu1 aJain, Siddhartha1 aKovacs-Deak, Matt1 aKumar, Vinayak, M.1 aSchaeffer, Luke1 aWang, Daochen1 aWhitmeyer, Michael uarXiv:2310.0800401441nas a2200193 4500008004100000245006200041210006200103260001300165520087300178100001601051700001901067700001501086700001701101700002501118700002001143700002701163700002001190856003701210 2023 eng d00aRealization of 1D Anyons with Arbitrary Statistical Phase0 aRealization of 1D Anyons with Arbitrary Statistical Phase c6/2/20233 a

Low-dimensional quantum systems can host anyons, particles with exchange statistics that are neither bosonic nor fermionic. Despite indications of a wealth of exotic phenomena, the physics of anyons in one dimension (1D) remains largely unexplored. Here, we realize Abelian anyons in 1D with arbitrary exchange statistics using ultracold atoms in an optical lattice, where we engineer the statistical phase via a density-dependent Peierls phase. We explore the dynamical behavior of two anyons undergoing quantum walks, and observe the anyonic Hanbury Brown-Twiss effect, as well as the formation of bound states without on-site interactions. Once interactions are introduced, we observe spatially asymmetric transport in contrast to the symmetric dynamics of bosons and fermions. Our work forms the foundation for exploring the many-body behavior of 1D anyons.

1 aKwan, Joyce1 aSegura, Perrin1 aLi, Yanfei1 aKim, Sooshin1 aGorshkov, Alexey, V.1 aEckardt, André1 aBakkali-Hassani, Brice1 aGreiner, Markus uhttps://arxiv.org/abs/2306.0173701610nas a2200157 4500008004100000245005000041210005000091260001300141490000800154520116900162100002401331700001901355700001901374700002201393856003701415 2023 eng d00aShadow process tomography of quantum channels0 aShadow process tomography of quantum channels c4/4/20230 v1073 a

Quantum process tomography is a critical capability for building quantum computers, enabling quantum networks, and understanding quantum sensors. Like quantum state tomography, the process tomography of an arbitrary quantum channel requires a number of measurements that scale exponentially in the number of quantum bits affected. However, the recent field of shadow tomography, applied to quantum states, has demonstrated the ability to extract key information about a state with only polynomially many measurements. In this work, we apply the concepts of shadow state tomography to the challenge of characterizing quantum processes. We make use of the Choi isomorphism to directly apply rigorous bounds from shadow state tomography to shadow process tomography, and we find additional bounds on the number of measurements that are unique to process tomography. Our results, which include algorithms for implementing shadow process tomography enable new techniques including evaluation of channel concatenation and the application of channels to shadows of quantum states. This provides a dramatic improvement for understanding large-scale quantum systems.

1 aKunjummen, Jonathan1 aTran, Minh, C.1 aCarney, Daniel1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2110.0362901491nas a2200181 4500008004100000245008400041210006900125260001400194520089300208100003001101700002701131700003001158700002101188700001801209700002401227700002101251856003701272 2023 eng d00aSpin-selective strong light-matter coupling in a 2D hole gas-microcavity system0 aSpinselective strong lightmatter coupling in a 2D hole gasmicroc c2/12/20233 a

The interplay between time-reversal symmetry breaking and strong light-matter coupling in 2D gases brings intriguing aspects to polariton physics. This combination can lead to polarization/spin selective light-matter interaction in the strong coupling regime. In this work, we report such a selective strong light-matter interaction by harnessing a 2D gas in the quantum Hall regime coupled to a microcavity. Specifically, we demonstrate circular-polarization dependence of the vacuum Rabi splitting, as a function of magnetic field and hole density. We provide a quantitative understanding of the phenomenon by modeling the coupling of optical transitions between Landau levels to the microcavity. This method introduces a control tool over the spin degree of freedom in polaritonic semiconductor systems, paving the way for new experimental possibilities in light-matter hybrids.

1 aSuarez-Forero, Daniel, G.1 aSession, Deric, Weston1 aMehrabad, Mahmoud, Jalali1 aKnuppel, Patrick1 aFaelt, Stefan1 aWegscheider, Werner1 aHafezi, Mohammad uhttps://arxiv.org/abs/2302.0602301439nas a2200169 4500008004100000245004200041210004000083260001300123520098600136100002301122700001901145700001501164700001901179700001501198700001901213856003701232 2023 eng d00aA Watermark for Large Language Models0 aWatermark for Large Language Models c6/6/20233 a

Potential harms of large language models can be mitigated by watermarking model output, i.e., embedding signals into generated text that are invisible to humans but algorithmically detectable from a short span of tokens. We propose a watermarking framework for proprietary language models. The watermark can be embedded with negligible impact on text quality, and can be detected using an efficient open-source algorithm without access to the language model API or parameters. The watermark works by selecting a randomized set of "green" tokens before a word is generated, and then softly promoting use of green tokens during sampling. We propose a statistical test for detecting the watermark with interpretable p-values, and derive an information-theoretic framework for analyzing the sensitivity of the watermark. We test the watermark using a multi-billion parameter model from the Open Pretrained Transformer (OPT) family, and discuss robustness and security.

1 aKirchenbauer, John1 aGeiping, Jonas1 aWen, Yuxin1 aKatz, Jonathan1 aMiers, Ian1 aGoldstein, Tom uhttps://arxiv.org/abs/2301.1022602721nas a2200253 4500008004100000245016100041210006900202260001400271300001100285490000600296520192600302100002002228700001502248700001802263700001902281700001802300700001902318700001602337700002102353700001402374700002202388700002002410856003702430 2022 eng d00aAccurate and Efficient Quantum Computations of Molecular Properties Using Daubechies Wavelet Molecular Orbitals: A Benchmark Study against Experimental Data0 aAccurate and Efficient Quantum Computations of Molecular Propert c5/28/2022 a0203600 v33 a

Although quantum computation (QC) is regarded as a promising numerical method for computational quantum chemistry, current applications of quantum-chemistry calculations on quantum computers are limited to small molecules. This limitation can be ascribed to technical problems in building and manipulating more qubits and the associated complicated operations of quantum gates in a quantum circuit when the size of the molecular system becomes large. As a result, reducing the number of required qubits is necessary to make QC practical. Currently, the minimal STO-3G basis set is commonly used in benchmark studies because it requires the minimum number of spin orbitals. Nonetheless, the accuracy of using STO-3G is generally low and thus cannot provide useful predictions. We propose to adopt Daubechies wavelet functions as an accurate and efficient method for QCs of molecular electronic properties. We demonstrate that a minimal basis set constructed from Daubechies wavelet basis can yield accurate results through a better description of the molecular Hamiltonian, while keeping the number of spin orbitals minimal. With the improved Hamiltonian through Daubechies wavelets, we calculate vibrational frequencies for H2 and LiH using quantum-computing algorithm to show that the results are in excellent agreement with experimental data. As a result, we achieve quantum calculations in which accuracy is comparable with that of the full configuration interaction calculation using the cc-pVDZ basis set, whereas the computational cost is the same as that of a STO-3G calculation. Thus, our work provides a more efficient and accurate representation of the molecular Hamiltonian for efficient QCs of molecular systems, and for the first time demonstrates that predictions in agreement with experimental measurements are possible to be achieved with quantum resources available in near-term quantum computers.

1 aHong, Cheng-Lin1 aTsai, Ting1 aChou, Jyh-Pin1 aChen, Peng-Jen1 aTsai, Pei-Kai1 aChen, Yu-Cheng1 aKuo, En-Jui1 aSrolovitz, David1 aHu, Alice1 aCheng, Yuan-Chung1 aGoan, Hsi-Sheng uhttps://arxiv.org/abs/2205.1447602524nas a2200193 4500008004100000245007700041210006900118260001400187520188800201653004302089653002702132653003102159653003302190100001602223700001602239700001902255700001902274856003702293 2022 eng d00aArline Benchmarks: Automated Benchmarking Platform for Quantum Compilers0 aArline Benchmarks Automated Benchmarking Platform for Quantum Co c3/28/20223 a

Efficient compilation of quantum algorithms is vital in the era of Noisy Intermediate-Scale Quantum (NISQ) devices. While multiple open-source quantum compilation and circuit optimization frameworks are available, e.g. IBM Qiskit, CQC Tket, Google Cirq, Rigetti Quilc, PyZX, their relative performance is not always clear to a quantum programmer. The growth of complexity and diversity of quantum circuit compilation algorithms creates a demand for a dedicated tool for cross-benchmarking and profiling of inner workflow of the quantum compilation stack. We present an open-source software package, Arline Benchmarks, that is designed to perform automated benchmarking of quantum compilers with the focus on NISQ applications. The name "Arline" was given in honour of Arline Greenbaum Feynman, the first wife of Richard Feynman, the pioneer of quantum computing. We compared several quantum compilation frameworks based on a set of important metrics such as post-optimization gate counts, circuit depth, hardware-dependent circuit cost function, compiler run time etc. with a detailed analysis of metrics for each compilation stage. We performed a variety of compiler tests for random circuits and structured quantum algorithms (VQE, Trotter decomposition, Grover search, Option Pricing via Amplitude Estimation) for several popular quantum hardware architectures. Leveraging cross-platform functionality of Arline, we propose a concept of composite compilation pipeline that combines compiler-specific circuit optimization subroutines in a single compilation stack and finds an optimized sequence of compilation passes. By providing detailed insights into the compilation flow of quantum compilers, Arline Benchmarks offers a valuable toolkit for quantum computing researchers and software developers to gain additional insights into compilers' characteristics.

10aFOS: Computer and information sciences10aFOS: Physical sciences10aQuantum Physics (quant-ph)10aSoftware Engineering (cs.SE)1 aKharkov, Y.1 aIvanova, A.1 aMikhantiev, E.1 aKotelnikov, A. uhttps://arxiv.org/abs/2202.1402501081nas a2200157 4500008004100000245004200041210004200083260001300125520065300138100001600791700001400807700002400821700002000845700002100865856003700886 2022 eng d00aBoson Sampling for Generalized Bosons0 aBoson Sampling for Generalized Bosons c5/2/20223 a

We introduce the notion of "generalized bosons" whose exchange statistics resemble those of bosons, but the local bosonic commutator [ai,a†i]=1 is replaced by an arbitrary single-mode operator that is diagonal in the generalized Fock basis. Examples of generalized bosons include boson pairs and spins. We consider the analogue of the boson sampling task for these particles and observe that its output probabilities are still given by permanents, so that the results regarding hardness of sampling directly carry over. Finally, we propose implementations of generalized boson sampling in circuit-QED and ion-trap platforms.

1 aKuo, En-Jui1 aXu, Yijia1 aHangleiter, Dominik1 aGrankin, Andrey1 aHafezi, Mohammad uhttps://arxiv.org/abs/2204.0838902469nas a2200217 4500008004100000245001900041210001900060260001400079520185900093653003401952653004301986653002702029653003102056100002602087700001902113700001702132700002502149700002202174700001802196856003702214 2022 eng d00aBosonic Qiskit0 aBosonic Qiskit c9/22/20223 a

The practical benefits of hybrid quantum information processing hardware that contains continuous-variable objects (bosonic modes such as mechanical or electromagnetic oscillators) in addition to traditional (discrete-variable) qubits have recently been demonstrated by experiments with bosonic codes that reach the break-even point for quantum error correction and by efficient Gaussian boson sampling simulation of the Franck-Condon spectra of triatomic molecules that is well beyond the capabilities of current qubit-only hardware. The goal of this Co-design Center for Quantum Advantage (C2QA) project is to develop an instruction set architecture (ISA) for hybrid qubit/bosonic mode systems that contains an inventory of the fundamental operations and measurements that are possible in such hardware. The corresponding abstract machine model (AMM) would also contain a description of the appropriate error models associated with the gates, measurements and time evolution of the hardware. This information has been implemented as an extension of Qiskit. Qiskit is an opensource software development toolkit (SDK) for simulating the quantum state of a quantum circuit on a system with Python 3.7+ and for running the same circuits on prototype hardware within the IBM Quantum Lab. We introduce the Bosonic Qiskit software to enable the simulation of hybrid qubit/bosonic systems using the existing Qiskit software development kit. This implementation can be used for simulating new hybrid systems, verifying proposed physical systems, and modeling systems larger than can currently be constructed. We also cover tutorials and example use cases included within the software to study Jaynes- Cummings models, bosonic Hubbard models, plotting Wigner functions and animations, and calculating maximum likelihood estimations using Wigner functions.

10aEmerging Technologies (cs.ET)10aFOS: Computer and information sciences10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aStavenger, Timothy, J1 aCrane, Eleanor1 aSmith, Kevin1 aKang, Christopher, T1 aGirvin, Steven, M1 aWiebe, Nathan uhttps://arxiv.org/abs/2209.1115301438nas a2200133 4500008004100000245003700041210003700078260001400115520106600129100002401195700002901219700001901248856003701267 2022 eng d00aCertifying Temporal Correlations0 aCertifying Temporal Correlations c6/13/20223 a

Self-testing has been established as a major approach for quantum device certification based on experimental statistics under minimal assumptions. However, despite more than 20 years of research effort most of the self-testing protocols are restricted to spatial scenarios (Bell scenarios), without any temporal generalisations known. Under the scenario of sequential measurements performed on a single quantum system, we build upon previous works which used semi-definite programming (SDP) based methods to bound sequential measurement inequalities. For such SDPs, we show that the optimiser matrix is unique and moreover this uniqueness is robust to small deviations from the quantum bound. Further, we consider a generalised scenario in presence of quantum channels and draw analogies in the structure of Bell and sequential inequalities using the pseudo-density matrix formalism. These analogies allow us to show a practical use of maximal violations of sequential inequalities in the form of certification of quantum channels up to isometries. 

1 aShrotriya, Harshank1 aKwek, Kishor, Bharti Leo1 aBharti, Kishor uhttps://arxiv.org/abs/2206.0609201146nas a2200169 4500008004100000245005900041210005900100260001400159300001100173490000800184520067200192100001900864700001500883700001800898700002300916856003700939 2022 eng d00aChiral central charge from a single bulk wave function0 aChiral central charge from a single bulk wave function c4/28/2022 a1764020 v1283 a

A (2+1)-dimensional gapped quantum many-body system can have a topologically protected energy current at its edge. The magnitude of this current is determined entirely by the temperature and the chiral central charge, a quantity associated with the effective field theory of the edge. We derive a formula for the chiral central charge that, akin to the topological entanglement entropy, is completely determined by the many-body ground state wave function in the bulk. According to our formula, nonzero chiral central charge gives rise to a topological obstruction that prevents the ground state wave function from being real-valued in any local product basis.

1 aKim, Isaac, H.1 aShi, Bowen1 aKato, Kohtaro1 aAlbert, Victor, V. uhttps://arxiv.org/abs/2110.0693202685nas a2200253 4500008004100000245007700041210006900118260001400187520182700201653002102028653002702049653004202076653003502118653003002153653003102183653005202214100002302266700001602289700002102305700002202326700003002348700001602378856003702394 2022 eng d00aCodimension-2 defects and higher symmetries in (3+1)D topological phases0 aCodimension2 defects and higher symmetries in 31D topological ph c8/15/20223 a

(3+1)D topological phases of matter can host a broad class of non-trivial topological defects of codimension-1, 2, and 3, of which the well-known point charges and flux loops are special cases. The complete algebraic structure of these defects defines a higher category, and can be viewed as an emergent higher symmetry. This plays a crucial role both in the classification of phases of matter and the possible fault-tolerant logical operations in topological quantum error correcting codes. In this paper, we study several examples of such higher codimension defects from distinct perspectives. We mainly study a class of invertible codimension-2 topological defects, which we refer to as twist strings. We provide a number of general constructions for twist strings, in terms of gauging lower dimensional invertible phases, layer constructions, and condensation defects. We study some special examples in the context of Z2 gauge theory with fermionic charges, in Z2×Z2 gauge theory with bosonic charges, and also in non-Abelian discrete gauge theories based on dihedral (Dn) and alternating (A6) groups. The intersection between twist strings and Abelian flux loops sources Abelian point charges, which defines an H4 cohomology class that characterizes part of an underlying 3-group symmetry of the topological order. The equations involving background gauge fields for the 3-group symmetry have been explicitly written down for various cases. We also study examples of twist strings interacting with non-Abelian flux loops (defining part of a non-invertible higher symmetry), examples of non-invertible codimension-2 defects, and examples of interplay of codimension-2 defects with codimension-1 defects. We also find an example of geometric, not fully topological, twist strings in (3+1)D A6 gauge theory.

10aFOS: Mathematics10aFOS: Physical sciences10aHigh Energy Physics - Theory (hep-th)10aMathematical Physics (math-ph)10aQuantum Algebra (math.QA)10aQuantum Physics (quant-ph)10aStrongly Correlated Electrons (cond-mat.str-el)1 aBarkeshli, Maissam1 aChen, Yu-An1 aHuang, Sheng-Jie1 aKobayashi, Ryohei1 aTantivasadakarn, Nathanan1 aZhu, Guanyu uhttps://arxiv.org/abs/2208.0736701635nas a2200181 4500008004100000245010500041210006900146260001500215300001200230490000600242520106000248100001801308700002001326700002501346700002101371700002401392856003701416 2022 eng d00aCombining machine learning with physics: A framework for tracking and sorting multiple dark solitons0 aCombining machine learning with physics A framework for tracking c06/01/2022 a023163 0 v43 a

In ultracold-atom experiments, data often comes in the form of images which suffer information loss inherent in the techniques used to prepare and measure the system. This is particularly problematic when the processes of interest are complicated, such as interactions among excitations in Bose-Einstein condensates (BECs). In this paper, we describe a framework combining machine learning (ML) models with physics-based traditional analyses to identify and track multiple solitonic excitations in images of BECs. We use an ML-based object detector to locate the solitonic excitations and develop a physics-informed classifier to sort solitonic excitations into physically motivated subcategories. Lastly, we introduce a quality metric quantifying the likelihood that a specific feature is a longitudinal soliton. Our trained implementation of this framework, SolDet, is publicly available as an open-source python package. SolDet is broadly applicable to feature identification in cold-atom images when trained on a suitable user-provided dataset.

1 aGuo, Shangjie1 aKoh, Sophia, M.1 aFritsch, Amilson, R.1 aSpielman, I., B.1 aZwolak, Justyna, P. uhttps://arxiv.org/abs/2111.0488101840nas a2200253 4500008004100000245006100041210006000102260001400162520102500176653002701201653003901228653003101267653004701298653005201345100001401397700001301411700001701424700002301441700002501464700001801489700001801507700002401525856003701549 2022 eng d00aContinuous Symmetry Breaking in a Trapped-Ion Spin Chain0 aContinuous Symmetry Breaking in a TrappedIon Spin Chain c11/2/20223 a

One-dimensional systems exhibiting a continuous symmetry can host quantum phases of matter with true long-range order only in the presence of sufficiently long-range interactions. In most physical systems, however, the interactions are short-ranged, hindering the emergence of such phases in one dimension. Here we use a one-dimensional trapped-ion quantum simulator to prepare states with long-range spin order that extends over the system size of up to 23 spins and is characteristic of the continuous symmetry-breaking phase of matter. Our preparation relies on simultaneous control over an array of tightly focused individual-addressing laser beams, generating long-range spin-spin interactions. We also observe a disordered phase with frustrated correlations. We further study the phases at different ranges of interaction and the out-of-equilibrium response to symmetry-breaking perturbations. This work opens an avenue to study new quantum phases and out-of-equilibrium dynamics in low-dimensional systems.

10aFOS: Physical sciences10aQuantum Gases (cond-mat.quant-gas)10aQuantum Physics (quant-ph)10aStatistical Mechanics (cond-mat.stat-mech)10aStrongly Correlated Electrons (cond-mat.str-el)1 aFeng, Lei1 aKatz, Or1 aHaack, Casey1 aMaghrebi, Mohammad1 aGorshkov, Alexey, V.1 aGong, Zhexuan1 aCetina, Marko1 aMonroe, Christopher uhttps://arxiv.org/abs/2211.0127501282nas a2200181 4500008004100000245008800041210006900129260001300198520068100211653002700892653003100919100002900950700002000979700001900999700002201018700002301040856003701063 2022 eng d00aConvex optimization for non-equilibrium steady states on a hybrid quantum processor0 aConvex optimization for nonequilibrium steady states on a hybrid c4/7/20223 a

Finding the transient and steady state properties of open quantum systems is a central problem in various fields of quantum technologies. Here, we present a quantum-assisted algorithm to determine the steady states of open system dynamics. By reformulating the problem of finding the fixed point of Lindblad dynamics as a feasibility semi-definite program, we bypass several well known issues with variational quantum approaches to solving for steady states. We demonstrate that our hybrid approach allows us to estimate the steady states of higher dimensional open quantum systems and discuss how our method can find multiple steady states for systems with symmetries.

10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aLau, Jonathan, Wei Zhong1 aLim, Kian, Hwee1 aBharti, Kishor1 aKwek, Leong-Chuan1 aVinjanampathy, Sai uhttps://arxiv.org/abs/2204.0320302302nas a2200277 4500008004100000245004100041210004000082260001300122520150700135653003401642653003801676653001601714653004301730653001301773100002101786700001701807700001901824700002001843700002301863700001901886700002501905700002001930700001701950700002001967856003701987 2022 eng d00aCoVault: A Secure Analytics Platform0 aCoVault A Secure Analytics Platform c8/7/20223 a

In a secure analytics platform, data sources consent to the exclusive use of their data for a pre-defined set of analytics queries performed by a specific group of analysts, and for a limited period. If the platform is secure under a sufficiently strong threat model, it can provide the missing link to enabling powerful analytics of sensitive personal data, by alleviating data subjects' concerns about leakage and misuse of data. For instance, many types of powerful analytics that benefit public health, mobility, infrastructure, finance, or sustainable energy can be made differentially private, thus alleviating concerns about privacy. However, no platform currently exists that is sufficiently secure to alleviate concerns about data leakage and misuse; as a result, many types of analytics that would be in the interest of data subjects and the public are not done. CoVault uses a new multi-party implementation of functional encryption (FE) for secure analytics, which relies on a unique combination of secret sharing, multi-party secure computation (MPC), and different trusted execution environments (TEEs). CoVault is secure under a very strong threat model that tolerates compromise and side-channel attacks on any one of a small set of parties and their TEEs. Despite the cost of MPC, we show that CoVault scales to very large data sizes using map-reduce based query parallelization. For example, we show that CoVault can perform queries relevant to epidemic analytics at scale.

10aand Cluster Computing (cs.DC)10aCryptography and Security (cs.CR)10aDistributed10aFOS: Computer and information sciences10aParallel1 aDe Viti, Roberta1 aSheff, Isaac1 aGlaeser, Noemi1 aDinis, Baltasar1 aRodrigues, Rodrigo1 aKatz, Jonathan1 aBhattacharjee, Bobby1 aHithnawi, Anwar1 aGarg, Deepak1 aDruschel, Peter uhttps://arxiv.org/abs/2208.0378401358nas a2200157 4500008004100000245008900041210006900130260001500199520084100214100002501055700001801080700002001098700002101118700002401139856003701163 2022 eng d00aDark Solitons in Bose-Einstein Condensates: A Dataset for Many-body Physics Research0 aDark Solitons in BoseEinstein Condensates A Dataset for Manybody c05/17/20223 a

We establish a dataset of over 1.6×104 experimental images of Bose-Einstein condensates containing solitonic excitations to enable machine learning (ML) for many-body physics research. About 33 % of this dataset has manually assigned and carefully curated labels. The remainder is automatically labeled using SolDet -- an implementation of a physics-informed ML data analysis framework -- consisting of a convolutional-neural-network-based classifier and object detector as well as a statistically motivated physics-informed classifier and a quality metric. This technical note constitutes the definitive reference of the dataset, providing an opportunity for the data science community to develop more sophisticated analysis tools, to further understand nonlinear many-body physics, and even advance cold atom experiments.

1 aFritsch, Amilson, R.1 aGuo, Shangjie1 aKoh, Sophia, M.1 aSpielman, I., B.1 aZwolak, Justyna, P. uhttps://arxiv.org/abs/2205.0911401214nas a2200193 4500008004100000245008100041210006900122260001400191520059300205653003700798653002700835653003100862100001300893700001400906700002100920700002400941700001800965856003700983 2022 eng d00aDemonstration of three- and four-body interactions between trapped-ion spins0 aDemonstration of three and fourbody interactions between trapped c9/12/20223 a

Quantum processors use the native interactions between effective spins to simulate Hamiltonians or execute quantum gates. In most processors, the native interactions are pairwise, limiting the efficiency of controlling entanglement between many qubits. Here we experimentally demonstrate a new class of native interactions between trapped-ion qubits, extending conventional pairwise interactions to higher order. We realize three- and four-body spin interactions as examples, showing that high-order spin polynomials may serve as a new toolbox for quantum information applications.

10aAtomic Physics (physics.atom-ph)10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aKatz, Or1 aFeng, Lei1 aRisinger, Andrew1 aMonroe, Christopher1 aCetina, Marko uhttps://arxiv.org/abs/2209.0569101492nas a2200181 4500008004100000245008600041210006900127260001500196490000600211520094800217100001601165700002301181700002101204700001701225700001701242700001401259856003701273 2022 eng d00aEfficient Product Formulas for Commutators and Applications to Quantum Simulation0 aEfficient Product Formulas for Commutators and Applications to Q c03/10/20220 v43 a

We construct product formulas for exponentials of commutators and explore their applications. First, we directly construct a third-order product formula with six exponentials by solving polynomial equations obtained using the operator differential method. We then derive higher-order product formulas recursively from the third-order formula. We improve over previous recursive constructions, reducing the number of gates required to achieve the same accuracy. In addition, we demonstrate that the constituent linear terms in the commutator can be included at no extra cost. As an application, we show how to use the product formulas in a digital protocol for counterdiabatic driving, which increases the fidelity for quantum state preparation. We also discuss applications to quantum simulation of one-dimensional fermion chains with nearest- and next-nearest-neighbor hopping terms, and two-dimensional fractional quantum Hall phases.

1 aChen, Yu-An1 aChilds, Andrew, M.1 aHafezi, Mohammad1 aJiang, Zhang1 aKim, Hwanmun1 aXu, Yijia uhttps://arxiv.org/abs/2111.1217701498nas a2200301 4500008004100000245006800041210006800109260001400177520060600191653002700797653004400824653003100868100001700899700001600916700002500932700001800957700001300975700001800988700001901006700002101025700001401046700002201060700001601082700001901098700001801117700002401135856003701159 2022 eng d00aExperimental Implementation of an Efficient Test of Quantumness0 aExperimental Implementation of an Efficient Test of Quantumness c9/28/20223 a

A test of quantumness is a protocol where a classical user issues challenges to a quantum device to determine if it exhibits non-classical behavior, under certain cryptographic assumptions. Recent attempts to implement such tests on current quantum computers rely on either interactive challenges with efficient verification, or non-interactive challenges with inefficient (exponential time) verification. In this paper, we execute an efficient non-interactive test of quantumness on an ion-trap quantum computer. Our results significantly exceed the bound for a classical device's success.

10aFOS: Physical sciences10aOther Condensed Matter (cond-mat.other)10aQuantum Physics (quant-ph)1 aLewis, Laura1 aZhu, Daiwei1 aGheorghiu, Alexandru1 aNoel, Crystal1 aKatz, Or1 aHarraz, Bahaa1 aWang, Qingfeng1 aRisinger, Andrew1 aFeng, Lei1 aBiswas, Debopriyo1 aEgan, Laird1 aVidick, Thomas1 aCetina, Marko1 aMonroe, Christopher uhttps://arxiv.org/abs/2209.1431602003nas a2200217 4500008004100000245007300041210006900114260001300183520129800196653002701494653003101521653004701552100002001599700002201619700002101641700001601662700001801678700002401696700002801720856003701748 2022 eng d00aExperimental observation of thermalisation with noncommuting charges0 aExperimental observation of thermalisation with noncommuting cha c2/9/20223 a

Quantum simulators have recently enabled experimental observations of quantum many-body systems' internal thermalisation. Often, the global energy and particle number are conserved, and the system is prepared with a well-defined particle number - in a microcanonical subspace. However, quantum evolution can also conserve quantities, or charges, that fail to commute with each other. Noncommuting charges have recently emerged as a subfield at the intersection of quantum thermodynamics and quantum information. Until now, this subfield has remained theoretical. We initiate the experimental testing of its predictions, with a trapped-ion simulator. We prepare 6-15 spins in an approximate microcanonical subspace, a generalisation of the microcanonical subspace for accommodating noncommuting charges, which cannot necessarily have well-defined nontrivial values simultaneously. We simulate a Heisenberg evolution using laser-induced entangling interactions and collective spin rotations. The noncommuting charges are the three spin components. We find that small subsystems equilibrate to near a recently predicted non-Abelian thermal state. This work bridges quantum many-body simulators to the quantum thermodynamics of noncommuting charges, whose predictions can now be tested.

10aFOS: Physical sciences10aQuantum Physics (quant-ph)10aStatistical Mechanics (cond-mat.stat-mech)1 aKranzl, Florian1 aLasek, Aleksander1 aJoshi, Manoj, K.1 aKalev, Amir1 aBlatt, Rainer1 aRoos, Christian, F.1 aHalpern, Nicole, Yunger uhttps://arxiv.org/abs/2202.0465202469nas a2200241 4500008004100000245007800041210006900119260001500188520171200203653003801915653004301953653002701996653003102023100001302054700001402067700001402081700001802095700002002113700001602133700002502149700001602174856003702190 2022 eng d00aFIPS Compliant Quantum Secure Communication using Quantum Permutation Pad0 aFIPS Compliant Quantum Secure Communication using Quantum Permut c12/30/20223 a

Quantum computing has entered fast development track since Shor's algorithm was proposed in 1994. Multi-cloud services of quantum computing farms are currently available. One of which, IBM quantum computing, presented a road map showing their Kookaburra system with over 4158 qubits will be available in 2025. For the standardization of Post-Quantum Cryptography or PQC, the National Institute of Standards and Technology or NIST recently announced the first candidates for standardization with one algorithm for key encapsulation mechanism (KEM), Kyber, and three algorithms for digital signatures. NIST has also issued a new call for quantum-safe digital signature algorithms due June 1, 2023. This timeline shows that FIPS-certified quantum-safe TLS protocol would take a predictably long time. However, "steal now, crack later" tactic requires protecting data against future quantum threat actors today. NIST recommended the use of a hybrid mode of TLS 1.3 with its extensions to support PQC. The hybrid mode works for certain cases but FIPS certification for the hybridized cryptomodule might still be required. This paper proposes to take a nested mode to enable TLS 1.3 protocol with quantum-safe data, which can be made available today and is FIPS compliant. We discussed the performance impacts of the handshaking phase of the nested TLS 1.3 with PQC and the symmetric encryption phase. The major impact on performance using the nested mode is in the data symmetric encryption with AES. To overcome this performance reduction, we suggest using quantum encryption with a quantum permutation pad for the data encryption with a minor performance reduction of less than 10 percent.

10aCryptography and Security (cs.CR)10aFOS: Computer and information sciences10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aHe, Alex1 aLou, Dafu1 aShe, Eric1 aGuo, Shangjie1 aWatson, Hareesh1 aWeng, Sibyl1 aPerepechaenko, Maria1 aKuang, Rand uhttps://arxiv.org/abs/2301.0006202101nas a2200217 4500008004100000245007000041210006900111260001500180520136900195653002101564653002701585653004201612653003001654653003101684653005201715100002301767700001601790700001801806700002201824856003701846 2022 eng d00aHigher-group symmetry in finite gauge theory and stabilizer codes0 aHighergroup symmetry in finite gauge theory and stabilizer codes c11/21/20223 a

A large class of gapped phases of matter can be described by topological finite group gauge theories. In this paper, we derive the d-group global symmetry and its 't Hooft anomaly for topological finite group gauge theories in (d+1) space-time dimensions, including non-Abelian gauge groups and Dijkgraaf-Witten twists. We focus on the 1-form symmetry generated by invertible (Abelian) magnetic defects and the higher-form symmetries generated by invertible topological defects decorated with lower dimensional gauged symmetry-protected topological (SPT) phases. We show that due to a generalization of the Witten effect and charge-flux attachment, the 1-form symmetry generated by the magnetic defects mixes with other symmetries into a higher group. We describe such higher-group symmetry in various lattice model examples. We discuss several applications, including the classification of fermionic SPT phases in (3+1)D for general fermionic symmetry groups, where we also derive a simpler formula for the [O5]∈H5(BG,U(1)) obstruction than has appeared in previous work. We also show how the d-group symmetry is related to fault-tolerant non-Pauli logical gates and a refined Clifford hierarchy in stabilizer codes. We construct new logical gates in stabilizer codes using the d-group symmetry, such as the control-Z gate in (3+1)D Z2 toric code.

10aFOS: Mathematics10aFOS: Physical sciences10aHigh Energy Physics - Theory (hep-th)10aQuantum Algebra (math.QA)10aQuantum Physics (quant-ph)10aStrongly Correlated Electrons (cond-mat.str-el)1 aBarkeshli, Maissam1 aChen, Yu-An1 aHsin, Po-Shen1 aKobayashi, Ryohei uhttps://arxiv.org/abs/2211.1176401533nas a2200157 4500008004100000245004800041210004800089260001400137520103000151100002101181700002001202700002801222700001701250700002801267856008001295 2022 eng d00aLinear growth of quantum circuit complexity0 aLinear growth of quantum circuit complexity c3/28/20223 a

The complexity of quantum states has become a key quantity of interest across various subfields of physics, from quantum computing to the theory of black holes. The evolution of generic quantum systems can be modelled by considering a collection of qubits subjected to sequences of random unitary gates. Here we investigate how the complexity of these random quantum circuits increases by considering how to construct a unitary operation from Haar-random two-qubit quantum gates. Implementing the unitary operation exactly requires a minimal number of gates—this is the operation’s exact circuit complexity. We prove a conjecture that this complexity grows linearly, before saturating when the number of applied gates reaches a threshold that grows exponentially with the number of qubits. Our proof overcomes difficulties in establishing lower bounds for the exact circuit complexity by combining differential topology and elementary algebraic geometry with an inductive construction of Clifford circuits.

1 aHaferkamp, Jonas1 aFaist, Philippe1 aKothakonda, Naga, B. T.1 aEisert, Jens1 aHalpern, Nicole, Yunger uhttps://quics.umd.edu/publications/linear-growth-quantum-circuit-complexity01849nas a2200181 4500008004100000245006500041210006400106260001400170520120700184653004101391653005301432653005401485653002701539100002001566700002201586700002201608856003701630 2022 eng d00aMachine-assisted discovery of integrable symplectic mappings0 aMachineassisted discovery of integrable symplectic mappings c3/22/20223 a

We present a new automated method for finding integrable symplectic maps of the plane. These dynamical systems possess a hidden symmetry associated with an existence of conserved quantities, i.e. integrals of motion. The core idea of the algorithm is based on the knowledge that the evolution of an integrable system in the phase space is restricted to a lower-dimensional submanifold. Limiting ourselves to polygon invariants of motion, we analyze the shape of individual trajectories thus successfully distinguishing integrable motion from chaotic cases. For example, our method rediscovers some of the famous McMillan-Suris integrable mappings and discrete Painlevé equations. In total, over 100 new integrable families are presented and analyzed; some of them are isolated in the space of parameters, and some of them are families with one parameter (or the ratio of parameters) being continuous or discrete. At the end of the paper, we suggest how newly discovered maps are related to a general 2D symplectic map via an introduction of discrete perturbation theory and propose a method on how to construct smooth near-integrable dynamical systems based on mappings with polygon invariants.

10aAccelerator Physics (physics.acc-ph)10aAdaptation and Self-Organizing Systems (nlin.AO)10aExactly Solvable and Integrable Systems (nlin.SI)10aFOS: Physical sciences1 aZolkin, Timofey1 aKharkov, Yaroslav1 aNagaitsev, Sergei uhttps://arxiv.org/abs/2201.1313302540nas a2200229 4500008004100000245009600041210006900137260001300206490000700219520184300226100002102069700001802090700001402108700001502122700002802137700002302165700002302188700002402211700001802235700002002253856003702273 2022 eng d00aMany-Body Quantum Teleportation via Operator Spreading in the Traversable Wormhole Protocol0 aManyBody Quantum Teleportation via Operator Spreading in the Tra c8/5/20220 v123 a

By leveraging shared entanglement between a pair of qubits, one can teleport a quantum state from one particle to another. Recent advances have uncovered an intrinsically many-body generalization of quantum teleportation, with an elegant and surprising connection to gravity. In particular, the teleportation of quantum information relies on many-body dynamics, which originate from strongly-interacting systems that are holographically dual to gravity; from the gravitational perspective, such quantum teleportation can be understood as the transmission of information through a traversable wormhole. Here, we propose and analyze a new mechanism for many-body quantum teleportation -- dubbed peaked-size teleportation. Intriguingly, peaked-size teleportation utilizes precisely the same type of quantum circuit as traversable wormhole teleportation, yet has a completely distinct microscopic origin: it relies upon the spreading of local operators under generic thermalizing dynamics and not gravitational physics. We demonstrate the ubiquity of peaked-size teleportation, both analytically and numerically, across a diverse landscape of physical systems, including random unitary circuits, the Sachdev-Ye-Kitaev model (at high temperatures), one-dimensional spin chains and a bulk theory of gravity with stringy corrections. Our results pave the way towards using many-body quantum teleportation as a powerful experimental tool for: (i) characterizing the size distributions of operators in strongly-correlated systems and (ii) distinguishing between generic and intrinsically gravitational scrambling dynamics. To this end, we provide a detailed experimental blueprint for realizing many-body quantum teleportation in both trapped ions and Rydberg atom arrays; effects of decoherence and experimental imperfections are analyzed.

1 aSchuster, Thomas1 aKobrin, Bryce1 aGao, Ping1 aCong, Iris1 aKhabiboulline, Emil, T.1 aLinke, Norbert, M.1 aLukin, Mikhail, D.1 aMonroe, Christopher1 aYoshida, Beni1 aYao, Norman, Y. uhttps://arxiv.org/abs/2102.0001001471nas a2200157 4500008004100000245005900041210005800100260001400158490000800172520102100180100001901201700001501220700001801235700002301253856003701276 2022 eng d00aModular commutator in gapped quantum many-body systems0 aModular commutator in gapped quantum manybody systems c8/26/20220 v1063 a

In arXiv:2110.06932, we argued that the chiral central charge -- a topologically protected quantity characterizing the edge theory of a gapped (2+1)-dimensional system -- can be extracted from the bulk by using an order parameter called the modular commutator. In this paper, we reveal general properties of the modular commutator and strengthen its relationship with the chiral central charge. First, we identify connections between the modular commutator and conditional mutual information, time reversal, and modular flow. Second, we prove, within the framework of the entanglement bootstrap program, that two topologically ordered media connected by a gapped domain wall must have the same modular commutator in their respective bulk. Third, we numerically calculate the value of the modular commutator for a bosonic lattice Laughlin state for finite sizes and extrapolate to the infinite-volume limit. The result of this extrapolation is consistent with the proposed formula up to an error of about 0.7%.

1 aKim, Isaac, H.1 aShi, Bowen1 aKato, Kohtaro1 aAlbert, Victor, V. uhttps://arxiv.org/abs/2110.1040001181nas a2200145 4500008004100000245008000041210006900121260001300190490000800203520073200211100001300943700001800956700002400974856003700998 2022 eng d00aN-body interactions between trapped ion qubits via spin-dependent squeezing0 aNbody interactions between trapped ion qubits via spindependent  c8/5/20220 v1293 a

We describe a simple protocol for the single-step generation of N-body entangling interactions between trapped atomic ion qubits. We show that qubit state-dependent squeezing operations and displacement forces on the collective atomic motion can generate full N-body interactions. Similar to the Mølmer-Sørensen two-body Ising interaction at the core of most trapped ion quantum computers and simulators, the proposed operation is relatively insensitive to the state of motion. We show how this N-body gate operation allows the single-step implementation of a family of N-bit gate operations such as the powerful N-Toffoli gate, which flips a single qubit if and only if all other N-1 qubits are in a particular state.

1 aKatz, Or1 aCetina, Marko1 aMonroe, Christopher uhttps://arxiv.org/abs/2202.0423001066nas a2200145 4500008004100000245006700041210006700108260001400175520061300189100002100802700001900823700002200842700001900864856003700883 2022 eng d00aNISQ algorithm for the matrix elements of a generic observable0 aNISQ algorithm for the matrix elements of a generic observable c5/20/20223 a

The calculation of off-diagonal matrix elements has various applications in fields such as nuclear physics and quantum chemistry. In this paper, we present a noisy intermediate scale quantum algorithm for estimating the diagonal and off-diagonal matrix elements of a generic observable in the energy eigenbasis of a given Hamiltonian. Several numerical simulations indicate that this approach can find many of the matrix elements even when the trial functions are randomly initialized across a wide range of parameter values without, at the same time, the need to prepare the energy eigenstates. 

1 aErbanni, Rebecca1 aBharti, Kishor1 aKwek, Leong-Chuan1 aPoletti, Dario uhttps://arxiv.org/abs/2205.1005801696nas a2200145 4500008004100000245005300041210005100094260001500145520127900160100001901439700001401458700001901472700002201491856003701513 2022 eng d00aPost-Quantum Security of the Even-Mansour Cipher0 aPostQuantum Security of the EvenMansour Cipher c12/14/20213 a

The Even-Mansour cipher is a simple method for constructing a (keyed) pseudorandom permutation E from a public random permutation~P:{0,1}n→{0,1}n. It is secure against classical attacks, with optimal attacks requiring qE queries to E and qP queries to P such that qE⋅qP≈2n. If the attacker is given \emph{quantum} access to both E and P, however, the cipher is completely insecure, with attacks using qE,qP=O(n) queries known. In any plausible real-world setting, however, a quantum attacker would have only \emph{classical} access to the keyed permutation~E implemented by honest parties, even while retaining quantum access to~P. Attacks in this setting with qE⋅q2P≈2n are known, showing that security degrades as compared to the purely classical case, but leaving open the question as to whether the Even-Mansour cipher can still be proven secure in this natural, "post-quantum" setting. We resolve this question, showing that any attack in that setting requires qE⋅q2P+qP⋅q2E≈2n. Our results apply to both the two-key and single-key variants of Even-Mansour. Along the way, we establish several generalizations of results from prior work on quantum-query lower bounds that may be of independent interest. 

1 aAlagic, Gorjan1 aBai, Chen1 aKatz, Jonathan1 aMajenz, Christian uhttps://arxiv.org/abs/2112.0753001152nas a2200157 4500008004100000245007900041210006900120260001400189520065900203100001900862700001400881700001900895700002200914700002000936856003800956 2022 eng d00aPost-Quantum Security of the (Tweakable) FX Construction, and Applications0 aPostQuantum Security of the Tweakable FX Construction and Applic c8/29/20223 a

The FX construction provides a way to increase the effective key length of a block cipher E. We prove security of a tweakable version of the FX construction in the post-quantum setting, i.e., against a quantum attacker given only classical access to the secretly keyed construction while retaining quantum access to E, a setting that seems to be the most relevant one for real-world applications. We then use our results to prove post-quantum security—in the same model—of the (plain) FX construction, Elephant (a finalist of NIST's lightweight cryptography standardization effort), and Chaskey (an ISO-standardized lightweight MAC

1 aAlagic, Gorjan1 aBai, Chen1 aKatz, Jonathan1 aMajenz, Christian1 aStruck, Patrick uhttps://eprint.iacr.org/2022/109701744nas a2200169 4500008004100000245007100041210006900112260001400181490000800195520123200203100002101435700001901456700002001475700002301495700001901518856003701537 2022 eng d00aProvably efficient machine learning for quantum many-body problems0 aProvably efficient machine learning for quantum manybody problem c9/26/20220 v3773 a

Classical machine learning (ML) provides a potentially powerful approach to solving challenging quantum many-body problems in physics and chemistry. However, the advantages of ML over more traditional methods have not been firmly established. In this work, we prove that classical ML algorithms can efficiently predict ground state properties of gapped Hamiltonians in finite spatial dimensions, after learning from data obtained by measuring other Hamiltonians in the same quantum phase of matter. In contrast, under widely accepted complexity theory assumptions, classical algorithms that do not learn from data cannot achieve the same guarantee. We also prove that classical ML algorithms can efficiently classify a wide range of quantum phases of matter. Our arguments are based on the concept of a classical shadow, a succinct classical description of a many-body quantum state that can be constructed in feasible quantum experiments and be used to predict many properties of the state. Extensive numerical experiments corroborate our theoretical results in a variety of scenarios, including Rydberg atom systems, 2D random Heisenberg models, symmetry-protected topological phases, and topologically ordered phases.

1 aHuang, Hsin-Yuan1 aKueng, Richard1 aTorlai, Giacomo1 aAlbert, Victor, V.1 aPreskill, John uhttps://arxiv.org/abs/2106.1262701490nas a2200205 4500008004100000245003100041210003100072260001500103520088200118653004301000653004301043653002701086653003101113100002301144700001901167700002201186700002101208700001801229856003701247 2022 eng d00aQuantum divide and conquer0 aQuantum divide and conquer c10/12/20223 a

The divide-and-conquer framework, used extensively in classical algorithm design, recursively breaks a problem of size n into smaller subproblems (say, a copies of size n/b each), along with some auxiliary work of cost Caux(n), to give a recurrence relation
C(n)≤aC(n/b)+Caux(n)
for the classical complexity C(n). We describe a quantum divide-and-conquer framework that, in certain cases, yields an analogous recurrence relation
CQ(n)≤a−−√CQ(n/b)+O(CauxQ(n))
that characterizes the quantum query complexity. We apply this framework to obtain near-optimal quantum query complexities for various string problems, such as (i) recognizing regular languages; (ii) decision versions of String Rotation and String Suffix; and natural parameterized versions of (iii) Longest Increasing Subsequence and (iv) Longest Common Subsequence.

10aData Structures and Algorithms (cs.DS)10aFOS: Computer and information sciences10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aChilds, Andrew, M.1 aKothari, Robin1 aKovacs-Deak, Matt1 aSundaram, Aarthi1 aWang, Daochen uhttps://arxiv.org/abs/2210.0641902845nas a2200541 4500008004100000245004700041210004700088260001300135520125300148653002701401653004401428653004901472653004201521653002901563653003101592100002501623700002001648700002101668700002501689700002001714700002201734700002001756700002001776700001801796700002101814700002101835700001601856700001801872700001501890700001901905700002101924700002401945700002201969700001801991700001902009700002002028700002402048700002402072700002302096700001902119700002002138700002202158700001802180700002102198700002602219700002102245856003702266 2022 eng d00aQuantum Simulation for High Energy Physics0 aQuantum Simulation for High Energy Physics c4/7/20223 a

It is for the first time that Quantum Simulation for High Energy Physics (HEP) is studied in the U.S. decadal particle-physics community planning, and in fact until recently, this was not considered a mainstream topic in the community. This fact speaks of a remarkable rate of growth of this subfield over the past few years, stimulated by the impressive advancements in Quantum Information Sciences (QIS) and associated technologies over the past decade, and the significant investment in this area by the government and private sectors in the U.S. and other countries. High-energy physicists have quickly identified problems of importance to our understanding of nature at the most fundamental level, from tiniest distances to cosmological extents, that are intractable with classical computers but may benefit from quantum advantage. They have initiated, and continue to carry out, a vigorous program in theory, algorithm, and hardware co-design for simulations of relevance to the HEP mission. This community whitepaper is an attempt to bring this exciting and yet challenging area of research to the spotlight, and to elaborate on what the promises, requirements, challenges, and potential solutions are over the next decade and beyond.

10aFOS: Physical sciences10aHigh Energy Physics - Lattice (hep-lat)10aHigh Energy Physics - Phenomenology (hep-ph)10aHigh Energy Physics - Theory (hep-th)10aNuclear Theory (nucl-th)10aQuantum Physics (quant-ph)1 aBauer, Christian, W.1 aDavoudi, Zohreh1 aBalantekin, Baha1 aBhattacharya, Tanmoy1 aCarena, Marcela1 ade Jong, Wibe, A.1 aDraper, Patrick1 aEl-Khadra, Aida1 aGemelke, Nate1 aHanada, Masanori1 aKharzeev, Dmitri1 aLamm, Henry1 aLi, Ying-Ying1 aLiu, Junyu1 aLukin, Mikhail1 aMeurice, Yannick1 aMonroe, Christopher1 aNachman, Benjamin1 aPagano, Guido1 aPreskill, John1 aRinaldi, Enrico1 aRoggero, Alessandro1 aSantiago, David, I.1 aSavage, Martin, J.1 aSiddiqi, Irfan1 aSiopsis, George1 aVan Zanten, David1 aWiebe, Nathan1 aYamauchi, Yukari1 aYeter-Aydeniz, Kübra1 aZorzetti, Silvia uhttps://arxiv.org/abs/2204.0338101806nas a2200181 4500008004100000245007200041210006900113260001500182520123900197653002701436653003101463100002001494700001601514700001801530700001901548700002001567856003701587 2022 eng d00aQuantum state tomography via non-convex Riemannian gradient descent0 aQuantum state tomography via nonconvex Riemannian gradient desce c10/10/20223 a

The recovery of an unknown density matrix of large size requires huge computational resources. The recent Factored Gradient Descent (FGD) algorithm and its variants achieved state-of-the-art performance since they could mitigate the dimensionality barrier by utilizing some of the underlying structures of the density matrix. Despite their theoretical guarantee of a linear convergence rate, the convergence in practical scenarios is still slow because the contracting factor of the FGD algorithms depends on the condition number κ of the ground truth state. Consequently, the total number of iterations can be as large as O(κ−−√ln(1ε)) to achieve the estimation error ε. In this work, we derive a quantum state tomography scheme that improves the dependence on κ to the logarithmic scale; namely, our algorithm could achieve the approximation error ε in O(ln(1κε)) steps. The improvement comes from the application of the non-convex Riemannian gradient descent (RGD). The contracting factor in our approach is thus a universal constant that is independent of the given state. Our theoretical results of extremely fast convergence and nearly optimal error bounds are corroborated by numerical results.

10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aHsu, Ming-Chien1 aKuo, En-Jui1 aYu, Wei-Hsuan1 aCai, Jian-Feng1 aHsieh, Min-Hsiu uhttps://arxiv.org/abs/2210.0471701714nas a2200181 4500008004100000245004400041210004400085260001500129490000800144520120900152100002801361700002801389700002101417700002001438700001701458700002001475856003701495 2022 eng d00aResource theory of quantum uncomplexity0 aResource theory of quantum uncomplexity c12/19/20220 v1063 a

Quantum complexity is emerging as a key property of many-body systems, including black holes, topological materials, and early quantum computers. A state's complexity quantifies the number of computational gates required to prepare the state from a simple tensor product. The greater a state's distance from maximal complexity, or "uncomplexity," the more useful the state is as input to a quantum computation. Separately, resource theories -- simple models for agents subject to constraints -- are burgeoning in quantum information theory. We unite the two domains, confirming Brown and Susskind's conjecture that a resource theory of uncomplexity can be defined. The allowed operations, fuzzy operations, are slightly random implementations of two-qubit gates chosen by an agent. We formalize two operational tasks, uncomplexity extraction and expenditure. Their optimal efficiencies depend on an entropy that we engineer to reflect complexity. We also present two monotones, uncomplexity measures that decline monotonically under fuzzy operations, in certain regimes. This work unleashes on many-body complexity the resource-theory toolkit from quantum information theory.

1 aHalpern, Nicole, Yunger1 aKothakonda, Naga, B. T.1 aHaferkamp, Jonas1 aMunson, Anthony1 aEisert, Jens1 aFaist, Philippe uhttps://arxiv.org/abs/2110.1137101923nas a2200241 4500008004100000245007300041210006900114260001400183520110600197653004301303653002701346653002901373653003901402653003101441653005201472100002001524700002801544700001501572700002401587700001601611700001701627856003701644 2022 eng d00aScalably learning quantum many-body Hamiltonians from dynamical data0 aScalably learning quantum manybody Hamiltonians from dynamical d c9/28/20223 a

The physics of a closed quantum mechanical system is governed by its Hamiltonian. However, in most practical situations, this Hamiltonian is not precisely known, and ultimately all there is are data obtained from measurements on the system. In this work, we introduce a highly scalable, data-driven approach to learning families of interacting many-body Hamiltonians from dynamical data, by bringing together techniques from gradient-based optimization from machine learning with efficient quantum state representations in terms of tensor networks. Our approach is highly practical, experimentally friendly, and intrinsically scalable to allow for system sizes of above 100 spins. In particular, we demonstrate on synthetic data that the algorithm works even if one is restricted to one simple initial state, a small number of single-qubit observables, and time evolution up to relatively short times. For the concrete example of the one-dimensional Heisenberg model our algorithm exhibits an error constant in the system size and scaling as the inverse square root of the size of the data set.

10aFOS: Computer and information sciences10aFOS: Physical sciences10aMachine Learning (cs.LG)10aQuantum Gases (cond-mat.quant-gas)10aQuantum Physics (quant-ph)10aStrongly Correlated Electrons (cond-mat.str-el)1 aWilde, Frederik1 aKshetrimayum, Augustine1 aRoth, Ingo1 aHangleiter, Dominik1 aSweke, Ryan1 aEisert, Jens uhttps://arxiv.org/abs/2209.1432802029nas a2200325 4500008004100000245006700041210006500108260001400173520109100187653003701278653002701315653003101342100001701373700001201390700002301402700001901425700001901444700001501463700001201478700002001490700001801510700001701528700002001545700001901565700001901584700002201603700001901625700002201644856003701666 2022 eng d00aSelf-Testing of a Single Quantum System: Theory and Experiment0 aSelfTesting of a Single Quantum System Theory and Experiment c3/17/20223 a

Certifying individual quantum devices with minimal assumptions is crucial for the development of quantum technologies. Here, we investigate how to leverage single-system contextuality to realize self-testing. We develop a robust self-testing protocol based on the simplest contextuality witness for the simplest contextual quantum system, the Klyachko-Can-Binicioğlu-Shumovsky (KCBS) inequality for the qutrit. We establish a lower bound on the fidelity of the state and the measurements (to an ideal configuration) as a function of the value of the witness under a pragmatic assumption on the measurements we call the KCBS orthogonality condition. We apply the method in an experiment with randomly chosen measurements on a single trapped 40Ca+ and near-perfect detection efficiency. The observed statistics allow us to self-test the system and provide the first experimental demonstration of quantum self-testing of a single system. Further, we quantify and report that deviations from our assumptions are minimal, an aspect previously overlooked by contextuality experiments.

10aAtomic Physics (physics.atom-ph)10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aHu, Xiao-Min1 aXie, Yi1 aArora, Atul, Singh1 aAi, Ming-Zhong1 aBharti, Kishor1 aZhang, Jie1 aWu, Wei1 aChen, Ping-Xing1 aCui, Jin-Ming1 aLiu, Bi-Heng1 aHuang, Yun-Feng1 aLi, Chuan-Feng1 aGuo, Guang-Can1 aRoland, Jérémie1 aCabello, Adán1 aKwek, Leong-Chuan uhttps://arxiv.org/abs/2203.0900302774nas a2200241 4500008004100000245009900041210006900140260001100209520197600220100001902196700001702215700001802232700001602250700001602266700001702282700002202299700001702321700001802338700001802356700001702374700002102391856012002412 2022 eng d00aStatus Report on the Third Round of the NIST Post-Quantum Cryptography Standardization Process0 aStatus Report on the Third Round of the NIST PostQuantum Cryptog c7/20223 a

The National Institute of Standards and Technology is in the process of selecting publickey cryptographic algorithms through a public, competition-like process. The new publickey cryptography standards will specify additional digital signature, public-key encryption, and key-establishment algorithms to augment Federal Information Processing Standard (FIPS) 186-4, Digital Signature Standard (DSS), as well as NIST Special Publication (SP) 800-56A Revision 3, Recommendation for Pair-Wise Key-Establishment Schemes Using Discrete Logarithm Cryptography, and SP 800-56B Revision 2, Recommendation for Pair-Wise Key Establishment Using Integer Factorization Cryptography. It is intended that these algorithms will be capable of protecting sensitive information well into the foreseeable future, including after the advent of quantum computers.

This report describes the evaluation and selection process of the NIST Post-Quantum Cryptography Standardization process third-round candidates based on public feedback and internal review. The report summarizes each of the 15 third-round candidate algorithms and identifies those selected for standardization, as well as those that will continue to be evaluated in a fourth round of analysis. The public-key encryption and key-establishment algorithm that will be standardized is CRYSTALS–KYBER. The digital signatures that will be standardized are CRYSTALS–Dilithium, FALCON, and SPHINCS+. While there are multiple signature algorithms selected, NIST recommends CRYSTALS–Dilithium as the primary algorithm to be implemented. In addition, four of the alternate key-establishment candidate algorithms will advance to a fourth round of evaluation: BIKE, Classic McEliece, HQC, and SIKE. These candidates are still being considered for future standardization. NIST will also issue a new Call for Proposals for public-key digital signature algorithms to augment and diversify its signature portfolio.

1 aAlagic, Gorjan1 aApon, Daniel1 aCooper, David1 aDang, Quynh1 aDang, Thinh1 aKelsey, John1 aLichtinger, Jacob1 aMiller, Carl1 aMoody, Dustin1 aPeralta, Rene1 aPerlner, Ray1 aRobinson, Angela uhttps://quics.umd.edu/publications/status-report-third-round-nist-post-quantum-cryptography-standardization-process01763nas a2200169 4500008004100000245007700041210006900118260001500187490000600202520123700208100002101445700002601466700002101492700001901513700002401532856003701556 2022 eng d00aTheoretical bounds on data requirements for the ray-based classification0 aTheoretical bounds on data requirements for the raybased classif c02/26/20220 v33 a

The problem of classifying high-dimensional shapes in real-world data grows in complexity as the dimension of the space increases. For the case of identifying convex shapes of different geometries, a new classification framework has recently been proposed in which the intersections of a set of one-dimensional representations, called rays, with the boundaries of the shape are used to identify the specific geometry. This ray-based classification (RBC) has been empirically verified using a synthetic dataset of two- and three-dimensional shapes [1] and, more recently, has also been validated experimentally [2]. Here, we establish a bound on the number of rays necessary for shape classification, defined by key angular metrics, for arbitrary convex shapes. For two dimensions, we derive a lower bound on the number of rays in terms of the shape's length, diameter, and exterior angles. For convex polytopes in R^N, we generalize this result to a similar bound given as a function of the dihedral angle and the geometrical parameters of polygonal faces. This result enables a different approach for estimating high-dimensional shapes using substantially fewer data elements than volumetric or surface-based approaches.

1 aWeber, Brian, J.1 aKalantre, Sandesh, S.1 aMcJunkin, Thomas1 aTaylor, J., M.1 aZwolak, Justyna, P. uhttps://arxiv.org/abs/2103.0957701880nas a2200229 4500008004100000245005800041210005800099260001500157490000700172520123000179100002001409700002101429700001701450700002601467700002001493700001701513700001801530700001901548700002201567700002401589856003701613 2022 eng d00aToward Robust Autotuning of Noisy Quantum dot Devices0 aToward Robust Autotuning of Noisy Quantum dot Devices c02/26/20220 v173 a

The current autotuning approaches for quantum dot (QD) devices, while showing some success, lack an assessment of data reliability. This leads to unexpected failures when noisy or otherwise low-quality data is processed by an autonomous system. In this work, we propose a framework for robust autotuning of QD devices that combines a machine learning (ML) state classifier with a data quality control module. The data quality control module acts as a "gatekeeper" system, ensuring that only reliable data are processed by the state classifier. Lower data quality results in either device recalibration or termination. To train both ML systems, we enhance the QD simulation by incorporating synthetic noise typical of QD experiments. We confirm that the inclusion of synthetic noise in the training of the state classifier significantly improves the performance, resulting in an accuracy of 95.0(9) % when tested on experimental data. We then validate the functionality of the data quality control module by showing that the state classifier performance deteriorates with decreasing data quality, as expected. Our results establish a robust and flexible ML framework for autonomous tuning of noisy QD devices.

1 aZiegler, Joshua1 aMcJunkin, Thomas1 aJoseph, E.S.1 aKalantre, Sandesh, S.1 aHarpt, Benjamin1 aSavage, D.E.1 aLagally, M.G.1 aEriksson, M.A.1 aTaylor, Jacob, M.1 aZwolak, Justyna, P. uhttps://arxiv.org/abs/2108.0004301797nas a2200229 4500008004100000245007000041210006800111260001400179300001200193490000800205520107400213653003701287653002701324653003901351653003101390100002101421700002401442700001901466700002301485700002201508856003701530 2022 eng d00aTweezer-programmable 2D quantum walks in a Hubbard-regime lattice0 aTweezerprogrammable 2D quantum walks in a Hubbardregime lattice c8/18/2022 a885-8890 v3773 a

Quantum walks provide a framework for understanding and designing quantum algorithms that is both intuitive and universal. To leverage the computational power of these walks, it is important to be able to programmably modify the graph a walker traverses while maintaining coherence. Here, we do this by combining the fast, programmable control provided by optical tweezer arrays with the scalable, homogeneous environment of an optical lattice. Using this new combination of tools we study continuous-time quantum walks of single atoms on a 2D square lattice, and perform proof-of-principle demonstrations of spatial search using these walks. When scaled to more particles, the capabilities demonstrated here can be extended to study a variety of problems in quantum information science and quantum simulation, including the deterministic assembly of ground and excited states in Hubbard models with tunable interactions, and performing versions of spatial search in a larger graph with increased connectivity, where search by quantum walk can be more effective.

10aAtomic Physics (physics.atom-ph)10aFOS: Physical sciences10aQuantum Gases (cond-mat.quant-gas)10aQuantum Physics (quant-ph)1 aYoung, Aaron, W.1 aEckner, William, J.1 aSchine, Nathan1 aChilds, Andrew, M.1 aKaufman, Adam, M. uhttps://arxiv.org/abs/2202.0120402137nas a2200169 4500008004100000245004200041210004200083260001300125520166200138100002101800700001701821700002401838700002101862700002201883700002501905856003701930 2021 eng d00aBehavior of Analog Quantum Algorithms0 aBehavior of Analog Quantum Algorithms c7/2/20213 a

Analog quantum algorithms are formulated in terms of Hamiltonians rather than unitary gates and include quantum adiabatic computing, quantum annealing, and the quantum approximate optimization algorithm (QAOA). These algorithms are promising candidates for near-term quantum applications, but they often require fine tuning via the annealing schedule or variational parameters. In this work, we explore connections between these analog algorithms, as well as limits in which they become approximations of the optimal procedure.Notably, we explore how the optimal procedure approaches a smooth adiabatic procedure but with a superposed oscillatory pattern that can be explained in terms of the interactions between the ground state and first excited state that effect the coherent error cancellation of diabatic transitions. Furthermore, we provide numeric and analytic evidence that QAOA emulates this optimal procedure with the length of each QAOA layer equal to the period of the oscillatory pattern. Additionally, the ratios of the QAOA bangs are determined by the smooth, non-oscillatory part of the optimal procedure. We provide arguments for these phenomena in terms of the product formula expansion of the optimal procedure. With these arguments, we conclude that different analog algorithms can emulate the optimal protocol under different limits and approximations. Finally, we present a new algorithm for better approximating the optimal protocol using the analytic and numeric insights from the rest of the paper. In practice, numerically, we find that this algorithm outperforms standard QAOA and naive quantum annealing procedures. 

1 aBrady, Lucas, T.1 aKocia, Lucas1 aBienias, Przemyslaw1 aBapat, Aniruddha1 aKharkov, Yaroslav1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2107.0121801867nas a2200157 4500008004100000245010800041210006900149260001400218520132800232100002401560700002001584700001901604700002401623700002501647856003701672 2021 eng d00aCircuit Quantum Electrodynamics in Hyperbolic Space: From Photon Bound States to Frustrated Spin Models0 aCircuit Quantum Electrodynamics in Hyperbolic Space From Photon  c5/13/20213 a

Circuit quantum electrodynamics is one of the most promising platforms for efficient quantum simulation and computation. In recent groundbreaking experiments, the immense flexibility of superconducting microwave resonators was utilized to realize hyperbolic lattices that emulate quantum physics in negatively curved space. Here we investigate experimentally feasible settings in which a few superconducting qubits are coupled to a bath of photons evolving on the hyperbolic lattice. We compare our numerical results for finite lattices with analytical results for continuous hyperbolic space on the Poincaré disk. We find good agreement between the two descriptions in the long-wavelength regime. We show that photon-qubit bound states have a curvature-limited size. We propose to use a qubit as a local probe of the hyperbolic bath, for example by measuring the relaxation dynamics of the qubit. We find that, although the boundary effects strongly impact the photonic density of states, the spectral density is well described by the continuum theory. We show that interactions between qubits are mediated by photons propagating along geodesics. We demonstrate that the photonic bath can give rise to geometrically-frustrated hyperbolic quantum spin models with finite-range or exponentially-decaying interaction.

1 aBienias, Przemyslaw1 aBoettcher, Igor1 aBelyansky, Ron1 aKollár, Alicia, J.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2105.0649002085nas a2200169 4500008004100000245004300041210004300084260001300127520161100140100002001751700002501771700002401796700002101820700001801841700001901859856003701878 2021 eng d00aCrystallography of Hyperbolic Lattices0 aCrystallography of Hyperbolic Lattices c5/3/20213 a

Hyperbolic lattices are a revolutionary platform for tabletop simulations of holography and quantum physics in curved space and facilitate efficient quantum error correcting codes. Their underlying geometry is non-Euclidean, and the absence of Bloch's theorem precludes a simple understanding of their band structure. Motivated by recent insights into hyperbolic band theory, we initiate a crystallography of hyperbolic lattices. We show that many hyperbolic lattices feature a hidden crystal structure characterized by unit cells, hyperbolic Bravais lattices, and associated symmetry groups. Using the mathematical framework of higher-genus Riemann surfaces and Fuchsian groups, we derive, for the first time, a list of example hyperbolic {p,q} lattices and their hyperbolic Bravais lattices, including five infinite families and several graphs relevant for experiments in circuit quantum electrodynamics and topolectrical circuits. Our results find application for both finite and infinite hyperbolic lattices. We describe a method to efficiently generate finite hyperbolic lattices of arbitrary size and explain why the present crystallography is the first step towards a complete band theory of hyperbolic lattices and apply it to construct Bloch wave Hamiltonians. This work lays the foundation for generalizing some of the most powerful concepts of solid state physics, such as crystal momentum and Brillouin zone, to the emerging field of hyperbolic lattices and tabletop simulations of gravitational theories, and reveals the connections to concepts from topology and algebraic geometry.

1 aBoettcher, Igor1 aGorshkov, Alexey, V.1 aKollár, Alicia, J.1 aMaciejko, Joseph1 aRayan, Steven1 aThomale, Ronny uhttps://arxiv.org/abs/2105.0108701900nas a2200157 4500008004100000245008000041210006900121260001400190520140900204100001601613700001801629700001801647700001901665700002101684856003701705 2021 eng d00aDecoding conformal field theories: from supervised to unsupervised learning0 aDecoding conformal field theories from supervised to unsupervise c7/10/20213 a

We use machine learning to classify rational two-dimensional conformal field theories. We first use the energy spectra of these minimal models to train a supervised learning algorithm. We find that the machine is able to correctly predict the nature and the value of critical points of several strongly correlated spin models using only their energy spectra. This is in contrast to previous works that use machine learning to classify different phases of matter, but do not reveal the nature of the critical point between phases. Given that the ground-state entanglement Hamiltonian of certain topological phases of matter is also described by conformal field theories, we use supervised learning on Réyni entropies and find that the machine is able to identify which conformal field theory describes the entanglement Hamiltonian with only the lowest few Réyni entropies to a high degree of accuracy. Finally, using autoencoders, an unsupervised learning algorithm, we find a hidden variable that has a direct correlation with the central charge and discuss prospects for using machine learning to investigate other conformal field theories, including higher-dimensional ones. Our results highlight that machine learning can be used to find and characterize critical points and also hint at the intriguing possibility to use machine learning to learn about more complex conformal field theories.

1 aKuo, En-Jui1 aSeif, Alireza1 aLundgren, Rex1 aWhitsitt, Seth1 aHafezi, Mohammad uhttps://arxiv.org/abs/2106.1348502078nas a2200277 4500008004100000245006700041210006600108260001500174520125200189100002201441700001801463700002501481700002101506700002401527700002501551700002101576700002001597700002501617700002601642700001601668700001901684700002301703700001801726700001901744856003701763 2021 eng d00aDevice-independent Randomness Expansion with Entangled Photons0 aDeviceindependent Randomness Expansion with Entangled Photons c01/28/20213 a

With the growing availability of experimental loophole-free Bell tests, it has become possible to implement a new class of device-independent random number generators whose output can be certified to be uniformly random without requiring a detailed model of the quantum devices used. However, all of these experiments require many input bits in order to certify a small number of output bits, and it is an outstanding challenge to develop a system that generates more randomness than is used. Here, we devise a device-independent spot-checking protocol which uses only uniform bits as input. Implemented with a photonic loophole-free Bell test, we can produce 24% more certified output bits (1,181,264,237) than consumed input bits (953,301,640), which is 5 orders of magnitude more efficient than our previous work [arXiv:1812.07786]. The experiment ran for 91.0 hours, creating randomness at an average rate of 3606 bits/s with a soundness error bounded by 5.7×10−7 in the presence of classical side information. Our system will allow for greater trust in public sources of randomness, such as randomness beacons, and the protocols may one day enable high-quality sources of private randomness as the device footprint shrinks.

1 aShalm, Lynden, K.1 aZhang, Yanbao1 aBienfang, Joshua, C.1 aSchlager, Collin1 aStevens, Martin, J.1 aMazurek, Michael, D.1 aAbellán, Carlos1 aAmaya, Waldimar1 aMitchell, Morgan, W.1 aAlhejji, Mohammad, A.1 aFu, Honghao1 aOrnstein, Joel1 aMirin, Richard, P.1 aNam, Sae, Woo1 aKnill, Emanuel uhttps://arxiv.org/abs/1912.1115801944nas a2200181 4500008004100000245006800041210006700109260001400176520137900190100002201569700001801591700001801609700002401627700002801651700002101679700002501700856003701725 2021 eng d00aDiscovering hydrodynamic equations of many-body quantum systems0 aDiscovering hydrodynamic equations of manybody quantum systems c11/3/20213 a

Simulating and predicting dynamics of quantum many-body systems is extremely challenging, even for state-of-the-art computational methods, due to the spread of entanglement across the system. However, in the long-wavelength limit, quantum systems often admit a simplified description, which involves a small set of physical observables and requires only a few parameters such as sound velocity or viscosity. Unveiling the relationship between these hydrodynamic equations and the underlying microscopic theory usually requires a great effort by condensed matter theorists. In the present paper, we develop a new machine-learning framework for automated discovery of effective equations from a limited set of available data, thus bypassing complicated analytical derivations. The data can be generated from numerical simulations or come from experimental quantum simulator platforms. Using integrable models, where direct comparisons can be made, we reproduce previously known hydrodynamic equations, strikingly discover novel equations and provide their derivation whenever possible. We discover new hydrodynamic equations describing dynamics of interacting systems, for which the derivation remains an outstanding challenge. Our approach provides a new interpretable method to study properties of quantum materials and quantum simulators in non-perturbative regimes.

1 aKharkov, Yaroslav1 aShtanko, Oles1 aSeif, Alireza1 aBienias, Przemyslaw1 aVan Regemortel, Mathias1 aHafezi, Mohammad1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2111.0238501381nas a2200205 4500008004100000245004900041210004700090260001400137520077400151100002000925700001900945700001500964700002400979700001901003700001901022700002301041700001501064700001301079856008301092 2021 eng d00aEasyPQC: Verifying Post-Quantum Cryptography0 aEasyPQC Verifying PostQuantum Cryptography c9/20/20213 a

EasyCrypt is a formal verification tool used extensively for formalizing concrete security proofs of cryptographic constructions. However, the EasyCrypt formal logics consider only classical attackers, which means that post-quantum security proofs cannot be formalized and machine-checked with this tool. In this paper we prove that a natural extension of the EasyCrypt core logics permits capturing a wide class of post-quantum cryptography proofs, settling a question raised by (Unruh, POPL 2019). Leveraging our positive result, we implement EasyPQC, an extension of EasyCrypt for post-quantum security proofs, and use EasyPQC to verify post-quantum security of three classic constructions: PRF-based MAC, Full Domain Hash and GPV08 identity-based encryption.

1 aBarbosa, Manuel1 aBarthe, Gilles1 aFan, Xiong1 aGrégoire, Benjamin1 aHung, Shih-Han1 aKatz, Jonathan1 aStrub, Pierre-Yves1 aWu, Xiaodi1 aZhou, Li uhttps://quics.umd.edu/publications/easypqc-verifying-post-quantum-cryptography02034nas a2200181 4500008004100000245008100041210006900122260001300191490000800204520146900212100001801681700002501699700002001724700002301744700002501767700002301792856003701815 2021 eng d00aEfficient quantum algorithm for dissipative nonlinear differential equations0 aEfficient quantum algorithm for dissipative nonlinear differenti c3/1/20210 v1183 a

While there has been extensive previous work on efficient quantum algorithms for linear differential equations, analogous progress for nonlinear differential equations has been severely limited due to the linearity of quantum mechanics. Despite this obstacle, we develop a quantum algorithm for initial value problems described by dissipative quadratic n-dimensional ordinary differential equations. Assuming R<1, where R is a parameter characterizing the ratio of the nonlinearity to the linear dissipation, this algorithm has complexity T2poly(logT,logn)/ϵ, where T is the evolution time and ϵ is the allowed error in the output quantum state. This is an exponential improvement over the best previous quantum algorithms, whose complexity is exponential in T. We achieve this improvement using the method of Carleman linearization, for which we give an improved convergence theorem. This method maps a system of nonlinear differential equations to an infinite-dimensional system of linear differential equations, which we discretize, truncate, and solve using the forward Euler method and the quantum linear system algorithm. We also provide a lower bound on the worst-case complexity of quantum algorithms for general quadratic differential equations, showing that the problem is intractable for R≥2–√. Finally, we discuss potential applications of this approach to problems arising in biology as well as in fluid and plasma dynamics.

1 aLiu, Jin-Peng1 aKolden, Herman, Øie1 aKrovi, Hari, K.1 aLoureiro, Nuno, F.1 aTrivisa, Konstantina1 aChilds, Andrew, M. uhttps://arxiv.org/abs/2011.0318502215nas a2200169 4500008004100000245006400041210006300105260001300168490000700181520171100188100002101899700002101920700002701941700002001968700002001988856003702008 2021 eng d00aEntanglement Phase Transitions in Measurement-Only Dynamics0 aEntanglement Phase Transitions in MeasurementOnly Dynamics c1/2/20210 v113 a

Unitary circuits subject to repeated projective measurements can undergo an entanglement phase transition (EPT) as a function of the measurement rate. This transition is generally understood in terms of a competition between the scrambling effects of unitary dynamics and the disentangling effects of measurements. We find that, surprisingly, EPTs are possible even in the absence of scrambling unitary dynamics, where they are best understood as arising from measurements alone. This motivates us to introduce \emph{measurement-only models}, in which the "scrambling" and "un-scrambling" effects driving the EPT are fundamentally intertwined and cannot be attributed to physically distinct processes. This represents a novel form of an EPT, conceptually distinct from that in hybrid unitary-projective circuits. We explore the entanglement phase diagrams, critical points, and quantum code properties of some of these measurement-only models. We find that the principle driving the EPTs in these models is \emph{frustration}, or mutual incompatibility, of the measurements. Suprisingly, an entangling (volume-law) phase is the generic outcome when measuring sufficiently long but still local (≳3-body) operators. We identify a class of exceptions to this behavior ("bipartite ensembles") which cannot sustain an entangling phase, but display dual area-law phases, possibly with different kinds of quantum order, separated by self-dual critical points. Finally, we introduce a measure of information spreading in dynamics with measurements and use it to demonstrate the emergence of a statistical light-cone, despite the non-locality inherent to quantum measurements.

1 aIppoliti, Matteo1 aGullans, Michael1 aGopalakrishnan, Sarang1 aHuse, David, A.1 aKhemani, Vedika uhttps://arxiv.org/abs/2004.0956002349nas a2200313 4500008004100000245007100041210006900112260001400181520145100195100001601646700003401662700001701696700001801713700001301731700001801744700001901762700002101781700001401802700002201816700001601838700002501854700001801879700001901897700002001916700002001936700001801956700002401974856003701998 2021 eng d00aInteractive Protocols for Classically-Verifiable Quantum Advantage0 aInteractive Protocols for ClassicallyVerifiable Quantum Advantag c12/9/20213 a

Achieving quantum computational advantage requires solving a classically intractable problem on a quantum device. Natural proposals rely upon the intrinsic hardness of classically simulating quantum mechanics; however, verifying the output is itself classically intractable. On the other hand, certain quantum algorithms (e.g. prime factorization via Shor's algorithm) are efficiently verifiable, but require more resources than what is available on near-term devices. One way to bridge the gap between verifiability and implementation is to use "interactions" between a prover and a verifier. By leveraging cryptographic functions, such protocols enable the classical verifier to enforce consistency in a quantum prover's responses across multiple rounds of interaction. In this work, we demonstrate the first implementation of an interactive quantum advantage protocol, using an ion trap quantum computer. We execute two complementary protocols -- one based upon the learning with errors problem and another where the cryptographic construction implements a computational Bell test. To perform multiple rounds of interaction, we implement mid-circuit measurements on a subset of trapped ion qubits, with subsequent coherent evolution. For both protocols, the performance exceeds the asymptotic bound for classical behavior; maintaining this fidelity at scale would conclusively demonstrate verifiable quantum advantage.

1 aZhu, Daiwei1 aKahanamoku-Meyer, Gregory, D.1 aLewis, Laura1 aNoel, Crystal1 aKatz, Or1 aHarraz, Bahaa1 aWang, Qingfeng1 aRisinger, Andrew1 aFeng, Lei1 aBiswas, Debopriyo1 aEgan, Laird1 aGheorghiu, Alexandru1 aNam, Yunseong1 aVidick, Thomas1 aVazirani, Umesh1 aYao, Norman, Y.1 aCetina, Marko1 aMonroe, Christopher uhttps://arxiv.org/abs/2112.0515601631nas a2200169 4500008004100000245009500041210006900136260001400205520107500219100001901294700002401313700002101337700002201358700001901380700002501399856003701424 2021 eng d00aLinear and continuous variable spin-wave processing using a cavity-coupled atomic ensemble0 aLinear and continuous variable spinwave processing using a cavit c9/30/20213 a

Spin-wave excitations in ensembles of atoms are gaining attention as a quantum information resource. However, current techniques with atomic spin waves do not achieve universal quantum information processing. We conduct a theoretical analysis of methods to create a high-capacity universal quantum processor and network node using an ensemble of laser-cooled atoms, trapped in a one-dimensional periodic potential and coupled to a ring cavity. We describe how to establish linear quantum processing using a lambda-scheme in a rubidium-atom system, calculate the expected experimental operational fidelities. Second, we derive an efficient method to achieve linear controllability with a single ensemble of atoms, rather than two-ensembles as proposed in [K. C. Cox et al. Spin-Wave Quantum Computing with Atoms in a Single-Mode Cavity, preprint 2021]. Finally, we propose to use the spin-wave processor for continuous-variable quantum information processing and present a scheme to generate large dual-rail cluster states useful for deterministic computing. 

1 aCox, Kevin, C.1 aBienias, Przemyslaw1 aMeyer, David, H.1 aFahey, Donald, P.1 aKunz, Paul, D.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2109.1524601733nas a2200133 4500008004100000245014300041210006900184260001400253520122700267100001601494700003001510700002201540856003701562 2021 eng d00aLocalization crossover and subdiffusive transport in a classical facilitated network model of a disordered, interacting quantum spin chain0 aLocalization crossover and subdiffusive transport in a classical c9/22/20213 a

We consider the random-field Heisenberg model, a paradigmatic model for many-body localization (MBL), and add a Markovian dephasing bath coupled to the Anderson orbitals of the model's non-interacting limit. We map this system to a classical facilitated hopping model that is computationally tractable for large system sizes, and investigate its dynamics. The classical model exhibits a robust crossover between an ergodic (thermal) phase and a frozen (localized) phase. The frozen phase is destabilized by thermal subregions (bubbles), which thermalize surrounding sites by providing a fluctuating interaction energy and so enable off-resonance particle transport. Investigating steady state transport, we observe that the interplay between thermal and frozen bubbles leads to a clear transition between diffusive and subdiffusive regimes. This phenomenology both describes the MBL system coupled to a bath, and provides a classical analogue for the many-body localization transition in the corresponding quantum model, in that the classical model displays long local memory times. It also highlights the importance of the details of the bath coupling in studies of MBL systems coupled to thermal environments.

1 aKlocke, Kai1 aWhite, Christopher, David1 aBuchhold, Michael uhttps://arxiv.org/abs/2109.1092601981nas a2200241 4500008004100000245005400041210005400095260001300149520129500162100002501457700002301482700002001505700002001525700002201545700002201567700001401589700001901603700001801622700001801640700002001658700002401678856003701702 2021 eng d00aObservation of a prethermal discrete time crystal0 aObservation of a prethermal discrete time crystal c2/2/20213 a

The conventional framework for defining and understanding phases of matter requires thermodynamic equilibrium. Extensions to non-equilibrium systems have led to surprising insights into the nature of many-body thermalization and the discovery of novel phases of matter, often catalyzed by driving the system periodically. The inherent heating from such Floquet drives can be tempered by including strong disorder in the system, but this can also mask the generality of non-equilibrium phases. In this work, we utilize a trapped-ion quantum simulator to observe signatures of a non-equilibrium driven phase without disorder: the prethermal discrete time crystal (PDTC). Here, many-body heating is suppressed not by disorder-induced many-body localization, but instead via high-frequency driving, leading to an expansive time window where non-equilibrium phases can emerge. We observe a number of key features that distinguish the PDTC from its many-body-localized disordered counterpart, such as the drive-frequency control of its lifetime and the dependence of time-crystalline order on the energy density of the initial state. Floquet prethermalization is thus presented as a general strategy for creating, stabilizing and studying intrinsically out-of-equilibrium phases of matter.

1 aKyprianidis, Antonis1 aMachado, Francisco1 aMorong, William1 aBecker, Patrick1 aCollins, Kate, S.1 aElse, Dominic, V.1 aFeng, Lei1 aHess, Paul, W.1 aNayak, Chetan1 aPagano, Guido1 aYao, Norman, Y.1 aMonroe, Christopher uhttps://arxiv.org/abs/2102.0169502060nas a2200217 4500008004100000245006500041210006400106260001400170520145900184100001501643700001201658700001501670700002001685700001301705700002001718700001501738700001201753700002501765700001501790856003701805 2021 eng d00aObservation of Stark many-body localization without disorder0 aObservation of Stark manybody localization without disorder c2/14/20213 a

Thermalization is a ubiquitous process of statistical physics, in which details of few-body observables are washed out in favor of a featureless steady state. Even in isolated quantum many-body systems, limited to reversible dynamics, thermalization typically prevails. However, in these systems, there is another possibility: many-body localization (MBL) can result in preservation of a non-thermal state. While disorder has long been considered an essential ingredient for this phenomenon, recent theoretical work has suggested that a quantum many-body system with a uniformly increasing field -- but no disorder -- can also exhibit MBL, resulting in `Stark MBL.' Here we realize Stark MBL in a trapped-ion quantum simulator and demonstrate its key properties: halting of thermalization and slow propagation of correlations. Tailoring the interactions between ionic spins in an effective field gradient, we directly observe their microscopic equilibration for a variety of initial states, and we apply single-site control to measure correlations between separate regions of the spin chain. Further, by engineering a varying gradient, we create a disorder-free system with coexisting long-lived thermalized and nonthermal regions. The results demonstrate the unexpected generality of MBL, with implications about the fundamental requirements for thermalization and with potential uses in engineering long-lived non-equilibrium quantum matter.

1 aMorong, W.1 aLiu, F.1 aBecker, P.1 aCollins, K., S.1 aFeng, L.1 aKyprianidis, A.1 aPagano, G.1 aYou, T.1 aGorshkov, Alexey, V.1 aMonroe, C. uhttps://arxiv.org/abs/2102.0725001277nas a2200169 4500008004100000022001400041245006300055210006300118260001400181490000800195520078700203100001900990700001901009700002001028700002201048856003701070 2021 eng d a2470-002900aProposal for gravitational direct detection of dark matter0 aProposal for gravitational direct detection of dark matter c8/23/20210 v1023 a

The only coupling dark matter is guaranteed to have with the standard model is through gravity. Here we propose a concept for direct dark matter detection using only this gravitational coupling. We suggest that an array of quantum-limited mechanical impulse sensors may be capable of detecting the correlated gravitational force created by a passing dark matter particle. We consider the effects of irreducible noise from couplings of the sensors to the environment and noise due to the quantum measurement process. We show that the signal from Planck-scale dark matter is in principle detectable using a large number of gram-scale sensors in a meter-scale array with sufficiently low quantum noise, and discuss some experimental challenges en route to achieving this target.

1 aCarney, Daniel1 aGhosh, Sohitri1 aKrnjaic, Gordan1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/1903.0049201360nas a2200229 4500008004100000020002200041022001400063245003700077210003700114260001200151300001700163490000800180520076100188100001900949700001700968700001900985700001301004700001901017700001701036700002101053856005601074 2021 eng d a978-3-95977-188-7 a1868-896900aProving Quantum Programs Correct0 aProving Quantum Programs Correct c06/2021 a21:1–21:190 v1933 a

As quantum computing progresses steadily from theory into practice, programmers will face
a common problem: How can they be sure that their code does what they intend it to do? This
paper presents encouraging results in the application of mechanized proof to the domain of quantum
programming in the context of the sqir development. It verifies the correctness of a range of a
quantum algorithms including Grover’s algorithm and quantum phase estimation, a key component
of Shor’s algorithm. In doing so, it aims to highlight both the successes and challenges of formal
verification in the quantum context and motivate the theorem proving community to target quantum
computing as an application domain.

1 aHietala, Kesha1 aRand, Robert1 aHung, Shih-Han1 aLi, Liyi1 aHicks, Michael1 aCohen, Liron1 aKaliszyk, Cezary uhttps://drops.dagstuhl.de/opus/volltexte/2021/1391601833nas a2200217 4500008004100000245007400041210006900115260001500184490000800199520114200207653004301349653002701392653002901419653003101448100001801479700002101497700001901518700001901537700002201556856003701578 2021 eng d00aQuantum Algorithms for Reinforcement Learning with a Generative Model0 aQuantum Algorithms for Reinforcement Learning with a Generative  c12/15/20210 v1393 a

Reinforcement learning studies how an agent should interact with an environment to maximize its cumulative reward. A standard way to study this question abstractly is to ask how many samples an agent needs from the environment to learn an optimal policy for a γ-discounted Markov decision process (MDP). For such an MDP, we design quantum algorithms that approximate an optimal policy (π∗), the optimal value function (v∗), and the optimal Q-function (q∗), assuming the algorithms can access samples from the environment in quantum superposition. This assumption is justified whenever there exists a simulator for the environment; for example, if the environment is a video game or some other program. Our quantum algorithms, inspired by value iteration, achieve quadratic speedups over the best-possible classical sample complexities in the approximation accuracy (ϵ) and two main parameters of the MDP: the effective time horizon (11−γ) and the size of the action space (A). Moreover, we show that our quantum algorithm for computing q∗ is optimal by proving a matching quantum lower bound.

10aFOS: Computer and information sciences10aFOS: Physical sciences10aMachine Learning (cs.LG)10aQuantum Physics (quant-ph)1 aWang, Daochen1 aSundaram, Aarthi1 aKothari, Robin1 aKapoor, Ashish1 aRoetteler, Martin uhttps://arxiv.org/abs/2112.0845101494nas a2200181 4500008004100000245004000041210004000081260001400121490000600135520100800141100002101149700002301170700002501193700001701218700001901235700002101254856003701275 2021 eng d00aQuantum routing with fast reversals0 aQuantum routing with fast reversals c8/24/20210 v53 a

We present methods for implementing arbitrary permutations of qubits under interaction constraints. Our protocols make use of previous methods for rapidly reversing the order of qubits along a path. Given nearest-neighbor interactions on a path of length n, we show that there exists a constant ϵ≈0.034 such that the quantum routing time is at most (1−ϵ)n, whereas any swap-based protocol needs at least time n−1. This represents the first known quantum advantage over swap-based routing methods and also gives improved quantum routing times for realistic architectures such as grids. Furthermore, we show that our algorithm approaches a quantum routing time of 2n/3 in expectation for uniformly random permutations, whereas swap-based protocols require time n asymptotically. Additionally, we consider sparse permutations that route k≤n qubits and give algorithms with quantum routing time at most n/3+O(k2) on paths and at most 2r/3+O(k2) on general graphs with radius r.

1 aBapat, Aniruddha1 aChilds, Andrew, M.1 aGorshkov, Alexey, V.1 aKing, Samuel1 aSchoute, Eddie1 aShastri, Hrishee uhttps://arxiv.org/abs/2103.0326402275nas a2200193 4500008004100000245007200041210006900113260001500182490000600197520168200203100002401885700002101909700002601930700002301956700002301979700002302002700001902025856003702044 2021 eng d00aRay-based framework for state identification in quantum dot devices0 aRaybased framework for state identification in quantum dot devic c06/17/20210 v23 a

Quantum dots (QDs) defined with electrostatic gates are a leading platform for a scalable quantum computing implementation. However, with increasing numbers of qubits, the complexity of the control parameter space also grows. Traditional measurement techniques, relying on complete or near-complete exploration via two-parameter scans (images) of the device response, quickly become impractical with increasing numbers of gates. Here, we propose to circumvent this challenge by introducing a measurement technique relying on one-dimensional projections of the device response in the multi-dimensional parameter space. Dubbed as the ray-based classification (RBC) framework, we use this machine learning (ML) approach to implement a classifier for QD states, enabling automated recognition of qubit-relevant parameter regimes. We show that RBC surpasses the 82 % accuracy benchmark from the experimental implementation of image-based classification techniques from prior work while cutting down the number of measurement points needed by up to 70 %. The reduction in measurement cost is a significant gain for time-intensive QD measurements and is a step forward towards the scalability of these devices. We also discuss how the RBC-based optimizer, which tunes the device to a multi-qubit regime, performs when tuning in the two- and three-dimensional parameter spaces defined by plunger and barrier gates that control the dots. This work provides experimental validation of both efficient state identification and optimization with ML techniques for non-traditional measurements in quantum systems with high-dimensional parameter spaces and time-intensive measurements.

1 aZwolak, Justyna, P.1 aMcJunkin, Thomas1 aKalantre, Sandesh, S.1 aNeyens, Samuel, F.1 aMacQuarrie, E., R.1 aEriksson, Mark, A.1 aTaylor, J., M. uhttps://arxiv.org/abs/2102.1178401694nas a2200169 4500008004100000245004400041210004400085260001500129520120900144100002801353700002801381700002101409700002001430700001701450700002001467856003701487 2021 eng d00aResource theory of quantum uncomplexity0 aResource theory of quantum uncomplexity c10/21/20213 a

Quantum complexity is emerging as a key property of many-body systems, including black holes, topological materials, and early quantum computers. A state's complexity quantifies the number of computational gates required to prepare the state from a simple tensor product. The greater a state's distance from maximal complexity, or ``uncomplexity,'' the more useful the state is as input to a quantum computation. Separately, resource theories -- simple models for agents subject to constraints -- are burgeoning in quantum information theory. We unite the two domains, confirming Brown and Susskind's conjecture that a resource theory of uncomplexity can be defined. The allowed operations, fuzzy operations, are slightly random implementations of two-qubit gates chosen by an agent. We formalize two operational tasks, uncomplexity extraction and expenditure. Their optimal efficiencies depend on an entropy that we engineer to reflect complexity. We also present two monotones, uncomplexity measures that decline monotonically under fuzzy operations, in certain regimes. This work unleashes on many-body complexity the resource-theory toolkit from quantum information theory.

1 aHalpern, Nicole, Yunger1 aKothakonda, Naga, B. T.1 aHaferkamp, Jonas1 aMunson, Anthony1 aEisert, Jens1 aFaist, Philippe uhttps://arxiv.org/abs/2110.1137101423nas a2200145 4500008004100000245005800041210005300099260001400152520098400166100001801150700003701168700001601205700001901221856003701240 2021 eng d00aRPPLNS: Pay-per-last-N-shares with a Randomised Twist0 aRPPLNS PayperlastNshares with a Randomised Twist c2/15/20213 a

"Pay-per-last-N-shares" (PPLNS) is one of the most common payout strategies used by mining pools in Proof-of-Work (PoW) cryptocurrencies. As with any payment scheme, it is imperative to study issues of incentive compatibility of miners within the pool. For PPLNS this question has only been partially answered; we know that reasonably-sized miners within a PPLNS pool prefer following the pool protocol over employing specific deviations. In this paper, we present a novel modification to PPLNS where we randomise the protocol in a natural way. We call our protocol "Randomised pay-per-last-N-shares" (RPPLNS), and note that the randomised structure of the protocol greatly simplifies the study of its incentive compatibility. We show that RPPLNS maintains the strengths of PPLNS (i.e., fairness, variance reduction, and resistance to pool hopping), while also being robust against a richer class of strategic mining than what has been shown for PPLNS.

1 aLazos, Philip1 aMarmolejo-Cossío, Francisco, J.1 aZhou, Xinyu1 aKatz, Jonathan uhttps://arxiv.org/abs/2102.0768101130nas a2200169 4500008004100000245006700041210006500108260001400173520060600187100001900793700002400812700002100836700001900857700002200876700002500898856003700923 2021 eng d00aSpin-Wave Quantum Computing with Atoms in a Single-Mode Cavity0 aSpinWave Quantum Computing with Atoms in a SingleMode Cavity c9/30/20213 a

We present a method for network-capable quantum computing that relies on holographic spin-wave excitations stored collectively in ensembles of qubits. We construct an orthogonal basis of spin waves in a one-dimensional array and show that high-fidelity universal linear controllability can be achieved using only phase shifts, applied in both momentum and position space. Neither single-site addressability nor high single-qubit cooperativity is required, and the spin waves can be read out with high efficiency into a single cavity mode for quantum computing and networking applications. 

1 aCox, Kevin, C.1 aBienias, Przemyslaw1 aMeyer, David, H.1 aKunz, Paul, D.1 aFahey, Donald, P.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2109.1525201688nas a2200133 4500008004100000245005300041210005200094260001500146520129100161100002301452700002301475700001901498856003701517 2021 eng d00aSurface code compilation via edge-disjoint paths0 aSurface code compilation via edgedisjoint paths c10/21/20213 a

We provide an efficient algorithm to compile quantum circuits for fault-tolerant execution. We target surface codes, which form a 2D grid of logical qubits with nearest-neighbor logical operations. Embedding an input circuit's qubits in surface codes can result in long-range two-qubit operations across the grid. We show how to prepare many long-range Bell pairs on qubits connected by edge-disjoint paths of ancillas in constant depth which can be used to perform these long-range operations. This forms one core part of our Edge-Disjoint Paths Compilation (EDPC) algorithm, by easily performing parallel long-range Clifford operations in constant depth. It also allows us to establish a connection between surface code compilation and several well-studied edge-disjoint paths problems. Similar techniques allow us to perform non-Clifford single-qubit rotations far from magic state distillation factories. In this case, we can easily find the maximum set of paths by a max-flow reduction, which forms the other major part of our EDPC algorithm. We compare EDPC to other compilation approaches including a SWAP-based algorithm, and find significantly improved performance for circuits built from parallel CNOTs, and for circuits which implement the multi-controlled X gate.

1 aBeverland, Michael1 aKliuchnikov, Vadym1 aSchoute, Eddie uhttps://arxiv.org/abs/2110.1149301551nas a2200181 4500008004100000245006000041210005800101300000800159490000600167520101600173100002701189700002401216700002301240700002701263700002001290700002201310856003701332 2021 eng d00aA Threshold for Quantum Advantage in Derivative Pricing0 aThreshold for Quantum Advantage in Derivative Pricing a4630 v53 a

We give an upper bound on the resources required for valuable quantum advantage in pricing derivatives. To do so, we give the first complete resource estimates for useful quantum derivative pricing, using autocallable and Target Accrual Redemption Forward (TARF) derivatives as benchmark use cases. We uncover blocking challenges in known approaches and introduce a new method for quantum derivative pricing - the re-parameterization method - that avoids them. This method combines pre-trained variational circuits with fault-tolerant quantum computing to dramatically reduce resource requirements. We find that the benchmark use cases we examine require 7.5k logical qubits and a T-depth of 46 million and thus estimate that quantum advantage would require a logical clock speed of 10Mhz. While the resource requirements given here are out of reach of current systems, we hope they will provide a roadmap for further improvements in algorithms, implementations, and planned hardware architectures. 

1 aChakrabarti, Shouvanik1 aKrishnakumar, Rajiv1 aMazzola, Guglielmo1 aStamatopoulos, Nikitas1 aWoerner, Stefan1 aZeng, William, J. uhttps://arxiv.org/abs/2012.0381901587nas a2200217 4500008004100000245005800041210005700099260001400156520092600170100003001096700002401126700002801150700002101178700002401199700002301223700001901246700002501265700002401290700001801314856003701332 2021 eng d00aTunable three-body loss in a nonlinear Rydberg medium0 aTunable threebody loss in a nonlinear Rydberg medium c9/28/20203 a

Long-range Rydberg interactions, in combination with electromagnetically induced transparency (EIT), give rise to strongly interacting photons where the strength, sign, and form of the interactions are widely tunable and controllable. Such control can be applied to both coherent and dissipative interactions, which provides the potential to generate novel few-photon states. Recently it has been shown that Rydberg-EIT is a rare system in which three-body interactions can be as strong or stronger than two-body interactions. In this work, we study a three-body scattering loss for Rydberg-EIT in a wide regime of single and two-photon detunings. Our numerical simulations of the full three-body wavefunction and analytical estimates based on Fermi's Golden Rule strongly suggest that the observed features in the outgoing photonic correlations are caused by the resonant enhancement of the three-body losses.

1 aHuerta, Dalia, P. Ornelas1 aBienias, Przemyslaw1 aCraddock, Alexander, N.1 aGullans, Michael1 aHachtel, Andrew, J.1 aKalinowski, Marcin1 aLyon, Mary, E.1 aGorshkov, Alexey, V.1 aRolston, Steven, L.1 aPorto, J., V. uhttps://arxiv.org/abs/2009.1359901276nas a2200157 4500008004100000245007700041210006900118260001300187520076900200100002200969700002400991700001901015700002201034700002501056856003701081 2020 eng d00aAsymmetric blockade and multi-qubit gates via dipole-dipole interactions0 aAsymmetric blockade and multiqubit gates via dipoledipole intera c6/3/20203 a

Due to their strong and tunable interactions, Rydberg atoms can be used to realize fast two-qubit entangling gates. We propose a generalization of a generic two-qubit Rydberg-blockade gate to multi-qubit Rydberg-blockade gates which involve both many control qubits and many target qubits simultaneously. This is achieved by using strong microwave fields to dress nearby Rydberg states, leading to asymmetric blockade in which control-target interactions are much stronger than control-control and target-target interactions. The implementation of these multi-qubit gates can drastically simplify both quantum algorithms and state preparation. To illustrate this, we show that a 25-atom GHZ state can be created using only three gates with an error of 7.8%.

1 aYoung, Jeremy, T.1 aBienias, Przemyslaw1 aBelyansky, Ron1 aKaufman, Adam, M.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2006.0248602481nas a2200229 4500008004100000245006800041210006700109260001300176490000700189520180000196100002401996700002102020700002602041700001902067700002302086700001902109700002002128700002402148700002302172700001902195856003702214 2020 eng d00aAuto-tuning of double dot devices in situ with machine learning0 aAutotuning of double dot devices in situ with machine learning c4/1/20200 v133 a

There are myriad quantum computing approaches, each having its own set of challenges to understand and effectively control their operation. Electrons confined in arrays of semiconductor nanostructures, called quantum dots (QDs), is one such approach. The easy access to control parameters, fast measurements, long qubit lifetimes, and the potential for scalability make QDs especially attractive. However, as the size of the QD array grows, so does the number of parameters needed for control and thus the tuning complexity. The current practice of manually tuning the qubits is a relatively time-consuming procedure and is inherently impractical for scaling up and applications. In this work, we report on the in situ implementation of an auto-tuning protocol proposed by Kalantre et al. [arXiv:1712.04914]. In particular, we discuss how to establish a seamless communication protocol between a machine learning (ML)-based auto-tuner and the experimental apparatus. We then show that a ML algorithm trained exclusively on synthetic data coming from a physical model to quantitatively classify the state of the QD device, combined with an optimization routine, can be used to replace manual tuning of gate voltages in devices. A success rate of over 85 % is determined for tuning to a double quantum dot regime when at least one of the plunger gates is initiated sufficiently close to the desired state. Modifications to the training network, fitness function, and optimizer are discussed as a path towards further improvement in the success rate when starting both near and far detuned from the target double dot range.

1 aZwolak, Justyna, P.1 aMcJunkin, Thomas1 aKalantre, Sandesh, S.1 aDodson, J., P.1 aMacQuarrie, E., R.1 aSavage, D., E.1 aLagally, M., G.1 aCoppersmith, S., N.1 aEriksson, Mark, A.1 aTaylor, J., M. uhttps://arxiv.org/abs/1909.0803001546nas a2200145 4500008004100000245006600041210006600107260001400173520107500187100001801262700002601280700003201306700002501338856003701363 2020 eng d00aClassical Models of Entanglement in Monitored Random Circuits0 aClassical Models of Entanglement in Monitored Random Circuits c4/14/20203 a

The evolution of entanglement entropy in quantum circuits composed of Haar-random gates and projective measurements shows versatile behavior, with connections to phase transitions and complexity theory. We reformulate the problem in terms of a classical Markov process for the dynamics of bipartition purities and establish a probabilistic cellular-automaton algorithm to compute entanglement entropy in monitored random circuits on arbitrary graphs. In one dimension, we further relate the evolution of the entropy to a simple classical spin model that naturally generalizes a two-dimensional lattice percolation problem. We also establish a Markov model for the evolution of the zeroth Rényi entropy and demonstrate that, in one dimension and in the limit of large local dimension, it coincides with the corresponding second-Rényi-entropy model. Finally, we extend the Markovian description to a more general setting that incorporates continuous-time dynamics, defined by stochastic Hamiltonians and weak local measurements continuously monitoring the system.

1 aShtanko, Oles1 aKharkov, Yaroslav, A.1 aGarcía-Pintos, Luis, Pedro1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2004.0673601603nas a2200145 4500008004100000245010500041210006900146260001400215520111300229100002901342700001501371700001901386700001501405856003701420 2020 eng d00aDistinct Critical Behaviors from the Same State in Quantum Spin and Population Dynamics Perspectives0 aDistinct Critical Behaviors from the Same State in Quantum Spin  c9/10/20203 a

There is a deep connection between the ground states of transverse-field spin systems and the late-time distributions of evolving viral populations -- within simple models, both are obtained from the principal eigenvector of the same matrix. However, that vector is the wavefunction amplitude in the quantum spin model, whereas it is the probability itself in the population model. We show that this seemingly minor difference has significant consequences: phase transitions which are discontinuous in the spin system become continuous when viewed through the population perspective, and transitions which are continuous become governed by new critical exponents. We introduce a more general class of models which encompasses both cases, and that can be solved exactly in a mean-field limit. Numerical results are also presented for a number of one-dimensional chains with power-law interactions. We see that well-worn spin models of quantum statistical mechanics can contain unexpected new physics and insights when treated as population-dynamical models and beyond, motivating further studies. 

1 aBaldwin, Christopher, L.1 aShivam, S.1 aSondhi, S., L.1 aKardar, M. uhttps://arxiv.org/abs/2009.0506401938nas a2200145 4500008004100000245007300041210006900114260001300183490000600196520143200202100001801634700001601652700001901668856010501687 2020 eng d00aEfficient randomness certification by quantum probability estimation0 aEfficient randomness certification by quantum probability estima c1/7/20200 v23 a

For practical applications of quantum randomness generation, it is important to certify and further produce a fixed block of fresh random bits with as few trials as possible. Consequently, protocols with high finite-data efficiency are preferred. To yield such protocols with respect to quantum side information, we develop quantum probability estimation. Our approach is applicable to device-independent as well as device-dependent scenarios, and it generalizes techniques from previous works [Miller and Shi, SIAM J. Comput. 46, 1304 (2017); Arnon-Friedman et al., Nat. Commun. 9, 459 (2018)]. Quantum probability estimation can adapt to changing experimental conditions, allows stopping the experiment as soon as the prespecified randomness goal is achieved, and can tolerate imperfect knowledge of the input distribution. Moreover, the randomness rate achieved at constant error is asymptotically optimal. For the device-independent scenario, our approach certifies the amount of randomness available in experimental results without first searching for relations between randomness and violations of fixed Bell inequalities. We implement quantum probability estimation for device-independent randomness generation in the CHSH Bell-test configuration, and we show significant improvements in finite-data efficiency, particularly at small Bell violations which are typical in current photonic loophole-free Bell tests.

1 aZhang, Yanbao1 aFu, Honghao1 aKnill, Emanuel uhttps://quics.umd.edu/publications/efficient-randomness-certification-quantum-probability-estimation01709nas a2200205 4500008004100000245006400041210006200105260001400167490000800181520108400189100002401273700002101297700002301318700002801341700003001369700002401399700001801423700002501441856003701466 2020 eng d00aExotic photonic molecules via Lennard-Jones-like potentials0 aExotic photonic molecules via LennardJoneslike potentials c9/19/20200 v1253 a

Ultracold systems offer an unprecedented level of control of interactions between atoms. An important challenge is to achieve a similar level of control of the interactions between photons. Towards this goal, we propose a realization of a novel Lennard-Jones-like potential between photons coupled to the Rydberg states via electromagnetically induced transparency (EIT). This potential is achieved by tuning Rydberg states to a F{ö}rster resonance with other Rydberg states. We consider few-body problems in 1D and 2D geometries and show the existence of self-bound clusters ("molecules") of photons. We demonstrate that for a few-body problem, the multi-body interactions have a significant impact on the geometry of the molecular ground state. This leads to phenomena without counterparts in conventional systems: For example, three photons in 2D preferentially arrange themselves in a line-configuration rather than in an equilateral-triangle configuration. Our result opens a new avenue for studies of many-body phenomena with strongly interacting photons.

1 aBienias, Przemyslaw1 aGullans, Michael1 aKalinowski, Marcin1 aCraddock, Alexander, N.1 aOrnelas-Huerta, Dalia, P.1 aRolston, Steven, L.1 aPorto, J., V.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2003.0786401465nas a2200265 4500008004100000245006700041210006500108260001500173490000800188520070100196100001800897700002200915700002500937700002400962700002500986700001801011700002101029700002001050700002501070700001601095700001701111700001501128700001901143856003701162 2020 eng d00aExperimental Low-Latency Device-Independent Quantum Randomness0 aExperimental LowLatency DeviceIndependent Quantum Randomness c12/24/20190 v1243 a

Applications of randomness such as private key generation and public randomness beacons require small blocks of certified random bits on demand. Device-independent quantum random number generators can produce such random bits, but existing quantum-proof protocols and loophole-free implementations suffer from high latency, requiring many hours to produce any random bits. We demonstrate device-independent quantum randomness generation from a loophole-free Bell test with a more efficient quantum-proof protocol, obtaining multiple blocks of 512 bits with an average experiment time of less than 5 min per block and with certified error bounded by 2−64≈5.42×10−20.

1 aZhang, Yanbao1 aShalm, Lynden, K.1 aBienfang, Joshua, C.1 aStevens, Martin, J.1 aMazurek, Michael, D.1 aNam, Sae, Woo1 aAbellán, Carlos1 aAmaya, Waldimar1 aMitchell, Morgan, W.1 aFu, Honghao1 aMiller, Carl1 aMink, Alan1 aKnill, Emanuel uhttps://arxiv.org/abs/1812.0778601216nas a2200157 4500008004100000245005000041210005000091260001500141490000800156520078000164100001900944700001900963700002000982700001901002856003701021 2020 eng d00aGravitational Direct Detection of Dark Matter0 aGravitational Direct Detection of Dark Matter c10/13/20200 v1023 a

The only coupling dark matter is guaranteed to have with the standard model is through gravity. Here we propose a concept for direct dark matter detection using only this gravitational coupling, enabling a new regime of detection. Leveraging dramatic advances in the ability to create, maintain, and probe quantum states of massive objects, we suggest that an array of quantum-limited impulse sensors may be capable of detecting the correlated gravitational force created by a passing dark matter particle. We present two concrete realizations of this scheme, using either mechanical resonators or freely-falling masses. With currently available technology, a meter-scale apparatus of this type could detect any dark matter candidate around the Planck mass or heavier.

1 aCarney, Daniel1 aGhosh, Sohitri1 aKrnjaic, Gordan1 aTaylor, J., M. uhttps://arxiv.org/abs/1903.0049201522nas a2200193 4500008004100000245005900041210005700100260001400157490000800171520097200179100002301151700001801174700001801192700001601210700002301226700001801249700002401267856003701291 2020 eng d00aMany-Body Dephasing in a Trapped-Ion Quantum Simulator0 aManyBody Dephasing in a TrappedIon Quantum Simulator c8/24/20200 v1253 a

How a closed interacting quantum many-body system relaxes and dephases as a function of time is a fundamental question in thermodynamic and statistical physics. In this work, we observe and analyse the persistent temporal fluctuations after a quantum quench of a tunable long-range interacting transverse-field Ising Hamiltonian realized with a trapped-ion quantum simulator. We measure the temporal fluctuations in the average magnetization of a finite-size system of spin-1/2 particles and observe the experimental evidence for the theoretically predicted regime of many-body dephasing. We experiment in a regime where the properties of the system are closely related to the integrable Hamiltonian with global spin-spin coupling, which enables analytical predictions even for the long-time non-integrable dynamics. We find that the measured fluctuations are exponentially suppressed with increasing system size, consistent with theoretical predictions. 

1 aKaplan, Harvey, B.1 aGuo, Lingzhen1 aTan, Wen, Lin1 aDe, Arinjoy1 aMarquardt, Florian1 aPagano, Guido1 aMonroe, Christopher uhttps://arxiv.org/abs/2001.0247702026nas a2200517 4500008004100000245006100041210006100102260001400163520075200177100001500929700001600944700001800960700001800978700001300996700001401009700001701023700001601040700001401056700001701070700001501087700001401102700002201116700001301138700001701151700001801168700001701186700001101203700001201214700001201226700001501238700001601253700001501269700001801284700001401302700001701316700001401333700001901347700001401366700001401380700001401394700001901408700001201427700001901439700001301458856003701471 2020 eng d00aMechanical Quantum Sensing in the Search for Dark Matter0 aMechanical Quantum Sensing in the Search for Dark Matter c8/13/20203 a

Numerous astrophysical and cosmological observations are best explained by the existence of dark matter, a mass density which interacts only very weakly with visible, baryonic matter. Searching for the extremely weak signals produced by this dark matter strongly motivate the development of new, ultra-sensitive detector technologies. Paradigmatic advances in the control and readout of massive mechanical systems, in both the classical and quantum regimes, have enabled unprecedented levels of sensitivity. In this white paper, we outline recent ideas in the potential use of a range of solid-state mechanical sensing technologies to aid in the search for dark matter in a number of energy scales and with a variety of coupling mechanisms.

1 aCarney, D.1 aKrnjaic, G.1 aMoore, D., C.1 aRegal, C., A.1 aAfek, G.1 aBhave, S.1 aBrubaker, B.1 aCorbitt, T.1 aCripe, J.1 aCrisosto, N.1 a.Geraci, A1 aGhosh, S.1 aHarris, J., G. E.1 aHook, A.1 aKolb, E., W.1 aKunjummen, J.1 aLang, R., F.1 aLi, T.1 aLin, T.1 aLiu, Z.1 aLykken, J.1 aMagrini, L.1 aManley, J.1 aMatsumoto, N.1 aMonte, A.1 aMonteiro, F.1 aPurdy, T.1 aRiedel, C., J.1 aSingh, R.1 aSingh, S.1 aSinha, K.1 aTaylor, J., M.1 aQin, J.1 aWilson, D., J.1 aZhao, Y. uhttps://arxiv.org/abs/2008.0607401309nas a2200169 4500008004100000245003800041210003800079260001400117490000800131520085000139100001900989700002401008700002601032700002501058700001901083856003701102 2020 eng d00aMinimal model for fast scrambling0 aMinimal model for fast scrambling c9/22/20200 v1253 a

We study quantum information scrambling in spin models with both long-range all-to-all and short-range interactions. We argue that a simple global, spatially homogeneous interaction together with local chaotic dynamics is sufficient to give rise to fast scrambling, which describes the spread of quantum information over the entire system in a time that is logarithmic in the system size. This is illustrated in two exactly solvable models: (1) a random circuit with Haar random local unitaries and a global interaction and (2) a classical model of globally coupled non-linear oscillators. We use exact numerics to provide further evidence by studying the time evolution of an out-of-time-order correlator and entanglement entropy in spin chains of intermediate sizes. Our results can be verified with state-of-the-art quantum simulators.

1 aBelyansky, Ron1 aBienias, Przemyslaw1 aKharkov, Yaroslav, A.1 aGorshkov, Alexey, V.1 aSwingle, Brian uhttps://arxiv.org/abs/2005.0536202031nas a2200145 4500008004100000245007100041210006900112260001400181490000800195520154100203100002801744700002701772700001601799856007001815 2020 eng d00aNoncommuting conserved charges in quantum many-body thermalization0 aNoncommuting conserved charges in quantum manybody thermalizatio c4/15/20200 v1013 a

In statistical mechanics, a small system exchanges conserved quantities—heat, particles, electric charge, etc.—with a bath. The small system thermalizes to the canonical ensemble or the grand canonical ensemble, etc., depending on the quantities. The conserved quantities are represented by operators usually assumed to commute with each other. This assumption was removed within quantum-information-theoretic (QI-theoretic) thermodynamics recently. The small system's long-time state was dubbed “the non-Abelian thermal state (NATS).” We propose an experimental protocol for observing a system thermalize to the NATS. We illustrate with a chain of spins, a subset of which forms the system of interest. The conserved quantities manifest as spin components. Heisenberg interactions push the conserved quantities between the system and the effective bath, the rest of the chain. We predict long-time expectation values, extending the NATS theory from abstract idealization to finite systems that thermalize with finite couplings for finite times. Numerical simulations support the analytics: The system thermalizes to near the NATS, rather than to the canonical prediction. Our proposal can be implemented with ultracold atoms, nitrogen-vacancy centers, trapped ions, quantum dots, and perhaps nuclear magnetic resonance. This work introduces noncommuting conserved quantities from QI-theoretic thermodynamics into quantum many-body physics: atomic, molecular, and optical physics and condensed matter.

1 aHalpern, Nicole, Yunger1 aBeverland, Michael, E.1 aKalev, Amir uhttps://journals.aps.org/pre/abstract/10.1103/PhysRevE.101.04211701259nas a2200157 4500008004100000245007100041210006900112260001400181520077600195100001300971700001700984700001601001700002501017700002201042856003701064 2020 eng d00aOptical quantum memory with optically inaccessible noble-gas spins0 aOptical quantum memory with optically inaccessible noblegas spin c7/17/20203 a

Optical quantum memories, which store and preserve the quantum state of photons, rely on a coherent mapping of the photonic state onto matter states that are optically accessible. Here we outline a new physical mechanism to map the state of photons onto the long-lived but optically inaccessible collective state of noble-gas spins. The mapping employs the coherent spin-exchange interaction arising from random collisions with alkali vapor. We analyze optimal strategies for high-efficiency storage and retrieval of non-classical light at various parameter regimes. Based on these strategies, we identify feasible experimental conditions for realizing efficient quantum memories with noble-gas spins having hours-long coherence times at room temperature and above

1 aKatz, Or1 aReches, Eran1 aShaham, Roy1 aGorshkov, Alexey, V.1 aFirstenberg, Ofer uhttps://arxiv.org/abs/2007.0877001576nas a2200157 4500008004100000245010800041210006900149260001400218490000600232520106400238100001701302700001601319700002701335700001901362856003701381 2020 eng d00aOptimal fermion-to-qubit mapping via ternary trees with applications to reduced quantum states learning0 aOptimal fermiontoqubit mapping via ternary trees with applicatio c5/26/20200 v43 a

We introduce a fermion-to-qubit mapping defined on ternary trees, where any single Majorana operator on an n-mode fermionic system is mapped to a multi-qubit Pauli operator acting nontrivially on ⌈log3(2n+1)⌉ qubits. The mapping has a simple structure and is optimal in the sense that it is impossible to construct Pauli operators in any fermion-to-qubit mapping acting nontrivially on less than log3(2n) qubits on average. We apply it to the problem of learning k-fermion reduced density matrix (RDM), a problem relevant in various quantum simulation applications. We show that using the ternary-tree mapping one can determine the elements of all k-fermion RDMs, to precision ϵ, by repeating a single quantum circuit for ≲(2n+1)kϵ−2 times. This result is based on a method we develop here that allows one to determine the elements of all k-qubit RDMs, to precision ϵ, by repeating a single quantum circuit for ≲3kϵ−2 times, independent of the system size. This improves over existing schemes for determining qubit RDMs.

1 aJiang, Zhang1 aKalev, Amir1 aMruczkiewicz, Wojciech1 aNeven, Hartmut uhttps://arxiv.org/abs/1910.1074601409nas a2200157 4500008004100000245006100041210006100102260001400163520091900177100002101096700002901117700002101146700002201167700002501189856003701214 2020 eng d00aOptimal Protocols in Quantum Annealing and QAOA Problems0 aOptimal Protocols in Quantum Annealing and QAOA Problems c3/19/20203 a

Quantum Annealing (QA) and the Quantum Approximate Optimization Algorithm (QAOA) are two special cases of the following control problem: apply a combination of two Hamiltonians to minimize the energy of a quantum state. Which is more effective has remained unclear. Here we apply the framework of optimal control theory to show that generically, given a fixed amount of time, the optimal procedure has the pulsed (or "bang-bang") structure of QAOA at the beginning and end but can have a smooth annealing structure in between. This is in contrast to previous works which have suggested that bang-bang (i.e., QAOA) protocols are ideal. Through simulations of various transverse field Ising models, we demonstrate that bang-anneal-bang protocols are more common. The general features identified here provide guideposts for the nascent experimental implementations of quantum optimization algorithms.

1 aBrady, Lucas, T.1 aBaldwin, Christopher, L.1 aBapat, Aniruddha1 aKharkov, Yaroslav1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2003.0895202249nas a2200133 4500008004100000245007900041210006900120260001500189520179100204100002401995700001902019700001902038856005802057 2020 eng d00aPosition Space Decoherence From Long-Range Interaction With Background Gas0 aPosition Space Decoherence From LongRange Interaction With Backg c06/05/20203 a

 Experiments in matter wave interferometry and optomechanics are increasing the spatial extent of wavefunctions of massive quantum systems; this gives rise to new sources of decoherence that must be characterized. Here we calculate the position space decoherence of a quantum particle due to interaction with a fluctuating classical background gas for several different force laws. We begin with the calculation of this effect for the Newton potential. To our knowledge, this calculation has not been done before. We then solve the same problem in the case of a Yukawa interaction, which interpolates between our long-range force result and the well-studied formula for collisional decoherence from a contact interaction. Unlike the contact interaction case, where the decoherence rate becomes independent of distance for large quantum particle separations, we observe that a long-range interaction leads to quadratic scaling of the decoherence rate with distance even at large separations. This work is relevant to the generation of massive superposition in optomechanical and atom beam experiments, and to conclude we comment on the use of this decoherence signal for gravitational detection of dark matter. 

1 aKunjummen, Jonathan1 aCarney, Daniel1 aTaylor, J., M. uhttp://meetings.aps.org/Meeting/DAMOP20/Session/S08.501854nas a2200193 4500008004100000245008800041210006900129260001400198520128100212100001501493700001701508700001501525700001601540700001701556700001401573700001901587700001701606856003701623 2020 eng d00aProbing XY phase transitions in a Josephson junction array with tunable frustration0 aProbing XY phase transitions in a Josephson junction array with  c1/22/20203 a

The seminal theoretical works of Berezinskii, Kosterlitz, and Thouless presented a new paradigm for phase transitions in condensed matter that are driven by topological excitations. These transitions have been extensively studied in the context of two-dimensional XY models -- coupled compasses -- and have generated interest in the context of quantum simulation. Here, we use a circuit quantum-electrodynamics architecture to study the critical behavior of engineered XY models through their dynamical response. In particular, we examine not only the unfrustrated case but also the fully-frustrated case which leads to enhanced degeneracy associated with the spin rotational [U(1)] and discrete chiral (Z2) symmetries. The nature of the transition in the frustrated case has posed a challenge for theoretical studies while direct experimental probes remain elusive. Here we identify the transition temperatures for both the unfrustrated and fully-frustrated XY models by probing a Josephson junction array close to equilibrium using weak microwave excitations and measuring the temperature dependence of the effective damping obtained from the complex reflection coefficient. We argue that our probing technique is primarily sensitive to the dynamics of the U(1) part.

1 aCosmic, R.1 aKawabata, K.1 aAshida, Y.1 aIkegami, H.1 aFurukawa, S.1 aPatil, P.1 aTaylor, J., M.1 aNakamura, Y. uhttps://arxiv.org/abs/2001.0787702048nas a2200145 4500008004100000245005900041210005900100260001500159520160200174100001801776700002201794700002601816700002301842856003701865 2020 eng d00aProgrammable Quantum Annealers as Noisy Gibbs Samplers0 aProgrammable Quantum Annealers as Noisy Gibbs Samplers c12/16/20203 a

Drawing independent samples from high-dimensional probability distributions represents the major computational bottleneck for modern algorithms, including powerful machine learning frameworks such as deep learning. The quest for discovering larger families of distributions for which sampling can be efficiently realized has inspired an exploration beyond established computing methods and turning to novel physical devices that leverage the principles of quantum computation. Quantum annealing embodies a promising computational paradigm that is intimately related to the complexity of energy landscapes in Gibbs distributions, which relate the probabilities of system states to the energies of these states. Here, we study the sampling properties of physical realizations of quantum annealers which are implemented through programmable lattices of superconducting flux qubits. Comprehensive statistical analysis of the data produced by these quantum machines shows that quantum annealers behave as samplers that generate independent configurations from low-temperature noisy Gibbs distributions. We show that the structure of the output distribution probes the intrinsic physical properties of the quantum device such as effective temperature of individual qubits and magnitude of local qubit noise, which result in a non-linear response function and spurious interactions that are absent in the hardware implementation. We anticipate that our methodology will find widespread use in characterization of future generations of quantum annealers and other emerging analog computing devices.

1 aVuffray, Marc1 aCoffrin, Carleton1 aKharkov, Yaroslav, A.1 aLokhov, Andrey, Y. uhttps://arxiv.org/abs/2012.0882702376nas a2200157 4500008004100000245005000041210004900091260001500140520192200155100002102077700002202098700002002120700001702140700002402157856003702181 2020 eng d00aQuantum coding with low-depth random circuits0 aQuantum coding with lowdepth random circuits c10/19/20203 a

Random quantum circuits have played a central role in establishing the computational advantages of near-term quantum computers over their conventional counterparts. Here, we use ensembles of low-depth random circuits with local connectivity in D≥1 spatial dimensions to generate quantum error-correcting codes. For random stabilizer codes and the erasure channel, we find strong evidence that a depth O(logN) random circuit is necessary and sufficient to converge (with high probability) to zero failure probability for any finite amount below the channel capacity for any D. Previous results on random circuits have only shown that O(N1/D) depth suffices or that O(log3N) depth suffices for all-to-all connectivity (D→∞). We then study the critical behavior of the erasure threshold in the so-called moderate deviation limit, where both the failure probability and the distance to the channel capacity converge to zero with N. We find that the requisite depth scales like O(logN) only for dimensions D≥2, and that random circuits require O(N−−√) depth for D=1. Finally, we introduce an "expurgation" algorithm that uses quantum measurements to remove logical operators that cause the code to fail by turning them into either additional stabilizers or into gauge operators in a subsystem code. With such targeted measurements, we can achieve sub-logarithmic depth in D≥2 spatial dimensions below capacity without increasing the maximum weight of the check operators. We find that for any rate beneath the capacity, high-performing codes with thousands of logical qubits are achievable with depth 4-8 expurgated random circuits in D=2 dimensions. These results indicate that finite-rate quantum codes are practically relevant for near-term devices and may significantly reduce the resource requirements to achieve fault tolerance for near-term applications. 

1 aGullans, Michael1 aKrastanov, Stefan1 aHuse, David, A.1 aJiang, Liang1 aFlammia, Steven, T. uhttps://arxiv.org/abs/2010.0977501627nas a2200193 4500008004100000245002900041210002900070260001400099300001500113490000800128520112700136100002801263700002301291700002301314700001901337700002001356700002001376856003701396 2020 eng d00aQuantum Coupon Collector0 aQuantum Coupon Collector c2/18/2020 a10:1-10:170 v1583 a

We study how efficiently a k-element set S⊆[n] can be learned from a uniform superposition |S⟩ of its elements. One can think of |S⟩=∑i∈S|i⟩/|S|−−−√ as the quantum version of a uniformly random sample over S, as in the classical analysis of the ``coupon collector problem.'' We show that if k is close to n, then we can learn S using asymptotically fewer quantum samples than random samples. In particular, if there are n−k=O(1) missing elements then O(k) copies of |S⟩ suffice, in contrast to the Θ(klogk) random samples needed by a classical coupon collector. On the other hand, if n−k=Ω(k), then Ω(klogk) quantum samples are~necessary. More generally, we give tight bounds on the number of quantum samples needed for every k and n, and we give efficient quantum learning algorithms. We also give tight bounds in the model where we can additionally reflect through |S⟩. Finally, we relate coupon collection to a known example separating proper and improper PAC learning that turns out to show no separation in the quantum case.

1 aArunachalam, Srinivasan1 aBelovs, Aleksandrs1 aChilds, Andrew, M.1 aKothari, Robin1 aRosmanis, Ansis1 ade Wolf, Ronald uhttps://arxiv.org/abs/2002.0768801529nas a2200145 4500008004100000245007400041210006900115260001500184490000800199520104100207100002601248700001701274700002201291856007001313 2020 eng d00aQuantum Lifshitz criticality in a frustrated two-dimensional XY model0 aQuantum Lifshitz criticality in a frustrated twodimensional XY m c01/09/20200 v1013 a

Antiferromagnetic quantum spin systems can exhibit a transition between collinear and spiral ground states,
driven by frustration. Classically this is a smooth crossover and the crossover point is termed a Lifshitz point.
Quantum fluctuations change the nature of the transition. In particular, it has been argued previously that in the two-dimensional (2D) case a spin liquid (SL) state is developed in the vicinity of the Lifshitz point, termed a Lifshitz SL. In the present work, using a field theory approach, we solve the Lifshitz quantum phase transition problem for the 2D frustrated XY model. Specifically, we show that, unlike the SU (2) symmetric Lifshitz case, in the XY model, the SL exists only at the critical point. At zero temperature we calculate nonuniversal critical exponents in the Néel and in the spin spiral state and relate these to properties of the SL. We also solve the transition problem at a finite temperature and discuss the role of topological excitations.

1 aKharkov, Yaroslav, A.1 aOitmaa, Jaan1 aSushkov, Oleg, P. uhttps://journals.aps.org/prb/abstract/10.1103/PhysRevB.101.03511401783nas a2200169 4500008004100000245010500041210006900146260001400215490000800229520122700237100002001464700002401484700001901508700002401527700002501551856003701576 2020 eng d00aQuantum Simulation of Hyperbolic Space with Circuit Quantum Electrodynamics: From Graphs to Geometry0 aQuantum Simulation of Hyperbolic Space with Circuit Quantum Elec c9/11/20200 v1023 a

We show how quantum many-body systems on hyperbolic lattices with nearest-neighbor hopping and local interactions can be mapped onto quantum field theories in continuous negatively curved space. The underlying lattices have recently been realized experimentally with superconducting resonators and therefore allow for a table-top quantum simulation of quantum physics in curved background. Our mapping provides a computational tool to determine observables of the discrete system even for large lattices, where exact diagonalization fails. As an application and proof of principle we quantitatively reproduce the ground state energy, spectral gap, and correlation functions of the noninteracting lattice system by means of analytic formulas on the Poincaré disk, and show how conformal symmetry emerges for large lattices. This sets the stage for studying interactions and disorder on hyperbolic graphs in the future. Our analysis also reveals in which sense discrete hyperbolic lattices emulate the continuous geometry of negatively curved space and thus can be used to resolve fundamental open problems at the interface of interacting many-body systems, quantum field theory in curved space, and quantum gravity.

1 aBoettcher, Igor1 aBienias, Przemyslaw1 aBelyansky, Ron1 aKollár, Alicia, J.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1910.1231801423nas a2200157 4500008004100000245006500041210006300106260001400169520093400183100002401117700002601141700002101167700002101188700001901209856003701228 2020 eng d00aRay-based classification framework for high-dimensional data0 aRaybased classification framework for highdimensional data c10/1/20203 a

While classification of arbitrary structures in high dimensions may require complete quantitative information, for simple geometrical structures, low-dimensional qualitative information about the boundaries defining the structures can suffice. Rather than using dense, multi-dimensional data, we propose a deep neural network (DNN) classification framework that utilizes a minimal collection of one-dimensional representations, called \emph{rays}, to construct the "fingerprint" of the structure(s) based on substantially reduced information. We empirically study this framework using a synthetic dataset of double and triple quantum dot devices and apply it to the classification problem of identifying the device state. We show that the performance of the ray-based classifier is already on par with traditional 2D images for low dimensional systems, while significantly cutting down the data acquisition cost.

1 aZwolak, Justyna, P.1 aKalantre, Sandesh, S.1 aMcJunkin, Thomas1 aWeber, Brian, J.1 aTaylor, J., M. uhttps://arxiv.org/abs/2010.0050001558nas a2200217 4500008004100000245008100041210006900122260001500191520086200206100002301068700001601091700002401107700002101131700003001152700002801182700002401210700001801234700002601252700002501278856003701303 2020 eng d00aResonant enhancement of three-body loss between strongly interacting photons0 aResonant enhancement of threebody loss between strongly interact c10/19/20203 a

Rydberg polaritons provide an example of a rare type of system where three-body interactions can be as strong or even stronger than two-body interactions. The three-body interactions can be either dispersive or dissipative, with both types possibly giving rise to exotic, strongly-interacting, and topological phases of matter. Despite past theoretical and experimental studies of the regime with dispersive interaction, the dissipative regime is still mostly unexplored. Using a renormalization group technique to solve the three-body Schrödinger equation, we show how the shape and strength of dissipative three-body forces can be universally enhanced for Rydberg polaritons. We demonstrate how these interactions relate to the transmission through a single-mode cavity, which can be used as a probe of the three-body physics in current experiment

1 aKalinowski, Marcin1 aWang, Yidan1 aBienias, Przemyslaw1 aGullans, Michael1 aOrnelas-Huerta, Dalia, P.1 aCraddock, Alexander, N.1 aRolston, Steven, L.1 aPorto, J., V.1 aBüchler, Hans, Peter1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/2010.0977201697nas a2200181 4500008004100000245007000041210006900111260001400180490000800194520115900202100002301361700001501384700001901399700002001418700001901438700002101457856003701478 2020 eng d00aSearch for composite dark matter with optically levitated sensors0 aSearch for composite dark matter with optically levitated sensor c11/2/20200 v1253 a

Results are reported from a search for a class of composite dark matter models with feeble, long-range interactions with normal matter. We search for impulses arising from passing dark matter particles by monitoring the mechanical motion of an optically levitated nanogram mass over the course of several days. Assuming such particles constitute the dominant component of dark matter, this search places upper limits on their interaction with neutrons of αn≤1.2×10−7 at 95\% confidence for dark matter masses between 1--10 TeV and mediator masses mφ≤0.1 eV. Due to the large enhancement of the cross-section for dark matter to coherently scatter from a nanogram mass (∼1029 times that for a single neutron) and the ability to detect momentum transfers as small as ∼200 MeV/c, these results provide sensitivity to certain classes of composite dark matter models that substantially exceeds existing searches, including those employing kg-scale or ton-scale targets. Extensions of these techniques can enable directionally-sensitive searches for a broad class of previously inaccessible heavy dark matter candidates. 

1 aMonteiro, Fernando1 aAfek, Gadi1 aCarney, Daniel1 aKrnjaic, Gordan1 aWang, Jiaxiang1 aMoore, David, C. uhttps://arxiv.org/abs/2007.1206702382nas a2200145 4500008004100000245007400041210006900115260001500184520192100199100001902120700002402139700001902163700001702182856003702199 2020 eng d00aSecure Quantum Two-Party Computation: Impossibility and Constructions0 aSecure Quantum TwoParty Computation Impossibility and Constructi c10/15/20203 a

Secure two-party computation considers the problem of two parties computing a joint function of their private inputs without revealing anything beyond the output of the computation. In this work, we take the first steps towards understanding the setting in which the two parties want to evaluate a joint quantum functionality while using only a classical channel between them. Our first result indicates that it is in general impossible to realize a two-party quantum functionality against malicious adversaries with black-box simulation, relying only on classical channels. The negative result stems from reducing the existence of a black-box simulator to an extractor for classical proof of quantum knowledge, which in turn leads to violation of the quantum no-cloning. Next, we introduce the notion of oblivious quantum function evaluation (OQFE). An OQFE is a two-party quantum cryptographic primitive with one fully classical party (Alice) whose input is (a classical description of a) quantum unitary, U, and a quantum party (Bob) whose input is a quantum state, ψ. In particular, Alice receives a classical output corresponding to the measurement of U(ψ) while Bob receives no output. In OQFE, Bob remains oblivious to Alice's input, while Alice learns nothing about ψ more than what can be learned from the output. We present two constructions, one secure against semi-honest parties and the other against malicious parties. Due to the no-go result mentioned above, we consider what is arguably the best possible notion obtainable in our model concerning malicious adversaries: one-sided simulation security. Our protocol relies on the assumption of injective homomorphic trapdoor OWFs, which in turn rely on the LWE problem. As a result, we put forward a first, simple and modular, construction of one-sided quantum two-party computation and quantum oblivious transfer over classical networks.

1 aCiamp, Michele1 aCojocaru, Alexandru1 aKashefi, Elham1 aMantri, Atul uhttps://arxiv.org/abs/2010.0792502441nas a2200181 4500008004100000245007300041210006900114260001300183520187800196100002702074700002402101700001902125700001902144700002202163700001702185700002002202856003702222 2020 eng d00aSecurity Limitations of Classical-Client Delegated Quantum Computing0 aSecurity Limitations of ClassicalClient Delegated Quantum Comput c7/3/20203 a

Secure delegated quantum computing allows a computationally weak client to outsource an arbitrary quantum computation to an untrusted quantum server in a privacy-preserving manner. One of the promising candidates to achieve classical delegation of quantum computation is classical-client remote state preparation (RSPCC), where a client remotely prepares a quantum state using a classical channel. However, the privacy loss incurred by employing RSPCC as a sub-module is unclear.
In this work, we investigate this question using the Constructive Cryptography framework by Maurer and Renner (ICS'11). We first identify the goal of RSPCC as the construction of ideal RSP resources from classical channels and then reveal the security limitations of using RSPCC. First, we uncover a fundamental relationship between constructing ideal RSP resources (from classical channels) and the task of cloning quantum states. Any classically constructed ideal RSP resource must leak to the server the full classical description (possibly in an encoded form) of the generated quantum state, even if we target computational security only. As a consequence, we find that the realization of common RSP resources, without weakening their guarantees drastically, is impossible due to the no-cloning theorem. Second, the above result does not rule out that a specific RSPCC protocol can replace the quantum channel at least in some contexts, such as the Universal Blind Quantum Computing (UBQC) protocol of Broadbent et al. (FOCS '09). However, we show that the resulting UBQC protocol cannot maintain its proven composable security as soon as RSPCC is used as a subroutine. Third, we show that replacing the quantum channel of the above UBQC protocol by the RSPCC protocol QFactory of Cojocaru et al. (Asiacrypt '19), preserves the weaker, game-based, security of UBQC.

1 aBadertscher, Christian1 aCojocaru, Alexandru1 aColisson, Léo1 aKashefi, Elham1 aLeichtle, Dominik1 aMantri, Atul1 aWallden, Petros uhttps://arxiv.org/abs/2007.0166801053nas a2200121 4500008004100000245007400041210006900115260001300184520066700197100001600864700001400880856003700894 2020 eng d00aSimulating Hamiltonian Dynamics with an Off-diagonal Series Expansion0 aSimulating Hamiltonian Dynamics with an Offdiagonal Series Expan c6/3/20203 a

We propose an efficient quantum algorithm for simulating the dynamics of general Hamiltonian systems. Our technique is based on a power series expansion of the time-evolution operator in its off-diagonal terms. The expansion decouples the dynamics due to the diagonal component of the Hamiltonian from the dynamics generated by its off-diagonal part, which we encode using the linear combination of unitaries technique. Our method has an optimal dependence on the desired precision and, as we illustrate, generally requires considerably fewer resources than the current state-of-the-art. We provide an analysis of resource costs for several sample models.

1 aKalev, Amir1 aHen, Itay uhttps://arxiv.org/abs/2006.0253903206nas a2200253 4500008004100000245010000041210006900141260001200210520236500222100001902587700002702606700001702633700001802650700001602668700001702684700001602701700001702717700001802734700001802752700001702770700002102787700002302808856012102831 2020 eng d00aStatus Report on the Second Round of the NIST Post-Quantum Cryptography Standardization Process0 aStatus Report on the Second Round of the NIST PostQuantum Crypto c07/20203 a

The National Institute of Standards and Technology is in the process of selecting one or more public-key cryptographic algorithms through a public, competition-like process. The new public-key cryptography standards will specify one or more additional digital signatures, public-key encryption, and key-establishment algorithms to augment Federal Information Processing Standard (FIPS) 186-4, Digital Signature Standard (DSS), as well as NIST Special Publication (SP) 800-56A Revision 3, Recommendation for Pair-Wise Key-Establishment Schemes Using Discrete Logarithm Cryptography, and SP 800-56B Revision 2, Recommendation for Pair-Wise Key Establishment Using Integer Factorization Cryptography. It is intended that these algorithms will be capable of protecting sensitive information well into the foreseeable future, including after the advent of quantum computers.

The NIST Post-Quantum Cryptography Standardization Process began in 2017 with 69 candidate algorithms that met both the minimum acceptance criteria and submission requirements. The first round lasted until January 2019, during which candidate algorithms were evaluated based on their security, performance, and other characteristics. NIST selected 26 algorithms to advance to the second round for more analysis. This report describes the evaluation and selection process, based on public feedback and internal review, of the second-round candidates. The report summarizes the 26 second-round candidate algorithms and identifies those selected to move forward to the third round of the competition. The third-round finalist public-key encryption and key-establishment algorithms are Classic McEliece, CRYSTALS-KYBER, NTRU, and SABER. The third-round finalists for digital signatures are CRYSTALS-DILITHIUM, FALCON, and Rainbow. These finalists will be considered for standardization at the end of the third round. In addition, eight alternate candidate algorithms will also advance to the third round: BIKE, FrodoKEM, HQC, NTRU Prime, SIKE, GeMSS, Picnic, and SPHINCS+. These additional candidates are still being considered for standardization, although this is unlikely to occur at the end of the third round. NIST hopes that the announcement of these finalists and additional candidates will serve to focus the cryptographic community’s attention during the next round.

1 aAlagic, Gorjan1 aAlperin-Sheriff, Jacob1 aApon, Daniel1 aCooper, David1 aDang, Quynh1 aKelsey, John1 aLiu, Yi-Kai1 aMiller, Carl1 aMoody, Dustin1 aPeralta, Rene1 aPerlner, Ray1 aRobinson, Angela1 aSmith-Tone, Daniel uhttps://quics.umd.edu/publications/status-report-second-round-nist-post-quantum-cryptography-standardization-process01030nas a2200157 4500008004100000245006700041210006700108260001400175520054300189100001900732700002900751700001700780700001900797700001900816856003700835 2020 eng d00aStudying viral populations with tools from quantum spin chains0 aStudying viral populations with tools from quantum spin chains c3/24/20203 a

We study Eigen's model of quasi-species, characterized by sequences that replicate with a specified fitness and mutate independently at single sites. The evolution of the population vector in time is then closely related to that of quantum spins in imaginary time. We employ multiple perspectives and tools from interacting quantum systems to examine growth and collapse of realistic viral populations, specifically certain HIV proteins. All approaches used, including the simplest perturbation theory, give consistent results.

1 aShivam, Saumya1 aBaldwin, Christopher, L.1 aBarton, John1 aKardar, Mehran1 aSondhi, S., L. uhttps://arxiv.org/abs/2003.1066801555nas a2200169 4500008004100000245005500041210005300096260001400149520105800163100002201221700002301243700001901266700002401285700002101309700001801330856003701348 2020 eng d00aSymmetries, graph properties, and quantum speedups0 aSymmetries graph properties and quantum speedups c6/23/20203 a

Aaronson and Ambainis (2009) and Chailloux (2018) showed that fully symmetric (partial) functions do not admit exponential quantum query speedups. This raises a natural question: how symmetric must a function be before it cannot exhibit a large quantum speedup?
In this work, we prove that hypergraph symmetries in the adjacency matrix model allow at most a polynomial separation between randomized and quantum query complexities. We also show that, remarkably, permutation groups constructed out of these symmetries are essentially the only permutation groups that prevent super-polynomial quantum speedups. We prove this by fully characterizing the primitive permutation groups that allow super-polynomial quantum speedups.
In contrast, in the adjacency list model for bounded-degree graphs (where graph symmetry is manifested differently), we exhibit a property testing problem that shows an exponential quantum speedup. These results resolve open questions posed by Ambainis, Childs, and Liu (2010) and Montanaro and de Wolf (2013).

1 aBen-David, Shalev1 aChilds, Andrew, M.1 aGilyen, Andras1 aKretschmer, William1 aPodder, Supartha1 aWang, Daochen uhttps://arxiv.org/abs/2006.1276001484nas a2200121 4500008004100000245004900041210004600090260001500136520114100151100001701292700001601309856003701325 2019 eng d00aAn approximate description of quantum states0 aapproximate description of quantum states c2019/11/133 a

We introduce an approximate description of an N-qubit state, which contains sufficient information to estimate the expectation value of any observable with precision independent of N. We show, in fact, that the error in the estimation of the observables' expectation values decreases as the inverse of the square root of the number of the system's identical preparations and increases, at most, linearly in a suitably defined, N-independent, seminorm of the observables. Building the approximate description of the N-qubit state only requires repetitions of single-qubit rotations followed by single-qubit measurements and can be considered for implementation on today's Noisy Intermediate-Scale Quantum (NISQ) computers. The access to the expectation values of all observables for a given state leads to an efficient variational method for the determination of the minimum eigenvalue of an observable. The method represents one example of the practical significance of the approximate description of the N-qubit state. We conclude by briefly discussing extensions to generative modelling and with fermionic operators

1 aPaini, Marco1 aKalev, Amir uhttps://arxiv.org/abs/1910.1054301524nas a2200145 4500008004100000245004700041210004400088260001500132520110100147100003701248700001801285700001901303700001901322856003701341 2019 eng d00aCompeting (Semi)-Selfish Miners in Bitcoin0 aCompeting SemiSelfish Miners in Bitcoin c06/11/20193 a

The Bitcoin protocol prescribes certain behavior by the miners who are responsible for maintaining and extending the underlying blockchain; in particular, miners who successfully solve a puzzle, and hence can extend the chain by a block, are supposed to release that block immediately. Eyal and Sirer showed, however, that a selfish miner is incentivized to deviate from the protocol and withhold its blocks under certain conditions. The analysis by Eyal and Sirer, as well as in followup work, considers a \emph{single} deviating miner (who may control a large fraction of the hashing power in the network) interacting with a remaining pool of honest miners. Here, we extend this analysis to the case where there are \emph{multiple} (non-colluding) selfish miners. We find that with multiple strategic miners, specific deviations from honest mining by multiple strategic agents can outperform honest mining, even if individually miners would not be incentivised to be dishonest. This previous point effectively renders the Bitcoin protocol to be less secure than previously thought. 

1 aMarmolejo-Cossío, Francisco, J.1 aBrigham, Eric1 aSela, Benjamin1 aKatz, Jonathan uhttps://arxiv.org/abs/1906.0450202955nas a2200397 4500008004100000245008600041210006900127260001500196520181200211100002102023700002302044700002002067700001702087700002202104700001702126700002502143700001802168700001902186700001702205700001702222700002702239700001502266700001702281700001802298700001702316700001602333700002002349700001902369700002302388700002502411700002402436700001802460700002002478700002202498856003702520 2019 eng d00aDevelopment of Quantum InterConnects for Next-Generation Information Technologies0 aDevelopment of Quantum InterConnects for NextGeneration Informat c12/13/20193 a

Just as classical information technology rests on a foundation built of interconnected information-processing systems, quantum information technology (QIT) must do the same. A critical component of such systems is the interconnect, a device or process that allows transfer of information between disparate physical media, for example, semiconductor electronics, individual atoms, light pulses in optical fiber, or microwave fields. While interconnects have been well engineered for decades in the realm of classical information technology, quantum interconnects (QuICs) present special challenges, as they must allow the transfer of fragile quantum states between different physical parts or degrees of freedom of the system. The diversity of QIT platforms (superconducting, atomic, solid-state color center, optical, etc.) that will form a quantum internet poses additional challenges. As quantum systems scale to larger size, the quantum interconnect bottleneck is imminent, and is emerging as a grand challenge for QIT. For these reasons, it is the position of the community represented by participants of the NSF workshop on Quantum Interconnects that accelerating QuIC research is crucial for sustained development of a national quantum science and technology program. Given the diversity of QIT platforms, materials used, applications, and infrastructure required, a convergent research program including partnership between academia, industry and national laboratories is required. This document is a summary from a U.S. National Science Foundation supported workshop held on 31 October - 1 November 2019 in Alexandria, VA. Attendees were charged to identify the scientific and community needs, opportunities, and significant challenges for quantum interconnects over the next 2-5 years. 

1 aAwschalom, David1 aBerggren, Karl, K.1 aBernien, Hannes1 aBhave, Sunil1 aCarr, Lincoln, D.1 aDavids, Paul1 aEconomou, Sophia, E.1 aEnglund, Dirk1 aFaraon, Andrei1 aFejer, Marty1 aGuha, Saikat1 aGustafsson, Martin, V.1 aHu, Evelyn1 aJiang, Liang1 aKim, Jungsang1 aKorzh, Boris1 aKumar, Prem1 aKwiat, Paul, G.1 aLončar, Marko1 aLukin, Mikhail, D.1 aMiller, David, A. B.1 aMonroe, Christopher1 aNam, Sae, Woo1 aNarang, Prineha1 aOrcutt, Jason, S. uhttps://arxiv.org/abs/1912.0664201930nas a2200133 4500008004100000245008000041210006900121260001400190520148400204100002801688700002701716700001601743856003701759 2019 eng d00aEquilibration to the non-Abelian thermal state in quantum many-body physics0 aEquilibration to the nonAbelian thermal state in quantum manybod c6/21/20193 a

In statistical mechanics, a small system exchanges conserved charges---heat, particles, electric charge, etc.---with a bath. The small system thermalizes to the canonical ensemble, or the grand canonical ensemble, etc., depending on the charges. The charges are usually represented by operators assumed to commute with each other. This assumption was removed within quantum-information-theoretic (QI-theoretic) thermodynamics recently. The small system's long-time state was dubbed "the non-Abelian thermal state (NATS)." We propose an experimental protocol for observing a system thermalize to the NATS. We illustrate with a chain of spins, a subset of which form the system of interest. The conserved charges manifest as spin components. Heisenberg interactions push the charges between the system and the effective bath, the rest of the chain. We predict long-time expectation values, extending the NATS theory from abstract idealization to finite systems that thermalize with finite couplings for finite times. Numerical simulations support the analytics: The system thermalizes to the NATS, rather than to the canonical prediction. Our proposal can be implemented with ultracold atoms, nitrogen-vacancy centers, trapped ions, quantum dots, and perhaps nuclear magnetic resonance. This work introduces noncommuting charges from QI-theoretic thermodynamics into quantum many-body physics: atomic, molecular, and optical physics and condensed matter. 

1 aHalpern, Nicole, Yunger1 aBeverland, Michael, E.1 aKalev, Amir uhttps://arxiv.org/abs/1906.0922701739nas a2200205 4500008004100000245013400041210006900175260001500244520106400259100001801323700001201341700002201353700001701375700002501392700001301417700001901430700002601449700002101475856003701496 2019 eng d00aFeshbach resonances in p-wave three-body recombination within Fermi-Fermi mixtures of open-shell 6Li and closed-shell 173Yb atoms0 aFeshbach resonances in pwave threebody recombination within Ferm c12/10/20193 a

We report on observations and modeling of interspecies magnetic Feshbach resonances in dilute ultracold mixtures of open-shell alkali-metal 6Li and closed-shell 173Yb atoms with temperatures just above quantum degeneracy for both fermionic species. Resonances are located by detecting magnetic-field-dependent atom loss due to three-body recombination. We resolve closely-located resonances that originate from a weak separation-dependent hyperfine coupling between the electronic spin of 6Li and the nuclear spin of 173Yb, and confirm their magnetic field spacing by ab initio electronic-structure calculations. Through quantitative comparisons of theoretical atom-loss profiles and experimental data at various temperatures between 1 μK and 20 μK, we show that three-body recombination in fermionic mixtures has a p-wave Wigner threshold behavior leading to characteristic asymmetric loss profiles. Such resonances can be applied towards the formation of ultracold doublet ground-state molecules and quantum simulation of superfluid p-wave pairing.

1 aGreen, Alaina1 aLi, Hui1 aToh, Jun, Hui See1 aTang, Xinxin1 aMcCormick, Katherine1 aLi, Ming1 aTiesinga, Eite1 aKotochigova, Svetlana1 aGupta, Subhadeep uhttps://arxiv.org/abs/1912.0487402376nas a2200409 4500008004100000245009100041210006900132260001500201520116700216100001801383700001701401700002201418700002001440700001901460700001901479700002301498700001901521700002101540700001901561700002201580700002001602700002201622700002201644700002101666700002201687700002301709700001901732700002001751700002701771700002201798700001801820700001901838700003001857700002401887700001801911856003701929 2019 eng d00aGround-state energy estimation of the water molecule on a trapped ion quantum computer0 aGroundstate energy estimation of the water molecule on a trapped c03/07/20193 a

Quantum computing leverages the quantum resources of superposition and entanglement to efficiently solve computational problems considered intractable for classical computers. Examples include calculating molecular and nuclear structure, simulating strongly-interacting electron systems, and modeling aspects of material function. While substantial theoretical advances have been made in mapping these problems to quantum algorithms, there remains a large gap between the resource requirements for solving such problems and the capabilities of currently available quantum hardware. Bridging this gap will require a co-design approach, where the expression of algorithms is developed in conjunction with the hardware itself to optimize execution. Here, we describe a scalable co-design framework for solving chemistry problems on a trapped ion quantum computer, and apply it to compute the ground-state energy of the water molecule. The robust operation of the trapped ion quantum computer yields energy estimates with errors approaching the chemical accuracy, which is the target threshold necessary for predicting the rates of chemical reaction dynamics.

1 aNam, Yunseong1 aChen, Jwo-Sy1 aPisenti, Neal, C.1 aWright, Kenneth1 aDelaney, Conor1 aMaslov, Dmitri1 aBrown, Kenneth, R.1 aAllen, Stewart1 aAmini, Jason, M.1 aApisdorf, Joel1 aBeck, Kristin, M.1 aBlinov, Aleksey1 aChaplin, Vandiver1 aChmielewski, Mika1 aCollins, Coleman1 aDebnath, Shantanu1 aDucore, Andrew, M.1 aHudek, Kai, M.1 aKeesan, Matthew1 aKreikemeier, Sarah, M.1 aMizrahi, Jonathan1 aSolomon, Phil1 aWilliams, Mike1 aWong-Campos, Jaime, David1 aMonroe, Christopher1 aKim, Jungsang uhttps://arxiv.org/abs/1902.1017101475nas a2200181 4500008004100000245010000041210006900141260001400210520088000224100001901104700002201123700002401145700002201169700002201191700001801213700002501231856003701256 2019 eng d00aNondestructive cooling of an atomic quantum register via state-insensitive Rydberg interactions0 aNondestructive cooling of an atomic quantum register via statein c7/28/20193 a

We propose a protocol for sympathetically cooling neutral atoms without destroying the quantum information stored in their internal states. This is achieved by designing state-insensitive Rydberg interactions between the data-carrying atoms and cold auxiliary atoms. The resulting interactions give rise to an effective phonon coupling, which leads to the transfer of heat from the data atoms to the auxiliary atoms, where the latter can be cooled by conventional methods. This can be used to extend the lifetime of quantum storage based on neutral atoms and can have applications for long quantum computations. The protocol can also be modified to realize state-insensitive interactions between the data and the auxiliary atoms but tunable and non-trivial interactions among the data atoms, allowing one to simultaneously cool and simulate a quantum spin-model. 

1 aBelyansky, Ron1 aYoung, Jeremy, T.1 aBienias, Przemyslaw1 aEldredge, Zachary1 aKaufman, Adam, M.1 aZoller, Peter1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1907.1115601912nas a2200265 4500008004100000245007900041210006900120260001500189520117500204100001601379700001501395700001201410700001501422700002001437700001101457700001301468700001901481700002001500700001701520700001501537700001701552700002501569700001501594856003701609 2019 eng d00aObservation of Domain Wall Confinement and Dynamics in a Quantum Simulator0 aObservation of Domain Wall Confinement and Dynamics in a Quantum c12/23/20193 a

Confinement is a ubiquitous mechanism in nature, whereby particles feel an attractive force that increases without bound as they separate. A prominent example is color confinement in particle physics, in which baryons and mesons are produced by quark confinement. Analogously, confinement can also occur in low-energy quantum many-body systems when elementary excitations are confined into bound quasiparticles. Here, we report the first observation of magnetic domain wall confinement in interacting spin chains with a trapped-ion quantum simulator. By measuring how correlations spread, we show that confinement can dramatically suppress information propagation and thermalization in such many-body systems. We are able to quantitatively determine the excitation energy of domain wall bound states from non-equilibrium quench dynamics. Furthermore, we study the number of domain wall excitations created for different quench parameters, in a regime that is difficult to model with classical computers. This work demonstrates the capability of quantum simulators for investigating exotic high-energy physics phenomena, such as quark collision and string breaking

1 aTan, W., L.1 aBecker, P.1 aLiu, F.1 aPagano, G.1 aCollins, K., S.1 aDe, A.1 aFeng, L.1 aKaplan, H., B.1 aKyprianidis, A.1 aLundgren, R.1 aMorong, W.1 aWhitsitt, S.1 aGorshkov, Alexey, V.1 aMonroe, C. uhttps://arxiv.org/abs/1912.1111701481nas a2200157 4500008004100000245006800041210006700109260001500176300001000191490000800201520102300209100002101232700001601253700001701269856003701286 2019 eng d00aParallel Self-Testing of the GHZ State with a Proof by Diagrams0 aParallel SelfTesting of the GHZ State with a Proof by Diagrams c01/29/2019 a43-660 v2873 a

Quantum self-testing addresses the following question: is it possible to verify the existence of a multipartite state even when one's measurement devices are completely untrusted? This problem has seen abundant activity in the last few years, particularly with the advent of parallel self-testing (i.e., testing several copies of a state at once), which has applications not only to quantum cryptography but also quantum computing. In this work we give the first error-tolerant parallel self-test in a three-party (rather than two-party) scenario, by showing that an arbitrary number of copies of the GHZ state can be self-tested. In order to handle the additional complexity of a three-party setting, we use a diagrammatic proof based on categorical quantum mechanics, rather than a typical symbolic proof. The diagrammatic approach allows for manipulations of the complicated tensor networks that arise in the proof, and gives a demonstration of the importance of picture-languages in quantum information.

1 aBreiner, Spencer1 aKalev, Amir1 aMiller, Carl uhttps://arxiv.org/abs/1806.0474401709nas a2200241 4500008004100000245007100041210006900112260001500181520103600196100001501232700002101247700001801268700001801286700002501304700001301329700001401342700001201356700001501368700001701383700001401400700001601414856003701430 2019 eng d00aProgrammable Quantum Simulations of Spin Systems with Trapped Ions0 aProgrammable Quantum Simulations of Spin Systems with Trapped Io c12/17/20193 a

Laser-cooled and trapped atomic ions form an ideal standard for the simulation of interacting quantum spin models. Effective spins are represented by appropriate internal energy levels within each ion, and the spins can be measured with near-perfect efficiency using state-dependent fluorescence techniques. By applying optical fields that exert optical dipole forces on the ions, their Coulomb interaction can be modulated in ways that give rise to long-range and tunable spin-spin interactions that can be reconfigured by shaping the spectrum and pattern of the laser fields. Here we review the theoretical mapping of atomic ions to interacting spin systems, the experimental preparation of complex equilibrium states, and the study of dynamical processes of this many-body interacting quantum system. The use of such quantum simulators for studying spin models may inform our understanding of exotic quantum materials and shed light on interacting quantum systems that cannot be modeled with conventional computers. 

1 aMonroe, C.1 aCampbell, W., C.1 aDuan, L., -M.1 aGong, Z., -X.1 aGorshkov, Alexey, V.1 aHess, P.1 aIslam, R.1 aKim, K.1 aPagano, G.1 aRicherme, P.1 aSenko, C.1 aYao, N., Y. uhttps://arxiv.org/abs/1912.0784501764nas a2200289 4500008004100000245007400041210006900115260001500184520095900199100001501158700001401173700001501187700002001202700001101222700001701233700001901250700002001269700001601289700002901305700001801334700001801352700001201370700001501382700002501397700001501422856003701437 2019 eng d00aQuantum Approximate Optimization with a Trapped-Ion Quantum Simulator0 aQuantum Approximate Optimization with a TrappedIon Quantum Simul c06/06/20193 a

Quantum computers and simulators may offer significant advantages over their classical counterparts, providing insights into quantum many-body systems and possibly solving exponentially hard problems, such as optimization and satisfiability. Here we report the first implementation of a shallow-depth Quantum Approximate Optimization Algorithm (QAOA) using an analog quantum simulator to estimate the ground state energy of the transverse field Ising model with tunable long-range interactions. First, we exhaustively search the variational control parameters to approximate the ground state energy with up to 40 trapped-ion qubits. We then interface the quantum simulator with a classical algorithm to more efficiently find the optimal set of parameters that minimizes the resulting energy of the system. We finally sample from the full probability distribution of the QAOA output with single-shot and efficient measurements of every qubit. 

1 aPagano, G.1 aBapat, A.1 aBecker, P.1 aCollins, K., S.1 aDe, A.1 aHess, P., W.1 aKaplan, H., B.1 aKyprianidis, A.1 aTan, W., L.1 aBaldwin, Christopher, L.1 aBrady, L., T.1 aDeshpande, A.1 aLiu, F.1 aJordan, S.1 aGorshkov, Alexey, V.1 aMonroe, C. uhttps://arxiv.org/abs/1906.0270001947nas a2200397 4500008004100000245005400041210005400095260001500149520085000164100001801014700001601032700002301048700002301071700002201094700002401116700001901140700001801159700001801177700002001195700002501215700001801240700001801258700001901276700001901295700001601314700002301330700001901353700001701372700002401389700001901413700002201432700001901454700001901473700002001492856003701512 2019 eng d00aQuantum Computer Systems for Scientific Discovery0 aQuantum Computer Systems for Scientific Discovery c12/16/20193 a

The great promise of quantum computers comes with the dual challenges of building them and finding their useful applications. We argue that these two challenges should be considered together, by co-designing full stack quantum computer systems along with their applications in order to hasten their development and potential for scientific discovery. In this context, we identify scientific and community needs, opportunities, and significant challenges for the development of quantum computers for science over the next 2-10 years. This document is written by a community of university, national laboratory, and industrial researchers in the field of Quantum Information Science and Technology, and is based on a summary from a U.S. National Science Foundation workshop on Quantum Computing held on October 21-22, 2019 in Alexandria, VA.

1 aAlexeev, Yuri1 aBacon, Dave1 aBrown, Kenneth, R.1 aCalderbank, Robert1 aCarr, Lincoln, D.1 aChong, Frederic, T.1 aDeMarco, Brian1 aEnglund, Dirk1 aFarhi, Edward1 aFefferman, Bill1 aGorshkov, Alexey, V.1 aHouck, Andrew1 aKim, Jungsang1 aKimmel, Shelby1 aLange, Michael1 aLloyd, Seth1 aLukin, Mikhail, D.1 aMaslov, Dmitri1 aMaunz, Peter1 aMonroe, Christopher1 aPreskill, John1 aRoetteler, Martin1 aSavage, Martin1 aThompson, Jeff1 aVazirani, Umesh uhttps://arxiv.org/abs/1912.0757702892nas a2200397 4500008004100000245005600041210005500097260001500152520177700167100001701944700002301961700002101984700002202005700001902027700001602046700001902062700002502081700002302106700002002129700002002149700002602169700002302195700002402218700002202242700002302264700001602287700001302303700002002316700002402336700001702360700001902377700001802396700002302414700002002437856003702457 2019 eng d00aQuantum Simulators: Architectures and Opportunities0 aQuantum Simulators Architectures and Opportunities c12/14/20193 a

Quantum simulators are a promising technology on the spectrum of quantum devices from specialized quantum experiments to universal quantum computers. These quantum devices utilize entanglement and many-particle behaviors to explore and solve hard scientific, engineering, and computational problems. Rapid development over the last two decades has produced more than 300 quantum simulators in operation worldwide using a wide variety of experimental platforms. Recent advances in several physical architectures promise a golden age of quantum simulators ranging from highly optimized special purpose simulators to flexible programmable devices. These developments have enabled a convergence of ideas drawn from fundamental physics, computer science, and device engineering. They have strong potential to address problems of societal importance, ranging from understanding vital chemical processes, to enabling the design of new materials with enhanced performance, to solving complex computational problems. It is the position of the community, as represented by participants of the NSF workshop on "Programmable Quantum Simulators," that investment in a national quantum simulator program is a high priority in order to accelerate the progress in this field and to result in the first practical applications of quantum machines. Such a program should address two areas of emphasis: (1) support for creating quantum simulator prototypes usable by the broader scientific community, complementary to the present universal quantum computer effort in industry; and (2) support for fundamental research carried out by a blend of multi-investigator, multi-disciplinary collaborations with resources for quantum simulator software, hardware, and education. 

1 aAltman, Ehud1 aBrown, Kenneth, R.1 aCarleo, Giuseppe1 aCarr, Lincoln, D.1 aDemler, Eugene1 aChin, Cheng1 aDeMarco, Brian1 aEconomou, Sophia, E.1 aEriksson, Mark, A.1 aFu, Kai-Mei, C.1 aGreiner, Markus1 aHazzard, Kaden, R. A.1 aHulet, Randall, G.1 aKollár, Alicia, J.1 aLev, Benjamin, L.1 aLukin, Mikhail, D.1 aMa, Ruichao1 aMi, Xiao1 aMisra, Shashank1 aMonroe, Christopher1 aMurch, Kater1 aNazario, Zaira1 aNi, Kang-Kuen1 aPotter, Andrew, C.1 aRoushan, Pedram uhttps://arxiv.org/abs/1912.0693801408nas a2200133 4500008004100000245008000041210006900121260001500190520097500205100001901180700001901199700001901218856003701237 2019 eng d00aStatistical Privacy in Distributed Average Consensus on Bounded Real Inputs0 aStatistical Privacy in Distributed Average Consensus on Bounded  c03/20/20193 a

This paper proposes a privacy protocol for distributed average consensus algorithms on bounded real-valued inputs that guarantees statistical privacy of honest agents' inputs against colluding (passive adversarial) agents, if the set of colluding agents is not a vertex cut in the underlying communication network. This implies that privacy of agents' inputs is preserved against t number of arbitrary colluding agents if the connectivity of the communication network is at least (t+1). A similar privacy protocol has been proposed for the case of bounded integral inputs in our previous paper~\cite{gupta2018information}. However, many applications of distributed consensus concerning distributed control or state estimation deal with real-valued inputs. Thus, in this paper we propose an extension of the privacy protocol in~\cite{gupta2018information}, for bounded real-valued agents' inputs, where bounds are known apriori to all the agents. 

1 aGupta, Nirupam1 aKatz, Jonathan1 aChopra, Nikhil uhttps://arxiv.org/abs/1903.0931501624nas a2200193 4500008004100000245009000041210006900131260001500200520100400215100001701219700002401236700001801260700001601278700002301294700002401317700002401341700002801365856003701393 2019 eng d00aToward convergence of effective field theory simulations on digital quantum computers0 aToward convergence of effective field theory simulations on digi c04/18/20193 a

We report results for simulating an effective field theory to compute the binding energy of the deuteron nucleus using a hybrid algorithm on a trapped-ion quantum computer. Two increasingly complex unitary coupled-cluster ansaetze have been used to compute the binding energy to within a few percent for successively more complex Hamiltonians. By increasing the complexity of the Hamiltonian, allowing more terms in the effective field theory expansion and calculating their expectation values, we present a benchmark for quantum computers based on their ability to scalably calculate the effective field theory with increasing accuracy. Our result of E4=−2.220±0.179MeV may be compared with the exact Deuteron ground-state energy −2.224MeV. We also demonstrate an error mitigation technique using Richardson extrapolation on ion traps for the first time. The error mitigation circuit represents a record for deepest quantum circuit on a trapped-ion quantum computer. 

1 aShehab, Omar1 aLandsman, Kevin, A.1 aNam, Yunseong1 aZhu, Daiwei1 aLinke, Norbert, M.1 aKeesan, Matthew, J.1 aPooser, Raphael, C.1 aMonroe, Christopher, R. uhttps://arxiv.org/abs/1904.0433801465nas a2200145 4500008004100000245006900041210006900110260001300179520101400192100001401206700001701220700002501237700002001262856003701282 2019 eng d00aTowards Bulk Metric Reconstruction from Extremal Area Variations0 aTowards Bulk Metric Reconstruction from Extremal Area Variations c04/09/193 a

The Ryu-Takayanagi and Hubeny-Rangamani-Takayanagi formulae suggest that bulk geometry emerges from the entanglement structure of the boundary theory. Using these formulae, we build on a result of Alexakis, Balehowsky, and Nachman to show that in four bulk dimensions, the entanglement entropies of boundary regions of disk topology uniquely fix the bulk metric in any region foliated by the corresponding HRT surfaces. More generally, for a bulk of any dimension , knowledge of the (variations of the) areas of two-dimensional boundary-anchored extremal surfaces of disk topology uniquely fixes the bulk metric wherever these surfaces reach. This result is covariant and not reliant on any symmetry assumptions; its applicability thus includes regions of strong dynamical gravity such as the early-time interior of black holes formed from collapse. While we only show uniqueness of the metric, the approach we present provides a clear path towards an\textit {explicit} spacetime metric reconstruction.

1 aBao, Ning1 aCao, ChunJun1 aFischetti, Sebastian1 aKeeler, Cynthia uhttps://arxiv.org/abs/1904.0483401015nas a2200133 4500008004100000245004800041210004800089260001400137490000700151520064300158100001600801700002700817856003700844 2019 eng d00aValidating and Certifying Stabilizer States0 aValidating and Certifying Stabilizer States c9/16/20190 v993 a

We propose a measurement scheme that validates the preparation of a target n-qubit stabilizer state. The scheme involves a measurement of n Pauli observables, a priori determined from the target stabilizer and which can be realized using single-qubit gates. Based on the proposed validation scheme, we derive an explicit expression for the worse-case fidelity, i.e., the minimum fidelity between the target stabilizer state and any other state consistent with the measured data. We also show that the worse-case fidelity can be certified, with high probability, using O(n) copies of the state of the system per measured observable.

1 aKalev, Amir1 aKyrillidis, Anastasios uhttps://arxiv.org/abs/1808.1078601653nas a2200169 4500008004100000245007700041210006900118260001500187300001100202490000700213520111300220100002301333700001701356700002501373700001601398856006901414 2018 eng d00aAbsence of Thermalization in Finite Isolated Interacting Floquet Systems0 aAbsence of Thermalization in Finite Isolated Interacting Floquet c2018/01/29 a0143110 v973 a

Conventional wisdom suggests that the long time behavior of isolated interacting periodically driven (Floquet) systems is a featureless maximal entropy state characterized by an infinite temperature. Efforts to thwart this uninteresting fixed point include adding sufficient disorder to realize a Floquet many-body localized phase or working in a narrow region of drive frequencies to achieve glassy non-thermal behavior at long time. Here we show that in clean systems the Floquet eigenstates can exhibit non-thermal behavior due to finite system size. We consider a one-dimensional system of spinless fermions with nearest-neighbor interactions where the interaction term is driven. Interestingly, even with no static component of the interaction, the quasienergy spectrum contains gaps and a significant fraction of the Floquet eigenstates, at all quasienergies, have non-thermal average doublon densities. We show that this non-thermal behavior arises due to emergent integrability at large interaction strength and discuss how the integrability breaks down with power-law behavior in system size.

1 aSeetharam, Karthik1 aTitum, Paraj1 aKolodrubetz, Michael1 aRefael, Gil uhttps://journals.aps.org/prb/abstract/10.1103/PhysRevB.97.01431101296nas a2200157 4500008004100000245005600041210005600097260001500153520081900168100001900987700002801006700002101034700002601055700002001081856003701101 2018 eng d00aBell monogamy relations in arbitrary qubit networks0 aBell monogamy relations in arbitrary qubit networks c2018/01/093 a

Characterizing trade-offs between simultaneous violations of multiple Bell inequalities in a large network of qubits is computationally demanding. We propose a graph-theoretic approach to efficiently produce Bell monogamy relations in arbitrary arrangements of qubits. All the relations obtained for bipartite Bell inequalities are tight and leverage only a single Bell monogamy relation. This feature is unique to bipartite Bell inequalities, as we show that there is no finite set of such elementary monogamy relations for multipartite inequalities. Nevertheless, many tight monogamy relations for multipartite inequalities can be obtained with our method as shown in explicit examples.

1 aTran, Minh, C.1 aRamanathan, Ravishankar1 aMcKague, Matthew1 aKaszlikowski, Dagomir1 aPaterek, Tomasz uhttps://arxiv.org/abs/1801.0307101856nas a2200169 4500008004100000245006600041210006500107260001500172300000700187490000600194520134900200100002401549700001601573700002201589700001901611856005601630 2018 eng d00aBQP-completeness of Scattering in Scalar Quantum Field Theory0 aBQPcompleteness of Scattering in Scalar Quantum Field Theory c2018/01/08 a440 v23 a

Recent work has shown that quantum computers can compute scattering probabilities in massive quantum field theories, with a run time that is polynomial in the number of particles, their energy, and the desired precision. Here we study a closely related quantum field-theoretical problem: estimating the vacuum-to-vacuum transition amplitude, in the presence of spacetime-dependent classical sources, for a massive scalar field theory in (1+1) dimensions. We show that this problem is BQP-hard; in other words, its solution enables one to solve any problem that is solvable in polynomial time by a quantum computer. Hence, the vacuum-to-vacuum amplitude cannot be accurately estimated by any efficient classical algorithm, even if the field theory is very weakly coupled, unless BQP=BPP. Furthermore, the corresponding decision problem can be solved by a quantum computer in a time scaling polynomially with the number of bits needed to specify the classical source fields, and this problem is therefore BQP-complete. Our construction can be regarded as an idealized architecture for a universal quantum computer in a laboratory system described by massive phi^4 theory coupled to classical spacetime-dependent sources.

1 aJordan, Stephen, P.1 aKrovi, Hari1 aLee, Keith, S. M.1 aPreskill, John uhttps://quantum-journal.org/papers/q-2018-01-08-44/02454nas a2200133 4500008004100000245005300041210005300094520206100147100002202208700001802230700001602248700001902264856003702283 2018 eng d00aClassical lower bounds from quantum upper bounds0 aClassical lower bounds from quantum upper bounds3 a

We prove lower bounds on complexity measures, such as the approximate degree of a Boolean function and the approximate rank of a Boolean matrix, using quantum arguments. We prove these lower bounds using a quantum query algorithm for the combinatorial group testing problem. 
We show that for any function f, the approximate degree of computing the OR of n copies of f is Omega(sqrt{n}) times the approximate degree of f, which is optimal. No such general result was known prior to our work, and even the lower bound for the OR of ANDs function was only resolved in 2013. 
We then prove an analogous result in communication complexity, showing that the logarithm of the approximate rank (or more precisely, the approximate gamma_2 norm) of F: X x Y -> {0,1} grows by a factor of Omega~(sqrt{n}) when we take the OR of n copies of F, which is also essentially optimal. As a corollary, we give a new proof of Razborov's celebrated Omega(sqrt{n}) lower bound on the quantum communication complexity of the disjointness problem. 
Finally, we generalize both these results from composition with the OR function to composition with arbitrary symmetric functions, yielding nearly optimal lower bounds in this setting as well.

1 aBen-David, Shalev1 aBouland, Adam1 aGarg, Ankit1 aKothari, Robin uhttps://arxiv.org/abs/1807.0625601463nas a2200229 4500008004100000245006800041210006700109520082000176100001500996700001701011700001901028700001601047700001701063700001501080700002001095700001401115700001901129700002201148700001101170700001501181856003701196 2018 eng d00aCryogenic Trapped-Ion System for Large Scale Quantum Simulation0 aCryogenic TrappedIon System for Large Scale Quantum Simulation3 a

We present a cryogenic ion trapping system designed for large scale quantum simulation of spin models. Our apparatus is based on a segmented-blade ion trap enclosed in a 4 K cryostat, which enables us to routinely trap over 100 171Yb+ ions in a linear configuration for hours due to a low background gas pressure from differential cryo-pumping. We characterize the cryogenic vacuum by using trapped ion crystals as a pressure gauge, measuring both inelastic and elastic collision rates with the molecular background gas. We demonstrate nearly equidistant ion spacing for chains of up to 44 ions using anharmonic axial potentials. This reliable production and lifetime enhancement of large linear ion chains will enable quantum simulation of spin models that are intractable with classical computer modelling.

1 aPagano, G.1 aHess, P., W.1 aKaplan, H., B.1 aTan, W., L.1 aRicherme, P.1 aBecker, P.1 aKyprianidis, A.1 aZhang, J.1 aBirckelbaw, E.1 aHernandez, M., R.1 aWu, Y.1 aMonroe, C. uhttps://arxiv.org/abs/1802.0311801943nas a2200121 4500008004100000245007800041210006900119520154200188100001801730700001901748700001701767856003701784 2018 eng d00aDynamic suppression of Rayleigh light scattering in dielectric resonators0 aDynamic suppression of Rayleigh light scattering in dielectric r3 a

The ultimate limits of performance for any classical optical system are set by sub-wavelength fluctuations within the host material, that may be frozen-in or even dynamically induced. The most common manifestation of such sub-wavelength disorder is Rayleigh light scattering, which is observed in nearly all wave-guiding technologies today and can lead to both irreversible radiative losses as well as undesirable intermodal coupling. While it has been shown that backscattering from disorder can be suppressed by breaking time-reversal symmetry in magneto-optic and topological insulator materials, common optical dielectrics possess neither of these properties. Here we demonstrate an optomechanical approach for dynamically suppressing Rayleigh backscattering within dielectric resonators. We achieve this by locally breaking time-reversal symmetry in a silica resonator through a Brillouin scattering interaction that is available in all materials. Near-complete suppression of Rayleigh backscattering is experimentally confirmed through three independent measurements -- the reduction of the back-reflections caused by scatterers, the elimination of a commonly seen normal-mode splitting effect, and by measurement of the reduction in intrinsic optical loss. More broadly, our results provide new evidence that it is possible to dynamically suppress Rayleigh backscattering within any optical dielectric medium, for achieving robust light propagation in nanophotonic devices in spite of the presence of scatterers or defects.

1 aKim, Seunghwi1 aTaylor, J., M.1 aBahl, Gaurav uhttps://arxiv.org/abs/1803.0236602638nas a2200265 4500008004100000245009500041210006900136260001500205300001200220490000800232520186000240100002102100700001902121700001802140700001802158700001502176700002002191700001902211700001602230700002502246700001802271700002402289700002202313856003702335 2018 eng d00aExperimentally Generated Randomness Certified by the Impossibility of Superluminal Signals0 aExperimentally Generated Randomness Certified by the Impossibili c2018/04/11 a223-2260 v5563 a

From dice to modern complex circuits, there have been many attempts to build increasingly better devices to generate random numbers. Today, randomness is fundamental to security and cryptographic systems, as well as safeguarding privacy. A key challenge with random number generators is that it is hard to ensure that their outputs are unpredictable. For a random number generator based on a physical process, such as a noisy classical system or an elementary quantum measurement, a detailed model describing the underlying physics is required to assert unpredictability. Such a model must make a number of assumptions that may not be valid, thereby compromising the integrity of the device. However, it is possible to exploit the phenomenon of quantum nonlocality with a loophole-free Bell test to build a random number generator that can produce output that is unpredictable to any adversary limited only by general physical principles. With recent technological developments, it is now possible to carry out such a loophole-free Bell test. Here we present certified randomness obtained from a photonic Bell experiment and extract 1024 random bits uniform to within 10−12. These random bits could not have been predicted within any physical theory that prohibits superluminal signaling and allows one to make independent measurement choices. To certify and quantify the randomness, we describe a new protocol that is optimized for apparatuses characterized by a low per-trial violation of Bell inequalities. We thus enlisted an experimental result that fundamentally challenges the notion of determinism to build a system that can increase trust in random sources. In the future, random number generators based on loophole-free Bell tests may play a role in increasing the security and trust of our cryptographic systems and infrastructure.

1 aBierhorst, Peter1 aKnill, Emanuel1 aGlancy, Scott1 aZhang, Yanbao1 aMink, Alan1 aJordan, Stephen1 aRommal, Andrea1 aLiu, Yi-Kai1 aChristensen, Bradley1 aNam, Sae, Woo1 aStevens, Martin, J.1 aShalm, Lynden, K. uhttps://arxiv.org/abs/1803.0621901691nas a2200169 4500008004100000245007000041210006900111260001500180300001300195490000600208520118500214100002701399700001301426700001901439700002601458856003701484 2018 eng d00aFractal Universality in Near-Threshold Magnetic Lanthanide Dimers0 aFractal Universality in NearThreshold Magnetic Lanthanide Dimers c2018/02/16 aeaap83080 v43 a

Ergodic quantum systems are often quite alike, whereas nonergodic, fractal systems are unique and display characteristic properties. We explore one of these fractal systems, weakly bound dysprosium lanthanide molecules, in an external magnetic field. As recently shown, colliding ultracold magnetic dysprosium atoms display a soft chaotic behavior with a small degree of disorder. We broaden this classification by investigating the generalized inverse participation ratio and fractal dimensions for large sets of molecular wave functions. Our exact close-coupling simulations reveal a dynamic phase transition from partially localized states to totally delocalized states and universality in its distribution by increasing the magnetic field strength to only a hundred Gauss (or 10 mT). Finally, we prove the existence of nonergodic delocalized phase in the system and explain the violation of ergodicity by strong coupling between near-threshold molecular states and the nearby continuum.

1 aMakrides, Constantinos1 aLi, Ming1 aTiesinga, Eite1 aKotochigova, Svetlana uhttps://arxiv.org/abs/1802.0958601552nas a2200217 4500008004100000245004800041210004800089260001500137300001100152490000700163520094200170100002001112700002301132700001601155700002101171700001601192700001201208700002401220700002101244856006901265 2018 eng d00aGeometry of the quantum set of correlations0 aGeometry of the quantum set of correlations c2018/02/07 a0221040 v973 a

It is well known that correlations predicted by quantum mechanics cannot be explained by any classical (local-realistic) theory. The relative strength of quantum and classical correlations is usually studied in the context of Bell inequalities, but this tells us little about the geometry of the quantum set of correlations. In other words, we do not have good intuition about what the quantum set actually looks like. In this paper we study the geometry of the quantum set using standard tools from convex geometry. We find explicit examples of rather counter-intuitive features in the simplest non-trivial Bell scenario (two parties, two inputs and two outputs) and illustrate them using 2-dimensional slice plots. We also show that even more complex features appear in Bell scenarios with more inputs or more parties. Finally, we discuss the limitations that the geometry of the quantum set imposes on the task of self-testing.

1 aGoh, Koon, Tong1 aKaniewski, Jedrzej1 aWolfe, Elie1 aVértesi, Tamás1 aWu, Xingyao1 aCai, Yu1 aLiang, Yeong-Cherng1 aScarani, Valerio uhttps://journals.aps.org/pra/abstract/10.1103/PhysRevA.97.02210401552nas a2200109 4500008004100000245008900041210006900130520116300199100002701362700001601389856003701405 2018 eng d00aImplicit regularization and solution uniqueness in over-parameterized matrix sensing0 aImplicit regularization and solution uniqueness in overparameter3 a

We consider whether algorithmic choices in over-parameterized linear matrix factorization introduce implicit regularization. We focus on noiseless matrix sensing over rank-r positive semi-definite (PSD) matrices in Rn×n, with a sensing mechanism that satisfies the restricted isometry property (RIP). The algorithm we study is that of \emph{factored gradient descent}, where we model the low-rankness and PSD constraints with the factorization UU⊤, where U∈Rn×r. Surprisingly, recent work argues that the choice of r≤n is not pivotal: even setting U∈Rn×n is sufficient for factored gradient descent to find the rank-r solution, which suggests that operating over the factors leads to an implicit regularization. In this note, we provide a different perspective. We show that, in the noiseless case, under certain conditions, the PSD constraint by itself is sufficient to lead to a unique rank-r matrix recovery, without implicit or explicit low-rank regularization. \emph{I.e.}, under assumptions, the set of PSD matrices, that are consistent with the observed data, is a singleton, irrespective of the algorithm used.

1 aKyrillidis, Anastasios1 aKalev, Amir uhttps://arxiv.org/abs/1806.0204601169nas a2200133 4500008004100000245009300041210006900134260001500203520072300218100001900941700001900960700001900979856003700998 2018 eng d00aInformation-Theoretic Privacy For Distributed Average Consensus: Bounded Integral Inputs0 aInformationTheoretic Privacy For Distributed Average Consensus B c03/28/20193 a

We propose an asynchronous distributed average consensus algorithm that guarantees information-theoretic privacy of honest agents' inputs against colluding passive adversarial agents, as long as the set of colluding passive adversarial agents is not a vertex cut in the underlying communication network. This implies that a network with (t+1)-connectivity guarantees information-theoretic privacy of honest agents' inputs against any t colluding agents. The proposed protocol is formed by composing a distributed privacy mechanism we provide with any (non-private) distributed average consensus algorithm. The agent' inputs are bounded integers, where the bounds are apriori known to all the agents.

1 aGupta, Nirupam1 aKatz, Jonathan1 aChopra, Nikhil uhttps://arxiv.org/abs/1809.0179406429nas a2200121 4500008004100000245006700041210006600108520603900174100001906213700001906232700001906251856003706270 2018 eng d00aInformation-Theoretic Privacy in Distributed Average Consensus0 aInformationTheoretic Privacy in Distributed Average Consensus3 a

We propose an asynchronous distributed average consensus algorithm that guarantees information-theoretic privacy of honest agents' inputs against colluding semi-honest (passively adversarial) agents, as long as the set of colluding semi-honest agents is not a vertex cut in the underlying communication network. This implies that a network with (t+1)-connectivity guarantees information-theoretic privacy of honest agents' inputs against any t colluding semi-honest agents. The proposed protocol is formed by composing a distributed privacy mechanism we provide with any (non-private) distributed average consensus algorithm. 

1 aGupta, Nirupam1 aKatz, Jonathan1 aChopra, Nikhil uhttps://arxiv.org/abs/1809.0179402049nas a2200145 4500008004100000245005200041210005100093260001500144300001100159490000700170520165600177100001701833700001601850856003701866 2018 eng d00aMeasurement Contextuality and Planck's Constant0 aMeasurement Contextuality and Plancks Constant c2018/07/12 a0730200 v203 a

Contextuality is a necessary resource for universal quantum computation and non-contextual quantum mechanics can be simulated efficiently by classical computers in many cases. Orders of Planck's constant, ℏ, can also be used to characterize the classical-quantum divide by expanding quantities of interest in powers of ℏ---all orders higher than ℏ0 can be interpreted as quantum corrections to the order ℏ0 term. We show that contextual measurements in finite-dimensional systems have formulations within the Wigner-Weyl-Moyal (WWM) formalism that require higher than order ℏ0 terms to be included in order to violate the classical bounds on their expectation values. As a result, we show that contextuality as a resource is equivalent to orders of ℏ as a resource within the WWM formalism. This explains why qubits can only exhibit state-independent contextuality under Pauli observables as in the Peres-Mermin square while odd-dimensional qudits can also exhibit state-dependent contextuality. In particular, we find that qubit Pauli observables lack an order ℏ0 contribution in their Weyl symbol and so exhibit contextuality regardless of the state being measured. On the other hand, odd-dimensional qudit observables generally possess non-zero order ℏ0 terms, and higher, in their WWM formulation, and so exhibit contextuality depending on the state measured: odd-dimensional qudit states that exhibit measurement contextuality have an order ℏ1 contribution that allows for the violation of classical bounds while states that do not exhibit measurement contextuality have insufficiently large order ℏ1 contributions.

1 aKocia, Lucas1 aLove, Peter uhttps://arxiv.org/abs/1711.0806601224nas a2200145 4500008004100000245008400041210006900125520074800194100001700942700001900959700001800978700002900996700001601025856003701041 2018 eng d00aMore is Less: Perfectly Secure Oblivious Algorithms in the Multi-Server Setting0 aMore is Less Perfectly Secure Oblivious Algorithms in the MultiS3 a

The problem of Oblivious RAM (ORAM) has traditionally been studied in a single-server setting, but more recently the multi-server setting has also been considered. Yet it is still unclear whether the multi-server setting has any inherent advantages, e.g., whether the multi-server setting can be used to achieve stronger security goals or provably better efficiency than is possible in the single-server case. In this work, we construct a perfectly secure 3-server ORAM scheme that outperforms the best known single-server scheme by a logarithmic factor. In the process, we also show, for the first time, that there exist specific algorithms for which multiple servers can overcome known lower bounds in the single-server setting. 

1 aChan, Hubert1 aKatz, Jonathan1 aNayak, Kartik1 aPolychroniadou, Antigoni1 aShi, Elaine uhttps://arxiv.org/abs/1809.0082502361nas a2200109 4500008004100000245014200041210006900183520192900252100001702181700001602198856003702214 2018 eng d00aThe Non-Disjoint Ontic States of the Grassmann Ontological Model, Transformation Contextuality, and the Single Qubit Stabilizer Subtheory0 aNonDisjoint Ontic States of the Grassmann Ontological Model Tran3 a

We show that it is possible to construct a preparation non-contextual ontological model that does not exhibit "transformation contextuality" for single qubits in the stabilizer subtheory. In particular, we consider the "blowtorch" map and show that it does not exhibit transformation contextuality under the Grassmann Wigner-Weyl-Moyal (WWM) qubit formalism. Furthermore, the transformation in this formalism can be fully expressed at order ℏ0 and so does not qualify as a candidate quantum phenomenon. In particular, we find that the Grassmann WWM formalism at order ℏ0 corresponds to an ontological model governed by an additional set of constraints arising from the relations defining the Grassmann algebra. Due to this additional set of constraints, the allowed probability distributions in this model do not form a single convex set when expressed in terms of disjoint ontic states and so cannot be mapped to models whose states form a single convex set over disjoint ontic states. However, expressing the Grassmann WWM ontological model in terms of non-disjoint ontic states corresponding to the monomials of the Grassmann algebra results in a single convex set. We further show that a recent result by Lillystone et al. that proves a broad class of preparation and measurement non-contextual ontological models must exhibit transformation contextuality lacks the generality to include the ontological model considered here; Lillystone et al.'s result is appropriately limited to ontological models whose states produce a single convex set when expressed in terms of disjoint ontic states. Therefore, we prove that for the qubit stabilizer subtheory to be captured by a preparation, transformation and measurement non-contextual ontological theory, it must be expressed in terms of non-disjoint ontic states, unlike the case for the odd-dimensional single-qudit stabilizer subtheory.

1 aKocia, Lucas1 aLove, Peter uhttps://arxiv.org/abs/1805.0951401444nas a2200169 4500008004100000245007500041210006900116260001500185490000600200520093200206100001701138700002201155700001901177700001901196700002201215856003701237 2018 eng d00aObservation of bound state self-interaction in a nano-eV atom collider0 aObservation of bound state selfinteraction in a nanoeV atom coll c2018/11/200 v93 a

Quantum mechanical scattering resonances for colliding particles occur when a continuum scattering state couples to a discrete bound state between them. The coupling also causes the bound state to interact with itself via the continuum and leads to a shift in the bound state energy, but, lacking knowledge of the bare bound state energy, measuring this self-energy via the resonance position has remained elusive. Here, we report on the direct observation of self-interaction by using a nano-eV atom collider to track the position of a magnetically-tunable Feshbach resonance through a parameter space spanned by energy and magnetic field. Our system of potassium and rubidium atoms displays a strongly non-monotonic resonance trajectory with an exceptionally large self-interaction energy arising from an interplay between the Feshbach bound state and a different, virtual bound state at a fixed energy near threshold.

1 aThomas, Ryan1 aChilcott, Matthew1 aTiesinga, Eite1 aDeb, Amita, B.1 aKjærgaard, Niels uhttps://arxiv.org/abs/1807.0117401180nas a2200157 4500008004100000245007300041210006900114490000800183520068500191100001800876700002900894700002400923700001600947700002200963856003700985 2018 eng d00aOptimal Pure-State Qubit Tomography via Sequential Weak Measurements0 aOptimal PureState Qubit Tomography via Sequential Weak Measureme0 v1213 a

The spin-coherent-state positive-operator-valued-measure (POVM) is a fundamental measurement in quantum science, with applications including tomography, metrology, teleportation, benchmarking, and measurement of Husimi phase space probabilities. We prove that this POVM is achieved by collectively measuring the spin projection of an ensemble of qubits weakly and isotropically. We apply this in the context of optimal tomography of pure qubits. We show numerically that through a sequence of weak measurements of random directions of the collective spin component, sampled discretely or in a continuous measurement with random controls, one can approach the optimal bound.

1 aShojaee, Ezad1 aJackson, Christopher, S.1 aRiofrio, Carlos, A.1 aKalev, Amir1 aDeutsch, Ivan, H. uhttps://arxiv.org/abs/1805.0101201661nas a2200121 4500008004100000245009700041210006900138520123700207100001301444700001901457700002601476856003701502 2018 eng d00aOrbital quantum magnetism in spin dynamics of strongly interacting magnetic lanthanide atoms0 aOrbital quantum magnetism in spin dynamics of strongly interacti3 a

Laser cooled lanthanide atoms are ideal candidates with which to study strong and unconventional quantum magnetism with exotic phases. Here, we use state-of-the-art closed-coupling simulations to model quantum magnetism for pairs of ultracold spin-6 erbium lanthanide atoms placed in a deep optical lattice. In contrast to the widely used single-channel Hubbard model description of atoms and molecules in an optical lattice, we focus on the single-site multi-channel spin evolution due to spin-dependent contact, anisotropic van der Waals, and dipolar forces. This has allowed us to identify the leading mechanism, orbital anisotropy, that governs molecular spin dynamics among erbium atoms. The large magnetic moment and combined orbital angular momentum of the 4f-shell electrons are responsible for these strong anisotropic interactions and unconventional quantum magnetism. Multi-channel simulations of magnetic Cr atoms under similar trapping conditions show that their spin-evolution is controlled by spin-dependent contact interactions that are distinct in nature from the orbital anisotropy in Er. The role of an external magnetic field and the aspect ratio of the lattice site on spin dynamics is also investigated.

1 aLi, Ming1 aTiesinga, Eite1 aKotochigova, Svetlana uhttps://arxiv.org/abs/1804.1010201770nas a2200145 4500008004100000245006300041210006200104260001500166300001200181490000700193520134000200100001901540700001601559856004901575 2018 eng d00aPhase Retrieval Without Small-Ball Probability Assumptions0 aPhase Retrieval Without SmallBall Probability Assumptions c2018/01/01 a485-5000 v643 a

In the context of the phase retrieval problem, it is known that certain natural classes of measurements, such as Fourier measurements and random Bernoulli measurements, do not lead to the unique reconstruction of all possible signals, even in combination with certain practically feasible random masks. To avoid this difficulty, the analysis is often restricted to measurement ensembles (or masks) that satisfy a small-ball probability condition, in order to ensure that the reconstruction is unique. This paper shows a complementary result: for random Bernoulli measurements, there is still a large class of signals that can be reconstructed uniquely, namely, those signals that are non-peaky. In fact, this result is much more general: it holds for random measurements sampled from any subgaussian distribution 2), without any small-ball conditions. This is demonstrated in two ways: 1) a proof of stability and uniqueness and 2) a uniform recovery guarantee for the PhaseLift algorithm. In all of these cases, the number of measurements m approaches the information-theoretic lower bound. Finally, for random Bernoulli measurements with erasures, it is shown that PhaseLift achieves uniform recovery of all signals (including peaky ones).

1 aKrahmer, Felix1 aLiu, Yi-Kai uhttp://ieeexplore.ieee.org/document/8052535/02679nas a2200181 4500008004100000245010000041210006900141260000900210300001300219490000700232520211600239100002402355700002602379700001602405700002002421700001902441856003702460 2018 eng d00aQFlow lite dataset: A machine-learning approach to the charge states in quantum dot experiments0 aQFlow lite dataset A machinelearning approach to the charge stat c2018 ae02058440 v133 a

Over the past decade, machine learning techniques have revolutionized how research is done, from designing new materials and predicting their properties to assisting drug discovery to advancing cybersecurity. Recently, we added to this list by showing how a machine learning algorithm (a so-called learner) combined with an optimization routine can assist experimental efforts in the realm of tuning semiconductor quantum dot (QD) devices. Among other applications, semiconductor QDs are a candidate system for building quantum computers. The present-day tuning techniques for bringing the QD devices into a desirable configuration suitable for quantum computing that rely on heuristics do not scale with the increasing size of the quantum dot arrays required for even near-term quantum computing demonstrations. Establishing a reliable protocol for tuning that does not rely on the gross-scale heuristics developed by experimentalists is thus of great importance. To implement the machine learning-based approach, we constructed a dataset of simulated QD device characteristics, such as the conductance and the charge sensor response versus the applied electrostatic gate voltages. Here, we describe the methodology for generating the dataset, as well as its validation in training convolutional neural networks. We show that the learner's accuracy in recognizing the state of a device is ~96.5 % in both current- and charge-sensor-based training. We also introduce a tool that enables other researchers to use this approach for further research: QFlow lite - a Python-based mini-software suite that uses the dataset to train neural networks to recognize the state of a device and differentiate between states in experimental data. This work gives the definitive reference for the new dataset that will help enable researchers to use it in their experiments or to develop new machine learning approaches and concepts

1 aZwolak, Justyna, P.1 aKalantre, Sandesh, S.1 aWu, Xingyao1 aRagole, Stephen1 aTaylor, J., M. uhttps://arxiv.org/abs/1809.1001802409nas a2200157 4500008004100000245009100041210006900132520188600201100003302087700001602120700001702136700002402153700002202177700001502199856003702214 2018 eng d00aQuantum SDP Solvers: Large Speed-ups, Optimality, and Applications to Quantum Learning0 aQuantum SDP Solvers Large Speedups Optimality and Applications t3 a

We give two new quantum algorithms for solving semidefinite programs (SDPs) providing quantum speed-ups. We consider SDP instances with m constraint matrices, each of dimension n, rank r, and sparsity s. The first algorithm assumes an input model where one is given access to entries of the matrices at unit cost. We show that it has run time O~(s2(m−−√ε−10+n−−√ε−12)), where ε is the error. This gives an optimal dependence in terms of m,n and quadratic improvement over previous quantum algorithms when m≈n. The second algorithm assumes a fully quantum input model in which the matrices are given as quantum states. We show that its run time is O~(m−−√+poly(r))⋅poly(logm,logn,B,ε−1), with B an upper bound on the trace-norm of all input matrices. In particular the complexity depends only poly-logarithmically in n and polynomially in r. We apply the second SDP solver to the problem of learning a good description of a quantum state with respect to a set of measurements: Given m measurements and copies of an unknown state ρ, we show we can find in time m−−√⋅poly(logm,logn,r,ε−1) a description of the state as a quantum circuit preparing a density matrix which has the same expectation values as ρ on the m measurements, up to error ε. The density matrix obtained is an approximation to the maximum entropy state consistent with the measurement data considered in Jaynes' principle from statistical mechanics. As in previous work, we obtain our algorithm by "quantizing" classical SDP solvers based on the matrix multiplicative weight method. One of our main technical contributions is a quantum Gibbs state sampler for low-rank Hamiltonians with a poly-logarithmic dependence on its dimension, which could be of independent interest.

1 aBrandão, Fernando, G. S. L.1 aKalev, Amir1 aLi, Tongyang1 aLin, Cedric, Yen-Yu1 aSvore, Krysta, M.1 aWu, Xiaodi uhttps://arxiv.org/abs/1710.0258102434nas a2200205 4500008004100000245006200041210006200103260001500165300001100180490000800191520186900199100001502068700001902083700001902102700001602121700001702137700001702154700002002171856003702191 2018 eng d00aRecovering quantum gates from few average gate fidelities0 aRecovering quantum gates from few average gate fidelities c2018/03/01 a1705020 v1213 a

Characterising quantum processes is a key task in and constitutes a challenge for the development of quantum technologies, especially at the noisy intermediate scale of today's devices. One method for characterising processes is randomised benchmarking, which is robust against state preparation and measurement (SPAM) errors, and can be used to benchmark Clifford gates. A complementing approach asks for full tomographic knowledge. Compressed sensing techniques achieve full tomography of quantum channels essentially at optimal resource efficiency. So far, guarantees for compressed sensing protocols rely on unstructured random measurements and can not be applied to the data acquired from randomised benchmarking experiments. It has been an open question whether or not the favourable features of both worlds can be combined. In this work, we give a positive answer to this question. For the important case of characterising multi-qubit unitary gates, we provide a rigorously guaranteed and practical reconstruction method that works with an essentially optimal number of average gate fidelities measured respect to random Clifford unitaries. Moreover, for general unital quantum channels we provide an explicit expansion into a unitary 2-design, allowing for a practical and guaranteed reconstruction also in that case. As a side result, we obtain a new statistical interpretation of the unitarity -- a figure of merit that characterises the coherence of a process. In our proofs we exploit recent representation theoretic insights on the Clifford group, develop a version of Collins' calculus with Weingarten functions for integration over the Clifford group, and combine this with proof techniques from compressed sensing.

1 aRoth, Ingo1 aKueng, Richard1 aKimmel, Shelby1 aLiu, Yi-Kai1 aGross, David1 aEisert, Jens1 aKliesch, Martin uhttps://arxiv.org/abs/1803.0057201897nas a2200109 4500008004100000245010200041210006900143520150500212100001701717700001601734856003701750 2018 eng d00aStationary Phase Method in Discrete Wigner Functions and Classical Simulation of Quantum Circuits0 aStationary Phase Method in Discrete Wigner Functions and Classic3 a

We apply the periodized stationary phase method to discrete Wigner functions of systems with odd prime dimension using results from p-adic number theory. We derive the Wigner-Weyl-Moyal (WWM) formalism with higher order ℏ corrections representing contextual corrections to non-contextual Clifford operations. We apply this formalism to a subset of unitaries that include diagonal gates such as the π8 gates. We characterize the stationary phase critical points as a quantum resource injecting contextuality and show that this resource allows for the replacement of the p2t points that represent t magic state Wigner functions on p-dimensional qudits by ≤pt points. We find that the π8 gate introduces the smallest higher order ℏ correction possible, requiring the lowest number of additional critical points compared to the Clifford gates. We then establish a relationship between the stabilizer rank of states and the number of critical points necessary to treat them in the WWM formalism. This allows us to exploit the stabilizer rank decomposition of two qutrit π8 gates to develop a classical strong simulation of a single qutrit marginal on t qutrit π8 gates that are followed by Clifford evolution, and show that this only requires calculating 3t2+1 critical points corresponding to Gauss sums. This outperforms the best alternative qutrit algorithm (based on Wigner negativity and scaling as ∼30.8t for 10−2 precision) for any number of π8 gates to full precision.

1 aKocia, Lucas1 aLove, Peter uhttps://arxiv.org/abs/1810.0362201846nas a2200169 4500008004100000245006600041210006500107520131000172100001701482700001801499700002801517700002501545700002201570700002301592700002401615856003701639 2018 eng d00aStudying community development: a network analytical approach0 aStudying community development a network analytical approach3 a

Research shows that community plays a central role in learning, and strong community engages students and aids in student persistence. Thus, understanding the function and structure of communities in learning environments is essential to education. We use social network analysis to explore the community dynamics of students in a pre-matriculation, two-week summer program. Unlike previous network analysis studies in PER, we build our networks from classroom video that has been coded for student interactions using labeled, directed ties. We define 3 types of interaction: on task interactions (regarding the assigned task), on topic interactions (having to do with science, technology, engineering, and mathematics (STEM)), and off topic interactions (unrelated to the assignment or STEM). To study the development of community in this program, we analyze the shift in conversation topicality over the course of the program. Conversations are more on-task toward the end of the program and we propose that this conversational shift represents a change in student membership within their forming community. 

1 aHass, C., A.1 aGenz, Florian1 aKustusch, Mary, Bridget1 aOuime, Pierre-P., A.1 aPomian, Katarzyna1 aSayre, Eleanor, C.1 aZwolak, Justyna, P. uhttps://arxiv.org/abs/1808.0819301813nas a2200169 4500008004100000245010100041210006900142260001500211490000600226520127000232100002701502700001701529700001901546700001901565700002201584856003701606 2017 eng d00aAbove threshold scattering about a Feshbach resonance for ultracold atoms in an optical collider0 aAbove threshold scattering about a Feshbach resonance for ultrac c2017/09/060 v83 a

Studies of magnetically tunable Feshbach resonances in ultracold atomic gases have predominantly been carried out in the zero collision-energy limit. Here, we explore above threshold collisions at well-defined energies in the vicinity of a narrow magnetic Feshbach resonance by means of a laser-based collider. Our experiment focuses on collisions between ground-state 87Rb atoms in the |F = 2,mF = 0i and |F = 1,mF = 1i hyperfine states, which have a known s-wave resonance at 9.040(7) G at threshold that strongly couples to inelastic channels, where 1 G = 10−4 T. Using our collider we can track the magnetic field shift in resonance position as the energy is tuned. This presents a challenge due to the narrow width of the resonance in conjunction with inherent broadening mechanisms of the collider. We find, however, that the narrow Feshbach scattering feature becomes imprinted on the spatial distribution of atoms in a fashion that allows for an accurate determination of resonance position as a function of collision energy through a shift in center-of-mass position of the outgoing clouds. This shift has a dispersive line shape with a zero value at the resonance position. We obtain excellent agreement with theory on the resonance position.

1 aHorvath, Milena, S. J.1 aThomas, Ryan1 aTiesinga, Eite1 aDeb, Amita, B.1 aKjærgaard, Niels uhttps://arxiv.org/abs/1704.0710901586nas a2200193 4500008004100000245007900041210006900120260001400189490000700203520099200210100002401202700002201226700002201248700001901270700002001289700002701309700001901336856003701355 2017 eng d00aDevelopment of a new UHV/XHV pressure standard (cold atom vacuum standard)0 aDevelopment of a new UHVXHV pressure standard cold atom vacuum s c2017/11/30 v543 a

The National Institute of Standards and Technology has recently begun a program to develop a primary pressure standard that is based on ultra-cold atoms, covering a pressure range of 1 x 10-6 to 1 x 10-10 Pa and possibly lower. These pressures correspond to the entire ultra-high vacuum range and extend into the extreme-high vacuum. This cold-atom vacuum standard (CAVS) is both a primary standard and absolute sensor of vacuum. The CAVS is based on the loss of cold, sensor atoms (such as the alkali-metal lithium) from a magnetic trap due to collisions with the background gas (primarily H2) in the vacuum. The pressure is determined from a thermally-averaged collision cross section, which is a fundamental atomic property, and the measured loss rate. The CAVS is primary because it will use collision cross sections determined from ab initio calculations for the Li + H2 system. Primary traceability is transferred to other systems of interest using sensitivity coefficients.

1 aScherschligt, Julia1 aFedchak, James, A1 aBarker, Daniel, S1 aEckel, Stephen1 aKlimov, Nikolai1 aMakrides, Constantinos1 aTiesinga, Eite uhttps://arxiv.org/abs/1801.1012015016nas a2200181 45000080041000002450084000412100069001252600015001943000011002094900007002205201446000227100002314687700002714710700001914737700001914756700002214775856003714797 2017 eng d00aDispersive optical detection of magnetic Feshbach resonances in ultracold gases0 aDispersive optical detection of magnetic Feshbach resonances in  c2017/08/18 a0227050 v963 a

Magnetically tunable Feshbach resonances in ultracold atomic systems are chiefly identified and characterized through time consuming atom loss spectroscopy. We describe an off-resonant dispersive optical probing technique to rapidly locate Feshbach resonances and demonstrate the method by locating four resonances of 87Rb, between the |F=1,mF=1 and |F=2,mF=0 states. Despite the loss features being 100 mG wide, we require only 21 experimental runs to explore a magnetic field range >18 G. The resonances consist of two known s-wave features in the vicinity of 9 G and 18 G and two previously unobserved p-wave features near 5 G and 10 G. We further utilize the dispersive approach to directly characterize the two-body loss dynamics for each Feshbach resonance.

1 aSawyer, Bianca, J.1 aHorvath, Milena, S. J.1 aTiesinga, Eite1 aDeb, Amita, B.1 aKjærgaard, Niels uhttps://arxiv.org/abs/1702.0221601808nas a2200169 4500008004100000245009500041210006900136260001500205300000800220490000600228520129700234100001801531700001601549700001901565700001701584856003701601 2017 eng d00aDynamically induced robust phonon transport and chiral cooling in an optomechanical system0 aDynamically induced robust phonon transport and chiral cooling i c2017/06/19 a2050 v83 a

The transport of sound and heat, in the form of phonons, has a fundamental material limit: disorder-induced scattering. In electronic and optical settings, introduction of chiral transport - in which carrier propagation exhibits broken parity symmetry - provides robustness against such disorder by preventing elastic backscattering. Here we experimentally demonstrate a path for achieving robust phonon transport even in the presence of material disorder, by dynamically inducing chirality through traveling-wave optomechanical coupling. Using this approach, we demonstrate dramatic optically-induced chiral transport for clockwise and counterclockwise phonons in a symmetric resonator. This induced chirality also enhances isolation from the thermal bath and leads to gain-free reduction of the intrinsic damping of the phonons. Surprisingly, this passive mechanism is also accompanied by a chiral reduction in heat load leading to a novel optical cooling of the mechanics. This technique has the potential to improve upon the fundamental thermal limits of resonant mechanical sensor, which cannot be otherwise attained through conventional optomechanical cooling.

1 aKim, Seunghwi1 aXu, Xunnong1 aTaylor, J., M.1 aBahl, Gaurav uhttps://arxiv.org/abs/1609.0867401121nas a2200169 4500008004100000245007000041210006900111260001500180300001100195490000800206520058700214100002200801700001900823700001900842700001700861856007300878 2017 eng d00aExperimental demonstration of cheap and accurate phase estimation0 aExperimental demonstration of cheap and accurate phase estimatio c2017/05/12 a1905020 v1183 a

We demonstrate experimental implementation of robust phase estimation (RPE) to learn the phases of X and Y rotations on a trapped Yb+ ion qubit. We estimate these phases with uncertainties less than 4 · 10−4 radians using as few as 176 total experimental samples per phase, and our estimates exhibit Heisenberg scaling. Unlike standard phase estimation protocols, RPE neither assumes perfect state preparation and measurement, nor requires access to ancillae. We cross-validate the results of RPE with the more resource-intensive protocol of gate set tomography.

1 aRudinger, Kenneth1 aKimmel, Shelby1 aLobser, Daniel1 aMaunz, Peter uhttps://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.19050201341nas a2200193 4500008004100000245007600041210006900117260001500186300001100201490000800212520075400220100002200974700001800996700002001014700001401034700002001048700001901068856006001087 2017 eng d00aExperimental Study of Optimal Measurements for Quantum State Tomography0 aExperimental Study of Optimal Measurements for Quantum State Tom c2017/10/13 a1504010 v1193 a

Quantum tomography is a critically important tool to evaluate quantum hardware, making it essential to develop optimized measurement strategies that are both accurate and efficient. We compare a variety of strategies using nearly pure test states. Those that are informationally complete for all states are found to be accurate and reliable even in the presence of errors in the measurements themselves, while those designed to be complete only for pure states are far more efficient but highly sensitive to such errors. Our results highlight the unavoidable trade-offs inherent in quantum tomography.

1 aSosa-Martinez, H.1 aLysne, N., K.1 aBaldwin, C., H.1 aKalev, A.1 aDeutsch, I., H.1 aJessen, P., S. uhttps://link.aps.org/doi/10.1103/PhysRevLett.119.15040101575nas a2200217 4500008004100000245010100041210006900142260001500211520089600226100002101122700001901143700001801162700001501180700002401195700001901219700001601238700002501254700001801279700002201297856003801319 2017 eng d00aExperimentally Generated Random Numbers Certified by the Impossibility of Superluminal Signaling0 aExperimentally Generated Random Numbers Certified by the Impossi c2017/02/163 a

Random numbers are an important resource for applications such as numerical simulation and secure communication. However, it is difficult to certify whether a physical random number generator is truly unpredictable. Here, we exploit the phenomenon of quantum nonlocality in a loophole-free photonic Bell test experiment for the generation of randomness that cannot be predicted within any physical theory that allows one to make independent measurement choices and prohibits superluminal signaling. To certify and quantify the randomness, we describe a new protocol that performs well in an experimental regime characterized by low violation of Bell inequalities. Applying an extractor function to our data, we obtained 256 new random bits, uniform to within 0.001.

1 aBierhorst, Peter1 aKnill, Emanuel1 aGlancy, Scott1 aMink, Alan1 aJordan, Stephen, P.1 aRommal, Andrea1 aLiu, Yi-Kai1 aChristensen, Bradley1 aNam, Sae, Woo1 aShalm, Lynden, K. uhttps://arxiv.org/abs/1702.05178#02582nas a2200169 4500008004100000245010100041210006900142260001500211520202200226100003302248700001602281700001702297700002402314700002202338700001502360856003702375 2017 eng d00aExponential Quantum Speed-ups for Semidefinite Programming with Applications to Quantum Learning0 aExponential Quantum Speedups for Semidefinite Programming with A c2017/10/063 a

We give semidefinite program (SDP) quantum solvers with an exponential speed-up over classical ones. Specifically, we consider SDP instances with m constraint matrices of dimension n, each of rank at most r, and assume that the input matrices of the SDP are given as quantum states (after a suitable normalization). Then we show there is a quantum algorithm that solves the SDP feasibility problem with accuracy ǫ by using √ m log m · poly(log n,r, ǫ −1 ) quantum gates. The dependence on n provides an exponential improvement over the work of Brand ˜ao and Svore [6] and the work of van Apeldoorn et al. [23], and demonstrates an exponential quantum speed-up when m and r are small. We apply the SDP solver to the problem of learning a good description of a quantum state with respect to a set of measurements: Given m measurements and a supply of copies of an unknown state ρ, we show we can find in time √ m log m · poly(log n,r, ǫ −1 ) a description of the state as a quantum circuit preparing a density matrix which has the same expectation values as ρ on the m measurements up to error ǫ. The density matrix obtained is an approximation to the maximum entropy state consistent with the measurement data considered in Jaynes’ principle. As in previous work, we obtain our algorithm by “quantizing” classical SDP solvers based on the matrix multiplicative weight update method. One of our main technical contributions is a quantum Gibbs state sampler for low-rank Hamiltonians with a poly-logarithmic dependence on its dimension based on the techniques developed in quantum principal component analysis, which could be of independent interest. Our quantum SDP solver is different from previous ones in the following two aspects: (1) it follows from a zero-sum game approach of Hazan [11] of solving SDPs rather than the primal-dual approach by Arora and Kale [5]; and (2) it does not rely on any sparsity assumption of the input matrices.

1 aBrandão, Fernando, G. S. L.1 aKalev, Amir1 aLi, Tongyang1 aLin, Cedric, Yen-Yu1 aSvore, Krysta, M.1 aWu, Xiaodi uhttps://arxiv.org/abs/1710.0258111923nas a2200205 45000080041000002450079000412100069001202600015001893000011002044900007002155201127900222100001911501700002511520700002011545700001711565700002311582700002011605700002311625856006911648 2017 eng d00aGenuine N -partite entanglement without N -partite correlation functions0 aGenuine N partite entanglement without N partite correlation fun c2017/06/26 a0623310 v953 a

A genuinely N-partite entangled state may display vanishing N-partite correlations measured for arbitrary local observables. In such states the genuine entanglement is noticeable solely in correlations between subsets of particles. A straightforward way to obtain such states for odd N is to design an “antistate” in which all correlations between an odd number of observers are exactly opposite. Evenly mixing a state with its antistate then produces a mixed state with no N-partite correlations, with many of them genuinely multiparty entangled. Intriguingly, all known examples of “entanglement without correlations” involve an odd number of particles. Here we further develop the idea of antistates, thereby shedding light on the different properties of even and odd particle systems. We conjecture that there is no antistate to any pure even-N-party entangled state making the simple construction scheme unfeasible. However, as we prove by construction, higher-rank examples of entanglement without correlations for arbitrary even N indeed exist. These classes of states exhibit genuine entanglement and even violate an N-partite Bell inequality, clearly demonstrating the nonclassical features of these states as well as showing their applicability for quantum information processing.

1 aTran, Minh, C.1 aZuppardo, Margherita1 ade Rosier, Anna1 aKnips, Lukas1 aLaskowski, Wieslaw1 aPaterek, Tomasz1 aWeinfurter, Harald uhttps://journals.aps.org/pra/abstract/10.1103/PhysRevA.95.06233101826nas a2200169 4500008004100000245005800041210005800099260001500157490000700172520131900179100001901498700002401517700002001541700001701561700002401578856005401602 2017 eng d00aHamiltonian Simulation with Optimal Sample Complexity0 aHamiltonian Simulation with Optimal Sample Complexity c2017/03/310 v133 a
We investigate the sample complexity of Hamiltonian simulation: how many copies of an unknown quantum state are required to simulate a Hamiltonian encoded by the density matrix of that state? We show that the procedure proposed by Lloyd, Mohseni, and Rebentrost [Nat. Phys., 10(9):631--633, 2014] is optimal for this task. We further extend their method to the case of multiple input states, showing how to simulate any Hermitian polynomial of the states provided. As applications, we derive optimal algorithms for commutator simulation and orthogonality testing, and we give a protocol for creating a coherent superposition of pure states, when given sample access to those states. We also show that this sample-based Hamiltonian simulation can be used as the basis of a universal model of quantum computation that requires only partial swap operations and simple single-qubit states.
 
 
1 aKimmel, Shelby1 aLin, Cedric, Yen-Yu1 aLow, Guang, Hao1 aOzols, Maris1 aYoder, Theodore, J. uhttps://www.nature.com/articles/s41534-017-0013-702365nas a2200181 4500008004100000245008600041210006900127260001500196520178600211100002601997700002402023700002002047700001602067700002402083700002002107700001902127856003702146 2017 eng d00aMachine Learning techniques for state recognition and auto-tuning in quantum dots0 aMachine Learning techniques for state recognition and autotuning c2017/12/133 a

Recent progress in building large-scale quantum devices for exploring quantum computing and simulation paradigms has relied upon effective tools for achieving and maintaining good experimental parameters, i.e. tuning up devices. In many cases, including in quantum-dot based architectures, the parameter space grows substantially with the number of qubits, and may become a limit to scalability. Fortunately, machine learning techniques for pattern recognition and image classification using so-called deep neural networks have shown surprising successes for computer-aided understanding of complex systems. In this work, we use deep and convolutional neural networks to characterize states and charge configurations of semiconductor quantum dot arrays when one can only measure a current-voltage characteristic of transport (here conductance) through such a device. For simplicity, we model a semiconductor nanowire connected to leads and capacitively coupled to depletion gates using the Thomas-Fermi approximation and Coulomb blockade physics. We then generate labeled training data for the neural networks, and find at least 90 % accuracy for charge and state identification for single and double dots purely from the dependence of the nanowire’s conductance upon gate voltages. Using these characterization networks, we can then optimize the parameter space to achieve a desired configuration of the array, a technique we call ‘auto-tuning’. Finally, we show how such techniques can be implemented in an experimental setting by applying our approach to an experimental data set, and outline further problems in this domain, from using charge sensing data to extensions to full one and two-dimensional arrays, that can be tackled with machine learning.

1 aKalantre, Sandesh, S.1 aZwolak, Justyna, P.1 aRagole, Stephen1 aWu, Xingyao1 aZimmerman, Neil, M.1 aStewart, M., D.1 aTaylor, J., M. uhttps://arxiv.org/abs/1712.0491401952nas a2200229 4500008004100000245009200041210006900133260001500202300001200217490000800229520128300237100001401520700001501534700001701549700002001566700001501586700001501601700002501616700001801641700001501659856004801674 2017 eng d00aObservation of a Many-Body Dynamical Phase Transition with a 53-Qubit Quantum Simulator0 aObservation of a ManyBody Dynamical Phase Transition with a 53Qu c2017/11/29 a601-6040 v5513 a

A quantum simulator is a restricted class of quantum computer that controls the interactions between quantum bits in a way that can be mapped to certain difficult quantum many-body problems. As more control is exerted over larger numbers of qubits, the simulator can tackle a wider range of problems, with the ultimate limit being a universal quantum computer that can solve general classes of hard problems. We use a quantum simulator composed of up to 53 qubits to study a non-equilibrium phase transition in the transverse field Ising model of magnetism, in a regime where conventional statistical mechanics does not apply. The qubits are represented by trapped ion spins that can be prepared in a variety of initial pure states. We apply a global long-range Ising interaction with controllable strength and range, and measure each individual qubit with near 99% efficiency. This allows the single-shot measurement of arbitrary many-body correlations for the direct probing of the dynamical phase transition and the uncovering of computationally intractable features that rely on the long-range interactions and high connectivity between the qubits.

1 aZhang, J.1 aPagano, G.1 aHess, P., W.1 aKyprianidis, A.1 aBecker, P.1 aKaplan, H.1 aGorshkov, Alexey, V.1 aGong, Z., -X.1 aMonroe, C. uhttps://www.nature.com/articles/nature2465417147nas a2200181 45000080041000002450100000412100069001412600015002103000011002254900007002365201657700243100001316820700002216833700002716855700001916882700002716901856003716928 2017 eng d00aPendular trapping conditions for ultracold polar molecules enforced by external electric fields0 aPendular trapping conditions for ultracold polar molecules enfor c2017/06/26 a0634220 v953 a

We theoretically investigate trapping conditions for ultracold polar molecules in optical lattices, when external magnetic and electric fields are simultaneously applied. Our results are based on an accurate electronic-structure calculation of the polar 23Na40K polar molecule in its absolute ground state combined with a calculation of its rovibrational-hyperfine motion. We find that an electric field strength of 5.26(15) kV/cm and an angle of 54.7 between this field and the polarization of the optical laser lead to a trapping design for 23Na40K molecules where decoherences due laser-intensity fluctuations and fluctuations in the direction of its polarization are kept to a minimum. One standard deviation systematic and statistical uncertainties are given in parenthesis. Under such conditions pairs of hyperfine-rotational states of v=0 molecules, used to induce tunable dipole-dipole interactions between them, experience ultrastable, matching trapping forces.

1 aLi, Ming1 aPetrov, Alexander1 aMakrides, Constantinos1 aTiesinga, Eite1 aKotochigova, Svetlanta uhttps://arxiv.org/abs/1703.0383901920nas a2200121 4500008004100000245004400041210004300085260001200128520157400140100001901714700001601733856004901749 2017 eng d00aPhase retrieval using unitary 2-designs0 aPhase retrieval using unitary 2designs c2017/073 a

We consider a variant of the phase retrieval problem, where vectors are replaced by unitary matrices, i.e., the unknown signal is a unitary matrix U, and the measurements consist of squared inner products |tr(C†U)|2 with unitary matrices C that are chosen by the observer. This problem has applications to quantum process tomography, when the unknown process is a unitary operation. We show that PhaseLift, a convex programming algorithm for phase retrieval, can be adapted to this matrix setting, using measurements that are sampled from unitary 4- and 2-designs. In the case of unitary 4-design measurements, we show that PhaseLift can reconstruct all unitary matrices, using a nearoptimal number of measurements. This extends previous work on PhaseLift using spherical 4-designs. In the case of unitary 2-design measurements, we show that PhaseLift still works pretty well on average: it recovers almost all signals, up to a constant additive error, using a near-optimal number of measurements. These 2-design measurements are convenient for quantum process tomography, as they can be implemented via randomized benchmarking techniques. This is the first positive result on PhaseLift using 2-designs.

1 aKimmel, Shelby1 aLiu, Yi-Kai uhttp://ieeexplore.ieee.org/document/8024414/01398nas a2200169 4500008004100000245006100041210006000102260001500162520088000177100002701057700001601084700001801100700002601118700002701144700002001171856003701191 2017 eng d00aProvable quantum state tomography via non-convex methods0 aProvable quantum state tomography via nonconvex methods c2017/11/193 a

With nowadays steadily growing quantum processors, it is required to develop new quantum tomography tools that are tailored for high-dimensional systems. In this work, we describe such a computational tool, based on recent ideas from non-convex optimization. The algorithm excels in the compressed-sensing-like setting, where only a few data points are measured from a lowrank or highly-pure quantum state of a high-dimensional system. We show that the algorithm can practically be used in quantum tomography problems that are beyond the reach of convex solvers, and, moreover, is faster than other state-of-the-art non-convex approaches. Crucially, we prove that, despite being a non-convex program, under mild conditions, the algorithm is guaranteed to converge to the global minimum of the problem; thus, it constitutes a provable quantum state tomography protocol.

1 aKyrillidis, Anastasios1 aKalev, Amir1 aPark, Dohuyng1 aBhojanapalli, Srinadh1 aCaramanis, Constantine1 aSanghavi, Sujay uhttps://arxiv.org/abs/1711.0252401362nas a2200157 4500008004100000245010600041210006900147260001500216300001400231490000700245520083800252100002301090700001901113700002301132856004901155 2017 eng d00aQuantum algorithm for systems of linear equations with exponentially improved dependence on precision0 aQuantum algorithm for systems of linear equations with exponenti c2017/12/21 a1920-19500 v463 a

Harrow, Hassidim, and Lloyd showed that for a suitably specified N×N matrix A and N-dimensional vector b⃗ , there is a quantum algorithm that outputs a quantum state proportional to the solution of the linear system of equations Ax⃗ =b⃗ . If A is sparse and well-conditioned, their algorithm runs in time poly(logN,1/ϵ), where ϵ is the desired precision in the output state. We improve this to an algorithm whose running time is polynomial in log(1/ϵ), exponentially improving the dependence on precision while keeping essentially the same dependence on other parameters. Our algorithm is based on a general technique for implementing any operator with a suitable Fourier or Chebyshev series representation. This allows us to bypass the quantum phase estimation algorithm, whose dependence on ϵ is prohibitive.

1 aChilds, Andrew, M.1 aKothari, Robin1 aSomma, Rolando, D. uhttp://epubs.siam.org/doi/10.1137/16M108707201240nas a2200121 4500008004100000245006900041210006900110260001500179520084800194100002001042700001901062856003701081 2017 eng d00aQuantum Algorithms for Graph Connectivity and Formula Evaluation0 aQuantum Algorithms for Graph Connectivity and Formula Evaluation c2017/04/033 a

We give a new upper bound on the quantum query complexity of deciding st-connectivity on certain classes of planar graphs, and show the bound is sometimes exponentially better than previous results. We then show Boolean formula evaluation reduces to deciding connectivity on just such a class of graphs. Applying the algorithm for st-connectivity to Boolean formula evaluation problems, we match the O( √ N) bound on the quantum query complexity of evaluating formulas on N variables, give a quadratic speed-up over the classical query complexity of a certain class of promise Boolean formulas, and show this approach can yield superpolynomial quantum/classical separations. These results indicate that this st-connectivity-based approach may be the “right” way of looking at quantum algorithms for formula evaluation.

1 aJeffery, Stacey1 aKimmel, Shelby uhttps://arxiv.org/abs/1704.0076501598nas a2200241 4500008004100000245005800041210005800099260001500157300001100172490000800183520093100191100001301122700001401135700001801149700001601167700001801183700001801201700001301219700001601232700001401248700002201262856007201284 2017 eng d00aQuantum state tomography via reduced density matrices0 aQuantum state tomography via reduced density matrices c2017/01/09 a0204010 v1183 a

Quantum state tomography via local measurements is an efficient tool for characterizing quantum states. However it requires that the original global state be uniquely determined (UD) by its local reduced density matrices (RDMs). In this work we demonstrate for the first time a class of states that are UD by their RDMs under the assumption that the global state is pure, but fail to be UD in the absence of that assumption. This discovery allows us to classify quantum states according to their UD properties, with the requirement that each class be treated distinctly in the practice of simplifying quantum state tomography. Additionally we experimentally test the feasibility and stability of performing quantum state tomography via the measurement of local RDMs for each class. These theoretical and experimental results advance the project of performing efficient and accurate quantum state tomography in practice.

1 aXin, Tao1 aLu, Dawei1 aKlassen, Joel1 aYu, Nengkun1 aJi, Zhengfeng1 aChen, Jianxin1 aMa, Xian1 aLong, Guilu1 aZeng, Bei1 aLaflamme, Raymond uhttp://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.02040102646nas a2200241 4500008004100000245008200041210006900123260001500192520190700207100002902114700002302143700001802166700002302184700001502207700002002222700002702242700002402269700001902293700002002312700001702332700001802349856003702367 2017 eng d00aOn the readiness of quantum optimization machines for industrial applications0 areadiness of quantum optimization machines for industrial applic c2017/08/313 a

There have been multiple attempts to demonstrate that quantum annealing and, in particular, quantum annealing on quantum annealing machines, has the potential to outperform current classical optimization algorithms implemented on CMOS technologies. The benchmarking of these devices has been controversial. Initially, random spin-glass problems were used, however, these were quickly shown to be not well suited to detect any quantum speedup. Subsequently, benchmarking shifted to carefully crafted synthetic problems designed to highlight the quantum nature of the hardware while (often) ensuring that classical optimization techniques do not perform well on them. Even worse, to date a true sign of improved scaling with the number problem variables remains elusive when compared to classical optimization techniques. Here, we analyze the readiness of quantum annealing machines for real-world application problems. These are typically not random and have an underlying structure that is hard to capture in synthetic benchmarks, thus posing unexpected challenges for optimization techniques, both classical and quantum alike. We present a comprehensive computational scaling analysis of fault diagnosis in digital circuits, considering architectures beyond D-wave quantum annealers. We find that the instances generated from real data in multiplier circuits are harder than other representative random spin-glass benchmarks with a comparable number of variables. Although our results show that transverse-field quantum annealing is outperformed by state-of-the-art classical optimization algorithms, these benchmark instances are hard and small in the size of the input, therefore representing the first industrial application ideally suited for near-term quantum annealers.

1 aPerdomo-Ortiz, Alejandro1 aFeldman, Alexander1 aOzaeta, Asier1 aIsakov, Sergei, V.1 aZhu, Zheng1 aO'Gorman, Bryan1 aKatzgraber, Helmut, G.1 aDiedrich, Alexander1 aNeven, Hartmut1 ade Kleer, Johan1 aLackey, Brad1 aBiswas, Rupak uhttps://arxiv.org/abs/1708.0978001315nas a2200145 4500008004100000245004100041210004100082260001500123300001100138490000600149520091300155100001601068700001701084856006801101 2017 eng d00aRigidity of the magic pentagram game0 aRigidity of the magic pentagram game c2017/11/02 a0150020 v33 a

A game is rigid if a near-optimal score guarantees, under the sole assumption of the validity of quantum mechanics, that the players are using an approximately unique quantum strategy. Rigidity has a vital role in quantum cryptography as it permits a strictly classical user to trust behavior in the quantum realm. This property can be traced back as far as 1998 (Mayers and Yao) and has been proved for multiple classes of games. In this paper we prove ridigity for the magic pentagram game, a simple binary constraint satisfaction game involving two players, five clauses and ten variables. We show that all near-optimal strategies for the pentagram game are approximately equivalent to a unique strategy involving real Pauli measurements on three maximally-entangled qubit pairs.

1 aKalev, Amir1 aMiller, Carl uhttp://iopscience.iop.org/article/10.1088/2058-9565/aa931d/meta01605nas a2200121 4500008004100000245006800041210006800109260001500177520121600192100001901408700001901427856003701446 2017 eng d00aRobust entanglement renormalization on a noisy quantum computer0 aRobust entanglement renormalization on a noisy quantum computer c2017/11/203 a

A method to study strongly interacting quantum many-body systems at and away from criticality is proposed. The method is based on a MERA-like tensor network that can be efficiently and reliably contracted on a noisy quantum computer using a number of qubits that is much smaller than the system size. We prove that the outcome of the contraction is stable to noise and that the estimated energy upper bounds the ground state energy. The stability, which we numerically substantiate, follows from the positivity of operator scaling dimensions under renormalization group flow. The variational upper bound follows from a particular assignment of physical qubits to different locations of the tensor network plus the assumption that the noise model is local. We postulate a scaling law for how well the tensor network can approximate ground states of lattice regulated conformal field theories in d spatial dimensions and provide evidence for the postulate. Under this postulate, a O(logd (1/δ))-qubit quantum computer can prepare a valid quantum-mechanical state with energy density δ above the ground state. In the presence of noise, δ = O( logd+1(1/)) can be achieved, where  is the noise strength.

1 aKim, Isaac, H.1 aSwingle, Brian uhttps://arxiv.org/abs/1711.0750001556nas a2200217 4500008004100000245006300041210006300104260001500167300001100182490000800193520094300201100002401144700001601168700001801184700001901202700001801221700002501239700002001264700001801284856003601302 2016 eng d00aAnomalous broadening in driven dissipative Rydberg systems0 aAnomalous broadening in driven dissipative Rydberg systems c2016/03/16 a1130010 v1163 aWe observe interaction-induced broadening of the two-photon 5s-18s transition in 87Rb atoms trapped in a 3D optical lattice. The measured linewidth increases by nearly two orders of magnitude with increasing atomic density and excitation strength, with corresponding suppression of resonant scattering and enhancement of off-resonant scattering. We attribute the increased linewidth to resonant dipole-dipole interactions of 18s atoms with spontaneously created populations of nearby np states. Over a range of initial atomic densities and excitation strengths, the transition width is described by a single function of the steady-state density of Rydberg atoms, and the observed resonant excitation rate corresponds to that of a two-level system with the measured, rather than natural, linewidth. The broadening mechanism observed here is likely to have negative implications for many proposals with coherently interacting Rydberg atoms.1 aGoldschmidt, E., A.1 aBoulier, T.1 aBrown, R., C.1 aKoller, S., B.1 aYoung, J., T.1 aGorshkov, Alexey, V.1 aRolston, S., L.1 aPorto, J., V. uhttp://arxiv.org/abs/1510.0871001522nas a2200133 4500008004100000245007000041210006900111260001500180520109400195100002301289700001601312700002401328856003601352 2016 eng d00aCo-Designing a Scalable Quantum Computer with Trapped Atomic Ions0 aCoDesigning a Scalable Quantum Computer with Trapped Atomic Ions c2016/02/093 aThe first generation of quantum computers are on the horizon, fabricated from quantum hardware platforms that may soon be able to tackle certain tasks that cannot be performed or modelled with conventional computers. These quantum devices will not likely be universal or fully programmable, but special-purpose processors whose hardware will be tightly co-designed with particular target applications. Trapped atomic ions are a leading platform for first generation quantum computers, but are also fundamentally scalable to more powerful general purpose devices in future generations. This is because trapped ion qubits are atomic clock standards that can be made identical to a part in 10^15, and their quantum circuit connectivity can be reconfigured through the use of external fields, without modifying the arrangement or architecture of the qubits themselves. In this article we show how a modular quantum computer of any size can be engineered from ion crystals, and how the wiring between ion trap qubits can be tailored to a variety of applications and quantum computing protocols.1 aBrown, Kenneth, R.1 aKim, Jaewan1 aMonroe, Christopher uhttp://arxiv.org/abs/1602.0284001255nas a2200157 4500008004100000245006900041210006900110260001500179300001100194490000700205520078100212100002700993700002201020700001901042856003601061 2016 eng d00aFlight of a heavy particle nonlinearly coupled to a quantum bath0 aFlight of a heavy particle nonlinearly coupled to a quantum bath c2016/01/28 a0143090 v933 a Fluctuation and dissipation are by-products of coupling to the `environment.' The Caldeira-Leggett model, a successful paradigm of quantum Brownian motion, views the environment as a collection of harmonic oscillators linearly coupled to the system. However, symmetry considerations may forbid a linear coupling, e.g. for a neutral particle in quantum electrodynamics. We argue that nonlinear couplings can lead to a fundamentally different behavior. Specifically, we consider a heavy particle quadratically coupled to quantum fluctuations of the bath. In one dimension the particle undergoes anomalous diffusion, unfolding as a power-law distribution in space, reminiscent of L\'{e}vy flights. We suggest condensed matter analogs where similar effects may arise. 1 aMaghrebi, Mohammad, F.1 aKrüger, Matthias1 aKardar, Mehran uhttp://arxiv.org/abs/1508.0058209134nas a2200205 4500008004100000245007700041210006900118260001500187300001000202490000600212520852300218100001708741700002208758700001908780700002308799700001808822700001908840700002208859856004708881 2016 eng d00aMultiple scattering dynamics of fermions at an isolated p-wave resonance0 aMultiple scattering dynamics of fermions at an isolated pwave re c2016/07/11 a120690 v73 a

The wavefunction for indistinguishable fermions is anti-symmetric under particle exchange, which directly leads to the Pauli exclusion principle, and hence underlies the structure of atoms and the properties of almost all materials. In the dynamics of collisions between two indistinguishable fermions this requirement strictly prohibits scattering into 90 degree angles. Here we experimentally investigate the collisions of ultracold clouds fermionic 40K atoms by directly measuring scattering distributions. With increasing collision energy we identify the Wigner threshold for p-wave scattering with its tell-tale dumb-bell shape and no 90 yield. Above this threshold effects of multiple scattering become manifest as deviations from the underlying binary p-wave shape, adding particles either isotropically or axially. A shape resonance for 40K facilitates the separate observation of these two processes. The isotropically enhanced multiple scattering mode is a generic p-wave threshold phenomenon, while the axially enhanced mode should occur in any colliding particle system with an elastic scattering resonance.

1 aThomas, Ryan1 aRoberts, Kris, O.1 aTiesinga, Eite1 aWade, Andrew, C.J.1 aBlakie, Blair1 aDeb, Amita, B.1 aKjærgaard, Niels uhttp://www.nature.com/articles/ncomms1206901464nas a2200169 4500008004100000022001400041245010200055210006900157260001500226300001400241490000700255520082200262100002301084700001901107700001901126856014901145 2016 eng d a0018-934000aPractical Approximation of Single-Qubit Unitaries by Single-Qubit Quantum Clifford and T Circuits0 aPractical Approximation of SingleQubit Unitaries by SingleQubit  c2016/01/01 a161 - 1720 v653 a

We present an algorithm, along with its implementation that finds T-optimal approximations of single-qubit Z-rotations using quantum circuits consisting of Clifford and T gates. Our algorithm is capable of handling errors in approximation down to size 10-15, resulting in the optimal single-qubit circuit designs required for implementation of scalable quantum algorithms. Our implementation along with the experimental results are available in the public domain.

1 aKliuchnikov, Vadym1 aMaslov, Dmitri1 aMosca, Michele uhttp://ieeexplore.ieee.org/lpdocs/epic03/wrapper.htm?arnumber=7056491http://xplorestaging.ieee.org/ielx7/12/7350319/7056491.pdf?arnumber=705649101933nas a2200277 4500008004100000245007200041210006900113260001500182300001100197490000700208520116900215100001301384700001901397700001401416700001801430700001401448700002501462700002301487700001701510700001701527700002101544700001801565700001401583700002201597856003601619 2016 eng d00aPure-state tomography with the expectation value of Pauli operators0 aPurestate tomography with the expectation value of Pauli operato c2016/03/31 a0321400 v933 a

We examine the problem of finding the minimum number of Pauli measurements needed to uniquely determine an arbitrary n-qubit pure state among all quantum states. We show that only 11 Pauli measurements are needed to determine an arbitrary two-qubit pure state compared to the full quantum state tomography with 16 measurements, and only 31 Pauli measurements are needed to determine an arbitrary three-qubit pure state compared to the full quantum state tomography with 64 measurements. We demonstrate that our protocol is robust under depolarizing error with simulated random pure states. We experimentally test the protocol on two- and three-qubit systems with nuclear magnetic resonance techniques. We show that the pure state tomography protocol saves us a number of measurements without considerable loss of fidelity. We compare our protocol with same-size sets of randomly selected Pauli operators and find that our selected set of Pauli measurements significantly outperforms those random sampling sets. As a direct application, our scheme can also be used to reduce the number of settings needed for pure-state tomography in quantum optical systems.

1 aMa, Xian1 aJackson, Tyler1 aZhou, Hui1 aChen, Jianxin1 aLu, Dawei1 aMazurek, Michael, D.1 aFisher, Kent, A.G.1 aPeng, Xinhua1 aKribs, David1 aResch, Kevin, J.1 aJi, Zhengfeng1 aZeng, Bei1 aLaflamme, Raymond uhttp://arxiv.org/abs/1601.0537901010nas a2200145 4500008004100000245007200041210006800113260001500181490000700196520056900203100001800772700001900790700001900809856003600828 2016 eng d00aA Quantum Version of Schöning's Algorithm Applied to Quantum 2-SAT0 aQuantum Version of Schönings Algorithm Applied to Quantum 2SAT c2016/03/220 v163 a

We study a quantum algorithm that consists of a simple quantum Markov process, and we analyze its behavior on restricted versions of Quantum 2-SAT. We prove that the algorithm solves this decision problem with high probability for n qubits, L clauses, and promise gap c in time O(n^2 L^2 c^{-2}). If the Hamiltonian is additionally polynomially gapped, our algorithm efficiently produces a state that has high overlap with the satisfying subspace. The Markov process we study is a quantum analogue of Sch\"oning's probabilistic algorithm for k-SAT.

1 aFarhi, Edward1 aKimmel, Shelby1 aTemme, Kristan uhttp://arxiv.org/abs/1603.0698501938nas a2200145 4500008004100000245004200041210003900083260001500122520154800137100001601685700001801701700001701719700001901736856003701755 2016 eng d00aA quasi-mode theory of chiral phonons0 aquasimode theory of chiral phonons c2016/12/293 a

The coherence properties of mechanical resonators are often limited by multiple unavoidable forms of loss -- including phonon-phonon and phonon-defect scattering -- which result in the scattering of sound into other resonant modes and into the phonon bath. Dynamic suppression of this scattering loss can lift constraints on device structure and can improve tolerance to defects in the material, even after fabrication. Inspired by recent experiments, here we introduce a model of phonon losses resulting from disorder in a whispering gallery mode resonator with acousto-optical coupling between optical and mechanical modes. We show that a typical elastic scattering mechanism of high quality factor (Q) mechanical modes flips the direction of phonon propagation via high-angle scattering, leading to damping into modes with the opposite parity. When the optical mode overlaps co-propagating high-Q and bulk mechanical modes, the addition of laser cooling via sideband-resolved damping of the mechanical mode of a chosen parity also damps and modifies the response of the bulk modes of the same parity. This, in turn, simultaneously improves the quality factor and reduces the thermal load of the counter-propagating high-Q modes, leading to the dynamical creation of a cold phononic shield. We compare our theoretical results to the recent experiments of Kim et al., and find quantitative agreement with our theory.

1 aXu, Xunnong1 aKim, Seunghwi1 aBahl, Gaurav1 aTaylor, J., M. uhttps://arxiv.org/abs/1612.0924001353nas a2200181 4500008004100000245006400041210006200105260001500167490000700182520077900189100002700968700001900995700002401014700002301038700001701061700002501078856006801103 2016 eng d00aRealizing Exactly Solvable SU(N) Magnets with Thermal Atoms0 aRealizing Exactly Solvable SUN Magnets with Thermal Atoms c2016/05/060 v933 a

We show that n thermal fermionic alkaline-earth-metal atoms in a flat-bottom trap allow one to robustly implement a spin model displaying two symmetries: the Sn symmetry that permutes atoms occupying different vibrational levels of the trap and the SU(N) symmetry associated with N nuclear spin states. The symmetries make the model exactly solvable, which, in turn, enables the analytic study of dynamical processes such as spin diffusion in this SU(N) system. We also show how to use this system to generate entangled states that allow for Heisenberg-limited metrology. This highly symmetric spin model should be experimentally realizable even when the vibrational levels are occupied according to a high-temperature thermal or an arbitrary nonthermal distribution.

1 aBeverland, Michael, E.1 aAlagic, Gorjan1 aMartin, Michael, J.1 aKoller, Andrew, P.1 aRey, Ana, M.1 aGorshkov, Alexey, V. uhttp://journals.aps.org/pra/abstract/10.1103/PhysRevA.93.05160121161nas a2200205 45000080041000000200022000410220014000632450069000772100068001462600015002143000016002294900007002455202053400252100002020786700002420806700002420830700002220854700002520876856005420901 2016 eng d a978-3-95977-013-2 a1868-896900aSpace-Efficient Error Reduction for Unitary Quantum Computations0 aSpaceEfficient Error Reduction for Unitary Quantum Computations c2016/04/27 a14:1--14:140 v553 a

This paper develops general space-efficient methods for error reduction for unitary quantum computation. Consider a polynomial-time quantum computation with completeness c and soundnesss, either with or without a witness (corresponding to QMA and BQP, respectively). To convert this computation into a new computation with error at most 2p, the most space-efficient method known requires extra workspace of O(plog1cs) qubits. This space requirement is too large for scenarios like logarithmic-space quantum computations. This paper presents error-reduction methods for unitary quantum computations (i.e., computations without intermediate measurements) that require extra workspace of just O(logpcs) qubits. This in particular gives the first methods of strong amplification for logarithmic-space unitary quantum computations with two-sided bounded error. This also leads to a number of consequences in complexity theory, such as the uselessness of quantum witnesses in bounded-error logarithmic-space unitary quantum computations, the PSPACE upper bound for QMA with exponentially-small completeness-soundness gap, and strong amplification for matchgate computations.

1 aFefferman, Bill1 aKobayashi, Hirotada1 aLin, Cedric, Yen-Yu1 aMorimae, Tomoyuki1 aNishimura, Harumichi uhttp://drops.dagstuhl.de/opus/volltexte/2016/629701656nas a2200193 4500008004100000245007500041210006900116260001500185300001400200490000800214520108600222100001801308700001501326700001901341700002401360700002301384700001801407856003701425 2015 eng d00a2D Superexchange mediated magnetization dynamics in an optical lattice0 a2D Superexchange mediated magnetization dynamics in an optical l c2015/04/30 a540 - 5440 v3483 a The competition of magnetic exchange interactions and tunneling underlies many complex quantum phenomena observed in real materials. We study non-equilibrium magnetization dynamics in an extended 2D system by loading effective spin-1/2 bosons into a spin-dependent optical lattice, and we use the lattice to separately control the resonance conditions for tunneling and superexchange. After preparing a non-equilibrium anti-ferromagnetically ordered state, we observe relaxation dynamics governed by two well-separated rates, which scale with the underlying Hamiltonian parameters associated with superexchange and tunneling. Remarkably, with tunneling off-resonantly suppressed, we are able to observe superexchange dominated dynamics over two orders of magnitude in magnetic coupling strength, despite the presence of vacancies. In this regime, the measured timescales are in agreement with simple theoretical estimates, but the detailed dynamics of this 2D, strongly correlated, and far-from-equilibrium quantum system remain out of reach of current computational techniques. 1 aBrown, R., C.1 aWyllie, R.1 aKoller, S., B.1 aGoldschmidt, E., A.1 aFoss-Feig, Michael1 aPorto, J., V. uhttp://arxiv.org/abs/1411.7036v101548nas a2200157 4500008004100000245010700041210006900148260001500217520099200232100001801224700001601242700002501258700001701283700001601300856007401316 2015 eng d00aAtom induced cavities and tunable long-range interactions between atoms trapped near photonic crystals0 aAtom induced cavities and tunable longrange interactions between c2015/03/033 a

Using cold atoms to simulate strongly interacting quantum systems represents an exciting frontier of physics. However, achieving tunable, coherent long-range interactions between atoms is an outstanding challenge, which currently leaves a large class of models inaccessible to quantum simulation. Here, we propose a solution exploiting the powerful new platform of cold atoms trapped near nano-photonic systems. We show that the dielectric contrast of an atom trapped near a photonic crystal can seed a localized cavity mode around the atomic position. In a dynamic form of “all-atomic” cavity QED, the length of these cavity modes can be tuned, and atoms separated by the order of the e↵ective cavity length can interact coherently with each other. Considering realistic conditions such as fabrication disorder and photon losses, coherent long-range potentials or spin interactions can be dominant in the system over length scales up to hundreds of wavelengths.

1 aDouglas, J, S1 aHabibian, H1 aGorshkov, Alexey, V.1 aKimble, H, J1 aChang, D, E uhttp://www.nature.com/nphoton/journal/v9/n5/full/nphoton.2015.57.html01241nas a2200157 4500008004100000245005800041210005800099260001500157300001100172490000700183520080300190100001400993700002001007700001901027856003701046 2015 eng d00aBounds on quantum communication via Newtonian gravity0 aBounds on quantum communication via Newtonian gravity c2015/01/15 a0150060 v173 aNewtonian gravity yields specific observable consequences, the most striking of which is the emergence of a $1/r^2$ force. In so far as communication can arise via such interactions between distant particles, we can ask what would be expected for a theory of gravity that only allows classical communication. Many heuristic suggestions for gravity-induced decoherence have this restriction implicitly or explicitly in their construction. Here we show that communication via a $1/r^2$ force has a minimum noise induced in the system when the communication cannot convey quantum information, in a continuous time analogue to Bell's inequalities. Our derived noise bounds provide tight constraints from current experimental results on any theory of gravity that does not allow quantum communication. 1 aKafri, D.1 aMilburn, G., J.1 aTaylor, J., M. uhttp://arxiv.org/abs/1404.3214v201589nas a2200193 4500008004100000245008100041210006900122260001500191300001100206490000700217520100800224100002301232700002501255700001901280700001901299700002001318700002101338856003601359 2015 eng d00aDemonstration of Robust Quantum Gate Tomography via Randomized Benchmarking0 aDemonstration of Robust Quantum Gate Tomography via Randomized B c2015/11/05 a1130190 v173 a Typical quantum gate tomography protocols struggle with a self-consistency problem: the gate operation cannot be reconstructed without knowledge of the initial state and final measurement, but such knowledge cannot be obtained without well-characterized gates. A recently proposed technique, known as randomized benchmarking tomography (RBT), sidesteps this self-consistency problem by designing experiments to be insensitive to preparation and measurement imperfections. We implement this proposal in a superconducting qubit system, using a number of experimental improvements including implementing each of the elements of the Clifford group in single `atomic' pulses and custom control hardware to enable large overhead protocols. We show a robust reconstruction of several single-qubit quantum gates, including a unitary outside the Clifford group. We demonstrate that RBT yields physical gate reconstructions that are consistent with fidelities obtained by randomized benchmarking. 1 aJohnson, Blake, R.1 ada Silva, Marcus, P.1 aRyan, Colm, A.1 aKimmel, Shelby1 aChow, Jerry, M.1 aOhki, Thomas, A. uhttp://arxiv.org/abs/1505.0668602223nas a2200193 4500008004100000245007100041210006900112260001500181300001200196490000800208520166400216100002001880700001901900700002301919700001701942700001601959700001801975856003601993 2015 eng d00aEntangling two transportable neutral atoms via local spin exchange0 aEntangling two transportable neutral atoms via local spin exchan c2015/11/02 a208-2110 v5273 a To advance quantum information science a constant pursuit is the search for physical systems that meet the stringent requirements for creating and preserving quantum entanglement. In atomic physics, robust two-qubit entanglement is typically achieved by strong, long-range interactions in the form of Coulomb interactions between ions or dipolar interactions between Rydberg atoms. While these interactions allow fast gates, atoms subject to these interactions must overcome the associated coupling to the environment and cross-talk among qubits. Local interactions, such as those requiring significant wavefunction overlap, can alleviate these detrimental effects yet present a new challenge: To distribute entanglement, qubits must be transported, merged for interaction, and then isolated for storage and subsequent operations. Here we show how, via a mobile optical tweezer, it is possible to prepare and locally entangle two ultracold neutral atoms, and then separate them while preserving their entanglement. While ultracold neutral atom experiments have measured dynamics consistent with spin entanglement, we are now able to demonstrate two-particle coherence via application of a local gradient and parity measurements; this new entanglement-verification protocol could be applied to arbitrary spin-entangled states of spatially-separated atoms. The local entangling operation is achieved via ultracold spin-exchange interactions, and quantum tunneling is used to combine and separate atoms. Our toolset provides a framework for dynamically entangling remote qubits via local operations within a large-scale quantum register. 1 aKaufman, A., M.1 aLester, B., J.1 aFoss-Feig, Michael1 aWall, M., L.1 aRey, A., M.1 aRegal, C., A. uhttp://arxiv.org/abs/1507.0558601274nas a2200181 4500008004100000245010400041210006900145260001500214300001200229490000800241520071300249100002100962700001500983700002100998700001901019700001701038856003701055 2015 eng d00aFrom membrane-in-the-middle to mirror-in-the-middle with a high-reflectivity sub-wavelength grating0 aFrom membraneinthemiddle to mirrorinthemiddle with a highreflect c2015/01/02 a81 - 880 v5273 aWe demonstrate a "membrane in the middle" optomechanical system using a silicon nitride membrane patterned as a subwavelength grating. The grating has a reflectivity of over 99.8%, effectively creating two sub-cavities, with free spectral ranges of 6 GHz, optically coupled via photon tunneling. Measurements of the transmission and reflection spectra show an avoided crossing where the two sub-cavities simultaneously come into resonance, with a frequency splitting of 54 MHz. We derive expressions for the lineshapes of the symmetric and antisymmetric modes at the avoided crossing, and infer the grating reflection, transmission, absorption, and scattering through comparison with the experimental data. 1 aStambaugh, Corey1 aXu, Haitan1 aKemiktarak, Utku1 aTaylor, J., M.1 aLawall, John uhttp://arxiv.org/abs/1407.1709v101453nas a2200145 4500008004100000245007600041210006900117260001500186300001200201520099300213100002301206700002301229700001901252856003601271 2015 eng d00aHamiltonian simulation with nearly optimal dependence on all parameters0 aHamiltonian simulation with nearly optimal dependence on all par c2015/01/08 a792-8093 a We present an algorithm for sparse Hamiltonian simulation that has optimal dependence on all parameters of interest (up to log factors). Previous algorithms had optimal or near-optimal scaling in some parameters at the cost of poor scaling in others. Hamiltonian simulation via a quantum walk has optimal dependence on the sparsity $d$ at the expense of poor scaling in the allowed error $\epsilon$. In contrast, an approach based on fractional-query simulation provides optimal scaling in $\epsilon$ at the expense of poor scaling in $d$. Here we combine the two approaches, achieving the best features of both. By implementing a linear combination of quantum walk steps with coefficients given by Bessel functions, our algorithm achieves near-linear scaling in $\tau := d \|H\|_{\max} t$ and sublogarithmic scaling in $1/\epsilon$. Our dependence on $\epsilon$ is optimal, and we prove a new lower bound showing that no algorithm can have sublinear dependence on $\tau$. 1 aBerry, Dominic, W.1 aChilds, Andrew, M.1 aKothari, Robin uhttp://arxiv.org/abs/1501.0171501704nas a2200169 4500008004100000245006100041210006100102260001500163520120900178100001501387700002101402700001701423700002001440700001701460700001901477856003801496 2015 eng d00aObservation of optomechanical buckling phase transitions0 aObservation of optomechanical buckling phase transitions c2015/10/163 a

Correlated phases of matter provide long-term stability for systems as diverse as solids, magnets, and potential exotic quantum materials. Mechanical systems, such as relays and buckling transition spring switches can yield similar stability by exploiting non-equilibrium phase transitions. Curiously, in the optical domain, observations of such phase transitions remain elusive. However, efforts to integrate optical and mechanical systems -- optomechanics -- suggest that a hybrid approach combining the quantum control of optical systems with the engineerability of mechanical systems may provide a new avenue for such explorations. Here we report the first observation of the buckling of an optomechanical system, in which transitions between stable mechanical states corresponding to both first- and second-order phase transitions are driven by varying laser power and detuning. Our results enable new applications in photonics and, given rapid progress in pushing optomechanical systems into the quantum regime, the potential for explorations of quantum phase transitions.

1 aXu, Haitan1 aKemiktarak, Utku1 aFan, Jingyun1 aRagole, Stephen1 aLawall, John1 aTaylor, J., M. uhttp://arxiv.org/abs/1510.04971v101035nas a2200181 4500008004100000020002200041022001400063245002300077210002300100260001500123300000900138490000700147520060100154100001900755700002400774700001900798856003600817 2015 eng d a978-3-939897-96-5 a1868-896900aOracles with Costs0 aOracles with Costs c2015/02/07 a1-260 v443 a While powerful tools have been developed to analyze quantum query complexity, there are still many natural problems that do not fit neatly into the black box model of oracles. We create a new model that allows multiple oracles with differing costs. This model captures more of the difficulty of certain natural problems. We test this model on a simple problem, Search with Two Oracles, for which we create a quantum algorithm that we prove is asymptotically optimal. We further give some evidence, using a geometric picture of Grover's algorithm, that our algorithm is exactly optimal. 1 aKimmel, Shelby1 aLin, Cedric, Yen-Yu1 aLin, Han-Hsuan uhttp://arxiv.org/abs/1502.0217401564nas a2200133 4500008004100000245008900041210006900130260001500199300001200214520109500226100001901321700001601340856007401356 2015 eng d00aPhase Retrieval Without Small-Ball Probability Assumptions: Stability and Uniqueness0 aPhase Retrieval Without SmallBall Probability Assumptions Stabil c2015/05/25 a411-4143 aWe study stability and uniqueness for the phase retrieval problem. That is, we ask when is a signal x ∈ R n stably and uniquely determined (up to small perturbations), when one performs phaseless measurements of the form yi = |a T i x| 2 (for i = 1, . . . , N), where the vectors ai ∈ R n are chosen independently at random, with each coordinate aij ∈ R being chosen independently from a fixed sub-Gaussian distribution D. It is well known that for many common choices of D, certain ambiguities can arise that prevent x from being uniquely determined. In this note we show that for any sub-Gaussian distribution D, with no additional assumptions, most vectors x cannot lead to such ambiguities. More precisely, we show stability and uniqueness for all sets of vectors T ⊂ R n which are not too peaky, in the sense that at most a constant fraction of their mass is concentrated on any one coordinate. The number of measurements needed to recover x ∈ T depends on the complexity of T in a natural way, extending previous results of Eldar and Mendelson [12].1 aKrahmer, Felix1 aLiu, Yi-Kai uhttp://ieeexplore.ieee.org/stamp/stamp.jsp?tp=&arnumber=7148923&tag=101216nas a2200121 4500008004100000245004700041210004600088260001500134520087400149100001901023700001601042856003601058 2015 eng d00aQuantum Compressed Sensing Using 2-Designs0 aQuantum Compressed Sensing Using 2Designs c2015/10/293 aWe develop a method for quantum process tomography that combines the efficiency of compressed sensing with the robustness of randomized benchmarking. Our method is robust to state preparation and measurement errors, and it achieves a quadratic speedup over conventional tomography when the unknown process is a generic unitary evolution. Our method is based on PhaseLift, a convex programming technique for phase retrieval. We show that this method achieves approximate recovery of almost all signals, using measurements sampled from spherical or unitary 2-designs. This is the first positive result on PhaseLift using 2-designs. We also show that exact recovery of all signals is possible using unitary 4-designs. Previous positive results for PhaseLift required spherical 4-designs, while PhaseLift was known to fail in certain cases when using spherical 2-designs.1 aKimmel, Shelby1 aLiu, Yi-Kai uhttp://arxiv.org/abs/1510.0888700602nas a2200193 4500008004100000022001400041245007400055210006900129260001500198300001400213490000600227100002000233700001700253700001600270700002500286700001900311700001800330856006000348 2015 eng d a1749-488500aQuantum many-body models with cold atoms coupled to photonic crystals0 aQuantum manybody models with cold atoms coupled to photonic crys c2015/04/04 a326 - 3310 v91 aDouglas, J., S.1 aHabibian, H.1 aHung, C.-L.1 aGorshkov, Alexey, V.1 aKimble, H., J.1 aChang, D., E. uhttp://www.nature.com/doifinder/10.1038/nphoton.2015.5701003nas a2200121 4500008004100000245005600041210005600097260001500153520063800168100002000806700001900826856003600845 2015 eng d00aQuantum vs Classical Proofs and Subset Verification0 aQuantum vs Classical Proofs and Subset Verification c2015/10/223 aWe study the ability of efficient quantum verifiers to decide properties of exponentially large subsets given either a classical or quantum witness. We develop a general framework that can be used to prove that QCMA machines, with only classical witnesses, cannot verify certain properties of subsets given implicitly via an oracle. We use this framework to prove an oracle separation between QCMA and QMA using an ``in-place'' permutation oracle, making the first progress on this question since Aaronson and Kuperberg in 2007. We also use the framework to prove a particularly simple standard oracle separation between QCMA and AM.1 aFefferman, Bill1 aKimmel, Shelby uhttp://arxiv.org/abs/1510.0675001534nas a2200157 4500008004100000245007200041210006900113260001500182300001100197490000700208520106200215100001901277700002001296700002401316856003601340 2015 eng d00aRobust Single-Qubit Process Calibration via Robust Phase Estimation0 aRobust SingleQubit Process Calibration via Robust Phase Estimati c2015/12/08 a0623150 v923 a An important step in building a quantum computer is calibrating experimentally implemented quantum gates to produce operations that are close to ideal unitaries. The calibration step involves estimating the error in gates and then using controls to correct the implementation. Quantum process tomography is a standard technique for estimating these errors, but is both time consuming, (when one only wants to learn a few key parameters), and requires resources, like perfect state preparation and measurement, that might not be available. With the goal of efficiently estimating specific errors using minimal resources, we develop a parameter estimation technique, which can gauge two key parameters (amplitude and off-resonance errors) in a single-qubit gate with provable robustness and efficiency. In particular, our estimates achieve the optimal efficiency, Heisenberg scaling. Our main theorem making this possible is a robust version of the phase estimation procedure of Higgins et al. [B. L. Higgins, New J. Phys. 11, 073023 (2009)]. 1 aKimmel, Shelby1 aLow, Guang, Hao1 aYoder, Theodore, J. uhttp://arxiv.org/abs/1502.0267701945nas a2200205 4500008004100000245007600041210006900117260001500186300001100201490000700212520133700219100001901556700001901575700001901594700002401613700002701637700001801664700001901682856003801701 2015 eng d00aSelf-heterodyne detection of the {\it in-situ} phase of an atomic-SQUID0 aSelfheterodyne detection of the it insitu phase of an atomicSQUI c2015/09/03 a0336020 v923 a We present theoretical and experimental analysis of an interferometric measurement of the {\it in-situ} phase drop across and current flow through a rotating barrier in a toroidal Bose-Einstein condensate (BEC). This experiment is the atomic analog of the rf-superconducting quantum interference device (SQUID). The phase drop is extracted from a spiral-shaped density profile created by the spatial interference of the expanding toroidal BEC and a reference BEC after release from all trapping potentials. We characterize the interferometer when it contains a single particle, which is initially in a coherent superposition of a torus and reference state, as well as when it contains a many-body state in the mean-field approximation. The single-particle picture is sufficient to explain the origin of the spirals, to relate the phase-drop across the barrier to the geometry of a spiral, and to bound the expansion times for which the {\it in-situ} phase can be accurately determined. Mean-field estimates and numerical simulations show that the inter-atomic interactions shorten the expansion time scales compared to the single-particle case. Finally, we compare the mean-field simulations with our experimental data and confirm that the interferometer indeed accurately measures the {\it in-situ} phase drop. 1 aMathew, Ranchu1 aKumar, Avinash1 aEckel, Stephen1 aJendrzejewski, Fred1 aCampbell, Gretchen, K.1 aEdwards, Mark1 aTiesinga, Eite uhttp://arxiv.org/abs/1506.09149v201120nas a2200181 4500008004100000245006700041210006700108260001500175300001100190490000800201520058500209100002300794700002300817700001900840700001900859700002300878856003700901 2015 eng d00aSimulating Hamiltonian dynamics with a truncated Taylor series0 aSimulating Hamiltonian dynamics with a truncated Taylor series c2015/03/03 a0905020 v1143 a We describe a simple, efficient method for simulating Hamiltonian dynamics on a quantum computer by approximating the truncated Taylor series of the evolution operator. Our method can simulate the time evolution of a wide variety of physical systems. As in another recent algorithm, the cost of our method depends only logarithmically on the inverse of the desired precision, which is optimal. However, we simplify the algorithm and its analysis by using a method for implementing linear combinations of unitary operations to directly apply the truncated Taylor series. 1 aBerry, Dominic, W.1 aChilds, Andrew, M.1 aCleve, Richard1 aKothari, Robin1 aSomma, Rolando, D. uhttp://arxiv.org/abs/1412.4687v100466nas a2200145 4500008004100000245006400041210006400105300001100169490000800180100001700188700001700205700002500222700001400247856005900261 2014 eng d00aBeyond the spin model approximation for Ramsey spectroscopy0 aBeyond the spin model approximation for Ramsey spectroscopy a1230010 v1121 aKoller, A, P1 aBeverland, M1 aGorshkov, Alexey, V.1 aRey, A, M uhttp://link.aps.org/doi/10.1103/PhysRevLett.112.12300101005nas a2200157 4500008004100000245006000041210005800101260001500159300001100174490000700185520056500192100001400757700001900771700002000790856003700810 2014 eng d00aA classical channel model for gravitational decoherence0 aclassical channel model for gravitational decoherence c2014/06/26 a0650200 v163 aWe show that, by treating the gravitational interaction between two mechanical resonators as a classical measurement channel, a gravitational decoherence model results that is equivalent to a model first proposed by Diosi. The resulting decoherence model implies that the classically mediated gravitational interaction between two gravitationally coupled resonators cannot create entanglement. The gravitational decoherence rate ( and the complementary heating rate) is of the order of the gravitationally induced normal mode splitting of the two resonators. 1 aKafri, D.1 aTaylor, J., M.1 aMilburn, G., J. uhttp://arxiv.org/abs/1401.0946v102001nas a2200181 4500008004100000020002200041245007600063210006900139260001500208300001200223520144000235100002301675700002301698700001901721700001901740700002301759856003701782 2014 eng d a978-1-4503-2710-700aExponential improvement in precision for simulating sparse Hamiltonians0 aExponential improvement in precision for simulating sparse Hamil c2014/05/31 a283-2923 a We provide a quantum algorithm for simulating the dynamics of sparse Hamiltonians with complexity sublogarithmic in the inverse error, an exponential improvement over previous methods. Specifically, we show that a $d$-sparse Hamiltonian $H$ acting on $n$ qubits can be simulated for time $t$ with precision $\epsilon$ using $O\big(\tau \frac{\log(\tau/\epsilon)}{\log\log(\tau/\epsilon)}\big)$ queries and $O\big(\tau \frac{\log^2(\tau/\epsilon)}{\log\log(\tau/\epsilon)}n\big)$ additional 2-qubit gates, where $\tau = d^2 \|{H}\|_{\max} t$. Unlike previous approaches based on product formulas, the query complexity is independent of the number of qubits acted on, and for time-varying Hamiltonians, the gate complexity is logarithmic in the norm of the derivative of the Hamiltonian. Our algorithm is based on a significantly improved simulation of the continuous- and fractional-query models using discrete quantum queries, showing that the former models are not much more powerful than the discrete model even for very small error. We also simplify the analysis of this conversion, avoiding the need for a complex fault correction procedure. Our simplification relies on a new form of "oblivious amplitude amplification" that can be applied even though the reflection about the input state is unavailable. Finally, we prove new lower bounds showing that our algorithms are optimal as a function of the error. 1 aBerry, Dominic, W.1 aChilds, Andrew, M.1 aCleve, Richard1 aKothari, Robin1 aSomma, Rolando, D. uhttp://arxiv.org/abs/1312.1414v201571nas a2200217 4500008004100000245007400041210006900115260001500184300001400199490000800213520093800221100002001159700001901179700002101198700001701219700002301236700002301259700001601282700001801298856003701316 2014 eng d00aHong-Ou-Mandel atom interferometry in tunnel-coupled optical tweezers0 aHongOuMandel atom interferometry in tunnelcoupled optical tweeze c2014/06/26 a306 - 3090 v3453 a The quantum statistics of atoms is typically observed in the behavior of an ensemble via macroscopic observables. However, quantum statistics modifies the behavior of even two particles, inducing remarkable consequences that are at the heart of quantum science. Here we demonstrate near-complete control over all the internal and external degrees of freedom of two laser-cooled 87Rb atoms trapped in two optical tweezers. This full controllability allows us to implement a massive-particle analog of a Hong-Ou-Mandel interferometer where atom tunneling plays the role of a photon beamsplitter. We use the interferometer to probe the effect of quantum statistics on the two-atom dynamics under tunable initial conditions, chosen to adjust the degree of atomic indistinguishability. Our work thereby establishes laser-cooled atoms in optical tweezers as a new route to bottom-up engineering of scalable, low-entropy quantum systems. 1 aKaufman, A., M.1 aLester, B., J.1 aReynolds, C., M.1 aWall, M., L.1 aFoss-Feig, Michael1 aHazzard, K., R. A.1 aRey, A., M.1 aRegal, C., A. uhttp://arxiv.org/abs/1312.7182v201828nas a2200145 4500008004100000245015000041210006900191260001400260490000700274520129600281100002701577700002201604700001901626856003701645 2014 eng d00aNonequilibrium quantum fluctuations of a dispersive medium: Spontaneous emission, photon statistics, entropy generation, and stochastic motion 0 aNonequilibrium quantum fluctuations of a dispersive medium Spont c2014/7/160 v903 a We study the implications of quantum fluctuations of a dispersive medium, under steady rotation, either in or out of thermal equilibrium with its environment. A rotating object exhibits a quantum instability by dissipating its mechanical motion via spontaneous emission of photons, as well as internal heat generation. Universal relations are derived for the radiated energy and angular momentum as trace formulas involving the object's scattering matrix. We also compute the quantum noise by deriving the full statistics of the radiated photons out of thermal and/or dynamic equilibrium. The (entanglement) entropy generation is quantified, and the total entropy is shown to be always increasing. Furthermore, we derive a Fokker-Planck equation governing the stochastic angular motion resulting from the fluctuating back-reaction frictional torque. As a result, we find a quantum limit on the uncertainty of the object's angular velocity in steady rotation. Finally, we show in some detail that a rotating object drags nearby objects, making them spin parallel to its axis of rotation. A scalar toy model is introduced in the first part to simplify the technicalities and ease the conceptual complexities; a detailed discussion of quantum electrodynamics is presented in the second part. 1 aMaghrebi, Mohammad, F.1 aJaffe, Robert, L.1 aKardar, Mehran uhttp://arxiv.org/abs/1401.0701v100657nas a2200229 4500008004100000245006300041210006200104300000800166490000800174100001400182700002500196700001600221700001700237700001400254700001900268700001300287700001300300700001000313700001600323700001700339856007100356 2014 eng d00aProbing many-body interactions in an optical lattice clock0 aProbing manybody interactions in an optical lattice clock a3110 v3401 aRey, A, M1 aGorshkov, Alexey, V.1 aKraus, C, V1 aMartin, M, J1 aBishof, M1 aSwallows, M, D1 aZhang, X1 aBenko, C1 aYe, J1 aLemke, N, D1 aLudlow, A, D uhttp://www.sciencedirect.com/science/article/pii/S000349161300254601850nas a2200205 4500008004100000245008200041210006900123260001500192490000700207520120600214100002601420700002601446700002301472700002701495700002701522700001701549700002101566700002001587856003701607 2014 eng d00aQuantum correlations and entanglement in far-from-equilibrium spin systems 0 aQuantum correlations and entanglement in farfromequilibrium spin c2014/12/150 v903 a By applying complementary analytic and numerical methods, we investigate the dynamics of spin-$1/2$ XXZ models with variable-range interactions in arbitrary dimensions. The dynamics we consider is initiated from uncorrelated states that are easily prepared in experiments, and can be equivalently viewed as either Ramsey spectroscopy or a quantum quench. Our primary focus is the dynamical emergence of correlations and entanglement in these far-from-equilibrium interacting quantum systems: we characterize these correlations by the entanglement entropy, concurrence, and squeezing, which are inequivalent measures of entanglement corresponding to different quantum resources. In one spatial dimension, we show that the time evolution of correlation functions manifests a non-perturbative dynamic singularity. This singularity is characterized by a universal power-law exponent that is insensitive to small perturbations. Explicit realizations of these models in current experiments using polar molecules, trapped ions, Rydberg atoms, magnetic atoms, and alkaline-earth and alkali atoms in optical lattices, along with the relative merits and limitations of these different systems, are discussed. 1 aHazzard, Kaden, R. A.1 avan den Worm, Mauritz1 aFoss-Feig, Michael1 aManmana, Salvatore, R.1 aTorre, Emanuele, Dalla1 aPfau, Tilman1 aKastner, Michael1 aRey, Ana, Maria uhttp://arxiv.org/abs/1406.0937v101337nas a2200169 4500008004100000245007700041210006900118260001400187490000600201520082000207100001901027700002501046700001901071700002301090700001701113856003701130 2014 eng d00aRobust Extraction of Tomographic Information via Randomized Benchmarking0 aRobust Extraction of Tomographic Information via Randomized Benc c2014/3/250 v43 a We describe how randomized benchmarking can be used to reconstruct the unital part of any trace-preserving quantum map, which in turn is sufficient for the full characterization of any unitary evolution, or more generally, any unital trace-preserving evolution. This approach inherits randomized benchmarking's robustness to preparation and measurement imperfections, therefore avoiding systematic errors caused by these imperfections. We also extend these techniques to efficiently estimate the average fidelity of a quantum map to unitary maps outside of the Clifford group. The unitaries we consider include operations commonly used to achieve universal quantum computation in a fault-tolerant setting. In addition, we rigorously bound the time and sampling complexities of randomized benchmarking procedures. 1 aKimmel, Shelby1 ada Silva, Marcus, P.1 aRyan, Colm, A.1 aJohnson, Blake, R.1 aOhki, Thomas uhttp://arxiv.org/abs/1306.2348v101596nas a2200169 4500008004100000245004400041210004300085260001400128490000700142520114800149100001801297700001801315700001701333700002501350700001401375856003701389 2014 eng d00aSymmetric Extension of Two-Qubit States0 aSymmetric Extension of TwoQubit States c2014/9/170 v903 a Quantum key distribution uses public discussion protocols to establish shared secret keys. In the exploration of ultimate limits to such protocols, the property of symmetric extendibility of underlying bipartite states $\rho_{AB}$ plays an important role. A bipartite state $\rho_{AB}$ is symmetric extendible if there exits a tripartite state $\rho_{ABB'}$, such that the $AB$ marginal state is identical to the $AB'$ marginal state, i.e. $\rho_{AB'}=\rho_{AB}$. For a symmetric extendible state $\rho_{AB}$, the first task of the public discussion protocol is to break this symmetric extendibility. Therefore to characterize all bi-partite quantum states that possess symmetric extensions is of vital importance. We prove a simple analytical formula that a two-qubit state $\rho_{AB}$ admits a symmetric extension if and only if $\tr(\rho_B^2)\geq \tr(\rho_{AB}^2)-4\sqrt{\det{\rho_{AB}}}$. Given the intimate relationship between the symmetric extension problem and the quantum marginal problem, our result also provides the first analytical necessary and sufficient condition for the quantum marginal problem with overlapping marginals. 1 aChen, Jianxin1 aJi, Zhengfeng1 aKribs, David1 aLütkenhaus, Norbert1 aZeng, Bei uhttp://arxiv.org/abs/1310.3530v201395nas a2200169 4500008004100000245006500041210006500106260001500171300001000186490000700196520090400203100002301107700001901130700001701149700002201166856003701188 2013 eng d00aEasy and hard functions for the Boolean hidden shift problem0 aEasy and hard functions for the Boolean hidden shift problem c2013/04/16 a50-790 v223 a We study the quantum query complexity of the Boolean hidden shift problem. Given oracle access to f(x+s) for a known Boolean function f, the task is to determine the n-bit string s. The quantum query complexity of this problem depends strongly on f. We demonstrate that the easiest instances of this problem correspond to bent functions, in the sense that an exact one-query algorithm exists if and only if the function is bent. We partially characterize the hardest instances, which include delta functions. Moreover, we show that the problem is easy for random functions, since two queries suffice. Our algorithm for random functions is based on performing the pretty good measurement on several copies of a certain state; its analysis relies on the Fourier transform. We also use this approach to improve the quantum rejection sampling approach to the Boolean hidden shift problem. 1 aChilds, Andrew, M.1 aKothari, Robin1 aOzols, Maris1 aRoetteler, Martin uhttp://arxiv.org/abs/1304.4642v101243nas a2200181 4500008004100000245012700041210006900168260001400237490000700251520064800258100002100906700001900927700001700946700001500963700002200978700002401000856003701024 2013 eng d00aExperimental Performance of a Quantum Simulator: Optimizing Adiabatic Evolution and Identifying Many-Body Ground States 0 aExperimental Performance of a Quantum Simulator Optimizing Adiab c2013/7/310 v883 a We use local adiabatic evolution to experimentally create and determine the ground state spin ordering of a fully-connected Ising model with up to 14 spins. Local adiabatic evolution -- in which the system evolution rate is a function of the instantaneous energy gap -- is found to maximize the ground state probability compared with other adiabatic methods while only requiring knowledge of the lowest $\sim N$ of the $2^N$ Hamiltonian eigenvalues. We also demonstrate that the ground state ordering can be experimentally identified as the most probable of all possible spin configurations, even when the evolution is highly non-adiabatic. 1 aRicherme, Philip1 aSenko, Crystal1 aSmith, Jacob1 aLee, Aaron1 aKorenblit, Simcha1 aMonroe, Christopher uhttp://arxiv.org/abs/1305.2253v101523nas a2200181 4500008004100000245009800041210006900139260001500208300001000223520092900233100002101162700002201183700001701205700001601222700002401238700002801262856005101290 2013 eng d00aMultilingual Summarization: Dimensionality Reduction and a Step Towards Optimal Term Coverage0 aMultilingual Summarization Dimensionality Reduction and a Step T c2013/08/09 a55-633 aIn this paper we present three term weighting approaches for multi-lingual document summarization and give results on the DUC 2002 data as well as on the 2013 Multilingual Wikipedia feature articles data set. We introduce a new intervalbounded nonnegative matrix factorization. We use this new method, latent semantic analysis (LSA), and latent Dirichlet allocation (LDA) to give three term-weighting methods for multi-document multi-lingual summarization. Results on DUC and TAC data, as well as on the MultiLing 2013 data, demonstrate that these methods are very promising, since they achieve oracle coverage scores in the range of humans for 6 of the 10 test languages. Finally, we present three term weighting approaches for the MultiLing13 single document summarization task on the Wikipedia featured articles. Our submissions signifi- cantly outperformed the baseline in 19 out of 41 languages. 1 aConroy, John, M.1 aDavis, Sashka, T.1 aKubina, Jeff1 aLiu, Yi-Kai1 aO'Leary, Dianne, P.1 aSchlesinger, Judith, D. uhttp://aclweb.org/anthology/W/W13/W13-3108.pdf01256nas a2200121 4500008004100000245004400041210004200085260001500127520092000142100001601062700001901078856003701097 2013 eng d00aA noise inequality for classical forces0 anoise inequality for classical forces c2013/11/183 aLorentz invariance requires local interactions, with force laws such as the Coulomb interaction arising via virtual exchange of force carriers such as photons. Many have considered the possibility that, at long distances or large mass scales, this process changes in some way to lead to classical behavior. Here we hypothesize that classical behavior could be due to an inability of some force carriers to convey entanglement, a characteristic measure of nonlocal, quantum behavior. We then prove that there exists a local test that allows one to verify entanglement generation, falsifying our hypothesis. Crucially, we show that noise measurements can directly verify entanglement generation. This provides a step forward for a wide variety of experimental systems where traditional entanglement tests are challenging, including entanglement generation by gravity alone between macroscopic torsional oscillators. 1 aKafri, Dvir1 aTaylor, J., M. uhttp://arxiv.org/abs/1311.4558v101759nas a2200169 4500008004100000245008100041210006900122260001400191490000700205520124300212100002101455700001801476700001901494700002101513700001801534856003701552 2013 eng d00aPreparation of Non-equilibrium Nuclear Spin States in Double Quantum Dots 0 aPreparation of Nonequilibrium Nuclear Spin States in Double Quan c2013/7/150 v883 a We theoretically study the dynamic polarization of lattice nuclear spins in GaAs double quantum dots containing two electrons. In our prior work [Phys. Rev. Lett. 104, 226807 (2010)] we identified three regimes of long-term dynamics, including the build up of a large difference in the Overhauser fields across the dots, the saturation of the nuclear polarization process associated with formation of so-called "dark states," and the elimination of the difference field. In particular, when the dots are different sizes we found that the Overhauser field becomes larger in the smaller dot. Here we present a detailed theoretical analysis of these problems including a model of the polarization dynamics and the development of a new numerical method to efficiently simulate semiclassical central-spin problems. When nuclear spin noise is included, the results agree with our prior work indicating that large difference fields and dark states are stable configurations, while the elimination of the difference field is unstable; however, in the absence of noise we find all three steady states are achieved depending on parameters. These results are in good agreement with dynamic nuclear polarization experiments in double quantum dots. 1 aGullans, Michael1 aKrich, J., J.1 aTaylor, J., M.1 aHalperin, B., I.1 aLukin, M., D. uhttp://arxiv.org/abs/1212.6953v300905nas a2200133 4500008004100000245003600041210003400077260001500111300001100126490000700137520057100144100001900715856003700734 2013 eng d00aQuantum Adversary (Upper) Bound0 aQuantum Adversary Upper Bound c2013/04/05 a1 - 140 v193 a We describe a method to upper bound the quantum query complexity of Boolean formula evaluation problems, using fundamental theorems about the general adversary bound. This nonconstructive method can give an upper bound on query complexity without producing an algorithm. For example, we describe an oracle problem which we prove (non-constructively) can be solved in $O(1)$ queries, where the previous best quantum algorithm uses a polylogarithmic number of queries. We then give an explicit $O(1)$-query algorithm for this problem based on span programs. 1 aKimmel, Shelby uhttp://arxiv.org/abs/1101.0797v501289nas a2200205 4500008004100000245007500041210006900116260001300185490000800198520067800206100002100884700001900905700002200924700001700946700001500963700001900978700002500997700002401022856003701046 2013 eng d00aQuantum Catalysis of Magnetic Phase Transitions in a Quantum Simulator0 aQuantum Catalysis of Magnetic Phase Transitions in a Quantum Sim c2013/9/50 v1113 a We control quantum fluctuations to create the ground state magnetic phases of a classical Ising model with a tunable longitudinal magnetic field using a system of 6 to 10 atomic ion spins. Due to the long-range Ising interactions, the various ground state spin configurations are separated by multiple first-order phase transitions, which in our zero temperature system cannot be driven by thermal fluctuations. We instead use a transverse magnetic field as a quantum catalyst to observe the first steps of the complete fractal devil's staircase, which emerges in the thermodynamic limit and can be mapped to a large number of many-body and energy-optimization problems. 1 aRicherme, Philip1 aSenko, Crystal1 aKorenblit, Simcha1 aSmith, Jacob1 aLee, Aaron1 aIslam, Rajibul1 aCampbell, Wesley, C.1 aMonroe, Christopher uhttp://arxiv.org/abs/1303.6983v201052nas a2200145 4500008004100000245005700041210005600098260001500154490000700169520062400176100002700800700002300827700001900850856003700869 2013 eng d00aQuantum Cherenkov Radiation and Non-contact Friction0 aQuantum Cherenkov Radiation and Noncontact Friction c2013/10/210 v883 a We present a number of arguments to demonstrate that a quantum analog of Cherenkov effect occurs when two dispersive objects are in relative motion. Specifically we show that two semi-infinite plates experience friction beyond a threshold velocity which, in their center-of-mass frame, is the phase speed of light within their medium. The loss in mechanical energy is radiated away through the plates before getting fully absorbed in the form of heat. By deriving various correlation functions inside and outside the two plates, we explicitly compute the radiation, and discuss its dependence on the reference frame. 1 aMaghrebi, Mohammad, F.1 aGolestanian, Ramin1 aKardar, Mehran uhttp://arxiv.org/abs/1304.4909v201136nas a2200145 4500008004100000245005800041210005600099260001300155490000700168520070900175100002700884700002300911700001900934856003700953 2013 eng d00aA Scattering Approach to the Dynamical Casimir Effect0 aScattering Approach to the Dynamical Casimir Effect c2013/1/70 v873 a We develop a unified scattering approach to dynamical Casimir problems which can be applied to both accelerating boundaries, as well as dispersive objects in relative motion. A general (trace) formula is derived for the radiation from accelerating boundaries. Applications are provided for objects with different shapes in various dimensions, and undergoing rotational or linear motion. Within this framework, photon generation is discussed in the context of a modulated optical mirror. For dispersive objects, we find general results solely in terms of the scattering matrix. Specifically, we discuss the vacuum friction on a rotating object, and the friction on an atom moving parallel to a surface. 1 aMaghrebi, Mohammad, F.1 aGolestanian, Ramin1 aKardar, Mehran uhttp://arxiv.org/abs/1210.1842v201034nas a2200169 4500008004100000245005800041210005700099260001500156490000800171520053900179100002100718700001800739700002300757700002900780700001800809856003700827 2013 eng d00aSingle-photon nonlinear optics with graphene plasmons0 aSinglephoton nonlinear optics with graphene plasmons c2013/12/110 v1113 a We show that it is possible to realize significant nonlinear optical interactions at the few photon level in graphene nanostructures. Our approach takes advantage of the electric field enhancement associated with the strong confinement of graphene plasmons and the large intrinsic nonlinearity of graphene. Such a system could provide a powerful platform for quantum nonlinear optical control of light. As an example, we consider an integrated optical device that exploits this large nonlinearity to realize a single photon switch. 1 aGullans, Michael1 aChang, D., E.1 aKoppens, F., H. L.1 ade Abajo, F., J. García1 aLukin, M., D. uhttp://arxiv.org/abs/1309.2651v300867nas a2200145 4500008004100000245007400041210006900115260001500184520040100199100002300600700002000623700001900643700002200662856003700684 2013 eng d00aA Time-Efficient Quantum Walk for 3-Distinctness Using Nested Updates0 aTimeEfficient Quantum Walk for 3Distinctness Using Nested Update c2013/02/283 a We present an extension to the quantum walk search framework that facilitates quantum walks with nested updates. We apply it to give a quantum walk algorithm for 3-Distinctness with query complexity ~O(n^{5/7}), matching the best known upper bound (obtained via learning graphs) up to log factors. Furthermore, our algorithm has time complexity ~O(n^{5/7}), improving the previous ~O(n^{3/4}). 1 aChilds, Andrew, M.1 aJeffery, Stacey1 aKothari, Robin1 aMagniez, Frederic uhttp://arxiv.org/abs/1302.7316v102008nas a2200193 4500008004100000245007500041210006900116260001400185490000700199520143800206100001801644700002101662700001801683700002401701700001701725700002101742700001401763856003701777 2013 eng d00aUniqueness of Quantum States Compatible with Given Measurement Results0 aUniqueness of Quantum States Compatible with Given Measurement R c2013/7/110 v883 a We discuss the uniqueness of quantum states compatible with given results for measuring a set of observables. For a given pure state, we consider two different types of uniqueness: (1) no other pure state is compatible with the same measurement results and (2) no other state, pure or mixed, is compatible with the same measurement results. For case (1), it is known that for a d-dimensional Hilbert space, there exists a set of 4d-5 observables that uniquely determines any pure state. We show that for case (2), 5d-7 observables suffice to uniquely determine any pure state. Thus there is a gap between the results for (1) and (2), and we give some examples to illustrate this. The case of observables corresponding to reduced density matrices (RDMs) of a multipartite system is also discussed, where we improve known bounds on local dimensions for case (2) in which almost all pure states are uniquely determined by their RDMs. We further discuss circumstances where (1) can imply (2). We use convexity of the numerical range of operators to show that when only two observables are measured, (1) always implies (2). More generally, if there is a compact group of symmetries of the state space which has the span of the observables measured as the set of fixed points, then (1) implies (2). We analyze the possible dimensions for the span of such observables. Our results extend naturally to the case of low rank quantum states. 1 aChen, Jianxin1 aDawkins, Hillary1 aJi, Zhengfeng1 aJohnston, Nathaniel1 aKribs, David1 aShultz, Frederic1 aZeng, Bei uhttp://arxiv.org/abs/1212.3503v202285nas a2200133 4500008004100000245005900041210005900100260001500159520189000174100001802064700001802082700001402100856003702114 2013 eng d00aUniversal Entanglers for Bosonic and Fermionic Systems0 aUniversal Entanglers for Bosonic and Fermionic Systems c2013/05/313 a A universal entangler (UE) is a unitary operation which maps all pure product states to entangled states. It is known that for a bipartite system of particles $1,2$ with a Hilbert space $\mathbb{C}^{d_1}\otimes\mathbb{C}^{d_2}$, a UE exists when $\min{(d_1,d_2)}\geq 3$ and $(d_1,d_2)\neq (3,3)$. It is also known that whenever a UE exists, almost all unitaries are UEs; however to verify whether a given unitary is a UE is very difficult since solving a quadratic system of equations is NP-hard in general. This work examines the existence and construction of UEs of bipartite bosonic/fermionic systems whose wave functions sit in the symmetric/antisymmetric subspace of $\mathbb{C}^{d}\otimes\mathbb{C}^{d}$. The development of a theory of UEs for these types of systems needs considerably different approaches from that used for UEs of distinguishable systems. This is because the general entanglement of identical particle systems cannot be discussed in the usual way due to the effect of (anti)-symmetrization which introduces "pseudo entanglement" that is inaccessible in practice. We show that, unlike the distinguishable particle case, UEs exist for bosonic/fermionic systems with Hilbert spaces which are symmetric (resp. antisymmetric) subspaces of $\mathbb{C}^{d}\otimes\mathbb{C}^{d}$ if and only if $d\geq 3$ (resp. $d\geq 8$). To prove this we employ algebraic geometry to reason about the different algebraic structures of the bosonic/fermionic systems. Additionally, due to the relatively simple coherent state form of unentangled bosonic states, we are able to give the explicit constructions of two bosonic UEs. Our investigation provides insight into the entanglement properties of systems of indisitinguishable particles, and in particular underscores the difference between the entanglement structures of bosonic, fermionic and distinguishable particle systems. 1 aKlassen, Joel1 aChen, Jianxin1 aZeng, Bei uhttp://arxiv.org/abs/1305.7489v101021nas a2200169 4500008004100000245009300041210006900134260001500203300001200218490000700230520048600237100002400723700002400747700001800771700002500789856003700814 2012 eng d00aAchieving perfect completeness in classical-witness quantum Merlin-Arthur proof systems0 aAchieving perfect completeness in classicalwitness quantum Merli c2012/05/01 a461-4710 v123 a This paper proves that classical-witness quantum Merlin-Arthur proof systems can achieve perfect completeness. That is, QCMA = QCMA1. This holds under any gate set with which the Hadamard and arbitrary classical reversible transformations can be exactly implemented, e.g., {Hadamard, Toffoli, NOT}. The proof is quantumly nonrelativizing, and uses a simple but novel quantum technique that additively adjusts the success probability, which may be of independent interest. 1 aJordan, Stephen, P.1 aKobayashi, Hirotada1 aNagaj, Daniel1 aNishimura, Harumichi uhttp://arxiv.org/abs/1111.5306v201029nas a2200121 4500008004100000245004700041210004700088260001500135520068500150100001600835700001900851856003700870 2012 eng d00aAlgorithmic Cooling of a Quantum Simulator0 aAlgorithmic Cooling of a Quantum Simulator c2012/07/303 aControlled quantum mechanical devices provide a means of simulating more complex quantum systems exponentially faster than classical computers. Such "quantum simulators" rely heavily upon being able to prepare the ground state of Hamiltonians, whose properties can be used to calculate correlation functions or even the solution to certain classical computations. While adiabatic preparation remains the primary means of producing such ground states, here we provide a different avenue of preparation: cooling to the ground state via simulated dissipation. This is in direct analogy to contemporary efforts to realize generalized forms of simulated annealing in quantum systems. 1 aKafri, Dvir1 aTaylor, J., M. uhttp://arxiv.org/abs/1207.7111v101318nas a2200145 4500008004100000245008900041210006900130260001300199490000800212520084800220100002201068700001901090700002601109856003701135 2012 eng d00aAnisotropy induced Feshbach resonances in a quantum dipolar gas of magnetic atoms 0 aAnisotropy induced Feshbach resonances in a quantum dipolar gas  c2012/9/70 v1093 a We explore the anisotropic nature of Feshbach resonances in the collision between ultracold magnetic submerged-shell dysprosium atoms, which can only occur due to couplings to rotating bound states. This is in contrast to well-studied alkali-metal atom collisions, where most Feshbach resonances are hyperfine induced and due to rotation-less bound states. Our novel first-principle coupled-channel calculation of the collisions between open-4f-shell spin-polarized bosonic dysprosium reveals a striking correlation between the anisotropy due to magnetic dipole-dipole and electrostatic interactions and the Feshbach spectrum as a function of an external magnetic field. Over a 20 mT magnetic field range we predict about a dozen Feshbach resonances and show that the resonance locations are exquisitely sensitive to the dysprosium isotope. 1 aPetrov, Alexander1 aTiesinga, Eite1 aKotochigova, Svetlana uhttp://arxiv.org/abs/1203.4172v100399nas a2200145 4500008004100000245003500041210003500076300001100111490000700122100001600129700001300145700002500158700001700183856005300200 2012 eng d00aCavity QED with atomic mirrors0 aCavity QED with atomic mirrors a0630030 v141 aChang, D, E1 aJiang, L1 aGorshkov, Alexey, V.1 aKimble, H, J uhttp://iopscience.iop.org/1367-2630/14/6/063003/01607nas a2200181 4500008004100000245005700041210005500098260001500153300001100168490000700179520111800186100001801304700001801322700001701340700001701357700001401374856003701388 2012 eng d00aGround-State Spaces of Frustration-Free Hamiltonians0 aGroundState Spaces of FrustrationFree Hamiltonians c2012/01/01 a1022010 v533 a We study the ground-state space properties for frustration-free Hamiltonians. We introduce a concept of `reduced spaces' to characterize local structures of ground-state spaces. For a many-body system, we characterize mathematical structures for the set $\Theta_k$ of all the $k$-particle reduced spaces, which with a binary operation called join forms a semilattice that can be interpreted as an abstract convex structure. The smallest nonzero elements in $\Theta_k$, called atoms, are analogs of extreme points. We study the properties of atoms in $\Theta_k$ and discuss its relationship with ground states of $k$-local frustration-free Hamiltonians. For spin-1/2 systems, we show that all the atoms in $\Theta_2$ are unique ground states of some 2-local frustration-free Hamiltonians. Moreover, we show that the elements in $\Theta_k$ may not be the join of atoms, indicating a richer structure for $\Theta_k$ beyond the convex structure. Our study of $\Theta_k$ deepens the understanding of ground-state space properties for frustration-free Hamiltonians, from a new angle of reduced spaces. 1 aChen, Jianxin1 aJi, Zhengfeng1 aKribs, David1 aWei, Zhaohui1 aZeng, Bei uhttp://arxiv.org/abs/1112.0762v101508nas a2200145 4500008004100000245005300041210005300094260001500147520109300162100001801255700001801273700002001291700001401311856003701325 2012 eng d00aMinimum Entangling Power is Close to Its Maximum0 aMinimum Entangling Power is Close to Its Maximum c2012/10/043 a Given a quantum gate $U$ acting on a bipartite quantum system, its maximum (average, minimum) entangling power is the maximum (average, minimum) entanglement generation with respect to certain entanglement measure when the inputs are restricted to be product states. In this paper, we mainly focus on the 'weakest' one, i.e., the minimum entangling power, among all these entangling powers. We show that, by choosing von Neumann entropy of reduced density operator or Schmidt rank as entanglement measure, even the 'weakest' entangling power is generically very close to its maximal possible entanglement generation. In other words, maximum, average and minimum entangling powers are generically close. We then study minimum entangling power with respect to other Lipschitiz-continuous entanglement measures and generalize our results to multipartite quantum systems. As a straightforward application, a random quantum gate will almost surely be an intrinsically fault-tolerant entangling device that will always transform every low-entangled state to near-maximally entangled state. 1 aChen, Jianxin1 aJi, Zhengfeng1 aKribs, David, W1 aZeng, Bei uhttp://arxiv.org/abs/1210.1296v101592nas a2200205 4500008004100000245012500041210006900166260001500235520091800250100001801168700002001186700002601206700002001232700001901252700001901271700001801290700002101308700002001329856003701349 2012 eng d00aPhotonic quantum simulation of ground state configurations of Heisenberg square and checkerboard lattice spin systems 0 aPhotonic quantum simulation of ground state configurations of He c2012/05/123 a Photonic quantum simulators are promising candidates for providing insight into other small- to medium-sized quantum systems. The available photonic quantum technology is reaching the state where significant advantages arise for the quantum simulation of interesting questions in Heisenberg spin systems. Here we experimentally simulate such spin systems with single photons and linear optics. The effective Heisenberg-type interactions among individual single photons are realized by quantum interference at the tunable direction coupler followed by the measurement process. The effective interactions are characterized by comparing the entanglement dynamics using pairwise concurrence of a four-photon quantum system. We further show that photonic quantum simulations of generalized Heisenberg interactions on a four-site square lattice and a six-site checkerboard lattice are in reach of current technology. 1 aMa, Xiao-song1 aDakic, Borivoje1 aKropatsche, Sebastian1 aNaylor, William1 aChan, Yang-hao1 aGong, Zhe-Xuan1 aDuan, Lu-ming1 aZeilinger, Anton1 aWalther, Philip uhttp://arxiv.org/abs/1205.2801v101667nas a2200145 4500008004100000245006400041210006200105260001400167490000700181520123200188100002701420700001801447700001901465856003701484 2012 eng d00aPolymer-mediated entropic forces between scale-free objects0 aPolymermediated entropic forces between scalefree objects c2012/12/30 v863 a The number of configurations of a polymer is reduced in the presence of a barrier or an obstacle. The resulting loss of entropy adds a repulsive component to other forces generated by interaction potentials. When the obstructions are scale invariant shapes (such as cones, wedges, lines or planes) the only relevant length scales are the polymer size R_0 and characteristic separations, severely constraining the functional form of entropic forces. Specifically, we consider a polymer (single strand or star) attached to the tip of a cone, at a separation h from a surface (or another cone). At close proximity, such that h<= 3, and we give a linear-size circuit of depth 2 that requires Omega (n^{5/9}) queries. Applications of these results include a Omega (n^{19/18}) lower bound for Boolean matrix product verification, a nearly tight characterization of the quantum query complexity of evaluating constant-depth circuits with bounded fanout, new formula gate count lower bounds for several functions including PARITY, and a construction of an AC^0 circuit of linear size that can only be evaluated by a formula with Omega(n^{2-epsilon}) gates. 1 aChilds, Andrew, M.1 aKimmel, Shelby1 aKothari, Robin uhttp://arxiv.org/abs/1112.0548v101417nas a2200253 4500008004100000245008300041210006900124260001500193300001100208490000700219520068500226100002200911700001600933700002300949700001900972700002300991700001901014700001801033700001701051700001801068700001601086700002401102856003701126 2012 eng d00aQuantum Simulation of Spin Models on an Arbitrary Lattice with Trapped Ions 0 aQuantum Simulation of Spin Models on an Arbitrary Lattice with T c2012/09/27 a0950240 v143 a A collection of trapped atomic ions represents one of the most attractive platforms for the quantum simulation of interacting spin networks and quantum magnetism. Spin-dependent optical dipole forces applied to an ion crystal create long-range effective spin-spin interactions and allow the simulation of spin Hamiltonians that possess nontrivial phases and dynamics. Here we show how appropriate design of laser fields can provide for arbitrary multidimensional spin-spin interaction graphs even for the case of a linear spatial array of ions. This scheme uses currently existing trap technology and is scalable to levels where classical methods of simulation are intractable. 1 aKorenblit, Simcha1 aKafri, Dvir1 aCampbell, Wess, C.1 aIslam, Rajibul1 aEdwards, Emily, E.1 aGong, Zhe-Xuan1 aLin, Guin-Dar1 aDuan, Luming1 aKim, Jungsang1 aKim, Kihwan1 aMonroe, Christopher uhttp://arxiv.org/abs/1201.0776v101124nas a2200181 4500008004100000245005300041210005300094260001500147300001100162490000700173520063000180100001800810700001800828700002400846700002100870700001400891856003700905 2012 eng d00aRank Reduction for the Local Consistency Problem0 aRank Reduction for the Local Consistency Problem c2012/02/09 a0222020 v533 a We address the problem of how simple a solution can be for a given quantum local consistency instance. More specifically, we investigate how small the rank of the global density operator can be if the local constraints are known to be compatible. We prove that any compatible local density operators can be satisfied by a low rank global density operator. Then we study both fermionic and bosonic versions of the N-representability problem as applications. After applying the channel-state duality, we prove that any compatible local channels can be obtained through a global quantum channel with small Kraus rank. 1 aChen, Jianxin1 aJi, Zhengfeng1 aKlyachko, Alexander1 aKribs, David, W.1 aZeng, Bei uhttp://arxiv.org/abs/1106.3235v201932nas a2200169 4500008004100000245005700041210005500098260001500153300001200168520144400180100002701624700002101651700001601672700002101688700001601709856003701725 2012 eng d00aA Spectral Algorithm for Latent Dirichlet Allocation0 aSpectral Algorithm for Latent Dirichlet Allocation c2012/04/30 a193-2143 a The problem of topic modeling can be seen as a generalization of the clustering problem, in that it posits that observations are generated due to multiple latent factors (e.g., the words in each document are generated as a mixture of several active topics, as opposed to just one). This increased representational power comes at the cost of a more challenging unsupervised learning problem of estimating the topic probability vectors (the distributions over words for each topic), when only the words are observed and the corresponding topics are hidden. We provide a simple and efficient learning procedure that is guaranteed to recover the parameters for a wide class of mixture models, including the popular latent Dirichlet allocation (LDA) model. For LDA, the procedure correctly recovers both the topic probability vectors and the prior over the topics, using only trigram statistics (i.e., third order moments, which may be estimated with documents containing just three words). The method, termed Excess Correlation Analysis (ECA), is based on a spectral decomposition of low order moments (third and fourth order) via two singular value decompositions (SVDs). Moreover, the algorithm is scalable since the SVD operations are carried out on $k\times k$ matrices, where $k$ is the number of latent factors (e.g. the number of topics), rather than in the $d$-dimensional observed space (typically $d \gg k$). 1 aAnandkumar, Animashree1 aFoster, Dean, P.1 aHsu, Daniel1 aKakade, Sham, M.1 aLiu, Yi-Kai uhttp://arxiv.org/abs/1204.6703v400969nas a2200145 4500008004100000245006800041210006700109260001300176490000800189520052100197100002700718700002200745700001900767856003700786 2012 eng d00aSpontaneous emission by rotating objects: A scattering approach0 aSpontaneous emission by rotating objects A scattering approach c2012/6/70 v1083 a We study the quantum electrodynamics (QED) vacuum in the presence of a body rotating along its axis of symmetry and show that the object spontaneously emits energy if it is lossy. The radiated power is expressed as a general trace formula solely in terms of the scattering matrix, making an explicit connection to the conjecture of Zel'dovich [JETP Lett. 14, 180 (1971)] on rotating objects. We further show that a rotating body drags along nearby objects while making them spin parallel to its own rotation axis. 1 aMaghrebi, Mohammad, F.1 aJaffe, Robert, L.1 aKardar, Mehran uhttp://arxiv.org/abs/1202.1485v201009nas a2200157 4500008004100000020002200041245009100063210006900154260001500223300001200238520050600250100001600756700001900772700002300791856003700814 2012 eng d a978-1-4503-1115-100aSuper-Polynomial Quantum Speed-ups for Boolean Evaluation Trees with Hidden Structure0 aSuperPolynomial Quantum Speedups for Boolean Evaluation Trees wi c2012/01/08 a249-2653 a We give a quantum algorithm for evaluating a class of boolean formulas (such as NAND trees and 3-majority trees) on a restricted set of inputs. Due to the structure of the allowed inputs, our algorithm can evaluate a depth $n$ tree using $O(n^{2+\log\omega})$ queries, where $\omega$ is independent of $n$ and depends only on the type of subformulas within the tree. We also prove a classical lower bound of $n^{\Omega(\log\log n)}$ queries, thus showing a (small) super-polynomial speed-up. 1 aZhan, Bohua1 aKimmel, Shelby1 aHassidim, Avinatan uhttp://arxiv.org/abs/1101.0796v301641nas a2200193 4500008004100000245005000041210004900091260001500140300001600155490000800171520110300179100002701282700002401309700001901333700001701352700002201369700001901391856003701410 2011 eng d00aCasimir force between sharp-shaped conductors0 aCasimir force between sharpshaped conductors c2011/04/11 a6867 - 68710 v1083 a Casimir forces between conductors at the sub-micron scale cannot be ignored in the design and operation of micro-electromechanical (MEM) devices. However, these forces depend non-trivially on geometry, and existing formulae and approximations cannot deal with realistic micro-machinery components with sharp edges and tips. Here, we employ a novel approach to electromagnetic scattering, appropriate to perfect conductors with sharp edges and tips, specifically to wedges and cones. The interaction of these objects with a metal plate (and among themselves) is then computed systematically by a multiple-scattering series. For the wedge, we obtain analytical expressions for the interaction with a plate, as functions of opening angle and tilt, which should provide a particularly useful tool for the design of MEMs. Our result for the Casimir interactions between conducting cones and plates applies directly to the force on the tip of a scanning tunneling probe; the unexpectedly large temperature dependence of the force in these configurations should attract immediate experimental interest. 1 aMaghrebi, Mohammad, F.1 aRahi, Sahand, Jamal1 aEmig, Thorsten1 aGraham, Noah1 aJaffe, Robert, L.1 aKardar, Mehran uhttp://arxiv.org/abs/1010.3223v101352nas a2200145 4500008004100000245007400041210006900115260001500184490000700199520089800206100002001104700002001124700002501144856003701169 2011 eng d00ad-Wave Superfluidity in Optical Lattices of Ultracold Polar Molecules0 adWave Superfluidity in Optical Lattices of Ultracold Polar Molec c2011/12/290 v843 a Recent work on ultracold polar molecules, governed by a generalization of the t-J Hamiltonian, suggests that molecules may be better suited than atoms for studying d-wave superfluidity due to stronger interactions and larger tunability of the system. We compute the phase diagram for polar molecules in a checkerboard lattice consisting of weakly coupled square plaquettes. In the simplest experimentally realizable case where there is only tunneling and an XX-type spin-spin interaction, we identify the parameter regime where d-wave superfluidity occurs. We also find that the inclusion of a density-density interaction destroys the superfluid phase and that the inclusion of a spin-density or an Ising-type spin-spin interaction can enhance the superfluid phase. We also propose schemes for experimentally realizing the perturbative calculations exhibiting enhanced d-wave superfluidity. 1 aKuns, Kevin, A.1 aRey, Ana, Maria1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/1110.5330v201014nas a2200157 4500008004100000245004500041210004500086260001500131300001000146490000700156520059200163100002700755700001800782700001900800856003700819 2011 eng d00aEntropic force of polymers on a cone tip0 aEntropic force of polymers on a cone tip c2011/12/01 a660020 v963 a We consider polymers attached to the tip of a cone, and the resulting force due to entropy loss on approaching a plate (or another cone). At separations shorter than the polymer radius of gyration R_g, the only relevant length scale is the tip-plate (or tip-tip) separation h, and the entropic force is given by F=A kT/h. The universal amplitude A can be related to (geometry dependent) correlation exponents of long polymers. We compute A for phantom polymers, and for self-avoiding (including star) polymers by epsilon-expansion, as well as by numerical simulations in 3 dimensions. 1 aMaghrebi, Mohammad, F.1 aKantor, Yacov1 aKardar, Mehran uhttp://arxiv.org/abs/1109.5658v201380nas a2200145 4500008004100000245006200041210006100103260001500164300001200179490000600191520095800197100002301155700001901178856003701197 2011 eng d00aQuantum query complexity of minor-closed graph properties0 aQuantum query complexity of minorclosed graph properties c2011/01/01 a661-6720 v93 a We study the quantum query complexity of minor-closed graph properties, which include such problems as determining whether an $n$-vertex graph is planar, is a forest, or does not contain a path of a given length. We show that most minor-closed properties---those that cannot be characterized by a finite set of forbidden subgraphs---have quantum query complexity \Theta(n^{3/2}). To establish this, we prove an adversary lower bound using a detailed analysis of the structure of minor-closed properties with respect to forbidden topological minors and forbidden subgraphs. On the other hand, we show that minor-closed properties (and more generally, sparse graph properties) that can be characterized by finitely many forbidden subgraphs can be solved strictly faster, in o(n^{3/2}) queries. Our algorithms are a novel application of the quantum walk search framework and give improved upper bounds for several subgraph-finding problems. 1 aChilds, Andrew, M.1 aKothari, Robin uhttp://arxiv.org/abs/1011.1443v201327nas a2200157 4500008004100000245009200041210006900133260001400202490000700216520082400223100001901047700002401066700001901090700002301109856003701132 2010 eng d00aApproximating Turaev-Viro 3-manifold invariants is universal for quantum computation 0 aApproximating TuraevViro 3manifold invariants is universal for q c2010/10/80 v823 a The Turaev-Viro invariants are scalar topological invariants of compact, orientable 3-manifolds. We give a quantum algorithm for additively approximating Turaev-Viro invariants of a manifold presented by a Heegaard splitting. The algorithm is motivated by the relationship between topological quantum computers and (2+1)-D topological quantum field theories. Its accuracy is shown to be nontrivial, as the same algorithm, after efficient classical preprocessing, can solve any problem efficiently decidable by a quantum computer. Thus approximating certain Turaev-Viro invariants of manifolds presented by Heegaard splittings is a universal problem for quantum computation. This establishes a novel relation between the task of distinguishing non-homeomorphic 3-manifolds and the power of a general quantum computer. 1 aAlagic, Gorjan1 aJordan, Stephen, P.1 aKoenig, Robert1 aReichardt, Ben, W. uhttp://arxiv.org/abs/1003.0923v101401nas a2200217 4500008004100000245005600041210005600097260001300153490000800166520081300174100002100987700001801008700001901026700001401045700002101059700001901080700001401099700001501113700001801128856003701146 2010 eng d00aDynamic Nuclear Polarization in Double Quantum Dots0 aDynamic Nuclear Polarization in Double Quantum Dots c2010/6/40 v1043 aWe theoretically investigate the controlled dynamic polarization of lattice nuclear spins in GaAs double quantum dots containing two electrons. Three regimes of long-term dynamics are identified, including the build up of a large difference in the Overhauser fields across the dots, the saturation of the nuclear polarization process associated with formation of so-called "dark states," and the elimination of the difference field. We show that in the case of unequal dots, build up of difference fields generally accompanies the nuclear polarization process, whereas for nearly identical dots, build up of difference fields competes with polarization saturation in dark states. The elimination of the difference field does not, in general, correspond to a stable steady state of the polarization process. 1 aGullans, Michael1 aKrich, J., J.1 aTaylor, J., M.1 aBluhm, H.1 aHalperin, B., I.1 aMarcus, C., M.1 aStopa, M.1 aYacoby, A.1 aLukin, M., D. uhttp://arxiv.org/abs/1003.4508v201041nas a2200121 4500008004100000245006000041210006000101260001500161520066400176100002300840700001900863856003700882 2010 eng d00aSimulating sparse Hamiltonians with star decompositions0 aSimulating sparse Hamiltonians with star decompositions c2010/03/183 a We present an efficient algorithm for simulating the time evolution due to a sparse Hamiltonian. In terms of the maximum degree d and dimension N of the space on which the Hamiltonian H acts for time t, this algorithm uses (d^2(d+log* N)||Ht||)^{1+o(1)} queries. This improves the complexity of the sparse Hamiltonian simulation algorithm of Berry, Ahokas, Cleve, and Sanders, which scales like (d^4(log* N)||Ht||)^{1+o(1)}. To achieve this, we decompose a general sparse Hamiltonian into a small sum of Hamiltonians whose graphs of non-zero entries have the property that every connected component is a star, and efficiently simulate each of these pieces. 1 aChilds, Andrew, M.1 aKothari, Robin uhttp://arxiv.org/abs/1003.3683v201370nas a2200157 4500008004100000245004700041210004700088260001400135490000700149520092300156100003001079700002101109700001901130700002601149856003701175 2009 eng d00aEntanglement Cost of Nonlocal Measurements0 aEntanglement Cost of Nonlocal Measurements c2009/7/150 v803 a For certain joint measurements on a pair of spatially separated particles, we ask how much entanglement is needed to carry out the measurement exactly. For a class of orthogonal measurements on two qubits with partially entangled eigenstates, we present upper and lower bounds on the entanglement cost. The upper bound is based on a recent result by D. Berry [Phys. Rev. A 75, 032349 (2007)]. The lower bound, based on the entanglement production capacity of the measurement, implies that for almost all measurements in the class we consider, the entanglement required to perform the measurement is strictly greater than the average entanglement of its eigenstates. On the other hand, we show that for any complete measurement in d x d dimensions that is invariant under all local Pauli operations, the cost of the measurement is exactly equal to the average entanglement of the states associated with the outcomes. 1 aBandyopadhyay, Somshubhro1 aBrassard, Gilles1 aKimmel, Shelby1 aWootters, William, K. uhttp://arxiv.org/abs/0809.2264v401322nas a2200121 4500008004100000245006100041210006000102260001500162520094400177100002301121700001901144856003701163 2009 eng d00aLimitations on the simulation of non-sparse Hamiltonians0 aLimitations on the simulation of nonsparse Hamiltonians c2009/08/313 a The problem of simulating sparse Hamiltonians on quantum computers is well studied. The evolution of a sparse N x N Hamiltonian H for time t can be simulated using O(||Ht||poly(log N)) operations, which is essentially optimal due to a no--fast-forwarding theorem. Here, we consider non-sparse Hamiltonians and show significant limitations on their simulation. We generalize the no--fast-forwarding theorem to dense Hamiltonians, ruling out generic simulations taking time o(||Ht||), even though ||H|| is not a unique measure of the size of a dense Hamiltonian $H$. We also present a stronger limitation ruling out the possibility of generic simulations taking time poly(||Ht||,log N), showing that known simulations based on discrete-time quantum walk cannot be dramatically improved in general. On the positive side, we show that some non-sparse Hamiltonians can be simulated efficiently, such as those with graphs of small arboricity. 1 aChilds, Andrew, M.1 aKothari, Robin uhttp://arxiv.org/abs/0908.4398v201547nas a2200157 4500008004100000245009000041210006900131260001500200300001100215490000700226520105100233100002601284700001901310700002301329856003701352 2009 eng d00aMulti-channel modelling of the formation of vibrationally cold polar KRb molecules 0 aMultichannel modelling of the formation of vibrationally cold po c2009/05/14 a0550430 v113 a We describe the theoretical advances that influenced the experimental creation of vibrationally and translationally cold polar $^{40}$K$^{87}$Rb molecules \cite{nphys08,science08}. Cold molecules were created from very-weakly bound molecules formed by magnetic field sweeps near a Feshbach resonance in collisions of ultra-cold $^{40}$K and $^{87}$Rb atoms. Our analysis include the multi-channel bound-state calculations of the hyperfine and Zeeman mixed X$^1\Sigma^+$ and a$^3\Sigma^+$ vibrational levels. We find excellent agreement with the hyperfine structure observed in experimental data. In addition, we studied the spin-orbit mixing in the intermediate state of the Raman transition. This allowed us to investigate its effect on the vibrationally-averaged transition dipole moment to the lowest ro-vibrational level of the X$^1\Sigma^+$ state. Finally, we obtained an estimate of the polarizability of the initial and final ro-vibrational states of the Raman transition near frequencies relevant for optical trapping of the molecules. 1 aKotochigova, Svetlana1 aTiesinga, Eite1 aJulienne, Paul, S. uhttp://arxiv.org/abs/0901.1486v100824nas a2200205 4500008004100000245007200041210006900113300001100182490000900193100001300202700001200215700002500227700001600252700001600268700001900284700001900303700001600322700002000338856026000358 2008 eng d00aOptimizing Slow and Stored Light for Multidisciplinary Applications0 aOptimizing Slow and Stored Light for Multidisciplinary Applicati a69040C0 v69041 aKlein, M1 aXiao, Y1 aGorshkov, Alexey, V.1 aHohensee, M1 aLeung, C, D1 aBrowning, M, R1 aPhillips, D, F1 aNovikova, I1 aWalsworth, R, L uhttp://spie.org/x648.xml?product_id=772216&Search_Origin=QuickSearch&Search_Results_URL=http://spie.org/x1636.xml&Alternate_URL=http://spie.org/x18509.xml&Alternate_URL_Name=timeframe&Alternate_URL_Value=Exhibitors&UseJavascript=1&Please_Wait_URL=http://s01766nas a2200181 4500008004100000245008100041210006900122260001500191300001800206490000800224520121000232100001701442700002401459700002001483700002001503700002401523856003701547 2008 eng d00aPolynomial-time quantum algorithm for the simulation of chemical dynamics 0 aPolynomialtime quantum algorithm for the simulation of chemical  c2008/11/24 a18681 - 186860 v1053 a The computational cost of exact methods for quantum simulation using classical computers grows exponentially with system size. As a consequence, these techniques can only be applied to small systems. By contrast, we demonstrate that quantum computers could exactly simulate chemical reactions in polynomial time. Our algorithm uses the split-operator approach and explicitly simulates all electron-nuclear and inter-electronic interactions in quadratic time. Surprisingly, this treatment is not only more accurate than the Born-Oppenheimer approximation, but faster and more efficient as well, for all reactions with more than about four atoms. This is the case even though the entire electronic wavefunction is propagated on a grid with appropriately short timesteps. Although the preparation and measurement of arbitrary states on a quantum computer is inefficient, here we demonstrate how to prepare states of chemical interest efficiently. We also show how to efficiently obtain chemically relevant observables, such as state-to-state transition probabilities and thermal reaction rates. Quantum computers using these techniques could outperform current classical computers with one hundred qubits. 1 aKassal, Ivan1 aJordan, Stephen, P.1 aLove, Peter, J.1 aMohseni, Masoud1 aAspuru-Guzik, Alán uhttp://arxiv.org/abs/0801.2986v300624nas a2200169 4500008004100000245005800041210005800099300001100157490000900168100001600177700002500193700001900218700001200237700001300249700002000262856017200282 2007 eng d00aOptimization of slow and stored light in atomic vapor0 aOptimization of slow and stored light in atomic vapor a64820M0 v64821 aNovikova, I1 aGorshkov, Alexey, V.1 aPhillips, D, F1 aXiao, Y1 aKlein, M1 aWalsworth, R, L uhttp://spiedigitallibrary.aip.org/getabs/servlet/GetabsServlet?prog=normal&id=PSISDG00648200000164820M000001&idtype=cvips&gifs=Yes&bproc=volrange&scode=6400%20-%20649901196nas a2200217 4500008004100000245005900041210005800100260001500158490000700173520059700180100001100777700001200788700002300800700001800823700001700841700001900858700001700877700002100894700001900915856004400934 2005 eng d00aSodium Bose-Einstein Condensates in an Optical Lattice0 aSodium BoseEinstein Condensates in an Optical Lattice c2005/10/100 v723 a The phase transition from a superfluid to a Mott insulator has been observed in a $^{23}$Na Bose-Einstein condensate. A dye laser detuned $\approx 5$nm red of the Na $3^2$S$ \to 3^2$P$_{1/2}$ transition was used to form the three dimensional optical lattice. The heating effects of the small detuning as well as the three-body decay processes constrained the timescale of the experiment. Certain lattice detunings were found to induce a large loss of atoms. These loss features were shown to be due to photoassociation of atoms to vibrational levels in the Na$_2$ $(1) ^3\Sigma_g^+$ state. 1 aXu, K.1 aLiu, Y.1 aAbo-Shaeer, J., R.1 aMukaiyama, T.1 aChin, J., K.1 aMiller, D., E.1 aKetterle, W.1 aJones, Kevin, M.1 aTiesinga, Eite uhttp://arxiv.org/abs/cond-mat/0507288v101059nas a2200145 4500008004100000245006200041210006100103260001400164490000700178520062000185100002200805700001900827700002300846856004400869 2005 eng d00aSpontaneous dissociation of long-range Feshbach molecules0 aSpontaneous dissociation of longrange Feshbach molecules c2005/1/180 v943 a We study the spontaneous dissociation of diatomic molecules produced in cold atomic gases via magnetically tunable Feshbach resonances. We provide a universal formula for the lifetime of these molecules that relates their decay to the scattering length and the loss rate constant for inelastic spin relaxation. Our universal treatment as well as our exact coupled channels calculations for $^{85}$Rb dimers predict a suppression of the decay over several orders of magnitude when the scattering length is increased. Our predictions are in good agreement with recent measurements of the lifetime of $^{85}$Rb$_2$. 1 aKoehler, Thorsten1 aTiesinga, Eite1 aJulienne, Paul, S. uhttp://arxiv.org/abs/cond-mat/0408387v202281nas a2200181 4500008004100000245009200041210006900133260001500202300001600217490000700233520170600240100002101946700002201967700002401989700001902013700002302032856004402055 2004 eng d00aAdiabatic association of ultracold molecules via magnetic field tunable interactions 0 aAdiabatic association of ultracold molecules via magnetic field  c2004/09/14 a3457 - 35000 v373 a We consider in detail the situation of applying a time dependent external magnetic field to a 87Rb atomic Bose-Einstein condensate held in a harmonic trap, in order to adiabatically sweep the interatomic interactions across a Feshbach resonance to produce diatomic molecules. To this end, we introduce a minimal two-body Hamiltonian depending on just five measurable parameters of a Feshbach resonance, which accurately determines all low energy binary scattering observables, in particular, the molecular conversion efficiency of just two atoms. Based on this description of the microscopic collision phenomena, we use the many-body theory of T. Koehler and K. Burnett [Phys. Rev. A 65, 033601 (2002)] to study the efficiency of the association of molecules in a 87Rb Bose-Einstein condensate during a linear passage of the magnetic field strength across the 100 mT Feshbach resonance. We explore different, experimentally accessible, parameter regimes, and compare the predictions of Landau-Zener, configuration interaction, and two level mean field calculations with those of the microscopic many-body approach. Our comparative studies reveal a remarkable insensitivity of the molecular conversion efficiency with respect to both the details of the microscopic binary collision physics and the coherent nature of the Bose-Einstein condensed gas, provided that the magnetic field strength is varied linearly. We provide the reasons for this universality of the molecular production achieved by linear ramps of the magnetic field strength, and identify the Landau-Zener coefficient determined by F.H. Mies et al. [Phys. Rev. A 61, 022721 (2000)] as the main parameter that controls the efficiency. 1 aGoral, Krzysztof1 aKoehler, Thorsten1 aGardiner, Simon, A.1 aTiesinga, Eite1 aJulienne, Paul, S. uhttp://arxiv.org/abs/cond-mat/0312178v501322nas a2200169 4500008004100000245007000041210006900111260001400180490000700194520079400201100002300995700002301018700002601041700001901067700002301086856004301109 2003 eng d00aUltracold collision properties of metastable alkaline-earth atoms0 aUltracold collision properties of metastable alkalineearth atoms c2003/2/130 v903 a Ultra-cold collisions of spin-polarized 24Mg,40Ca, and 88Sr in the metastable 3P2 excited state are investigated. We calculate the long-range interaction potentials and estimate the scattering length and the collisional loss rate as a function of magnetic field. The estimates are based on molecular potentials between 3P2 alkaline-earth atoms obtained from ab initio atomic and molecular structure calculations. The scattering lengths show resonance behavior due to the appearance of a molecular bound state in a purely long-range interaction potential and are positive for magnetic fields below 50 mT. A loss-rate model shows that losses should be smallest near zero magnetic field and for fields slightly larger than the resonance field, where the scattering length is also positive. 1 aDerevianko, Andrei1 aPorsev, Sergey, G.1 aKotochigova, Svetlana1 aTiesinga, Eite1 aJulienne, Paul, S. uhttp://arxiv.org/abs/physics/0210076v101384nas a2200181 4500008004100000245004300041210004000084260001500124520088400139100001601023700002001039700002301059700001601082700001901098700001801117700002301135856004401158 2003 eng d00aUltracold Cs$_2$ Feshbach Spectroscopy0 aUltracold Cs2 Feshbach Spectroscopy c2003/12/233 a We have observed and located more than 60 magnetic field-induced Feshbach resonances in ultracold collisions of ground-state $^{133}$Cs atoms. These resonances are associated with molecular states with up to four units of rotational angular momentum, and are detected through variations in the elastic, inelastic, and radiative collision cross sections. These observations allow us to greatly improve upon the interaction potentials between two cesium atoms and to reproduce the positions of most resonances to accuracies better than 0.5%. Based on the relevant coupling scheme between the electron spin, nuclear spin, and orbital angular momenta of the nuclei, quantum numbers and energy structure of the molecular states beneath the dissociation continuum are revealed. Finally, we predict the relevant collision properties for cesium Bose-Einstein condensation experiments. 1 aChin, Cheng1 aVuletic, Vladan1 aKerman, Andrew, J.1 aChu, Steven1 aTiesinga, Eite1 aLeo, Paul, J.1 aWilliams, Carl, J. uhttp://arxiv.org/abs/cond-mat/0312613v201258nas a2200181 4500008004100000245005500041210005500096260001400151490000700165520074300172100001600915700002300931700002200954700001700976700002200993700001701015856004401032 2001 eng d00aUniversal simulation of Markovian quantum dynamics0 aUniversal simulation of Markovian quantum dynamics c2001/11/90 v643 a Although the conditions for performing arbitrary unitary operations to simulate the dynamics of a closed quantum system are well understood, the same is not true of the more general class of quantum operations (also known as superoperators) corresponding to the dynamics of open quantum systems. We propose a framework for the generation of Markovian quantum dynamics and study the resources needed for universality. For the case of a single qubit, we show that a single nonunitary process is necessary and sufficient to generate all unital Markovian quantum dynamics, whereas a set of processes parametrized by one continuous parameter is needed in general. We also obtain preliminary results for the unital case in higher dimensions. 1 aBacon, Dave1 aChilds, Andrew, M.1 aChuang, Isaac, L.1 aKempe, Julia1 aLeung, Debbie, W.1 aZhou, Xinlan uhttp://arxiv.org/abs/quant-ph/0008070v2