01576nas a2200181 4500008004100000022001400041245006300055210006100118260001400179300001600193490000600209520107500215100001701290700001701307700001801324700001501342856003701357 2024 eng d a2475-142100aA Case for Synthesis of Recursive Quantum Unitary Programs0 aCase for Synthesis of Recursive Quantum Unitary Programs c12/5/2023 a1759–17880 v83 a

Quantum programs are notoriously difficult to code and verify due to unintuitive quantum knowledge associated with quantum programming. Automated tools relieving the tedium and errors associated with low-level quantum details would hence be highly desirable. In this paper, we initiate the study of program synthesis for quantum unitary programs that recursively define a family of unitary circuits for different input sizes, which are widely used in existing quantum programming languages. Specifically, we present QSynth, the first quantum program synthesis framework, including a new inductive quantum programming language, its specification, a sound logic for reasoning, and an encoding of the reasoning procedure into SMT instances. By leveraging existing SMT solvers, QSynth successfully synthesizes ten quantum unitary programs including quantum adder circuits, quantum eigenvalue inversion circuits and Quantum Fourier Transformation, which can be readily transpiled to executable programs on major quantum platforms, e.g., Q#, IBM Qiskit, and AWS Braket.

1 aDeng, Haowei1 aTao, Runzhou1 aPeng, Yuxiang1 aWu, Xiaodi uhttps://arxiv.org/abs/2311.1150301833nas a2200145 4500008004100000245008700041210006900128260001400197520137500211100001601586700001501602700001801617700001501635856003701650 2024 eng d00aExpanding Hardware-Efficiently Manipulable Hilbert Space via Hamiltonian Embedding0 aExpanding HardwareEfficiently Manipulable Hilbert Space via Hami c1/16/20243 a

Many promising quantum applications depend on the efficient quantum simulation of an exponentially large sparse Hamiltonian, a task known as sparse Hamiltonian simulation, which is fundamentally important in quantum computation. Although several theoretically appealing quantum algorithms have been proposed for this task, they typically require a black-box query model of the sparse Hamiltonian, rendering them impractical for near-term implementation on quantum devices.
In this paper, we propose a technique named Hamiltonian embedding. This technique simulates a desired sparse Hamiltonian by embedding it into the evolution of a larger and more structured quantum system, allowing for more efficient simulation through hardware-efficient operations. We conduct a systematic study of this new technique and demonstrate significant savings in computational resources for implementing prominent quantum applications. As a result, we can now experimentally realize quantum walks on complicated graphs (e.g., binary trees, glued-tree graphs), quantum spatial search, and the simulation of real-space Schrödinger equations on current trapped-ion and neutral-atom platforms. Given the fundamental role of Hamiltonian evolution in the design of quantum algorithms, our technique markedly expands the horizon of implementable quantum advantages in the NISQ era.

1 aLeng, Jiaqi1 aLi, Joseph1 aPeng, Yuxiang1 aWu, Xiaodi uhttps://arxiv.org/abs/2401.0855001716nas a2200169 4500008004100000245005800041210005800099260001300157520120700170100002501377700002001402700001801422700002801440700001901468700002201487856003701509 2024 eng d00aIntegrability of Goldilocks quantum cellular automata0 aIntegrability of Goldilocks quantum cellular automata c4/3/20243 a

Goldilocks quantum cellular automata (QCA) have been simulated on quantum hardware and produce emergent small-world correlation networks. In Goldilocks QCA, a single-qubit unitary is applied to each qubit in a one-dimensional chain subject to a balance constraint: a qubit is updated if its neighbors are in opposite basis states. Here, we prove that a subclass of Goldilocks QCA -- including the one implemented experimentally -- map onto free fermions and therefore can be classically simulated efficiently. We support this claim with two independent proofs, one involving a Jordan--Wigner transformation and one mapping the integrable six-vertex model to QCA. We compute local conserved quantities of these QCA and predict experimentally measurable expectation values. These calculations can be applied to test large digital quantum computers against known solutions. In contrast, typical Goldilocks QCA have equilibration properties and quasienergy-level statistics that suggest nonintegrability. Still, the latter QCA conserve one quantity useful for error mitigation. Our work provides a parametric quantum circuit with tunable integrability properties with which to test quantum hardware.

1 aHillberry, Logan, E.1 aPiroli, Lorenzo1 aVernier, Eric1 aHalpern, Nicole, Yunger1 aProsen, Tomaž1 aCarr, Lincoln, D. uhttps://arxiv.org/abs/2404.0299401910nas a2200121 4500008004100000245008000041210006900121260001300190520150500203100002001708700002301728856003701751 2024 eng d00aQuantum One-Wayness of the Single-Round Sponge with Invertible Permutations0 aQuantum OneWayness of the SingleRound Sponge with Invertible Per c3/7/20243 a

Sponge hashing is a novel class of cryptographic hash algorithms which underlies the current international hash function standard SHA-3. In a nutshell, a sponge function takes as input a bit-stream of any length and processes it via a simple iterative procedure: it repeatedly feeds each block of the input into a so-called block function, and then produces a short digest which consists of a subset of the final output bits. While much is known about the post-quantum security of the sponge construction in the case when the block function is modeled as a random function or permutation, the case of invertible permutations, which more accurately models the construction underlying SHA-3, has so far remained a fundamental open problem.
In this work, we make new progress towards overcoming this barrier and show several results. First, we prove the "double-sided zero-search" conjecture proposed by Unruh (eprint' 2021) and show that finding zero-pairs in a random 2n-bit permutation requires at least Ω(2n/2) many queries -- and this is tight due to Grover's algorithm. At the core of our proof lies a novel "symmetrization argument" which uses insights from the theory of Young subgroups. Second, we consider more general variants of the double-sided search problem and show similar query lower bounds for them. As an application, we prove the quantum one-wayness of the single-round sponge with invertible permutations in the quantum random oracle model.

1 aCarolan, Joseph1 aPoremba, Alexander uhttps://arxiv.org/abs/2403.0474002067nas a2200169 4500008004100000245008100041210006900122260001300191520151900204100002001723700002701743700002001770700002301790700001901813700002801832856003701860 2024 eng d00aQuantum thermodynamics of nonequilibrium processes in lattice gauge theories0 aQuantum thermodynamics of nonequilibrium processes in lattice ga c4/3/20243 a

A key objective in nuclear and high-energy physics is to describe nonequilibrium dynamics of matter, e.g., in the early universe and in particle colliders, starting from the Standard Model. Classical-computing methods, via the framework of lattice gauge theory, have experienced limited success in this mission. Quantum simulation of lattice gauge theories holds promise for overcoming computational limitations. Because of local constraints (Gauss's laws), lattice gauge theories have an intricate Hilbert-space structure. This structure complicates the definition of thermodynamic properties of systems coupled to reservoirs during equilibrium and nonequilibrium processes. We show how to define thermodynamic quantities such as work and heat using strong-coupling thermodynamics, a framework that has recently burgeoned within the field of quantum thermodynamics. Our definitions suit instantaneous quenches, simple nonequilibrium processes undertaken in quantum simulators. To illustrate our framework, we compute the work and heat exchanged during a quench in a Z2 lattice gauge theory coupled to matter in 1+1 dimensions. The thermodynamic quantities, as functions of the quench parameter, evidence an expected phase transition. For general thermal states, we derive a simple relation between a quantum many-body system's entanglement Hamiltonian, measurable with quantum-information-processing tools, and the Hamiltonian of mean force, used to define strong-coupling thermodynamic quantities.

1 aDavoudi, Zohreh1 aJarzynski, Christopher1 aMueller, Niklas1 aOruganti, Greeshma1 aPowers, Connor1 aHalpern, Nicole, Yunger uhttps://arxiv.org/abs/2404.0296502177nas a2200181 4500008004100000022001400041245009400055210006900149260001500218300001600233490000600249520163700255100001801892700001701910700001601927700001501943856003701958 2024 eng d a2475-142100aSimuQ: A Framework for Programming Quantum Hamiltonian Simulation with Analog Compilation0 aSimuQ A Framework for Programming Quantum Hamiltonian Simulation c11/19/2023 a2425–24550 v83 a

Quantum Hamiltonian simulation, which simulates the evolution of quantum systems and probes quantum phenomena, is one of the most promising applications of quantum computing. Recent experimental results suggest that Hamiltonian-oriented analog quantum simulation would be advantageous over circuit-oriented digital quantum simulation in the Noisy Intermediate-Scale Quantum (NISQ) machine era. However, programming analog quantum simulators is much more challenging due to the lack of a unified interface between hardware and software. In this paper, we design and implement SimuQ, the first framework for quantum Hamiltonian simulation that supports Hamiltonian programming and pulse-level compilation to heterogeneous analog quantum simulators. Specifically, in SimuQ, front-end users specify the target quantum system with Hamiltonian Modeling Language, and the Hamiltonian-level programmability of analog quantum simulators is specified through a new abstraction called the abstract analog instruction set (AAIS) and programmed in AAIS Specification Language by hardware providers. Through a solver-based compilation, SimuQ generates executable pulse schedules for real devices to simulate the evolution of desired quantum systems, which is demonstrated on superconducting (IBM), neutral-atom (QuEra), and trapped-ion (IonQ) quantum devices. Moreover, we demonstrate the advantages of exposing the Hamiltonian-level programmability of devices with native operations or interaction-based gates and establish a small benchmark of quantum simulation to evaluate SimuQ's compiler with the above analog quantum simulators.

1 aPeng, Yuxiang1 aYoung, Jacob1 aLiu, Pengyu1 aWu, Xiaodi uhttps://arxiv.org/abs/2303.0277502465nas 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/2210.1475702370nas a2200145 4500008004100000245008400041210006900125260001500194520190500209100002102114700001602135700001802151700001802169856003702187 2023 eng d00aCompressed gate characterization for quantum devices with time-correlated noise0 aCompressed gate characterization for quantum devices with timeco c12/22/20233 a

As quantum devices make steady progress towards intermediate scale and fault-tolerant quantum computing, it is essential to develop rigorous and efficient measurement protocols that account for known sources of noise. Most existing quantum characterization protocols such as gate set tomography and randomized benchmarking assume the noise acting on the qubits is Markovian. However, this assumption is often not valid, as for the case of 1/f charge noise or hyperfine nuclear spin noise. Here, we present a general framework for quantum process tomography (QPT) in the presence of time-correlated noise. We further introduce fidelity benchmarks that quantify the relative strength of different sources of Markovian and non-Markovian noise. As an application of our method, we perform a comparative theoretical and experimental analysis of silicon spin qubits. We first develop a detailed noise model that accounts for the dominant sources of noise and validate the model against experimental data. Applying our framework for time-correlated QPT, we find that the number of independent parameters needed to characterize one and two-qubit gates can be compressed by 10x and 100x, respectively, when compared to the fully generic case. These compressions reduce the amount of tomographic measurements needed in experiment, while also significantly speeding up numerical simulations of noisy quantum circuit dynamics compared to time-dependent Hamiltonian simulation. Using this compressed noise model, we find good agreement between our theoretically predicted process fidelities and two qubit interleaved randomized benchmarking fidelities of 99.8% measured in recent experiments on silicon spin qubits. More broadly, our formalism can be directly extended to develop efficient and scalable tuning protocols for high-fidelity control of large-arrays of quantum devices with non-Markovian noise.

1 aGullans, Michael1 aCaranti, M.1 aMills, A., R.1 aPetta, J., R. uhttps://arxiv.org/abs/2307.1443201495nas a2200181 4500008004100000245008500041210006900126260001400195490000800209520092100217100001901138700002101157700002701178700002301205700002001228700002801248856003701276 2023 eng d00aCritical phase and spin sharpening in SU(2)-symmetric monitored quantum circuits0 aCritical phase and spin sharpening in SU2symmetric monitored qua c8/17/20230 v1083 a

Monitored quantum circuits exhibit entanglement transitions at certain measurement rates. Such a transition separates phases characterized by how much information an observer can learn from the measurement outcomes. We study SU(2)-symmetric monitored quantum circuits, using exact numerics and a mapping onto an effective statistical-mechanics model. Due to the symmetry's non-Abelian nature, measuring qubit pairs allows for nontrivial entanglement scaling even in the measurement-only limit. We find a transition between a volume-law entangled phase and a critical phase whose diffusive purification dynamics emerge from the non-Abelian symmetry. Additionally, we numerically identify a "spin-sharpening transition." On one side is a phase in which the measurements can efficiently identify the system's total spin quantum number; on the other side is a phase in which measurements cannot.

1 aMajidy, Shayan1 aAgrawal, Utkarsh1 aGopalakrishnan, Sarang1 aPotter, Andrew, C.1 aVasseur, Romain1 aHalpern, Nicole, Yunger uhttps://arxiv.org/abs/2305.1335601740nas 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/2308.1224602278nas a2200205 4500008004100000245008100041210006900122260001400191520163500205100001701840700002101857700002801878700002001906700001501926700002301941700002201964700002501986700002402011856003702035 2023 eng d00aLattice quantum chromodynamics at large isospin density: 6144 pions in a box0 aLattice quantum chromodynamics at large isospin density 6144 pio c7/27/20233 a

We present an algorithm to compute correlation functions for systems with the quantum numbers of many identical mesons from lattice quantum chromodynamics (QCD). The algorithm is numerically stable and allows for the computation of n-pion correlation functions for n∈{1,…,N} using a single N×N matrix decomposition, improving on previous algorithms. We apply the algorithm to calculations of correlation functions with up to 6144 π+s using two ensembles of gauge field configurations generated with quark masses corresponding to a pion mass mπ=170 MeV and spacetime volumes of (4.43×8.8) fm4 and (5.83×11.6) fm4. We also discuss statistical techniques for the analysis of such systems, in which the correlation functions vary over many orders of magnitude. In particular, we observe that the many-pion correlation functions are well approximated by log-normal distributions, allowing the extraction of the energies of these systems. Using these energies, the large-isospin-density, zero-baryon-density region of the QCD phase diagram is explored. A peak is observed in the energy density at an isospin chemical potential μI∼1.5mπ, signalling the transition into a Bose-Einstein condensed phase. The isentropic speed of sound in the medium is seen to exceed the ideal-gas (conformal) limit (c2s≤1/3) over a wide range of chemical potential before falling towards the asymptotic expectation at μI∼15mπ. These, and other thermodynamic observables, indicate that the isospin chemical potential must be large for the system to be well described by an ideal gas or perturbative QCD.

1 aAbbott, Ryan1 aDetmold, William1 aRomero-López, Fernando1 aDavoudi, Zohreh1 aIlla, Marc1 aParreño, Assumpta1 aPerry, Robert, J.1 aShanahan, Phiala, E.1 aWagman, Michael, L. uhttps://arxiv.org/abs/2307.1501402618nas 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/2312.1616601834nas a2200217 4500008004100000245007700041210006900118260001400187520122500201100001101426700001301437700001601450700001501466700001201481700001401493700001501507700002501522700001701547700001501564856003701579 2023 eng d00aNon-equilibrium critical scaling and universality in a quantum simulator0 aNonequilibrium critical scaling and universality in a quantum si c9/19/20233 a

Universality and scaling laws are hallmarks of equilibrium phase transitions and critical phenomena. However, extending these concepts to non-equilibrium systems is an outstanding challenge. Despite recent progress in the study of dynamical phases, the universality classes and scaling laws for non-equilibrium phenomena are far less understood than those in equilibrium. In this work, using a trapped-ion quantum simulator with single-ion resolution, we investigate the non-equilibrium nature of critical fluctuations following a quantum quench to the critical point. We probe the scaling of spin fluctuations after a series of quenches to the critical Hamiltonian of a long-range Ising model. With systems of up to 50 spins, we show that the amplitude and timescale of the post-quench fluctuations scale with system size with distinct universal critical exponents. While a generic quench can lead to thermal critical behaviour, we find that a second quench from one critical state to another (i.e. a double quench) results in critical behaviour that does not have an equilibrium counterpart. Our results demonstrate the ability of quantum simulators to explore universal scaling beyond the equilibrium paradigm.

1 aDe, A.1 aCook, P.1 aCollins, K.1 aMorong, W.1 aPaz, D.1 aTitum, P.1 aPagano, G.1 aGorshkov, Alexey, V.1 aMaghrebi, M.1 aMonroe, C. uhttps://arxiv.org/abs/2309.1085605435nas 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/2312.0973302012nas a2200145 4500008004100000245008500041210006900126260001300195520155500208100001801763700001701781700001601798700001501814856003701829 2023 eng d00aSimuQ: A Domain-Specific Language For Quantum Simulation With Analog Compilation0 aSimuQ A DomainSpecific Language For Quantum Simulation With Anal c3/5/20233 a

Hamiltonian simulation is one of the most promising applications of quantum computing. Recent experimental results suggest that continuous-time analog quantum simulation would be advantageous over gate-based digital quantum simulation in the Noisy Intermediate-Size Quantum (NISQ) machine era. However, programming such analog quantum simulators is much more challenging due to the lack of a unified interface between hardware and software, and the only few known examples are all hardware-specific. In this paper, we design and implement SimuQ, the first domain-specific language for Hamiltonian simulation that supports pulse-level compilation to heterogeneous analog quantum simulators. Specifically, in SimuQ, front-end users will specify the target Hamiltonian evolution with a Hamiltonian modeling language, and the programmability of analog simulators is specified through a new abstraction called the abstract analog instruction set by hardware providers. Through a solver-based compilation, SimuQ will generate the pulse-level instruction schedule on the target analog simulator for the desired Hamiltonian evolution, which has been demonstrated on pulse-controlled superconducting (Qiskit Pulse) and neutral-atom (QuEra Bloqade) quantum systems, as well as on normal circuit-based digital quantum machines. Moreover, we also demonstrate the advantage of analog compilation over digital compilation on IBM machines, the use of SimuQ for resource estimation for hypothetical machines, and a scalability test of SimuQ's compilation.

1 aPeng, Yuxiang1 aYoung, Jacob1 aLiu, Pengyu1 aWu, Xiaodi uhttps://arxiv.org/abs/2303.0277502547nas a2200205 4500008004100000245006500041210006400106260001400170490000900184520193000193653002702123653003102150100002002181700002202201700002302223700002202246700001702268700001902285856003702304 2023 eng d00aTime-energy uncertainty relation for noisy quantum metrology0 aTimeenergy uncertainty relation for noisy quantum metrology c12/5/20230 v4(4)3 a

Detection of weak forces and precise measurement of time are two of the many applications of quantum metrology to science and technology. We consider a quantum system initialized in a pure state and whose evolution is goverened by a Hamiltonian H; a measurement can later estimate the time t for which the system has evolved. In this work, we introduce and study a fundamental trade-off which relates the amount by which noise reduces the accuracy of a quantum clock to the amount of information about the energy of the clock that leaks to the environment. Specifically, we consider an idealized scenario in which Alice prepares an initial pure state of the clock, allows the clock to evolve for a time t that is not precisely known, and then transmits the clock through a noisy channel to Bob. The environment (Eve) receives any information that is lost. We prove that Bob's loss of quantum Fisher information (QFI) about t is equal to Eve's gain of QFI about a complementary energy parameter. We also prove a more general trade-off that applies when Bob and Eve wish to estimate the values of parameters associated with two non-commuting observables. We derive the necessary and sufficient conditions for the accuracy of the clock to be unaffected by the noise. These are a subset of the Knill-Laflamme error-correction conditions; states satisfying these conditions are said to form a metrological code. We provide a scheme to construct metrological codes in the stabilizer formalism. We show that there are metrological codes that cannot be written as a quantum error-correcting code with similar distance in which the Hamiltonian acts as a logical operator, potentially offering new schemes for constructing states that do not lose any sensitivity upon application of a noisy channel. We discuss applications of our results to sensing using a many-body state subject to erasure or amplitude-damping noise.

10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aFaist, Philippe1 aWoods, Mischa, P.1 aAlbert, Victor, V.1 aRenes, Joseph, M.1 aEisert, Jens1 aPreskill, John uhttps://arxiv.org/abs/2207.1370701459nas a2200145 4500008004100000245005100041210004300092260001400135520105500149100001901204700001401223700002301237700001601260856003701276 2023 eng d00aOn the Two-sided Permutation Inversion Problem0 aTwosided Permutation Inversion Problem c6/23/20233 a

In the permutation inversion problem, the task is to find the preimage of some challenge value, given oracle access to the permutation. This is a fundamental problem in query complexity, and appears in many contexts, particularly cryptography. In this work, we examine the setting in which the oracle allows for quantum queries to both the forward and the inverse direction of the permutation -- except that the challenge value cannot be submitted to the latter. Within that setting, we consider two options for the inversion algorithm: whether it can get quantum advice about the permutation, and whether it must produce the entire preimage (search) or only the first bit (decision). We prove several theorems connecting the hardness of the resulting variations of the inversion problem, and establish a number of lower bounds. Our results indicate that, perhaps surprisingly, the inversion problem does not become significantly easier when the adversary is granted oracle access to the inverse, provided it cannot query the challenge itself.

1 aAlagic, Gorjan1 aBai, Chen1 aPoremba, Alexander1 aShi, Kaiyan uhttps://arxiv.org/abs/2306.1372902171nas a2200289 4500008004100000245007500041210006900116260001400185520131000199100002201509700002001531700002001551700002401571700002401595700002001619700001901639700002001658700002901678700001801707700002001725700001801745700002301763700001701786700001701803700002401820856003701844 2023 eng d00aVerifiable measurement-based quantum random sampling with trapped ions0 aVerifiable measurementbased quantum random sampling with trapped c7/26/20233 a

Quantum computers are now on the brink of outperforming their classical counterparts. One way to demonstrate the advantage of quantum computation is through quantum random sampling performed on quantum computing devices. However, existing tools for verifying that a quantum device indeed performed the classically intractable sampling task are either impractical or not scalable to the quantum advantage regime. The verification problem thus remains an outstanding challenge. Here, we experimentally demonstrate efficiently verifiable quantum random sampling in the measurement-based model of quantum computation on a trapped-ion quantum processor. We create random cluster states, which are at the heart of measurement-based computing, up to a size of 4 x 4 qubits. Moreover, by exploiting the structure of these states, we are able to recycle qubits during the computation to sample from entangled cluster states that are larger than the qubit register. We then efficiently estimate the fidelity to verify the prepared states--in single instances and on average--and compare our results to cross-entropy benchmarking. Finally, we study the effect of experimental noise on the certificates. Our results and techniques provide a feasible path toward a verified demonstration of a quantum advantage.

1 aRingbauer, Martin1 aHinsche, Marcel1 aFeldker, Thomas1 aFaehrmann, Paul, K.1 aBermejo-Vega, Juani1 aEdmunds, Claire1 aPostler, Lukas1 aStricker, Roman1 aMarciniak, Christian, D.1 aMeth, Michael1 aPogorelov, Ivan1 aBlatt, Rainer1 aSchindler, Philipp1 aEisert, Jens1 aMonz, Thomas1 aHangleiter, Dominik uhttps://arxiv.org/abs/2307.1442402045nas a2200337 4500008004100000245009200041210006900133260001500202300001100217490000800228520091000236100001301146700001301159700001401172700001701186700002001203700001401223700001401237700001601251700001901267700001801286700001701304700002101321700001501342700002001357700001701377700001701394700001801411700001801429856026001447 2022 eng d00aClosing the Locality and Detection Loopholes in Multiparticle Entanglement Self-Testing0 aClosing the Locality and Detection Loopholes in Multiparticle En c06/23/2022 a2504010 v1283 a

First proposed by Mayers and Yao, self-testing provides a certification method to infer the underlying physics of quantum experiments in a black-box scenario. Numerous demonstrations have been reported to self-test various types of entangled states. However, all the multiparticle self-testing experiments reported so far suffer from both detection and locality loopholes. Here, we report the first experimental realization of multiparticle entanglement self-testing closing the locality loophole in a photonic system, and the detection loophole in a superconducting system, respectively. We certify three-party and four-party GHZ states with at least 0.84 (1) and 0.86 (3) fidelities in a device-independent way. These results can be viewed as a meaningful advance in multiparticle loophole-free self-testing, and also significant progress on the foundations of quantum entanglement certification.

1 aWu, Dian1 aZhao, Qi1 aWang, Can1 aHuang, Liang1 aJiang, Yang-Fan1 aBai, Bing1 aZhou, You1 aGu, Xue-Mei1 aLiu, Feng-Ming1 aMao, Ying-Qiu1 aSun, Qi-Chao1 aChen, Ming-Cheng1 aZhang, Jun1 aPeng, Cheng-Zhi1 aZhu, Xiao-Bo1 aZhang, Qiang1 aLu, Chao-Yang1 aPan, Jian-Wei uhttps://www.researchgate.net/profile/Dian-Wu/publication/361497881_Closing_the_Locality_and_Detection_Loopholes_in_Multiparticle_Entanglement_Self-Testing/links/62b55a8c1010dc02cc57530c/Closing-the-Locality-and-Detection-Loopholes-in-Multiparticle-Entangl01745nas a2200181 4500008004100000245009400041210006900135260001500204300001100219490000800230520117000238100002401408700001901432700002801451700002601479700002101505856003701526 2022 eng d00aExperimentally Measuring Rolling and Sliding in Three-Dimensional Dense Granular Packings0 aExperimentally Measuring Rolling and Sliding in ThreeDimensional c06/18/2022 a0480010 v1293 a

We experimentally measure a three-dimensional (3D) granular system’s reversibility under cyclic compression. We image the grains using a refractive-index-matched fluid, then analyze the images using the artificial intelligence of variational autoencoders. These techniques allow us to track all the grains’ translations and 3D rotations with accuracy sufficient to infer sliding and rolling displacements. Our observations reveal unique roles played by 3D rotational motions in granular flows. We find that rotations and contact-point motion dominate the dynamics in the bulk, far from the perturbation’s source. Furthermore, we determine that 3D rotations are irreversible under cyclic compression. Consequently, contact-point sliding, which is dissipative, accumulates throughout the cycle. Using numerical simulations whose accuracy our experiment supports, we discover that much of the dissipation occurs in the bulk, where grains rotate more than they translate. Our observations suggest that the analysis of 3D rotations is needed for understanding granular materials’ unique and powerful ability to absorb and dissipate energy.

1 aBenson, Zackery, A.1 aPeshkov, Anton1 aHalpern, Nicole, Yunger1 aRichardson, Derek, C.1 aLosert, Wolfgang uhttps://arxiv.org/abs/2108.1197502469nas 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/2301.0006201641nas a2200181 4500008004100000245008700041210006900128260001400197520106300211100001801274700002301292700002101315700002001336700002701356700002001383700001901403856003701422 2022 eng d00aInfinite-randomness criticality in monitored quantum dynamics with static disorder0 aInfiniterandomness criticality in monitored quantum dynamics wit c5/27/20223 a

We consider a model of monitored quantum dynamics with quenched spatial randomness: specifically, random quantum circuits with spatially varying measurement rates. These circuits undergo a measurement-induced phase transition (MIPT) in their entanglement structure, but the nature of the critical point differs drastically from the case with constant measurement rate. In particular, at the critical measurement rate, we find that the entanglement of a subsystem of size ℓ scales as S∼ℓ√; moreover, the dynamical critical exponent z=∞. The MIPT is flanked by Griffiths phases with continuously varying dynamical exponents. We argue for this infinite-randomness scenario on general grounds and present numerical evidence that it captures some features of the universal critical properties of MIPT using large-scale simulations of Clifford circuits. These findings demonstrate that the relevance and irrelevance of perturbations to the MIPT can naturally be interpreted using a powerful heuristic known as the Harris criterion. 

1 aZabalo, Aidan1 aWilson, Justin, H.1 aGullans, Michael1 aVasseur, Romain1 aGopalakrishnan, Sarang1 aHuse, David, A.1 aPixley, J., H. uhttps://arxiv.org/abs/2205.1400201919nas a2200193 4500008004100000245005700041210005600098260001400154520133700168653002701505653003101532100001601563700002101579700002201600700002701622700001901649700002001668856003701688 2022 eng d00aMulti-Angle QAOA Does Not Always Need All Its Angles0 aMultiAngle QAOA Does Not Always Need All Its Angles c9/23/20223 a

Introducing additional tunable parameters to quantum circuits is a powerful way of improving performance without increasing hardware requirements. A recently introduced multi-angle extension of the quantum approximate optimization algorithm (ma-QAOA) significantly improves the solution from QAOA by allowing the parameters for each term in the Hamiltonian to vary independently. However, prior results suggest that there is considerable redundancy in parameters, the removal of which would reduce the cost of parameter optimization. In this work, we show numerically that problem symmetries can be used to reduce the number of parameters used by ma-QAOA without decreasing the solution quality. We study MaxCut on all 7,565 connected, non-isomorphic 8-node graphs with a non-trivial symmetry group and show numerically that in 67.4\% of these graphs, symmetry can be used to reduce the number of parameters with no decrease in the objective, with the average ratio of parameters reduced by 28.1\%. Moreover, we show that in 35.9\% of the graphs this can be achieved by simply using the largest symmetry. For the graphs where reducing the number of parameters leads to a decrease in the objective, the largest symmetry can be used to reduce the parameter count by 37.1\% at the cost of only a 6.1\% decrease in the objective.

10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aShi, Kaiyan1 aHerrman, Rebekah1 aShaydulin, Ruslan1 aChakrabarti, Shouvanik1 aPistoia, Marco1 aLarson, Jeffrey uhttps://arxiv.org/abs/2209.1183902003nas a2200205 4500008004100000245008600041210006900127260001300196300001100209490000800220520132800228100002501556700002001581700003501601700002101636700002401657700002801681700002801709856006001737 2022 eng d00aNegative Quasiprobabilities Enhance Phase Estimation in Quantum-Optics Experiment0 aNegative Quasiprobabilities Enhance Phase Estimation in QuantumO c6/2/2022 a2205040 v1283 a

Operator noncommutation, a hallmark of quantum theory, limits measurement precision, according to uncertainty principles. Wielded correctly, though, noncommutation can boost precision. A recent foundational result relates a metrological advantage with negative quasiprobabilities—quantum extensions of probabilities—engendered by noncommuting operators. We crystallize the relationship in an equation that we prove theoretically and observe experimentally. Our proof-of-principle optical experiment features a filtering technique that we term partially postselected amplification (PPA). Using PPA, we measure a wave plate’s birefringent phase. PPA amplifies, by over two orders of magnitude, the information obtained about the phase per detected photon. In principle, PPA can boost the information obtained from the average filtered photon by an arbitrarily large factor. The filter’s amplification of systematic errors, we find, bounds the theoretically unlimited advantage in practice. PPA can facilitate any phase measurement and mitigates challenges that scale with trial number, such as proportional noise and detector saturation. By quantifying PPA’s metrological advantage with quasiprobabilities, we reveal deep connections between quantum foundations and precision measurement.

1 aLupu-Gladstein, Noah1 aYilmaz, Batuhan1 aArvidsson-Shukur, David, R. M.1 aBrodutch, Aharon1 aPang, Arthur, O. T.1 aSteinberg, Aephraim, M.1 aHalpern, Nicole, Yunger uhttps://link.aps.org/doi/10.1103/PhysRevLett.128.22050401066nas 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/2205.1005801727nas a2200205 4500008004100000245008700041210006900128260001400197490000800211520109000219100001801309700002101327700002301348700002001371700002701391700002701418700002001445700001901465856003701484 2022 eng d00aOperator Scaling Dimensions and Multifractality at Measurement-Induced Transitions0 aOperator Scaling Dimensions and Multifractality at MeasurementIn c2/11/20220 v1283 a

Repeated local measurements of quantum many body systems can induce a phase transition in their entanglement structure. These measurement-induced phase transitions (MIPTs) have been studied for various types of dynamics, yet most cases yield quantitatively similar values of the critical exponents, making it unclear if there is only one underlying universality class. Here, we directly probe the properties of the conformal field theories governing these MIPTs using a numerical transfer-matrix method, which allows us to extract the effective central charge, as well as the first few low-lying scaling dimensions of operators at these critical points. Our results provide convincing evidence that the generic and Clifford MIPTs for qubits lie in different universality classes and that both are distinct from the percolation transition for qudits in the limit of large onsite Hilbert space dimension. For the generic case, we find strong evidence of multifractal scaling of correlation functions at the critical point, reflected in a continuous spectrum of scaling dimensions.

1 aZabalo, Aidan1 aGullans, Michael1 aWilson, Justin, H.1 aVasseur, Romain1 aLudwig, Andreas, W. W.1 aGopalakrishnan, Sarang1 aHuse, David, A.1 aPixley, J., H. uhttps://arxiv.org/abs/2107.0339302380nas a2200181 4500008004100000245007100041210006900112260001400181300000800195490000600203520186000209100001302069700002302082700002402105700001902129700001302148856003702161 2022 eng d00aProvably accurate simulation of gauge theories and bosonic systems0 aProvably accurate simulation of gauge theories and bosonic syste c9/20/2022 a8160 v63 a

Quantum many-body systems involving bosonic modes or gauge fields have infinite-dimensional local Hilbert spaces which must be truncated to perform simulations of real-time dynamics on classical or quantum computers. To analyze the truncation error, we develop methods for bounding the rate of growth of local quantum numbers such as the occupation number of a mode at a lattice site, or the electric field at a lattice link. Our approach applies to various models of bosons interacting with spins or fermions, and also to both abelian and non-abelian gauge theories. We show that if states in these models are truncated by imposing an upper limit Λ on each local quantum number, and if the initial state has low local quantum numbers, then an error at most ϵ can be achieved by choosing Λ to scale polylogarithmically with ϵ−1, an exponential improvement over previous bounds based on energy conservation. For the Hubbard-Holstein model, we numerically compute a bound on Λ that achieves accuracy ϵ, obtaining significantly improved estimates in various parameter regimes. We also establish a criterion for truncating the Hamiltonian with a provable guarantee on the accuracy of time evolution. Building on that result, we formulate quantum algorithms for dynamical simulation of lattice gauge theories and of models with bosonic modes; the gate complexity depends almost linearly on spacetime volume in the former case, and almost quadratically on time in the latter case. We establish a lower bound showing that there are systems involving bosons for which this quadratic scaling with time cannot be improved. By applying our result on the truncation error in time evolution, we also prove that spectrally isolated energy eigenstates can be approximated with accuracy ϵ by truncating local quantum numbers at Λ=polylog(ϵ−1).

1 aTong, Yu1 aAlbert, Victor, V.1 aMcClean, Jarrod, R.1 aPreskill, John1 aSu, Yuan uhttps://arxiv.org/abs/2110.0694201744nas 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/2106.1262702845nas 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/2204.0338101949nas a2200193 4500008004100000245005300041210005200094260001500146520133800161653004301499653002701542653003101569653002901600653003101629100001801660700002001678700002001698856003701718 2022 eng d00aSample-optimal classical shadows for pure states0 aSampleoptimal classical shadows for pure states c11/21/20223 a

We consider the classical shadows task for pure states in the setting of both joint and independent measurements. The task is to measure few copies of an unknown pure state ρ in order to learn a classical description which suffices to later estimate expectation values of observables. Specifically, the goal is to approximate Tr(Oρ) for any Hermitian observable O to within additive error ϵ provided Tr(O2)≤B and ∥O∥=1. Our main result applies to the joint measurement setting, where we show Θ~(B−−√ϵ−1+ϵ−2) samples of ρ are necessary and sufficient to succeed with high probability. The upper bound is a quadratic improvement on the previous best sample complexity known for this problem. For the lower bound, we see that the bottleneck is not how fast we can learn the state but rather how much any classical description of ρ can be compressed for observable estimation. In the independent measurement setting, we show that O(Bd−−−√ϵ−1+ϵ−2) samples suffice. Notably, this implies that the random Clifford measurements algorithm of Huang, Kueng, and Preskill, which is sample-optimal for mixed states, is not optimal for pure states. Interestingly, our result also uses the same random Clifford measurements but employs a different estimator.

10aFOS: Computer and information sciences10aFOS: Physical sciences10aInformation Theory (cs.IT)10aMachine Learning (cs.LG)10aQuantum Physics (quant-ph)1 aGrier, Daniel1 aPashayan, Hakop1 aSchaeffer, Luke uhttps://arxiv.org/abs/2211.1181001649nas a2200193 4500008004100000245007500041210006900116260001300185490000600198520110000204100001401304700001301318700001701331700001301348700002101361700001801382700001801400856003701418 2022 eng d00aA scheme to create and verify scalable entanglement in optical lattice0 ascheme to create and verify scalable entanglement in optical lat c9/4/20220 v83 a

To achieve scalable quantum information processing, great efforts have been devoted to the creation of large-scale entangled states in various physical systems. Ultracold atom in optical lattice is considered as one of the promising platforms due to its feasible initialization and parallel manipulation. In this work, we propose an efficient scheme to generate and characterize global entanglement in the optical lattice. With only two-layer quantum circuits, the generation utilizes two-qubit entangling gates based on the superexchange interaction in double wells. The parallelism of these operations enables the generation to be fast and scalable. To verify the entanglement of this non-stabilizer state, we mainly design three complementary detection protocols which are less resource-consuming compared to the full tomography. In particular, one just needs two homogenous local measurement settings to identify the entanglement property. Our entanglement generation and verification protocols provide the foundation for the further quantum information processing in optical lattice.

1 aZhou, You1 aXiao, Bo1 aDa Li, Meng-1 aZhao, Qi1 aYuan, Zhen-Sheng1 aMa, Xiongfeng1 aPan, Jian-Wei uhttps://arxiv.org/abs/2209.0153101392nas a2200229 4500008004100000245008100041210006900122260001400191520061400205653002700819653005300846653004900899653003100948100001900979700001700998700001901015700002001034700002401054700002501078700002201103856003701125 2022 eng d00aSnowmass 2021 White Paper: Tabletop experiments for infrared quantum gravity0 aSnowmass 2021 White Paper Tabletop experiments for infrared quan c3/22/20223 a

Progress in the quantum readout and control of mechanical devices from single atoms to large masses may enable a first generation of experiments probing the gravitational interaction in the quantum regime, conceivably within the next decade. In this Snowmass whitepaper, we briefly outline the possibilities and challenges facing the realization of these experiments. In particular, we emphasize the need for detailed theories of modifications to the usual effective QFT of gravitons in the infrared regime E/L3≪mPl/ℓ3Pl in which these experiments operate, and relations to possible UV completions.

10aFOS: Physical sciences10aGeneral Relativity and Quantum Cosmology (gr-qc)10aHigh Energy Physics - Phenomenology (hep-ph)10aQuantum Physics (quant-ph)1 aCarney, Daniel1 aChen, Yanbei1 aGeraci, Andrew1 aMüller, Holger1 aPanda, Cristian, D.1 aStamp, Philip, C. E.1 aTaylor, Jacob, M. uhttps://arxiv.org/abs/2203.1184602149nas a2200457 4500008004100000245005300041210005200094260001400146520077300160653005700933653002700990653004601017653004901063100003401112700002201146700002101168700001901189700001901208700002201227700001901249700002201268700002501290700001901315700001701334700001901351700002101370700002101391700001801412700001401430700002701444700002201471700002201493700001601515700002001531700001701551700002501568700002201593700001401615700002501629856003701654 2022 eng d00aSnowmass 2021 White Paper: The Windchime Project0 aSnowmass 2021 White Paper The Windchime Project c3/14/20223 a

The absence of clear signals from particle dark matter in direct detection experiments motivates new approaches in disparate regions of viable parameter space. In this Snowmass white paper, we outline the Windchime project, a program to build a large array of quantum-enhanced mechanical sensors. The ultimate aim is to build a detector capable of searching for Planck mass-scale dark matter purely through its gravitational coupling to ordinary matter. In the shorter term, we aim to search for a number of other physics targets, especially some ultralight dark matter candidates. Here, we discuss the basic design, open R&D challenges and opportunities, current experimental efforts, and both short- and long-term physics targets of the Windchime project.

10aCosmology and Nongalactic Astrophysics (astro-ph.CO)10aFOS: Physical sciences10aHigh Energy Physics - Experiment (hep-ex)10aHigh Energy Physics - Phenomenology (hep-ph)1 aCollaboration, The, Windchime1 aAttanasio, Alaina1 aBhave, Sunil, A.1 aBlanco, Carlos1 aCarney, Daniel1 aDemarteau, Marcel1 aElshimy, Bahaa1 aFebbraro, Michael1 aFeldman, Matthew, A.1 aGhosh, Sohitri1 aHickin, Abby1 aHong, Seongjin1 aLang, Rafael, F.1 aLawrie, Benjamin1 aLi, Shengchao1 aLiu, Zhen1 aMaldonado, Juan, P. A.1 aMarvinney, Claire1 aOo, Hein, Zay Yar1 aPai, Yun-Yi1 aPooser, Raphael1 aQin, Juehang1 aSparmann, Tobias, J.1 aTaylor, Jacob, M.1 aTian, Hao1 aTunnell, Christopher uhttps://arxiv.org/abs/2203.0724202774nas 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-process02392nas a2200181 4500008004100000245006700041210006600108260001400174520183100188653002702019653003102046100001602077700001802093700002702111700002002138700001502158856003702173 2022 eng d00aTailoring three-dimensional topological codes for biased noise0 aTailoring threedimensional topological codes for biased noise c11/3/20223 a

Tailored topological stabilizer codes in two dimensions have been shown to exhibit high storage threshold error rates and improved subthreshold performance under biased Pauli noise. Three-dimensional (3D) topological codes can allow for several advantages including a transversal implementation of non-Clifford logical gates, single-shot decoding strategies, parallelized decoding in the case of fracton codes as well as construction of fractal lattice codes. Motivated by this, we tailor 3D topological codes for enhanced storage performance under biased Pauli noise. We present Clifford deformations of various 3D topological codes, such that they exhibit a threshold error rate of 50% under infinitely biased Pauli noise. Our examples include the 3D surface code on the cubic lattice, the 3D surface code on a checkerboard lattice that lends itself to a subsystem code with a single-shot decoder, the 3D color code, as well as fracton models such as the X-cube model, the Sierpinski model and the Haah code. We use the belief propagation with ordered statistics decoder (BP-OSD) to study threshold error rates at finite bias. We also present a rotated layout for the 3D surface code, which uses roughly half the number of physical qubits for the same code distance under appropriate boundary conditions. Imposing coprime periodic dimensions on this rotated layout leads to logical operators of weight O(n) at infinite bias and a corresponding exp[−O(n)] subthreshold scaling of the logical failure rate, where n is the number of physical qubits in the code. Even though this scaling is unstable due to the existence of logical representations with O(1) low-rate Pauli errors, the number of such representations scales only polynomially for the Clifford-deformed code, leading to an enhanced effective distance.

10aFOS: Physical sciences10aQuantum Physics (quant-ph)1 aHuang, Eric1 aPesah, Arthur1 aChubb, Christopher, T.1 aVasmer, Michael1 aDua, Arpit uhttps://arxiv.org/abs/2211.0211601692nas a2200133 4500008004100000245007800041210006900119260001500188520126500203100001801468700002001486700001501506856003701521 2021 eng d00aAlgebraic Reasoning of Quantum Programs via Non-Idempotent Kleene Algebra0 aAlgebraic Reasoning of Quantum Programs via NonIdempotent Kleene c10/13/20213 a

We investigate the algebraic reasoning of quantum programs inspired by the success of classical program analysis based on Kleene algebra. One prominent example of such is the famous Kleene Algebra with Tests (KAT), which has furnished both theoretical insights and practical tools. The succinctness of algebraic reasoning would be especially desirable for scalable analysis of quantum programs, given the involvement of exponential-size matrices in most of the existing methods. A few key features of KAT including the idempotent law and the nice properties of classical tests, however, fail to hold in the context of quantum programs due to their unique quantum features, especially in branching. We propose the Non-idempotent Kleena Algebra (NKA) as a natural alternative and identify complete and sound semantic models for NKA as well as their appropriate quantum interpretations. In light of applications of KAT, we are able to demonstrate algebraic proofs in NKA of quantum compiler optimization and the normal form of quantum while-programs. Moreover, we extend NKA with Tests (i.e., NKAT), where tests model quantum predicates following the rules of effect algebra, and illustrate how to encode propositional quantum Hoare logic as NKAT theorems.

1 aPeng, Yuxiang1 aYing, Mingsheng1 aWu, Xiaodi uhttps://arxiv.org/abs/2110.0701801979nas a2200277 4500008004100000245007600041210006900117260001400186520117400200100001301374700001801387700002101405700002901426700001601455700002001471700001801491700001501509700002001524700002301544700001801567700002101585700001801606700002101624700001901645856003701664 2021 eng d00aChiral transport of hot carriers in graphene in the quantum Hall regime0 aChiral transport of hot carriers in graphene in the quantum Hall c10/3/20213 a

Photocurrent (PC) measurements can reveal the relaxation dynamics of photo-excited hot carriers beyond the linear response of conventional transport experiments, a regime important for carrier multiplication. In graphene subject to a magnetic field, PC measurements are able to probe the existence of Landau levels with different edge chiralities which is exclusive to relativistic electron systems. Here, we report the accurate measurement of PC in graphene in the quantum Hall regime. Prominent PC oscillations as a function of gate voltage on samples' edges are observed. These oscillation amplitudes form an envelope which depends on the strength of the magnetic field, as does the PCs' power dependence and their saturation behavior. We explain these experimental observations through a model using optical Bloch equations, incorporating relaxations through acoustic-, optical- phonons and Coulomb interactions. The simulated PC agrees with our experimental results, leading to a unified understanding of the chiral PC in graphene at various magnetic field strengths, and providing hints for the occurrence of a sizable carrier multiplication. 

1 aCao, Bin1 aGrass, Tobias1 aGazzano, Olivier1 aPatel, Kishan, Ashokbhai1 aHu, Jiuning1 aMüller, Markus1 aHuber, Tobias1 aAnzi, Luca1 aWatanabe, Kenji1 aTaniguchi, Takashi1 aNewell, David1 aGullans, Michael1 aSordan, Roman1 aHafezi, Mohammad1 aSolomon, Glenn uhttps://arxiv.org/abs/2110.0107902114nas a2200181 4500008004100000245005300041210005300094260001500147490000600162520160200168100002201770700002601792700001801818700001801836700001901854700002201873856003701895 2021 eng d00aEfficient quantum measurement of Pauli operators0 aEfficient quantum measurement of Pauli operators c01/19/20210 v53 a

Estimating the expectation value of an observable is a fundamental task in quantum computation. Unfortunately, it is often impossible to obtain such estimates directly, as the computer is restricted to measuring in a fixed computational basis. One common solution splits the observable into a weighted sum of Pauli operators and measures each separately, at the cost of many measurements. An improved version first groups mutually commuting Pauli operators together and then measures all operators within each group simultaneously. The effectiveness of this depends on two factors. First, to enable simultaneous measurement, circuits are required to rotate each group to the computational basis. In our work, we present two efficient circuit constructions that suitably rotate any group of k commuting n-qubit Pauli operators using at most kn−k(k+1)/2 and O(kn/logk) two-qubit gates respectively. Second, metrics that justifiably measure the effectiveness of a grouping are required. In our work, we propose two natural metrics that operate under the assumption that measurements are distributed optimally among groups. Motivated by our new metrics, we introduce SORTED INSERTION, a grouping strategy that is explicitly aware of the weighting of each Pauli operator in the observable. Our methods are numerically illustrated in the context of the Variational Quantum Eigensolver, where the observables in question are molecular Hamiltonians. As measured by our metrics, SORTED INSERTION outperforms four conventional greedy colouring algorithms that seek the minimum number of groups.

1 aCrawford, Ophelia1 avan Straaten, Barnaby1 aWang, Daochen1 aParks, Thomas1 aCampbell, Earl1 aBrierley, Stephen uhttps://arxiv.org/abs/1908.0694200984nas a2200133 4500008004100000245005500041210005100096260001400147520059000161100002600751700001700777700001900794856003700813 2021 eng d00aAn explicit vector algorithm for high-girth MaxCut0 aexplicit vector algorithm for highgirth MaxCut c8/27/20213 a

We give an approximation algorithm for MaxCut and provide guarantees on the average fraction of edges cut on d-regular graphs of girth ≥2k. For every d≥3 and k≥4, our approximation guarantees are better than those of all other classical and quantum algorithms known to the authors. Our algorithm constructs an explicit vector solution to the standard semidefinite relaxation of MaxCut and applies hyperplane rounding. It may be viewed as a simplification of the previously best known technique, which approximates Gaussian wave processes on the infinite d-regular tree.

1 aThompson, Jessica, K.1 aParekh, Ojas1 aMarwaha, Kunal uhttps://arxiv.org/abs/2108.1247701304nas a2200133 4500008004100000245010100041210006900142260001400211520085700225100001701082700001901099700001501118856003701133 2021 eng d00aHyper-Invariant MERA: Approximate Holographic Error Correction Codes with Power-Law Correlations0 aHyperInvariant MERA Approximate Holographic Error Correction Cod c3/15/20213 a

We consider a class of holographic tensor networks that are efficiently contractible variational ansatze, manifestly (approximate) quantum error correction codes, and can support power-law correlation functions. In the case when the network consists of a single type of tensor that also acts as an erasure correction code, we show that it cannot be both locally contractible and sustain power-law correlation functions. Motivated by this no-go theorem, and the desirability of local contractibility for an efficient variational ansatz, we provide guidelines for constructing networks consisting of multiple types of tensors that can support power-law correlation. We also provide an explicit construction of one such network, which approximates the holographic HaPPY pentagon code in the limit where variational parameters are taken to be small.

1 aCao, ChunJun1 aPollack, Jason1 aWang, Yixu uhttps://arxiv.org/abs/2103.0863101981nas 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/2102.0725001237nas a2200253 4500008004100000245004100041210004100082260001300123520055200136100001900688700002400707700002100731700002000752700002700772700001800799700001600817700001700833700002000850700002100870700001900891700001300910700002300923856003700946 2021 eng d00aQuantum Machine Learning for Finance0 aQuantum Machine Learning for Finance c9/9/20213 a

Quantum computers are expected to surpass the computational capabilities of classical computers during this decade, and achieve disruptive impact on numerous industry sectors, particularly finance. In fact, finance is estimated to be the first industry sector to benefit from Quantum Computing not only in the medium and long terms, but even in the short term. This review paper presents the state of the art of quantum algorithms for financial applications, with particular focus to those use cases that can be solved via Machine Learning.

1 aPistoia, Marco1 aAhmad, Syed, Farhan1 aAjagekar, Akshay1 aButs, Alexander1 aChakrabarti, Shouvanik1 aHerman, Dylan1 aHu, Shaohan1 aJena, Andrew1 aMinssen, Pierre1 aNiroula, Pradeep1 aRattew, Arthur1 aSun, Yue1 aYalovetzky, Romina uhttps://arxiv.org/abs/2109.0429801478nas a2200277 4500008004100000245005400041210005300095260001400148300001100162490000800173520078100181100001300962700001300975700001600988700001901004700001401023700001801037700001401055700001601069700001401085700001101099700001701110700001801127700001801145856003701163 2021 eng d00aRobust Self-Testing of Multiparticle Entanglement0 aRobust SelfTesting of Multiparticle Entanglement c12/7/2021 a2305030 v1273 a

Quantum self-testing is a device-independent way to certify quantum states and measurements using only the input-output statistics, with minimal assumptions about the quantum devices. Due to the high demand on tolerable noise, however, experimental self-testing was limited to two-photon systems. Here, we demonstrate the first robust self-testing for multi-particle quantum entanglement. We prepare two examples of four-photon graph states, the Greenberger-Horne-Zeilinger (GHZ) states with a fidelity of 0.957(2) and the linear cluster states with a fidelity of 0.945(2). Based on the observed input-output statistics, we certify the genuine four-photon entanglement and further estimate their qualities with respect to realistic noise in a device-independent manner.

1 aWu, Dian1 aZhao, Qi1 aGu, Xue-Mei1 aZhong, Han-Sen1 aZhou, You1 aPeng, Li-Chao1 aQin, Jian1 aLuo, Yi-Han1 aChen, Kai1 aLi, Li1 aLe Liu, Nai-1 aLu, Chao-Yang1 aPan, Jian-Wei uhttps://arxiv.org/abs/2105.1029801449nas a2200169 4500008004100000245007200041210006900113260001500182520093700197100002301134700001701157700001601174700001501190700001801205700001901223856003701242 2021 eng d00aSpin chains, defects, and quantum wires for the quantum-double edge0 aSpin chains defects and quantum wires for the quantumdouble edge c11/23/20213 a

Non-Abelian defects that bind Majorana or parafermion zero modes are prominent in several topological quantum computation schemes. Underpinning their established understanding is the quantum Ising spin chain, which can be recast as a fermionic model or viewed as a standalone effective theory for the surface-code edge -- both of which harbor non-Abelian defects. We generalize these notions by deriving an effective Ising-like spin chain describing the edge of quantum-double topological order. Relating Majorana and parafermion modes to anyonic strings, we introduce quantum-double generalizations of non-Abelian defects. We develop a way to embed finite-group valued qunits into those valued in continuous groups. Using this embedding, we provide a continuum description of the spin chain and recast its non-interacting part as a quantum wire via addition of a Wess-Zumino-Novikov-Witten term and non-Abelian bosonization.

1 aAlbert, Victor, V.1 aAasen, David1 aXu, Wenqing1 aJi, Wenjie1 aAlicea, Jason1 aPreskill, John uhttps://arxiv.org/abs/2111.1209601359nas a2200157 4500008004100000245003200041210003200073260001400105520093200119100002001051700002001071700002701091700002201118700002401140856003701164 2021 eng d00aSynchronous Values of Games0 aSynchronous Values of Games c9/29/20213 a

We study synchronous values of games, especially synchronous games. It is known that a synchronous game has a perfect strategy if and only if it has a perfect synchronous strategy. However, we give examples of synchronous games, in particular graph colouring games, with synchronous value that is strictly smaller than their ordinary value. Thus, the optimal strategy for a synchronous game need not be synchronous. We derive a formula for the synchronous value of an XOR game as an optimization problem over a spectrahedron involving a matrix related to the cost matrix. We give an example of a game such that the synchronous value of repeated products of the game is strictly increasing. We show that the synchronous quantum bias of the XOR of two XOR games is not multiplicative. Finally, we derive geometric and algebraic conditions that a set of projections that yields the synchronous value of a game must satisfy.

1 aHelton, William1 aMousavi, Hamoon1 aNezhadi, Seyed, Sajjad1 aPaulsen, Vern, I.1 aRussell, Travis, B. uhttps://arxiv.org/abs/2109.1474101587nas 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/2009.1359901742nas a2200169 4500008004100000245004400041210004400085260001500129520128400144100001301428700002301441700001901464700001801483700001501501700001901516856003701535 2021 eng d00aVerified Compilation of Quantum Oracles0 aVerified Compilation of Quantum Oracles c12/13/20213 a

Quantum algorithms often apply classical operations, such as arithmetic or predicate checks, over a quantum superposition of classical data; these so-called oracles are often the largest components of a quantum algorithm. To ease the construction of efficient, correct oracle functions, this paper presents VQO, a high-assurance framework implemented with the Coq proof assistant. The core of VQO is OQASM, the oracle quantum assembly language. OQASM operations move qubits among three different bases via the Quantum Fourier Transform and Hadamard operations, thus admitting important optimizations, but without inducing entanglement and the exponential blowup that comes with it. OQASM's design enabled us to prove correct VQO's compilers -- from a simple imperative language called OQIMP to OQASM, and from OQASM to SQIR, a general-purpose quantum assembly language -- and allowed us to efficiently test properties of OQASM programs using the QuickChick property-based testing framework. We have used VQO to implement oracles used in Shor's and Grover's algorithms, as well as several common arithmetic operators. VQO's oracles have performance comparable to those produced by Quipper, a state-of-the-art but unverified quantum programming platform.

1 aLi, Liyi1 aVoichick, Finnegan1 aHietala, Kesha1 aPeng, Yuxiang1 aWu, Xiaodi1 aHicks, Michael uhttps://arxiv.org/abs/2112.0670001472nas a2200145 4500008004100000022001400041245007400055210006900129260001400198490000800212520103000220100002101250700001801271856003701289 2020 eng d a2469-995000aCoherent transport of spin by adiabatic passage in quantum dot arrays0 aCoherent transport of spin by adiabatic passage in quantum dot a c9/17/20200 v1023 a

We introduce an adiabatic transfer protocol for spin states in large quantum dot arrays that is based on time-dependent modulation of the Heisenberg exchange interaction in the presence of a magnetic field gradient. We refer to this protocol as spin-CTAP (coherent transport by adiabatic passage) in analogy to a related protocol developed for charge state transfer in quantum dot arrays. The insensitivity of this adiabatic protocol to pulse imperfections has potential advantages for reading out extended spin qubit arrays. When the static exchange interaction varies across the array, a quantum-controlled version of spin-CTAP is possible, where the transfer process is conditional on the spin states in the middle of the array. This conditional operation can be used to generate N-qubit entangled GHZ states. Using a realistic noise model, we analyze the robustness of the spin-CTAP operations and find that high-fidelity (>95%) spin eigenstate transfer and GHZ state preparation is feasible in current devices.

1 aGullans, Michael1 aPetta, J., R. uhttps://arxiv.org/abs/2007.1058201446nas a2200133 4500008004100000245007400041210006900115260001400184490000800198520103000206100002101236700001801257856003701275 2020 eng d00aCoherent transport of spin by adiabatic passage in quantum dot arrays0 aCoherent transport of spin by adiabatic passage in quantum dot a c9/17/20200 v1023 a

We introduce an adiabatic transfer protocol for spin states in large quantum dot arrays that is based on time-dependent modulation of the Heisenberg exchange interaction in the presence of a magnetic field gradient. We refer to this protocol as spin-CTAP (coherent transport by adiabatic passage) in analogy to a related protocol developed for charge state transfer in quantum dot arrays. The insensitivity of this adiabatic protocol to pulse imperfections has potential advantages for reading out extended spin qubit arrays. When the static exchange interaction varies across the array, a quantum-controlled version of spin-CTAP is possible, where the transfer process is conditional on the spin states in the middle of the array. This conditional operation can be used to generate N-qubit entangled GHZ states. Using a realistic noise model, we analyze the robustness of the spin-CTAP operations and find that high-fidelity (>95%) spin eigenstate transfer and GHZ state preparation is feasible in current devices.

1 aGullans, Michael1 aPetta, J., R. uhttps://arxiv.org/abs/2007.1058202409nas a2200193 4500008004100000245006700041210006700108260001500175490000700190520183800197100002002035700001902055700002302074700001802097700002402115700002002139700001902159856003702178 2020 eng d00aContinuous symmetries and approximate quantum error correction0 aContinuous symmetries and approximate quantum error correction c10/26/20200 v103 a

Quantum error correction and symmetry arise in many areas of physics, including many-body systems, metrology in the presence of noise, fault-tolerant computation, and holographic quantum gravity. Here we study the compatibility of these two important principles. If a logical quantum system is encoded into n physical subsystems, we say that the code is covariant with respect to a symmetry group G if a G transformation on the logical system can be realized by performing transformations on the individual subsystems. For a G-covariant code with G a continuous group, we derive a lower bound on the error correction infidelity following erasure of a subsystem. This bound approaches zero when the number of subsystems n or the dimension d of each subsystem is large. We exhibit codes achieving approximately the same scaling of infidelity with n or d as the lower bound. Leveraging tools from representation theory, we prove an approximate version of the Eastin-Knill theorem: If a code admits a universal set of transversal gates and corrects erasure with fixed accuracy, then, for each logical qubit, we need a number of physical qubits per subsystem that is inversely proportional to the error parameter. We construct codes covariant with respect to the full logical unitary group, achieving good accuracy for large d (using random codes) or n (using codes based on W-states). We systematically construct codes covariant with respect to general groups, obtaining natural generalizations of qubit codes to, for instance, oscillators and rotors. In the context of the AdS/CFT correspondence, our approach provides insight into how time evolution in the bulk corresponds to time evolution on the boundary without violating the Eastin-Knill theorem, and our five-rotor code can be stacked to form a covariant holographic code.

1 aFaist, Philippe1 aNezami, Sepehr1 aAlbert, Victor, V.1 aSalton, Grant1 aPastawski, Fernando1 aHayden, Patrick1 aPreskill, John uhttps://arxiv.org/abs/1902.0771401709nas 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/2003.0786401522nas 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/2008.0607401494nas a2200181 4500008004100000245005100041210005100092260001500143300001100158490000700169520100800176100001401184700001701198700002501215700001901240700001601259856003701275 2020 eng d00aMore of the Bulk from Extremal Area Variations0 aMore of the Bulk from Extremal Area Variations c12/24/2020 a0470010 v383 a

It was shown recently, building on work of Alexakis, Balehowksy, and Nachman that the geometry of (some portion of) a manifold with boundary is uniquely fixed by the areas of a foliation of two-dimensional disk-shaped surfaces anchored to the boundary. In the context of AdS/CFT, this implies that (a portion of) a four-dimensional bulk geometry can be fixed uniquely from the entanglement entropies of disk-shaped boundary regions, subject to several constraints. In this Note, we loosen some of these constraints, in particular allowing for the bulk foliation of extremal surfaces to be local and removing the constraint of disk topology; these generalizations ensure uniqueness of more of the deep bulk geometry by allowing for e.g. surfaces anchored on disconnected asymptotic boundaries, or HRT surfaces past a phase transition. We also explore in more depth the generality of the local foliation requirement, showing that even in a highly dynamical geometry like AdS-Vaidya it is satisfied.

1 aBao, Ning1 aCao, ChunJun1 aFischetti, Sebastian1 aPollack, Jason1 aZhong, Yibo uhttps://arxiv.org/abs/2009.0785001795nas a2200157 4500008004100000245008800041210006900129260001400198520128700212100002501499700001701524700002201541700001901563700001801582856003701600 2020 eng d00aA note on blind contact tracing at scale with applications to the COVID-19 pandemic0 anote on blind contact tracing at scale with applications to the  c4/10/20203 a

The current COVID-19 pandemic highlights the utility of contact tracing, when combined with case isolation and social distancing, as an important tool for mitigating the spread of a disease [1]. Contact tracing provides a mechanism of identifying individuals with a high likelihood of previous exposure to a contagious disease, allowing additional precautions to be put in place to prevent continued transmission. Here we consider a cryptographic approach to contact tracing based on secure two-party computation (2PC). We begin by considering the problem of comparing a set of location histories held by two parties to determine whether they have come within some threshold distance while at the same time maintaining the privacy of the location histories. We propose a solution to this problem using pre-shared keys, adapted from an equality testing protocol due to Ishai et al [2]. We discuss how this protocol can be used to maintain privacy within practical contact tracing scenarios, including both app-based approaches and approaches which leverage location history held by telecoms and internet service providers. We examine the efficiency of this approach and show that existing infrastructure is sufficient to support anonymised contact tracing at a national level.

1 aFitzsimons, Jack, K.1 aMantri, Atul1 aPisarczyk, Robert1 aRainforth, Tom1 aZhao, Zhikuan uhttps://arxiv.org/abs/2004.0511601697nas a2200205 4500008004100000245010900041210006900150260001300219520100800232100003001240700002801270700003101298700002401329700001601353700001601369700002501385700002301410700002101433856003701454 2020 eng d00aOn-demand indistinguishable single photons from an efficient and pure source based on a Rydberg ensemble0 aOndemand indistinguishable single photons from an efficient and  c3/4/20203 a

Single photons coupled to atomic systems have shown to be a promising platform for developing quantum technologies. Yet a bright on-demand, highly pure and highly indistinguishable single-photon source compatible with atomic platforms is lacking. In this work, we demonstrate such a source based on a strongly interacting Rydberg system. The large optical nonlinearities in a blockaded Rydberg ensemble convert coherent light into a single-collective excitation that can be coherently retrieved as a quantum field. We observe a single-transverse-mode efficiency up to 0.18(2), g(2)=2.0(1.5)×10−4, and indistinguishability of 0.982(7), making this system promising for scalable quantum information applications. Accounting for losses, we infer a generation probability up to 0.40(4). Furthermore, we investigate the effects of contaminant Rydberg excitations on the source efficiency. Finally, we introduce metrics to benchmark the performance of on-demand single-photon sources. 

1 aOrnelas-Huerta, Dalia, P.1 aCraddock, Alexander, N.1 aGoldschmidt, Elizabeth, A.1 aHachtel, Andrew, J.1 aWang, Yidan1 aBienias, P.1 aGorshkov, Alexey, V.1 aRolston, Steve, L.1 aPorto, James, V. uhttps://arxiv.org/abs/2003.0220201854nas 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/2001.0787702521nas a2200169 4500008004100000245006600041210006200107260001400169300000700183490000600190520198300196100001902179700002002198700001702218700002302235856009302258 2020 eng d00aOn Quantum Chosen-Ciphertext Attacks and Learning with Errors0 aQuantum ChosenCiphertext Attacks and Learning with Errors c3/21/2020 a100 v43 a

Large-scale quantum computing poses a major threat to classical public-key cryptography. Recently, strong “quantum access” security models have shown that numerous symmetric-key cryptosystems are also vulnerable. In this paper, we consider classical encryption in a model that grants the adversary quantum oracle access to encryption and decryption, but where we restrict the latter to non-adaptive (i.e., pre-challenge) queries only. We formalize this model using appropriate notions of ciphertext indistinguishability and semantic security (which are equivalent by standard arguments) and call it QCCA1 in analogy to the classical CCA1 security model. We show that the standard pseudorandom function ( PRF )-based encryption schemes are QCCA1 -secure when instantiated with quantum-secure primitives. Our security proofs use a strong bound on quantum random-access codes with shared randomness. Revisiting plain IND−CPA -secure Learning with Errors ( LWE ) encryption, we show that leaking only a single quantum decryption query (and no other leakage or queries of any kind) allows the adversary to recover the full secret key with constant success probability. Information-theoretically, full recovery of the key in the classical setting requires at least a linear number of decryption queries. Our results thus challenge the notion that LWE is unconditionally “just as secure” quantumly as it is classically. The algorithm at the core of our attack is a new variant of the well-known Bernstein–Vazirani algorithm. Finally, we emphasize that our results should not be interpreted as a weakness of these cryptosystems in their stated security setting (i.e., post-quantum chosen-plaintext secrecy). Rather, our results mean that, if these cryptosystems are exposed to chosen-ciphertext attacks (e.g., as a result of deployment in an inappropriate real-world setting) then quantum attacks are even more devastating than classical ones.

1 aAlagic, Gorjan1 aJeffery, Stacey1 aOzols, Maris1 aPoremba, Alexander uhttps://quics.umd.edu/publications/quantum-chosen-ciphertext-attacks-and-learning-errors01558nas 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/2010.0977201214nas a2200145 4500008004100000245004500041210004500086260001300131490000700144520081700151100002300968700002100991700001901012856003701031 2020 eng d00aRobust Encoding of a Qubit in a Molecule0 aRobust Encoding of a Qubit in a Molecule c9/1/20200 v103 a

We construct quantum error-correcting codes that embed a finite-dimensional code space in the infinite-dimensional Hilbert space of rotational states of a rigid body. These codes, which protect against both drift in the body’s orientation and small changes in its angular momentum, may be well suited for robust storage and coherent processing of quantum information using rotational states of a polyatomic molecule. Extensions of such codes to rigid bodies with a symmetry axis are compatible with rotational states of diatomic molecules as well as nuclear states of molecules and atoms. We also describe codes associated with general non-Abelian groups and develop orthogonality relations for coset spaces, laying the groundwork for quantum information processing with exotic configuration spaces.

1 aAlbert, Victor, V.1 aCovey, Jacob, P.1 aPreskill, John uhttps://arxiv.org/abs/1911.0009901588nas a2200157 4500008004100000245006600041210006600107260001400173490000800187520113200195100001701327700001701344700001701361700001501378856003701393 2020 eng d00aSimulating large quantum circuits on a small quantum computer0 aSimulating large quantum circuits on a small quantum computer c12/8/20200 v1253 a

Limited quantum memory is one of the most important constraints for near-term quantum devices. Understanding whether a small quantum computer can simulate a larger quantum system, or execute an algorithm requiring more qubits than available, is both of theoretical and practical importance. In this Letter, we introduce cluster parameters K and d of a quantum circuit. The tensor network of such a circuit can be decomposed into clusters of size at most d with at most K qubits of inter-cluster quantum communication. Our main result is a simulation scheme of any (K,d)-clustered quantum circuit on a d-qubit machine in time roughly 2O(K). An important application of our result is the simulation of clustered quantum systems---such as large molecules---that can be partitioned into multiple significantly smaller clusters with weak interactions among them. Another potential application is quantum optimization: we demonstrate numerically that variational quantum eigensolvers can still perform well when restricted to clustered circuits, thus making it feasible to study large quantum systems on small quantum devices.

1 aPeng, Tianyi1 aHarrow, Aram1 aOzols, Maris1 aWu, Xiaodi uhttps://arxiv.org/abs/1904.0010203206nas 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-process01555nas 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/2006.1276001870nas a2200181 4500008004100000245008300041210006900124260001300193490000600206520132100212100002001533700002101553700002401574700001801598700001801616700001701634856003701651 2020 eng d00aTowards analog quantum simulations of lattice gauge theories with trapped ions0 aTowards analog quantum simulations of lattice gauge theories wit c4/8/20200 v23 a

Gauge field theories play a central role in modern physics and are at the heart of the Standard Model of elementary particles and interactions. Despite significant progress in applying classical computational techniques to simulate gauge theories, it has remained a challenging task to compute the real-time dynamics of systems described by gauge theories. An exciting possibility that has been explored in recent years is the use of highly-controlled quantum systems to simulate, in an analog fashion, properties of a target system whose dynamics are difficult to compute. Engineered atom-laser interactions in a linear crystal of trapped ions offer a wide range of possibilities for quantum simulations of complex physical systems. Here, we devise practical proposals for analog simulation of simple lattice gauge theories whose dynamics can be mapped onto spin-spin interactions in any dimension. These include 1+1D quantum electrodynamics, 2+1D Abelian Chern-Simons theory coupled to fermions, and 2+1D pure Z2 gauge theory. The scheme proposed, along with the optimization protocol applied, will have applications beyond the examples presented in this work, and will enable scalable analog quantum simulation of Heisenberg spin models in any number of dimensions and with arbitrary interaction strengths.

1 aDavoudi, Zohreh1 aHafezi, Mohammad1 aMonroe, Christopher1 aPagano, Guido1 aSeif, Alireza1 aShaw, Andrew uhttps://arxiv.org/abs/1908.0321001484nas 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/1910.1054301240nas a2200145 4500008004100000245006500041210006400106260001500170520080100185100001800986700001601004700001801020700001901038856003701057 2019 eng d00aBeyond Spontaneous Emission: Giant Atom Bounded in Continuum0 aBeyond Spontaneous Emission Giant Atom Bounded in Continuum c12/20/20193 a

The quantum coupling of individual superconducting qubits to microwave photons leads to remarkable experimental opportunities. Here we consider the phononic case where the qubit is coupled to an electromagnetic surface acoustic wave antenna that enables supersonic propagation of the qubit oscillations. This can be considered as a giant atom that is many phonon wavelengths long. We study an exactly solvable toy model that captures these effects, and find that this non-Markovian giant atom has a suppressed relaxation, as well as an effective vacuum coupling between a qubit excitation and a localized wave packet of sound, even in the absence of a cavity for the sound waves. Finally, we consider practical implementations of these ideas in current surface acoustic wave devices. 

1 aGuo, Shangjie1 aWang, Yidan1 aPurdy, Thomas1 aTaylor, J., M. uhttps://arxiv.org/abs/1912.0998001746nas a2200193 4500008004100000245006800041210006700109260001500176490000900191520117800200100001601378700001801394700001701412700001801429700001901447700002401466700002501490856003701515 2019 eng d00aConfined Dynamics in Long-Range Interacting Quantum Spin Chains0 aConfined Dynamics in LongRange Interacting Quantum Spin Chains c04/17/20190 v122 3 a

We study the quasiparticle excitation and quench dynamics of the one-dimensional transverse-field Ising model with power-law (1/rα) interactions. We find that long-range interactions give rise to a confining potential, which couples pairs of domain walls (kinks) into bound quasiparticles, analogous to mesonic bound states in high-energy physics. We show that these bound states have dramatic consequences for the non-equilibrium dynamics following a global quantum quench, such as suppressed spreading of quantum information and oscillations of order parameters. The masses of these bound states can be read out from the Fourier spectrum of these oscillating order parameters. We then use a two-kink model to qualitatively explain the phenomenon of long-range-interaction-induced confinement. The masses of the bound states predicted by this model are in good quantitative agreement with exact diagonalization results. Moreover, we illustrate that these bound states lead to weak thermalization of local observables for initial states with energy near the bottom of the many-body energy spectrum. Our work is readily applicable to current trapped-ion experiments.

1 aLiu, Fangli1 aLundgren, Rex1 aTitum, Paraj1 aPagano, Guido1 aZhang, Jiehang1 aMonroe, Christopher1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1810.0236501980nas a2200193 4500008004100000245011000041210006900151260001500220520137500235100001801610700001601628700001401644700001501658700001301673700002501686700002001711700001801731856003701749 2019 eng d00aFloquet engineering of optical lattices with spatial features and periodicity below the diffraction limit0 aFloquet engineering of optical lattices with spatial features an c06/18/20193 a

Floquet engineering or coherent time periodic driving of quantum systems has been successfully used to synthesize Hamiltonians with novel properties. In ultracold atomic systems, this has led to experimental realizations of artificial gauge fields, topological band structures, and observation of dynamical localization, to name just a few. Here we present a Floquet-based framework to stroboscopically engineer Hamiltonians with spatial features and periodicity below the diffraction limit of light used to create them by time-averaging over various configurations of a 1D optical Kronig-Penney (KP) lattice. The KP potential is a lattice of narrow subwavelength barriers spaced by half the optical wavelength (λ/2) and arises from the non-linear optical response of the atomic dark state. Stroboscopic control over the strength and position of this lattice requires time-dependent adiabatic manipulation of the dark state spin composition. We investigate adiabaticity requirements and shape our time-dependent light fields to respect the requirements. We apply this framework to show that a λ/4-spaced lattice can be synthesized using realistic experimental parameters as an example, discuss mechanisms that limit lifetimes in these lattices, explore candidate systems and their limitations, and treat adiabatic loading into the ground band of these lattices.

1 aSubhankar, S.1 aBienias, P.1 aTitum, P.1 aTsui, T-C.1 aWang, Y.1 aGorshkov, Alexey, V.1 aRolston, S., L.1 aPorto, J., V. uhttps://arxiv.org/abs/1906.0764602376nas 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/1902.1017101196nas a2200193 4500008004100000245009600041210006900137260001400206490000800220520059500228100001600823700002200839700001600861700001800877700002400895700002100919700002500940856003700965 2019 eng d00aHeisenberg-Scaling Measurement Protocol for Analytic Functions with Quantum Sensor Networks0 aHeisenbergScaling Measurement Protocol for Analytic Functions wi c10/7/20190 v1003 a

We generalize past work on quantum sensor networks to show that, for d input parameters, entanglement can yield a factor O(d) improvement in mean squared error when estimating an analytic function of these parameters. We show that the protocol is optimal for qubit sensors, and conjecture an optimal protocol for photons passing through interferometers. Our protocol is also applicable to continuous variable measurements, such as one quadrature of a field operator. We outline a few potential applications, including calibration of laser operations in trapped ion quantum computing.

1 aQian, Kevin1 aEldredge, Zachary1 aGe, Wenchao1 aPagano, Guido1 aMonroe, Christopher1 aPorto, James, V.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1901.0904202399nas a2200145 4500008004100000245007900041210006900120300001400189520193400203100001902137700002002156700001702176700002302193856003702216 2019 eng d00aOn non-adaptive quantum chosen-ciphertext attacks and Learning with Errors0 anonadaptive quantum chosenciphertext attacks and Learning with E a1:1-1:23 3 a

Large-scale quantum computing is a significant threat to classical public-key cryptography. In strong "quantum access" security models, numerous symmetric-key cryptosystems are also vulnerable. We consider classical encryption in a model which grants the adversary quantum oracle access to encryption and decryption, but where the latter is restricted to non-adaptive (i.e., pre-challenge) queries only. We define this model formally using appropriate notions of ciphertext indistinguishability and semantic security (which are equivalent by standard arguments) and call it QCCA1 in analogy to the classical CCA1 security model. Using a bound on quantum random-access codes, we show that the standard PRF- and PRP-based encryption schemes are QCCA1-secure when instantiated with quantum-secure primitives. We then revisit standard IND-CPA-secure Learning with Errors (LWE) encryption and show that leaking just one quantum decryption query (and no other queries or leakage of any kind) allows the adversary to recover the full secret key with constant success probability. In the classical setting, by contrast, recovering the key uses a linear number of decryption queries, and this is optimal. The algorithm at the core of our attack is a (large-modulus version of) the well-known Bernstein-Vazirani algorithm. We emphasize that our results should *not* be interpreted as a weakness of these cryptosystems in their stated security setting (i.e., post-quantum chosen-plaintext secrecy). Rather, our results mean that, if these cryptosystems are exposed to chosen-ciphertext attacks (e.g., as a result of deployment in an inappropriate real-world setting) then quantum attacks are even more devastating than classical ones. 

1 aAlagic, Gorjan1 aJeffery, Stacey1 aOzols, Maris1 aPoremba, Alexander uhttps://arxiv.org/abs/1808.0965501912nas 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/1912.1111702010nas a2200409 4500008004100000245006800041210006600109260001500175520084400190100001901034700002601053700002001079700002001099700002001119700001701139700002501156700002201181700001901203700001701222700002201239700002101261700002501282700001901307700002301326700001801349700001901367700002101386700002101407700001501428700002001443700002401463700001801487700002301505700001901528700001601547856003701563 2019 eng d00aOpportunities for Nuclear Physics & Quantum Information Science0 aOpportunities for Nuclear Physics Quantum Information Science c03/13/20193 a

his whitepaper is an outcome of the workshop Intersections between Nuclear Physics and Quantum Information held at Argonne National Laboratory on 28-30 March 2018 [www.phy.anl.gov/npqi2018/]. The workshop brought together 116 national and international experts in nuclear physics and quantum information science to explore opportunities for the two fields to collaborate on topics of interest to the U.S. Department of Energy (DOE) Office of Science, Office of Nuclear Physics, and more broadly to U.S. society and industry. The workshop consisted of 22 invited and 10 contributed talks, as well as three panel discussion sessions. Topics discussed included quantum computation, quantum simulation, quantum sensing, nuclear physics detectors, nuclear many-body problem, entanglement at collider energies, and lattice gauge theories.

1 aCloët, I., C.1 aDietrich, Matthew, R.1 aArrington, John1 aBazavov, Alexei1 aBishof, Michael1 aFreese, Adam1 aGorshkov, Alexey, V.1 aGrassellino, Anna1 aHafidi, Kawtar1 aJacob, Zubin1 aMcGuigan, Michael1 aMeurice, Yannick1 aMeziani, Zein-Eddine1 aMueller, Peter1 aMuschik, Christine1 aOsborn, James1 aOtten, Matthew1 aPetreczky, Peter1 aPolakovic, Tomas1 aPoon, Alan1 aPooser, Raphael1 aRoggero, Alessandro1 aSaffman, Mark1 aVanDevender, Brent1 aZhang, Jiehang1 aZohar, Erez uhttps://arxiv.org/abs/1903.0545301709nas 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/1912.0693801259nas a2200145 4500008004100000245005700041210005600098490000800154520083800162100001701000700002101017700001701038700002101055856003701076 2019 eng d00aReQWIRE: Reasoning about Reversible Quantum Circuits0 aReQWIRE Reasoning about Reversible Quantum Circuits0 v2873 a

Common quantum algorithms make heavy use of ancillae: scratch qubits that are initialized at some state and later returned to that state and discarded. Existing quantum circuit languages let programmers assert that a qubit has been returned to the |0> state before it is discarded, allowing for a range of optimizations. However, existing languages do not provide the tools to verify these assertions, introducing a potential source of errors. In this paper we present methods for verifying that ancillae are discarded in the desired state, and use these methods to implement a verified compiler from classical functions to quantum oracles.

1 aRand, Robert1 aPaykin, Jennifer1 aLee, Dong-Ho1 aZdancewic, Steve uhttps://arxiv.org/abs/1901.1011802754nas a2200229 4500008004100000245009900041210006900140520205300209100001902262700002402281700001302305700001502318700001302333700001702346700001402363700001602377700001602393700001702409700001902426700001602445856006302461 2019 eng d00aStatus Report on the First Round of the NIST Post-Quantum Cryptography Standardization Process0 aStatus Report on the First Round of the NIST PostQuantum Cryptog3 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 publickey cryptography standards will specify one or more additional digital signature, public-key
encryption, and key-establishment algorithms to augment FIPS 186-4, Digital Signature Standard
(DSS), as well as special publications SP 800-56A Revision 2, Recommendation for Pair-Wise
Key Establishment Schemes Using Discrete Logarithm Cryptography, and SP 800-56B,
Recommendation for Pair-Wise Key-Establishment Schemes Using Integer Factorization. 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.
In November 2017, 82 candidate algorithms were submitted to NIST for consideration. Among
these, 69 met both the minimum acceptance criteria and our submission requirements, and were
accepted as First-Round Candidates on Dec. 20, 2017, marking the beginning of the First Round
of the NIST Post-Quantum Cryptography Standardization Process. This report describes the
evaluation criteria and selection process, based on public feedback and internal review of the
first-round candidates, and summarizes the 26 candidate algorithms announced on January 30,
2019 for moving forward to the second round of the competition. The 17 Second-Round
Candidate public-key encryption and key-establishment algorithms are BIKE, Classic McEliece,
CRYSTALS-KYBER, FrodoKEM, HQC, LAC, LEDAcrypt (merger of LEDAkem/LEDApkc),
NewHope, NTRU (merger of NTRUEncrypt/NTRU-HRSS-KEM), NTRU Prime, NTS-KEM,
ROLLO (merger of LAKE/LOCKER/Ouroboros-R), Round5 (merger of Hila5/Round2), RQC,
SABER, SIKE, and Three Bears. The 9 Second-Round Candidates for digital signatures are
CRYSTALS-DILITHIUM, FALCON, GeMSS, LUOV, MQDSS, Picnic, qTESLA, Rainbow,
and SPHINCS+.

1 aAlagic, Gorjan1 aAlperin-Sheriff, J.1 aApon, D.1 aCooper, D.1 aDang, Q.1 aMiller, Carl1 aMoody, D.1 aPeralta, R.1 aPerlner, R.1 aRobinson, A.1 aSmith-Tone, D.1 aLiu, Yi-Kai uhttps://nvlpubs.nist.gov/nistpubs/ir/2019/NIST.IR.8240.pdf01624nas 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/1904.0433801296nas 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/1801.0307101390nas a2200145 4500008004100000245007200041210006900113520091900182100002201101700002101123700001801144700002601162700001901188856003701207 2018 eng d00aBose Condensation of Photons Thermalized via Laser Cooling of Atoms0 aBose Condensation of Photons Thermalized via Laser Cooling of At3 a

A Bose-Einstein condensate (BEC) is a quantum phase of matter achieved at low temperatures. Photons, one of the most prominent species of bosons, do not typically condense due to the lack of a particle number-conservation. We recently described a photon thermalization mechanism which gives rise to a grand canonical ensemble of light with effective photon number conservation between a subsystem and a particle reservoir. This mechanism occurs during Doppler laser cooling of atoms where the atoms serve as a temperature reservoir while the cooling laser photons serve as a particle reservoir. Here we address the question of the possibility of a BEC of photons in this laser cooling photon thermalization scenario and theoretically demonstrate that a Bose condensation of photons can be realized by cooling an ensemble of two-level atoms (realizable with alkaline earth atoms) inside a Fabry-Perot cavity.

1 aWang, Chiao-Hsuan1 aGullans, Michael1 aPorto, J., V.1 aPhillips, William, D.1 aTaylor, J., M. uhttps://arxiv.org/abs/1809.0777701856nas 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-2018-01-08-44/01379nas a2200217 4500008004100000245005600041210005400097520077800151100001600929700001800945700001300963700001400976700002200990700001501012700002001027700001401047700002001061700001801081700002501099856003701124 2018 eng d00aCoherent optical nano-tweezers for ultra-cold atoms0 aCoherent optical nanotweezers for ultracold atoms3 a

There has been a recent surge of interest and progress in creating subwavelength free-space optical potentials for ultra-cold atoms. A key open question is whether geometric potentials, which are repulsive and ubiquitous in the creation of subwavelength free-space potentials, forbid the creation of narrow traps with long lifetimes. Here, we show that it is possible to create such traps. We propose two schemes for realizing subwavelength traps and demonstrate their superiority over existing proposals. We analyze the lifetime of atoms in such traps and show that long-lived bound states are possible. This work opens a new frontier for the subwavelength control and manipulation of ultracold matter, with applications in quantum chemistry and quantum simulation.

1 aBienias, P.1 aSubhankar, S.1 aWang, Y.1 aTsui, T-C1 aJendrzejewski, F.1 aTiecke, T.1 aJuzeliūnas, G.1 aJiang, L.1 aRolston, S., L.1 aPorto, J., V.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1808.0248701523nas a2200205 4500008004100000245004800041210004500089260001500134300001200149490000800161520099800169100001101167700001501178700001301193700001801206700001901224700001901243700001801262856003701280 2018 eng d00aA Coherent Spin-Photon Interface in Silicon0 aCoherent SpinPhoton Interface in Silicon c2018/03/29 a599-6030 v5553 a

Electron spins in silicon quantum dots are attractive systems for quantum computing due to their long coherence times and the promise of rapid scaling using semiconductor fabrication techniques. While nearest neighbor exchange coupling of two spins has been demonstrated, the interaction of spins via microwave frequency photons could enable long distance spin-spin coupling and "all-to-all" qubit connectivity. Here we demonstrate strong-coupling between a single spin in silicon and a microwave frequency photon with spin-photon coupling rates g_s/(2π) > 10 MHz. The mechanism enabling coherent spin-photon interactions is based on spin-charge hybridization in the presence of a magnetic field gradient. In addition to spin-photon coupling, we demonstrate coherent control of a single spin in the device and quantum non-demolition spin state readout using cavity photons. These results open a direct path toward entangling single spins using microwave frequency photons.

1 aMi, X.1 aBenito, M.1 aPutz, S.1 aZajac, D., M.1 aTaylor, J., M.1 aBurkard, Guido1 aPetta, J., R. uhttps://arxiv.org/abs/1710.0326501974nas a2200181 4500008004100000245005000041210004800091260001500139520145800154100001101612700001501623700001301638700001801651700001901669700001901688700001801707856006701725 2018 eng d00aA coherent spin–photon interface in silicon0 acoherent spin–photon interface in silicon c2018/02/143 a

Electron spins in silicon quantum dots are attractive systems for quantum computing owing to their long coherence times and the promise of rapid scaling of the number of dots in a system using semiconductor fabrication techniques. Although nearest-neighbour exchange coupling of two spins has been demonstrated, the interaction of spins via microwave-frequency photons could enable long-distance spin–spin coupling and connections between arbitrary pairs of qubits (‘all-to-all’ connectivity) in a spin-based quantum processor. Realizing coherent spin–photon coupling is challenging because of the small magnetic-dipole moment of a single spin, which limits magnetic-dipole coupling rates to less than 1 kilohertz. Here we demonstrate strong coupling between a single spin in silicon and a single microwave-frequency photon, with spin–photon coupling rates of more than 10 megahertz. The mechanism that enables the coherent spin–photon interactions is based on spin–charge hybridization in the presence of a magnetic-field gradient. In addition to spin–photon coupling, we demonstrate coherent control and dispersive readout of a single spin. These results open up a direct path to entangling single spins using microwave-frequency photons.

1 aMi, X.1 aBenito, M.1 aPutz, S.1 aZajac, D., M.1 aTaylor, J., M.1 aBurkard, Guido1 aPetta, J., R. uhttps://www.nature.com/articles/nature25769#author-information01463nas 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/1802.0311804213nas a2200241 4500008004100000245006900041210006800110260001500178300001100193490000800204520348600212100001503698700002303713700002403736700001903760700001903779700002503798700002503823700001803848700002103866700002403887856006003911 2018 eng d00aDark state optical lattice with sub-wavelength spatial structure0 aDark state optical lattice with subwavelength spatial structure c2018/02/20 a0836010 v1203 a

We report on the experimental realization of a conservative optical lattice for cold atoms with a subwavelength spatial structure. The potential is based on the nonlinear optical response of three-level atoms in laser-dressed dark states, which is not constrained by the diffraction limit of the light generating the potential. The lattice consists of a one-dimensional array of ultranarrow barriers with widths less than 10 nm, well below the wavelength of the lattice light, physically realizing a Kronig-Penney potential. We study the band structure and dissipation of this lattice and find good agreement with theoretical predictions. Even on resonance, the observed lifetimes of atoms trapped in the lattice are as long as 44 ms, nearly 105times the excited state lifetime, and could be further improved with more laser intensity. The potential is readily generalizable to higher dimensions and different geometries, allowing, for example, nearly perfect box traps, narrow tunnel junctions for atomtronics applications, and dynamically generated lattices with subwavelength spacings.

1 aWang, Yang1 aSubhankar, Sarthak1 aBienias, Przemyslaw1 aLacki, Mateusz1 aTsui, Tsz-Chun1 aBaranov, Mikhail, A.1 aGorshkov, Alexey, V.1 aZoller, Peter1 aPorto, James, V.1 aRolston, Steven, L. uhttps://link.aps.org/doi/10.1103/PhysRevLett.120.08360103349nas a2200217 4500008004100000245008400041210006900125260001500194300001100209490000700220520266700227100002202894700002002916700001702936700003102953700002102984700002403005700002103029700002503050856005603075 2018 eng d00aDissipation induced dipole blockade and anti-blockade in driven Rydberg systems0 aDissipation induced dipole blockade and antiblockade in driven R c2018/02/28 a0234240 v973 a

We study theoretically and experimentally the competing blockade and antiblockade effects induced by spontaneously generated contaminant Rydberg atoms in driven Rydberg systems. These contaminant atoms provide a source of strong dipole-dipole interactions and play a crucial role in the system's behavior. We study this problem theoretically using two different approaches. The first is a cumulant expansion approximation, in which we ignore third-order and higher connected correlations. Using this approach for the case of resonant drive, a many-body blockade radius picture arises, and we find qualitative agreement with previous experimental results. We further predict that as the atomic density is increased, the Rydberg population's dependence on Rabi frequency will transition from quadratic to linear dependence at lower Rabi frequencies. We study this behavior experimentally by observing this crossover at two different atomic densities. We confirm that the larger density system has a smaller crossover Rabi frequency than the smaller density system. The second theoretical approach is a set of phenomenological inhomogeneous rate equations. We compare the results of our rate-equation model to the experimental observations [E. A. Goldschmidt et al.Phys. Rev. Lett. 116, 113001 (2016)] and find that these rate equations provide quantitatively good scaling behavior of the steady-state Rydberg population for both resonant and off-resonant drives.

1 aYoung, Jeremy, T.1 aBoulier, Thomas1 aMagnan, Eric1 aGoldschmidt, Elizabeth, A.1 aWilson, Ryan, M.1 aRolston, Steven, L.1 aPorto, James, V.1 aGorshkov, Alexey, V. uhttps://link.aps.org/doi/10.1103/PhysRevA.97.02342402685nas a2200205 4500008004100000245006300041210006100104260001500165300001100180490000700191520207900198100002102277700001802298700002202316700001602338700001902354700001802373700001902391856006902410 2018 eng d00aHigh-fidelity quantum gates in Si/SiGe double quantum dots0 aHighfidelity quantum gates in SiSiGe double quantum dots c2018/02/15 a0854210 v973 a

Motivated by recent experiments of Zajac et al. [Science 359, 439 (2018)], we theoretically describe high-fidelity two-qubit gates using the exchange interaction between the spins in neighboring quantum dots subject to a magnetic field gradient. We use a combination of analytical calculations and numerical simulations to provide the optimal pulse sequences and parameter settings for the gate operation. We present a synchronization method which avoids detrimental spin flips during the gate operation and provide details about phase mismatches accumulated during the two-qubit gates which occur due to residual exchange interaction, nonadiabatic pulses, and off-resonant driving. By adjusting the gate times, synchronizing the resonant and off-resonant transitions, and compensating these phase mismatches by phase control, the overall gate fidelity can be increased significantly.

1 aRuss, Maximilian1 aZajac, D., M.1 aSigillito, A., J.1 aBorjans, F.1 aTaylor, J., M.1 aPetta, J., R.1 aBurkard, Guido uhttps://journals.aps.org/prb/abstract/10.1103/PhysRevB.97.08542101224nas 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/1809.0082501686nas a2200181 4500008004100000245006900041210006900110260001500179490000700194520113900201100002001340700002401360700002201384700001801406700002501424700001801449856003701467 2018 eng d00aOptimization of photon storage fidelity in ordered atomic arrays0 aOptimization of photon storage fidelity in ordered atomic arrays c2018/08/310 v203 a

A major application for atomic ensembles consists of a quantum memory for light, in which an optical state can be reversibly converted to a collective atomic excitation on demand. There exists a well-known fundamental bound on the storage error, when the ensemble is describable by a continuous medium governed by the Maxwell-Bloch equations. The validity of this model can break down, however, in systems such as dense, ordered atomic arrays, where strong interference in emission can give rise to phenomena such as subradiance and "selective" radiance. Here, we develop a general formalism that finds the maximum storage efficiency for a collection of atoms with discrete, known positions, and a given spatial mode in which an optical field is sent. As an example, we apply this technique to study a finite two-dimensional square array of atoms. We show that such a system enables a storage error that scales with atom number Na like ∼(logNa)2/N2a, and that, remarkably, an array of just 4×4 atoms in principle allows for an efficiency comparable to a disordered ensemble with optical depth of around 600.

1 aManzoni, M., T.1 aMoreno-Cardoner, M.1 aAsenjo-Garcia, A.1 aPorto, J., V.1 aGorshkov, Alexey, V.1 aChang, D., E. uhttps://arxiv.org/abs/1710.0631202076nas a2200229 4500008004100000245007800041210006900119520136400188100002401552700001901576700002401595700001701619700002301636700002101659700001801680700002101698700001901719700002701738700001901765700002501784856003701809 2018 eng d00aPhoton propagation through dissipative Rydberg media at large input rates0 aPhoton propagation through dissipative Rydberg media at large in3 a

We study the dissipative propagation of quantized light in interacting Rydberg media under the conditions of electromagnetically induced transparency (EIT). Rydberg blockade physics in optically dense atomic media leads to strong dissipative interactions between single photons. The regime of high incoming photon flux constitutes a challenging many-body dissipative problem. We experimentally study in detail for the first time the pulse shapes and the second-order correlation function of the outgoing field and compare our data with simulations based on two novel theoretical approaches well-suited to treat this many-photon limit. At low incoming flux, we report good agreement between both theories and the experiment. For higher input flux, the intensity of the outgoing light is lower than that obtained from theoretical predictions. We explain this discrepancy using a simple phenomenological model taking into account pollutants, which are nearly-stationary Rydberg excitations coming from the reabsorption of scattered probe photons. At high incoming photon rates, the blockade physics results in unconventional shapes of measured correlation functions. 

1 aBienias, Przemyslaw1 aDouglas, James1 aParis-Mandoki, Asaf1 aTitum, Paraj1 aMirgorodskiy, Ivan1 aTresp, Christoph1 aZeuthen, Emil1 aGullans, Michael1 aManzoni, Marco1 aHofferberth, Sebastian1 aChang, Darrick1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1807.0758601386nas a2200193 4500008004100000245004800041210004700089260001500136520082300151100002300974700002300997700002101020700002101041700002401062700002501086700002701111700001701138856003701155 2018 eng d00aPhoton Subtraction by Many-Body Decoherence0 aPhoton Subtraction by ManyBody Decoherence c2018/03/133 a

We present an experimental and theoretical investigation of the scattering-induced decoherence of multiple photons stored in a strongly interacting atomic ensemble. We derive an exact solution to this many-body problem, allowing for a rigorous understanding of the underlying dissipative quantum dynamics. Combined with our experiments, this analysis demonstrates a correlated coherence-protection process, in which the induced decoherence of one photon can preserve the spatial coherence of all others. We discuss how this effect can be used to manipulate light at the quantum level, providing a robust mechanism for single-photon subtraction, and experimentally demonstrate this capability.

1 aMurray, Callum, R.1 aMirgorodskiy, Ivan1 aTresp, Christoph1 aBraun, Christoph1 aParis-Mandoki, Asaf1 aGorshkov, Alexey, V.1 aHofferberth, Sebastian1 aPohl, Thomas uhttps://arxiv.org/abs/1710.1004701932nas a2200157 4500008004100000245005300041210005300094260000900147520147500156100002201631700002101653700001801674700002601692700001901718856003701737 2018 eng d00aPhoton thermalization via laser cooling of atoms0 aPhoton thermalization via laser cooling of atoms c20183 a

Laser cooling of atomic motion enables a wide variety of technological and scientific explorations using cold atoms. Here we focus on the effect of laser cooling on the photons instead of on the atoms. Specifically, we show that non-interacting photons can thermalize with the atoms to a grand canonical ensemble with a non-zero chemical potential. This thermalization is accomplished via scattering of light between different optical modes, mediated by the laser cooling process. While optically thin modes lead to traditional laser cooling of the atoms, the dynamics of multiple scattering in optically thick modes has been more challenging to describe. We find that in an appropriate set of limits, multiple scattering leads to thermalization of the light with the atomic motion in a manner that approximately conserves total photon number between the laser beams and optically thick modes. In this regime, the subsystem corresponding to the thermalized modes is describable by a grand canonical ensemble with a chemical potential set by the energy of a single laser photon. We consider realization of this regime using two-level atoms in Doppler cooling, and find physically realistic conditions for rare earth atoms. With the addition of photon-photon interactions, this system could provide a new platform for exploring many-body physics.

1 aWang, Chiao-Hsuan1 aGullans, Michael1 aPorto, J., V.1 aPhillips, William, D.1 aTaylor, J., M. uhttps://arxiv.org/abs/1712.0864301748nas a2200157 4500008004100000245010900041210006900150260001500219300001100234490000700245520121100252100002101463700001901484700001801503856006901521 2018 eng d00aProbing electron-phonon interactions in the charge-photon dynamics of cavity-coupled double quantum dots0 aProbing electronphonon interactions in the chargephoton dynamics c2018/01/16 a0353050 v973 a

Electron-phonon coupling is known to play an important role in the charge dynamics of semiconductor quantum dots. Here we explore its role in the combined charge-photon dynamics of cavity-coupled double quantum dots. Previous work on these systems has shown that strong electron-phonon coupling leads to a large contribution to photoemission and gain from phonon-assisted emission and absorption processes. We compare the effects of this phonon sideband in three commonly investigated gate-defined quantum dot material systems: InAs nanowires and GaAs and Si two-dimensional electron gases (2DEGs). We compare our theory with existing experimental data from cavity-coupled InAs nanowire and GaAs 2DEG double quantum dots and find quantitative agreement only when the phonon sideband and photoemission processes during lead tunneling are taken into account. Finally, we show that the phonon sideband also leads to a sizable renormalization of the cavity frequency, which allows for direct spectroscopic probes of the electron-phonon coupling in these systems.

1 aGullans, Michael1 aTaylor, J., M.1 aPetta, J., R. uhttps://journals.aps.org/prb/abstract/10.1103/PhysRevB.97.03530501439nas a2200205 4500008004100000245005100041210005100092260001500143300001200158490000800170520087500178100001801053700002201071700001301093700001601106700001901122700001901141700001801160856005501178 2018 eng d00aResonantly driven CNOT gate for electron spins0 aResonantly driven CNOT gate for electron spins c2018/01/26 a439-4420 v3593 a

Single-qubit rotations and two-qubit CNOT operations are crucial ingredients for universal quantum computing. Although high-fidelity single-qubit operations have been achieved using the electron spin degree of freedom, realizing a robust CNOT gate has been challenging because of rapid nuclear spin dephasing and charge noise. We demonstrate an efficient resonantly driven CNOT gate for electron spins in silicon. Our platform achieves single-qubit rotations with fidelities greater than 99%, as verified by randomized benchmarking. Gate control of the exchange coupling allows a quantum CNOT gate to be implemented with resonant driving in ~200 nanoseconds. We used the CNOT gate to generate a Bell state with 78% fidelity (corrected for errors in state preparation and measurement). Our quantum dot device architecture enables multi-qubit algorithms in silicon.

1 aZajac, D., M.1 aSigillito, A., J.1 aRuss, M.1 aBorjans, F.1 aTaylor, J., M.1 aBurkard, Guido1 aPetta, J., R. uhttp://science.sciencemag.org/content/359/6374/43901238nas a2200157 4500008004100000245005100041210005000092520077600142100001600918700002100934700002200955700001800977700002300995700002501018856003701043 2018 eng d00aSingle-photon bound states in atomic ensembles0 aSinglephoton bound states in atomic ensembles3 a

We illustrate the existence of single-excitation bound states for propagating photons interacting with N two-level atoms. These bound states can be calculated from an effective spin model, and their existence relies on dissipation in the system. The appearance of these bound states is in a one-to-one correspondence with zeros in the single-photon transmission and with divergent bunching in the second-order photon-photon correlation function. We also formulate a dissipative version of Levinson's theorem for this system by looking at the relation between the number of bound states and the winding number of the transmission phases. This theorem allows a direct experimental measurement of the number of bound states using the measured transmission phases.

1 aWang, Yidan1 aGullans, Michael1 aBrowaeys, Antoine1 aPorto, J., V.1 aChang, Darrick, E.1 aGorshkov, Alexey, V. uhttps://arxiv.org/abs/1809.0114702029nas a2200205 4500008004100000245009100041210006900132490000900201520141200210100001901622700002001641700001801661700001701679700002001696700002001716700001601736700001701752700001701769856003701786 2018 eng d00aA spinor Bose-Einstein condensate phase-sensitive amplifier for SU(1,1) interferometry0 aspinor BoseEinstein condensate phasesensitive amplifier for SU110 vA 983 a

The SU(1,1) interferometer was originally conceived as a Mach-Zehnder interferometer with the beam-splitters replaced by parametric amplifiers. The parametric amplifiers produce states with correlations that result in enhanced phase sensitivity. F=1 spinor Bose-Einstein condensates (BECs) can serve as the parametric amplifiers for an atomic version of such an interferometer by collisionally producing entangled pairs of ⟨F=1,m=±1| atoms. We simulate the effect of single and double-sided seeding of the inputs to the amplifier using the truncated-Wigner approximation. We find that single-sided seeding degrades the performance of the interferometer exactly at the phase the unseeded interferometer should operate the best. Double-sided seeding results in a phase-sensitive amplifier, where the maximal sensitivity is a function of the phase relationship between the input states of the amplifier. In both single and double-sided seeding we find there exists an optimal phase shift that achieves sensitivity beyond the standard quantum limit. Experimentally, we demonstrate a spinor phase-sensitive amplifier using a BEC of 23Na in an optical dipole trap. This configuration could be used as an input to such an interferometer. We are able to control the initial phase of the double-seeded amplifier, and demonstrate sensitivity to initial population fractions as small as 0.1\%. 

1 aWrubel, J., P.1 aSchwettmann, A.1 aFahey, D., P.1 aGlassman, Z.1 aPechkis, H., K.1 aGriffin, P., F.1 aBarnett, R.1 aTiesinga, E.1 aLett, P., D. uhttps://arxiv.org/abs/1807.0667610586nas a2200301 4500008004100000245007200041210006900113520978200182100001609964700001609980700001909996700001810015700001610033700002210049700001510071700001310086700001210099700001610111700001210127700001410139700001510153700001710168700001610185700001610201700001310217700001710230856003710247 2018 eng d00aStudy of radon reduction in gases for rare event search experiments0 aStudy of radon reduction in gases for rare event search experime3 a

The noble elements, argon and xenon, are frequently employed as the target and event detector for weakly interacting particles such as neutrinos and Dark Matter. For such rare processes, background radiation must be carefully minimized. Radon provides one of the most significant contaminants since it is an inevitable product of trace amounts of natural uranium. To design a purification system for reducing such contamination, the adsorption characteristics of radon in nitrogen, argon, and xenon carrier gases on various types of charcoals with different adsorbing properties and intrinsic radioactive purities have been studied in the temperature range of 190-295 K at flow rates of 0.5 and 2 standard liters per minute. Essential performance parameters for the various charcoals include the average breakthrough times (τ), dynamic adsorption coefficients (ka) and the number of theoretical stages (n). It is shown that the ka-values for radon in nitrogen, argon, and xenon increase as the temperature of the charcoal traps decreases, and that they are significantly larger in nitrogen and argon than in xenon gas due to adsorption saturation effects. It is found that, unlike in xenon, the dynamic adsorption coefficients for radon in nitrogen and argon strictly obey the Arrhenius law. The experimental results strongly indicate that nitric acid etched Saratech is the best candidate among all used charcoal brands. It allows reducing total radon concentration in the LZ liquid Xe detector to meet the ultimate goal in the search for Dark Matter.

1 aPushkin, K.1 aAkerlof, C.1 aAnbajagane, D.1 aArmstrong, J.1 aArthurs, M.1 aBringewatt, Jacob1 aEdberg, T.1 aHall, C.1 aLei, M.1 aRaymond, R.1 aReh, M.1 aSaini, D.1 aSander, A.1 aSchaefer, J.1 aSeymour, D.1 aSwanson, N.1 aWang, Y.1 aLorenzon, W. uhttps://arxiv.org/abs/1805.1130601846nas 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/1808.0819301983nas a2200157 4500008004100000245007700041210006900118260001500187300001100202490000800213520147800221100001601699700001801715700001901733856007301752 2017 eng d00aCooling a harmonic oscillator by optomechanical modification of its bath0 aCooling a harmonic oscillator by optomechanical modification of  c2017/05/31 a2236020 v1183 a

Optomechanical systems show tremendous promise for high sensitivity sensing of forces and modification of mechanical properties via light. For example, similar to neutral atoms and trapped ions, laser cooling of mechanical motion by radiation pressure can take single mechanical modes to their ground state. Conventional optomechanical cooling is able to introduce additional damping channel to mechanical motion, while keeping its thermal noise at the same level, and as a consequence, the effective temperature of the mechanical mode is lowered. However, the ratio of temperature to quality factor remains roughly constant, preventing dramatic advances in quantum sensing using this approach. Here we propose an approach for simultaneously reducing the thermal load on a mechanical resonator while improving its quality factor. In essence, we use the optical interaction to dynamically modify the dominant damping mechanism, providing an optomechanically-induced effect analogous to a phononic band gap. The mechanical mode of interest is assumed to be weakly coupled to its heat bath but strongly coupled to a second mechanical mode, which is cooled by radiation pressure coupling to a red detuned cavity field. We also identify a realistic optomechanical design that has the potential to realize this novel cooling scheme.

1 aXu, Xunnong1 aPurdy, Thomas1 aTaylor, J., M. uhttps://journals.aps.org/prl/abstract/10.1103/PhysRevLett.118.22360202354nas a2200157 4500008004100000245007000041210006900111520185900180100001902039700002002058700002402078700001802102700001902120700002002139856003702159 2017 eng d00aEntanglement Wedge Reconstruction via Universal Recovery Channels0 aEntanglement Wedge Reconstruction via Universal Recovery Channel3 a

We apply and extend the theory of universal recovery channels from quantum information theory to address the problem of entanglement wedge reconstruction in AdS/CFT. It has recently been proposed that any low-energy local bulk operators in a CFT boundary region's entanglement wedge can be reconstructed on that boundary region itself. Existing work arguing for this proposal relies on algebraic consequences of the exact equivalence between bulk and boundary relative entropies, namely the theory of operator algebra quantum error correction. However, bulk and boundary relative entropies are only approximately equal in bulk effective field theory, and in similar situations it is known that predictions from exact entropic equalities can be qualitatively incorrect. The framework of universal recovery channels provides a robust demonstration of the entanglement wedge reconstruction conjecture in addition to new physical insights. Most notably, we find that a bulk operator acting in a given boundary region's entanglement wedge can be expressed as the response of the boundary region's modular Hamiltonian to a perturbation of the bulk state in the direction of the bulk operator. This formula can be interpreted as a noncommutative version of Bayes' rule that attempts to undo the noise induced by restricting to only a portion of the boundary, and has an integral representation in terms of modular flows. To reach these conclusions, we extend the theory of universal recovery channels to finite-dimensional operator algebras and demonstrate that recovery channels approximately preserve the multiplicative structure of the operator algebra

1 aCotler, Jordan1 aHayden, Patrick1 aPenington, Geoffrey1 aSalton, Grant1 aSwingle, Brian1 aWalter, Michael uhttps://arxiv.org/abs/1704.0583911923nas 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.95.06233101674nas a2200181 4500008004100000245007500041210006900116260001500185300001100200490000700211520113600218100001501354700001101369700001901380700001801399700001901417856005601436 2017 eng d00aInput-output theory for spin-photon coupling in Si double quantum dots0 aInputoutput theory for spinphoton coupling in Si double quantum  c2017/12/22 a2354340 v963 a

The interaction of qubits via microwave frequency photons enables long-distance qubit-qubit coupling and facilitates the realization of a large-scale quantum processor. However, qubits based on electron spins in semiconductor quantum dots have proven challenging to couple to microwave photons. In this theoretical work we show that a sizable coupling for a single electron spin is possible via spin-charge hybridization using a magnetic field gradient in a silicon double quantum dot. Based on parameters already shown in recent experiments, we predict optimal working points to achieve a coherent spin-photon coupling, an essential ingredient for the generation of long-range entanglement. Furthermore, we employ input-output theory to identify observable signatures of spin-photon coupling in the cavity output field, which may provide guidance to the experimental search for strong coupling in such spin-photon systems and opens the way to cavity-based readout of the spin qubit.

1 aBenito, M.1 aMi, X.1 aTaylor, J., M.1 aPetta, J., R.1 aBurkard, Guido uhttps://link.aps.org/doi/10.1103/PhysRevB.96.23543401952nas 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/1703.0383901398nas 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/1711.0252402646nas 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/1708.0978002019nas a2200217 4500008004100000245006500041210006300106260001500169300001100184490000600195520137300201100001601574700002501590700002101615700002701636700002601663700001801689700001601707700002301723856005501746 2017 eng d00aSimultaneous, Full Characterization of a Single-Photon State0 aSimultaneous Full Characterization of a SinglePhoton State c2017/11/15 a0410360 v73 a

As single-photon sources become more mature and are used more often in quantum information, communications, and measurement applications, their characterization becomes more important. Singlephoton-like light is often characterized by its brightness, as well as two quantum properties: the suppression of multiphoton content and the photon indistinguishability. While it is desirable to obtain these quantities from a single measurement, currently two or more measurements are required. Here, we show that using two-photon (n ¼ 2) number-resolving detectors, one can completely characterize single-photon-like states in a single measurement, where previously two or more measurements were necessary. We simultaneously determine the brightness, the suppression of multiphoton states, the indistinguishability, and the statistical distribution of Fock states to third order for a quantum light source. We find n ≥ 3 number-resolving detectors provide no additional advantage in the single-photon characterization. The new method extracts more information per experimental trial than a conventional measurement for all input states and is particularly more efficient for statistical mixtures of photon states. Thus, using this n ¼ 2, number-resolving detector scheme will provide advantages in a variety of quantum optics measurements and systems.

1 aThomay, Tim1 aPolyakov, Sergey, V.1 aGazzano, Olivier1 aGoldschmidt, Elizabeth1 aEldredge, Zachary, D.1 aHuber, Tobias1 aLoo, Vivien1 aSolomon, Glenn, S. uhttps://link.aps.org/doi/10.1103/PhysRevX.7.04103601290nas a2200121 4500008004100000245007000041210006900111260001500180520090300195100001701098700001601115856003701131 2017 eng d00aThermodynamic Analysis of Classical and Quantum Search Algorithms0 aThermodynamic Analysis of Classical and Quantum Search Algorithm c2017/09/293 a

We analyze the performance of classical and quantum search algorithms from a thermodynamic perspective, focusing on resources such as time, energy, and memory size. We consider two examples that are relevant to post-quantum cryptography: Grover’s search algorithm, and the quantum algorithm for collisionfinding. Using Bennett’s “Brownian” model of low-power reversible computation, we show classical algorithms that have the same asymptotic energy consumption as these quantum algorithms. Thus, the quantum advantage in query complexity does not imply a reduction in these thermodynamic resource costs. In addition, we present realistic estimates of the resource costs of quantum and classical search, for near-future computing technologies. We find that, if memory is cheap, classical exhaustive search can be surprisingly competitive with Grover’s algorithm.

1 aPerlner, Ray1 aLiu, Yi-Kai uhttps://arxiv.org/abs/1709.1051001530nas a2200217 4500008004100000245006000041210006000101260001500161300001100176490000800187520092200195100001501117700001601132700001601148700001101164700001901175700002101194700001901215700001801234856006001252 2017 eng d00aThreshold Dynamics of a Semiconductor Single Atom Maser0 aThreshold Dynamics of a Semiconductor Single Atom Maser c2017/08/31 a0977020 v1193 a

We demonstrate a single atom maser consisting of a semiconductor double quantum dot (DQD) that is embedded in a high-quality-factor microwave cavity. A finite bias drives the DQD out of equilibrium, resulting in sequential single electron tunneling and masing. We develop a dynamic tuning protocol that allows us to controllably increase the time-averaged repumping rate of the DQD at a fixed level detuning, and quantitatively study the transition through the masing threshold. We further examine the crossover from incoherent to coherent emission by measuring the photon statistics across the masing transition. The observed threshold behavior is in agreement with an existing single atom maser theory when small corrections from lead emission are taken into account.

1 aLiu, Y.-Y.1 aStehlik, J.1 aEichler, C.1 aMi, X.1 aHartke, T., R.1 aGullans, Michael1 aTaylor, J., M.1 aPetta, J., R. uhttps://link.aps.org/doi/10.1103/PhysRevLett.119.09770201580nas a2200181 4500008004100000245005200041210005200093260001500145300001100160490000700171520107600178100002301254700002101277700001901298700002001317700002401337856003701361 2017 eng d00aValley Blockade in a Silicon Double Quantum Dot0 aValley Blockade in a Silicon Double Quantum Dot c2017/11/13 a2053020 v963 a

Electrical transport in double quantum dots (DQDs) illuminates many interesting features of the dots' carrier states. Recent advances in silicon quantum information technologies have renewed interest in the valley states of electrons confined in silicon. Here we show measurements of DC transport through a mesa-etched silicon double quantum dot. Comparing bias triangles (i.e., regions of allowed current in DQDs) at positive and negative bias voltages we find a systematic asymmetry in the size of the bias triangles at the two bias polarities. Asymmetries of this nature are associated with blocking of tunneling events due to the occupation of a metastable state. Several features of our data lead us to conclude that the states involved are not simple spin states. Rather, we develop a model based on selective filling of valley states in the DQD that is consistent with all of the qualitative features of our data.

1 aPerron, Justin, K.1 aGullans, Michael1 aTaylor, J., M.1 aStewart, M., D.1 aZimmerman, Neil, M. uhttps://arxiv.org/abs/1607.0610701556nas 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/1510.0871001662nas a2200217 4500008004100000245004300041210004300084260001500127300001100142490000600153520108300159100001601242700001501258700001601273700001901289700001101308700002101319700001901340700001801359856006701377 2016 eng d00aDouble Quantum Dot Floquet Gain Medium0 aDouble Quantum Dot Floquet Gain Medium c2016/11/07 a0410270 v63 a

Strongly driving a two-level quantum system with light leads to a ladder of Floquet states separated by the photon energy. Nanoscale quantum devices allow the interplay of confined electrons, phonons, and photons to be studied under strong driving conditions. Here we show that a single electron in a periodically driven DQD functions as a "Floquet gain medium," where population imbalances in the DQD Floquet quasi-energy levels lead to an intricate pattern of gain and loss features in the cavity response. We further measure a large intra-cavity photon number n_c in the absence of a cavity drive field, due to equilibration in the Floquet picture. Our device operates in the absence of a dc current -- one and the same electron is repeatedly driven to the excited state to generate population inversion. These results pave the way to future studies of non-classical light and thermalization of driven quantum systems.

1 aStehlik, J.1 aLiu, Y.-Y.1 aEichler, C.1 aHartke, T., R.1 aMi, X.1 aGullans, Michael1 aTaylor, J., M.1 aPetta, J., R. uhttp://journals.aps.org/prx/abstract/10.1103/PhysRevX.6.04102701855nas a2200157 4500008004100000245011400041210006900155260001500224300001100239490000700250520131500257100001801572700002001590700001901610856006801629 2016 eng d00aA Hubbard model for ultracold bosonic atoms interacting via zero-point-energy induced three-body interactions0 aHubbard model for ultracold bosonic atoms interacting via zeropo c2016/04/19 a0436160 v933 a

We show that for ultra-cold neutral bosonic atoms held in a three-dimensional periodic potential or optical lattice, a Hubbard model with dominant, attractive three-body interactions can be generated. In fact, we derive that the effect of pair-wise interactions can be made small or zero starting from the realization that collisions occur at the zero-point energy of an optical lattice site and the strength of the interactions is energy dependent from effective-range contributions. We determine the strength of the two- and three-body interactions for scattering from van-der-Waals potentials and near Fano-Feshbach resonances. For van-der-Waals potentials, which for example describe scattering of alkaline-earth atoms, we find that the pair-wise interaction can only be turned off for species with a small negative scattering length, leaving the 88Sr isotope a possible candidate. Interestingly, for collisional magnetic Feshbach resonances this restriction does not apply and there often exist magnetic fields where the two-body interaction is small. We illustrate this result for several known narrow resonances between alkali-metal atoms as well as chromium atoms. Finally, we compare the size of the three-body interaction with hopping rates and describe limits due to three-body recombination.

1 aPaul, Saurabh1 aJohnson, P., R.1 aTiesinga, Eite uhttp://journals.aps.org/pra/abstract/10.1103/PhysRevA.93.04361601692nas a2200181 4500008004100000245007500041210006900116260001500185520116000200100001801360700001501378700001801393700001901411700001601430700001401446700001401460856003601474 2016 eng d00aJoint product numerical range and geometry of reduced density matrices0 aJoint product numerical range and geometry of reduced density ma c2016/06/233 aThe reduced density matrices of a many-body quantum system form a convex set, whose three-dimensional projection Θ is convex in R3. The boundary ∂Θ of Θ may exhibit nontrivial geometry, in particular ruled surfaces. Two physical mechanisms are known for the origins of ruled surfaces: symmetry breaking and gapless. In this work, we study the emergence of ruled surfaces for systems with local Hamiltonians in infinite spatial dimension, where the reduced density matrices are known to be separable as a consequence of the quantum de Finetti's theorem. This allows us to identify the reduced density matrix geometry with joint product numerical range Π of the Hamiltonian interaction terms. We focus on the case where the interaction terms have certain structures, such that ruled surface emerge naturally when taking a convex hull of Π. We show that, a ruled surface on ∂Θ sitting in Π has a gapless origin, otherwise it has a symmetry breaking origin. As an example, we demonstrate that a famous ruled surface, known as the oloid, is a possible shape of Θ, with two boundary pieces of symmetry breaking origin separated by two gapless lines.1 aChen, Jianxin1 aGuo, Cheng1 aJi, Zhengfeng1 aPoon, Yiu-Tung1 aYu, Nengkun1 aZeng, Bei1 aZhou, Jie uhttp://arxiv.org/abs/1606.0742201559nas a2200157 4500008004100000245008500041210006900126260001500195300001100210490000700221520104000228100002301268700002501291700001701316856006801333 2016 eng d00aMany-body decoherence dynamics and optimised operation of a single-photon switch0 aManybody decoherence dynamics and optimised operation of a singl c2016/09/13 a0920010 v183 a

We develop a theoretical framework to characterize the decoherence dynamics due to multi-photon scattering in an all-optical switch based on Rydberg atom induced nonlinearities. By incorporating the knowledge of this decoherence process into optimal photon storage and retrieval strategies, we establish optimised switching protocols for experimentally relevant conditions, and evaluate the corresponding limits in the achievable fidelities. Based on these results we work out a simplified description that reproduces recent experiments [arXiv:1511.09445] and provides a new interpretation in terms of many-body decoherence involving multiple incident photons and multiple gate excitations forming the switch. Aside from offering insights into the operational capacity of realistic photon switching capabilities, our work provides a complete description of spin wave decoherence in a Rydberg quantum optics setting, and has immediate relevance to a number of further applications employing photon storage in Rydberg media. 

1 aMurray, Callum, R.1 aGorshkov, Alexey, V.1 aPohl, Thomas uhttp://iopscience.iop.org/article/10.1088/1367-2630/18/9/09200101586nas a2200169 4500008004100000245006900041210006900110260001500179490000900194520108300203100002001286700001601306700001801322700001801340700002101358856003701379 2016 eng d00aMeasurement Protocol for the Entanglement Spectrum of Cold Atoms0 aMeasurement Protocol for the Entanglement Spectrum of Cold Atoms c2016/11/220 v6(4)3 a

Entanglement, and, in particular the entanglement spectrum, plays a major role in characterizing many-body quantum systems. While there has been a surge of theoretical works on the subject, no experimental measurement has been performed to date because of the lack of an implementable measurement scheme. Here, we propose a measurement protocol to access the entanglement spectrum of many-body states in experiments with cold atoms in optical lattices. Our scheme effectively performs a Ramsey spectroscopy of the entanglement Hamiltonian and is based on the ability to produce several copies of the state under investigation together with the possibility to perform a global swap gate between two copies conditioned on the state of an auxiliary qubit. We show how the required conditional swap gate can be implemented with cold atoms, either by using Rydberg interactions or coupling the atoms to a cavity mode. We illustrate these ideas on a simple (extended) Bose-Hubbard model where such a measurement protocol reveals topological features of the Haldane phase. 

1 aPichler, Hannes1 aZhu, Guanyu1 aSeif, Alireza1 aZoller, Peter1 aHafezi, Mohammad uhttps://arxiv.org/abs/1605.0862401525nas a2200145 4500008004100000245007500041210006900116260001500185520106700200100001801267700002001285700001901305700001901324856003601343 2016 eng d00aObservation of Optomechanical Quantum Correlations at Room Temperature0 aObservation of Optomechanical Quantum Correlations at Room Tempe c2016/05/183 a

By shining laser light through a nanomechanical beam, we measure the beam's thermally driven vibrations and perturb its motion with optical forces at a level dictated by the Heisenberg measurement-disturbance uncertainty relation. Such quantum backaction is typically difficult to observe at room temperature where the motion driven by optical quantum intensity fluctuations is many orders of magnitude smaller than the thermal motion. We demonstrate a cross-correlation technique to distinguish optically driven motion from thermally driven motion, observing this quantum backaction signature up to room temperature. While it is often difficult to absolutely calibrate optical detection, we use the scale of the quantum correlations, which is determined by fundamental constants, to gauge the size of thermal motion, demonstrating a path towards absolute thermometry with quantum mechanically calibrated ticks.

1 aPurdy, T., P.1 aGrutter, K., E.1 aSrinivasan, K.1 aTaylor, J., M. uhttp://arxiv.org/abs/1605.0566401486nas a2200181 4500008004100000245004800041210004800089260001500137300001100152490000700163520100000170100001801170700002101188700002301209700001901232700001701251856003601268 2016 eng d00aPhotoassociation of spin polarized Chromium0 aPhotoassociation of spin polarized Chromium c2016/02/29 a0214060 v933 aWe report the homonuclear photoassociation (PA) of ultracold 52Cr atoms in an optical dipole trap. This constitutes the first measurement of PA in an element with total electron spin S~>1. Although Cr, with its 7S3 ground and 7P4,3,2 excited states, is expected to have a complicated PA spectrum we show that a spin polarized cloud exhibits a remarkably simple PA spectrum when circularly polarized light is applied. Over a scan range of 20 GHz below the 7P3 asymptote we observe two distinct vibrational series each following a LeRoy-Bernstein law for a C3/R3 potential with excellent agreement. We determine the C3 coefficients of the Hund's case c) relativistic adiabatic potentials to be -1.83±0.02 a.u. and -1.46±0.01a.u.. Theoretical non-rotating Movre-Pichler calculations enable a first assignment of the series to Ω=6u and 5g potential energy curves. In a different set of experiments we disturb the selection rules by a transverse magnetic field which leads to additional PA series.1 aRührig, Jahn1 aBäuerle, Tobias1 aJulienne, Paul, S.1 aTiesinga, Eite1 aPfau, Tilman uhttp://arxiv.org/abs/1512.0437801933nas 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/1601.0537901224nas a2200169 4500008004100000245005300041210005300094260001500147300001100162490000700173520074800180100001800928700002400946700001800970700001900988856004701007 2016 eng d00aQuantifying the coherence of pure quantum states0 aQuantifying the coherence of pure quantum states c2016/10/07 a0423130 v943 a

In recent years, several measures have been proposed for characterizing the coherence of a given quantum state. We derive several results that illuminate how these measures behave when restricted to pure states. Notably, we present an explicit characterization of the closest incoherent state to a given pure state under the trace distance measure of coherence, and we affirm a recent conjecture that the ℓ1 measure of coherence of a pure state is never smaller than its relative entropy of coherence. We then use our result to show that the states maximizing the trace distance of coherence are exactly the maximally coherent states, and we derive a new inequality relating the negativity and distillable entanglement of pure states.

1 aChen, Jianxin1 aJohnston, Nathaniel1 aLi, Chi-Kwong1 aPlosker, Sarah uhttps://doi.org/10.1103/PhysRevA.94.04231301372nas a2200181 4500008004100000245007800041210006900119260001500188300001100203490000800214520084100222100002101063700001601084700001701100700001801117700001901135856003601154 2016 eng d00aSisyphus Thermalization of Photons in a Cavity-Coupled Double Quantum Dot0 aSisyphus Thermalization of Photons in a CavityCoupled Double Qua c2016/07/25 a0568010 v1173 a

A strongly driven quantum system, coupled to a thermalizing bath, generically evolves into a highly non-thermal state as the external drive competes with the equilibrating force of the bath. We demonstrate a notable exception to this picture for a microwave resonator interacting with a periodically driven double quantum dot (DQD). In the limit of strong driving and long times, we show that the resonator field can be driven into a thermal state with a chemical potential given by a harmonic of the drive frequency. Such tunable chemical potentials are achievable with current devices and would have broad utility for quantum simulation in circuit quantum electrodynamics. As an example, we show how several DQDs embedded in an array of microwave resonators can induce a phase transition to a Bose-Einstein condensate of light.

1 aGullans, Michael1 aStehlik, J.1 aLiu, Y., -Y.1 aPetta, J., R.1 aTaylor, J., M. uhttp://arxiv.org/abs/1512.0124801747nas a2200241 4500008004100000245009400041210006900135260001500204300001100219490000800230520106300238100001401301700001301315700001601328700001801344700001801362700001601380700002001396700001701416700001401433700002201447856003601469 2016 eng d00aTomography is necessary for universal entanglement detection with single-copy observables0 aTomography is necessary for universal entanglement detection wit c2016/06/07 a2305010 v1163 aEntanglement, one of the central mysteries of quantum mechanics, plays an essential role in numerous applications of quantum information theory. A natural question of both theoretical and experimental importance is whether universal entanglement detection is possible without full state tomography. In this work, we prove a no-go theorem that rules out this possibility for any non-adaptive schemes that employ single-copy measurements only. We also examine in detail a previously implemented experiment, which claimed to detect entanglement of two-qubit states via adaptive single-copy measurements without full state tomography. By performing the experiment and analyzing the data, we demonstrate that the information gathered is indeed sufficient to reconstruct the state. These results reveal a fundamental limit for single-copy measurements in entanglement detection, and provides a general framework to study the detection of other interesting properties of quantum states, such as the positivity of partial transpose and the k-symmetric extendibility.1 aLu, Dawei1 aXin, Tao1 aYu, Nengkun1 aJi, Zhengfeng1 aChen, Jianxin1 aLong, Guilu1 aBaugh, Jonathan1 aPeng, Xinhua1 aZeng, Bei1 aLaflamme, Raymond uhttp://arxiv.org/abs/1511.0058113859nas a2200145 45000080041000002450084000412100069001252600015001943000011002094900007002205201338100227100001813608700001913626856006813645 2016 eng d00aWannier functions using a discrete variable representation for optical lattices0 aWannier functions using a discrete variable representation for o c2016/09/07 a0336060 v943 a

We propose a numerical method using the discrete variable representation (DVR) for constructing real-valued Wannier functions localized in a unit cell for both symmetric and asymmetric periodic potentials. We apply these results to finding Wannier functions for ultracold atoms trapped in laser-generated optical lattices. Following S. Kivelson [Phys. Rev. B 26, 4269 (1982)], for a symmetric lattice with inversion symmetry, we construct Wannier functions as eigenstates of the position operators xˆ, yˆ, and zˆ restricted to single-particle Bloch functions belonging to one or more bands. To ensure that the Wannier functions are real-valued, we numerically obtain the band structure and real-valued eigenstates using a uniform Fourier grid DVR. We then show, by a comparison of tunneling energies, that the Wannier functions are accurate for both inversion-symmetric and asymmetric potentials to better than 10 significant digits when using double-precision arithmetic. The calculations are performed for an optical lattice with double-wells per unit cell with tunable asymmetry along the x axis and a single sinusoidal potential along the perpendicular directions. Localized functions at the two potential minima within each unit cell are similarly constructed, but using a superposition of single-particle solutions from the two lowest bands. We finally use these localized basis functions to determine the two-body interaction energies in the Bose-Hubbard model and show the dependence of these energies on lattice asymmetry.

1 aPaul, Saurabh1 aTiesinga, Eite uhttp://journals.aps.org/pra/abstract/10.1103/PhysRevA.94.03360601656nas 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/1411.7036v101250nas a2200217 4500008004100000245007700041210006900118260001500187300001100202490000700213520064200220100001800862700001800880700001800898700001900916700001300935700001600948700001400964700001700978856003700995 2015 eng d00aDiscontinuity of Maximum Entropy Inference and Quantum Phase Transitions0 aDiscontinuity of Maximum Entropy Inference and Quantum Phase Tra c2015/08/10 a0830190 v173 a In this paper, we discuss the connection between two genuinely quantum phenomena --- the discontinuity of quantum maximum entropy inference and quantum phase transitions at zero temperature. It is shown that the discontinuity of the maximum entropy inference of local observable measurements signals the non-local type of transitions, where local density matrices of the ground state change smoothly at the transition point. We then propose to use the quantum conditional mutual information of the ground state as an indicator to detect the discontinuity and the non-local type of quantum phase transitions in the thermodynamic limit. 1 aChen, Jianxin1 aJi, Zhengfeng1 aLi, Chi-Kwong1 aPoon, Yiu-Tung1 aShen, Yi1 aYu, Nengkun1 aZeng, Bei1 aZhou, Duanlu uhttp://arxiv.org/abs/1406.5046v201211nas a2200145 4500008004100000245006900041210006900110260001500179490000700194520077300201100001800974700001800992700001801010856003701028 2015 eng d00aDriving Rabi oscillations at the giant dipole resonance in xenon0 aDriving Rabi oscillations at the giant dipole resonance in xenon c11/23/20150 v923 a

Free-electron lasers (FELs) produce short and very intense light pulses in the XUV and x-ray regimes. We investigate the possibility to drive Rabi oscillations in xenon with an intense FEL pulse by using the unusually large dipole strength of the giant-dipole resonance (GDR). The GDR decays within less than 30 as due to its position, which is above the 4d ionization threshold. We find that intensities around 1018 W/cm2 are required to induce Rabi oscillations with a period comparable to the lifetime. The pulse duration should not exceed 100 as because xenon will be fully ionized within a few lifetimes. Rabi oscillations reveal themselves also in the photoelectron spectrum in form of Autler-Townes splittings extending over several tens of electronvolt.

1 aPabst, Stefan1 aWang, Daochen1 aSantra, Robin uhttps://arxiv.org/abs/1511.0005801270nas a2200193 4500008004100000245005700041210005700098260001500155300001100170490000700181520071900188100002700907700002000934700002100954700001700975700002200992700002501014856003701039 2015 eng d00aFractional Quantum Hall States of Rydberg Polaritons0 aFractional Quantum Hall States of Rydberg Polaritons c2015/03/31 a0338380 v913 a We propose a scheme for realizing fractional quantum Hall states of light. In our scheme, photons of two polarizations are coupled to different atomic Rydberg states to form two flavors of Rydberg polaritons that behave as an effective spin. An array of optical cavity modes overlapping with the atomic cloud enables the realization of an effective spin-1/2 lattice. We show that the dipolar interaction between such polaritons, inherited from the Rydberg states, can be exploited to create a flat, topological band for a single spin-flip excitation. At half filling, this gives rise to a photonic (or polaritonic) fractional Chern insulator -- a lattice-based, fractional quantum Hall state of light. 1 aMaghrebi, Mohammad, F.1 aYao, Norman, Y.1 aHafezi, Mohammad1 aPohl, Thomas1 aFirstenberg, Ofer1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/1411.6624v101515nas a2200181 4500008004100000245007100041210006900112260001500181300001100196490000700207520099200214100001701206700001601223700002101239700001901260700001801279856003601297 2015 eng d00aInjection Locking of a Semiconductor Double Quantum Dot Micromaser0 aInjection Locking of a Semiconductor Double Quantum Dot Micromas c2015/11/02 a0538020 v923 a Emission linewidth is an important figure of merit for masers and lasers. We recently demonstrated a semiconductor double quantum dot (DQD) micromaser where photons are generated through single electron tunneling events. Charge noise directly couples to the DQD energy levels, resulting in a maser linewidth that is more than 100 times larger than the Schawlow-Townes prediction. Here we demonstrate a linewidth narrowing of more than a factor 10 by locking the DQD emission to a coherent tone that is injected to the input port of the cavity. We measure the injection locking range as a function of cavity input power and show that it is in agreement with the Adler equation. The position and amplitude of distortion sidebands that appear outside of the injection locking range are quantitatively examined. Our results show that this unconventional maser, which is impacted by strong charge noise and electron-phonon coupling, is well described by standard laser models. 1 aLiu, Y., -Y.1 aStehlik, J.1 aGullans, Michael1 aTaylor, J., M.1 aPetta, J., R. uhttp://arxiv.org/abs/1508.0414701804nas a2200145 4500008004100000245007600041210006900117260001500186300001100201490000700212520133400219100001801553700001901571856006801590 2015 eng d00aLarge effective three-body interaction in a double-well optical lattice0 aLarge effective threebody interaction in a doublewell optical la c2015/08/03 a0236020 v923 a We study ultracold atoms in an optical lattice with two local minima per unit cell and show that the low energy states of a multi-band Bose-Hubbard (BH) Hamiltonian with only pair-wise interactions is equivalent to an effective single-band Hamiltonian with strong three-body interactions. We focus on a double-well optical lattice with a symmetric double well along the $x$ axis and single well structure along the perpendicular directions. Tunneling and two-body interaction energies are obtained from an exact band-structure calculation and numerically-constructed Wannier functions in order to construct a BH Hamiltonian spanning the lowest two bands. Our effective Hamiltonian is constructed from the ground state of the $N$-atom Hamiltonian for each unit cell obtained within the subspace spanned by the Wannier functions of two lowest bands. The model includes hopping between ground states of neighboring unit cells. We show that such an effective Hamiltonian has strong three-body interactions that can be easily tuned by changing the lattice parameters. Finally, relying on numerical mean-field simulations, we show that the effective Hamiltonian is an excellent approximation of the two-band BH Hamiltonian over a wide range of lattice parameters, both in the superfluid and Mott insulator regions. 1 aPaul, Saurabh1 aTiesinga, Eite uhttp://journals.aps.org/pra/abstract/10.1103/PhysRevA.92.02360201186nas a2200181 4500008004100000245004300041210004300084260001500127300000800142490000700150520060900157100002300766700003000789700001800819700001900837700001900856856012900875 2015 eng d00aOptomechanical reference accelerometer0 aOptomechanical reference accelerometer c2015/09/08 a6540 v523 a

We present an optomechanical accelerometer with high dynamic range, high bandwidth and read-out noise levels below 8 ${\mu}$g/$\sqrt{\mathrm{Hz}}$. The straightforward assembly and low cost of our device make it a prime candidate for on-site reference calibrations and autonomous navigation. We present experimental data taken with a vacuum sealed, portable prototype and deduce the achieved bias stability and scale factor accuracy. Additionally, we present a comprehensive model of the device physics that we use to analyze the fundamental noise sources and accuracy limitations of such devices.

1 aGerberding, Oliver1 aCervantes, Felipe, Guzman1 aMelcher, John1 aPratt, Jon, R.1 aTaylor, J., M. uhttp://iopscience.iop.org/article/10.1088/0026-1394/52/5/654/meta;jsessionid=C2B417A5CD50B9B57EE14C78E1783802.ip-10-40-1-10501003nas a2200181 4500008004100000245006900041210006800110260001500178300001100193490000800204520048000212100002100692700001700713700001600730700001800746700001900764856003800783 2015 eng d00aPhonon-Assisted Gain in a Semiconductor Double Quantum Dot Maser0 aPhononAssisted Gain in a Semiconductor Double Quantum Dot Maser c2015/05/13 a1968020 v1143 aWe develop a microscopic model for the recently demonstrated double quantum dot (DQD) maser. In characterizing the gain of this device we find that, in addition to the direct stimulated emission of photons, there is a large contribution from the simultaneous emission of a photon and a phonon, i.e., the phonon sideband. We show that this phonon-assisted gain typically dominates the overall gain which leads to masing. Recent experimental data are well fit with our model. 1 aGullans, Michael1 aLiu, Y., -Y.1 aStehlik, J.1 aPetta, J., R.1 aTaylor, J., M. uhttp://arxiv.org/abs/1501.03499v301150nas a2200193 4500008004100000245004800041210004800089260001500137300001400152490000800166520063700174100001700811700001600828700001600844700002100860700001900881700001800900856003800918 2015 eng d00aSemiconductor double quantum dot micromaser0 aSemiconductor double quantum dot micromaser c2015/01/15 a285 - 2870 v3473 a The coherent generation of light, from masers to lasers, relies upon the specific structure of the individual emitters that lead to gain. Devices operating as lasers in the few-emitter limit provide opportunities for understanding quantum coherent phenomena, from THz sources to quantum communication. Here we demonstrate a maser that is driven by single electron tunneling events. Semiconductor double quantum dots (DQDs) serve as a gain medium and are placed inside of a high quality factor microwave cavity. We verify maser action by comparing the statistics of the emitted microwave field above and below the maser threshold. 1 aLiu, Y., -Y.1 aStehlik, J.1 aEichler, C.1 aGullans, Michael1 aTaylor, J., M.1 aPetta, J., R. uhttp://arxiv.org/abs/1507.06359v101319nas a2200169 4500008004100000245004200041210004100083260001400124490000800138520086500146100001901011700001701030700002101047700002501068700001901093856003701112 2014 eng d00aKitaev chains with long-range pairing0 aKitaev chains with longrange pairing c2014/10/90 v1133 a We propose and analyze a generalization of the Kitaev chain for fermions with long-range $p$-wave pairing, which decays with distance as a power-law with exponent $\alpha$. Using the integrability of the model, we demonstrate the existence of two types of gapped regimes, where correlation functions decay exponentially at short range and algebraically at long range ($\alpha > 1$) or purely algebraically ($\alpha < 1$). Most interestingly, along the critical lines, long-range pairing is found to break conformal symmetry for sufficiently small $\alpha$. This is accompanied by a violation of the area law for the entanglement entropy in large parts of the phase diagram in the presence of a gap, and can be detected via the dynamics of entanglement following a quench. Some of these features may be relevant for current experiments with cold atomic ions. 1 aVodola, Davide1 aLepori, Luca1 aErcolessi, Elisa1 aGorshkov, Alexey, V.1 aPupillo, Guido uhttp://arxiv.org/abs/1405.5440v202620nas a2200253 4500008004100000245007300041210006900114260001300183300001200196490000800208520192500216100001402141700001702155700001502172700002302187700001602210700001402226700001902240700001802259700001402277700001902291700001902310856003702329 2014 eng d00aOptical detection of radio waves through a nanomechanical transducer0 aOptical detection of radio waves through a nanomechanical transd c2014/3/5 a81 - 850 v5073 aLow-loss transmission and sensitive recovery of weak radio-frequency (rf) and microwave signals is an ubiquitous technological challenge, crucial in fields as diverse as radio astronomy, medical imaging, navigation and communication, including those of quantum states. Efficient upconversion of rf-signals to an optical carrier would allow transmitting them via optical fibers dramatically reducing losses, and give access to the mature toolbox of quantum optical techniques, routinely enabling quantum-limited signal detection. Research in the field of cavity optomechanics has shown that nanomechanical oscillators can couple very strongly to either microwave or optical fields. An oscillator accommodating both functionalities would bear great promise as the intermediate platform in a radio-to-optical transduction cascade. Here, we demonstrate such an opto-electro-mechanical transducer utilizing a high-Q nanomembrane. A moderate voltage bias (<10V) is sufficient to induce strong coupling between the voltage fluctuations in a rf resonance circuit and the membrane's displacement, which is simultaneously coupled to light reflected off its metallized surface. The circuit acts as an antenna; the voltage signals it induces are detected as an optical phase shift with quantum-limited sensitivity. The half-wave voltage is in the microvolt range, orders of magnitude below that of standard optical modulators. The noise added by the membrane is suppressed by the electro-mechanical cooperativity C~6800 and has a temperature of 40mK, far below 300K where the entire device is operated. This corresponds to a sensitivity limit as low as 5 pV/Hz^1/2, or -210dBm/Hz in a narrow band around 1 MHz. Our work introduces an entirely new approach to all-optical, ultralow-noise detection of classical electronic signals, and sets the stage for coherent upconversion of low-frequency quantum signals to the optical domain. 1 aBagci, T.1 aSimonsen, A.1 aSchmid, S.1 aVillanueva, L., G.1 aZeuthen, E.1 aAppel, J.1 aTaylor, J., M.1 aSørensen, A.1 aUsami, K.1 aSchliesser, A.1 aPolzik, E., S. uhttp://arxiv.org/abs/1307.3467v201013nas a2200133 4500008004100000245006000041210006000101260001500161520060100176100002400777700002200801700001900823856003700842 2014 eng d00aQuantum Algorithms for Fermionic Quantum Field Theories0 aQuantum Algorithms for Fermionic Quantum Field Theories c2014/04/283 a Extending previous work on scalar field theories, we develop a quantum algorithm to compute relativistic scattering amplitudes in fermionic field theories, exemplified by the massive Gross-Neveu model, a theory in two spacetime dimensions with quartic interactions. The algorithm introduces new techniques to meet the additional challenges posed by the characteristics of fermionic fields, and its run time is polynomial in the desired precision and the energy. Thus, it constitutes further progress towards an efficient quantum algorithm for simulating the Standard Model of particle physics. 1 aJordan, Stephen, P.1 aLee, Keith, S. M.1 aPreskill, John uhttp://arxiv.org/abs/1404.7115v101375nas a2200157 4500008004100000245007100041210006900112260001500181300001400196490000700210520089800217100002401115700002201139700001901161856003701180 2014 eng d00aQuantum Computation of Scattering in Scalar Quantum Field Theories0 aQuantum Computation of Scattering in Scalar Quantum Field Theori c2014/09/01 a1014-10800 v143 a Quantum field theory provides the framework for the most fundamental physical theories to be confirmed experimentally, and has enabled predictions of unprecedented precision. However, calculations of physical observables often require great computational complexity and can generally be performed only when the interaction strength is weak. A full understanding of the foundations and rich consequences of quantum field theory remains an outstanding challenge. We develop a quantum algorithm to compute relativistic scattering amplitudes in massive phi-fourth theory in spacetime of four and fewer dimensions. The algorithm runs in a time that is polynomial in the number of particles, their energy, and the desired precision, and applies at both weak and strong coupling. Thus, it offers exponential speedup over existing classical methods at high precision or strong coupling. 1 aJordan, Stephen, P.1 aLee, Keith, S. M.1 aPreskill, John uhttp://arxiv.org/abs/1112.4833v101850nas 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/1406.0937v101304nas a2200169 4500008004100000245009000041210006900131260001400200490000700214520080200221100001501023700001901038700001601057700001201073700001201085856003701097 2014 eng d00aSpin-orbit-coupled topological Fulde-Ferrell states of fermions in a harmonic trap 0 aSpinorbitcoupled topological FuldeFerrell states of fermions in  c2014/11/70 v903 a Motivated by recent experimental breakthroughs in generating spin-orbit coupling in ultracold Fermi gases using Raman laser beams, we present a systematic study of spin-orbit-coupled Fermi gases confined in a quasi-one-dimensional trap in the presence of an in-plane Zeeman field (which can be realized using a finite two-photon Raman detuning). We find that a topological Fulde-Ferrell state will emerge, featuring finite-momentum Cooper pairing and zero-energy Majorana excitations localized near the edge of the trap based on the self-consistent Bogoliubov-de Genes (BdG) equations. We find analytically the wavefunctions of the Majorana modes. Finally using the time-dependent BdG we show how the finite-momentum pairing field manifests itself in the expansion dynamics of the atomic cloud. 1 aJiang, Lei1 aTiesinga, Eite1 aLiu, Xia-Ji1 aHu, Hui1 aPu, Han uhttp://arxiv.org/abs/1404.6211v100504nas a2200169 4500008004100000245005300041210005300094300000700147490000800154100002200162700002300184700001700207700002500224700002300249700002000272856004200292 2013 eng d00aAttractive Photons in a Quantum Nonlinear Medium0 aAttractive Photons in a Quantum Nonlinear Medium a710 v5021 aFirstenberg, Ofer1 aPeyronel, Thibault1 aLiang, Qi-Yu1 aGorshkov, Alexey, V.1 aLukin, Mikhail, D.1 aVuletic, Vladan uhttp://dx.doi.org/10.1038/nature1251201151nas a2200145 4500008004100000245005800041210005700099260001300156490000800169520073200177100002500909700001700934700001700951856003700968 2013 eng d00aDissipative Many-body Quantum Optics in Rydberg Media0 aDissipative Manybody Quantum Optics in Rydberg Media c2013/4/90 v1103 a We develop a theoretical framework for the dissipative propagation of quantized light in interacting optical media under conditions of electromagnetically induced transparency (EIT). The theory allows us to determine the peculiar spatiotemporal structure of the output of two complementary Rydberg-EIT-based light-processing modules: the recently demonstrated single-photon filter and the recently proposed single-photon subtractor, which, respectively, let through and absorb a single photon. In addition to being crucial for applications of these and other optical quantum devices, the theory opens the door to the study of exotic dissipative many-body dynamics of strongly interacting photons in nonlinear nonlocal media. 1 aGorshkov, Alexey, V.1 aNath, Rejish1 aPohl, Thomas uhttp://arxiv.org/abs/1211.7060v102343nas a2200133 4500008004100000245010800041210006900149260001400218490000700232520189600239100001802135700001902153856003702172 2013 eng d00aFormation and decay of Bose-Einstein condensates in an excited band of a double-well optical lattice 0 aFormation and decay of BoseEinstein condensates in an excited ba c2013/9/120 v883 a We study the formation and collision-aided decay of an ultra-cold atomic Bose-Einstein condensate in the first excited band of a double-well 2D-optical lattice with weak harmonic confinement in the perpendicular $z$ direction. This lattice geometry is based on an experiment by Wirth et al. The double well is asymmetric, with the local ground state in the shallow well nearly degenerate with the first excited state of the adjacent deep well. We compare the band structure obtained from a tight-binding (TB) model with that obtained numerically using a plane wave basis. We find the TB model to be in quantitative agreement for the lowest two bands, qualitative for next two bands, and inadequate for even higher bands. The band widths of the excited bands are much larger than the harmonic oscillator energy spacing in the $z$ direction. We then study the thermodynamics of a non-interacting Bose gas in the first excited band. We estimate the condensate fraction and critical temperature, $T_c$, as functions of lattice parameters. For typical atom numbers, the critical energy $k_BT_c$, with $k_B$ the Boltzmann constant, is larger than the excited band widths and harmonic oscillator energy. Using conservation of total energy and atom number, we show that the temperature increases after the lattice transformation. Finally, we estimate the time scale for a two-body collision-aided decay of the condensate as a function of lattice parameters. The decay involves two processes, the dominant one in which both colliding atoms decay to the ground band, and the second involving excitation of one atom to a higher band. For this estimate, we have used TB wave functions for the lowest four bands, and numerical estimates for higher bands. The decay rate rapidly increases with lattice depth, but stays smaller than the tunneling rate between the $s$ and $p$ orbitals in adjacent wells. 1 aPaul, Saurabh1 aTiesinga, Eite uhttp://arxiv.org/abs/1308.4449v100562nas a2200193 4500008004100000245005900041210005800100300000700158490000700165100001900172700001600191700001600207700001700223700001500240700002500255700001900280700001200299856005700311 2013 eng d00aQuantum Nonlinear Optics: Strongly Interacting Photons0 aQuantum Nonlinear Optics Strongly Interacting Photons a480 v241 aFirstenberg, O1 aLukin, M, D1 aPeyronel, T1 aLiang, Q, -Y1 aVuletic, V1 aGorshkov, Alexey, V.1 aHofferberth, S1 aPohl, T uhttp://www.osa-opn.org/abstract.cfm?URI=opn-24-12-4801731nas a2200145 4500008004100000245007000041210006900111260001300180490000700193520128300200100002401483700002201507700001901529856003701548 2013 eng d00aSoliton dynamics of an atomic spinor condensate on a Ring Lattice0 aSoliton dynamics of an atomic spinor condensate on a Ring Lattic c2013/3/60 v873 a We study the dynamics of macroscopically-coherent matter waves of an ultra-cold atomic spin-one or spinor condensate on a ring lattice of six sites and demonstrate a novel type of spatio-temporal internal Josephson effect. Using a discrete solitary mode of uncoupled spin components as an initial condition, the time evolution of this many-body system is found to be characterized by two dominant frequencies leading to quasiperiodic dynamics at various sites. The dynamics of spatially-averaged and spin-averaged degrees of freedom, however, is periodic enabling an unique identification of the two frequencies. By increasing the spin-dependent atom-atom interaction strength we observe a resonance state, where the ratio of the two frequencies is a characteristic integer multiple and the spin-and-spatial degrees of freedom oscillate in "unison". Crucially, this resonant state is found to signal the onset to chaotic dynamics characterized by a broad band spectrum. In a ferromagnetic spinor condensate with attractive spin-dependent interactions, the resonance is accompanied by a transition from oscillatory- to rotational-type dynamics as the time evolution of the relative phase of the matter wave of the individual spin projections changes from bounded to unbounded. 1 aSatija, Indubala, I1 aPando, Carlos, L.1 aTiesinga, Eite uhttp://arxiv.org/abs/1301.5851v101428nas a2200193 4500008004100000245006800041210006700109260001300176490000800189520085100197100002401048700002501072700002201097700002201119700001801141700001901159700001901178856003701197 2013 eng d00aSpinor dynamics in an antiferromagnetic spin-1 thermal Bose gas0 aSpinor dynamics in an antiferromagnetic spin1 thermal Bose gas c2013/7/90 v1113 a We present experimental observations of coherent spin-population oscillations in a cold thermal, Bose gas of spin-1 sodium-23 atoms. The population oscillations in a multi-spatial-mode thermal gas have the same behavior as those observed in a single-spatial-mode antiferromagnetic spinor Bose Einstein condensate. We demonstrate this by showing that the two situations are described by the same dynamical equations, with a factor of two change in the spin-dependent interaction coefficient, which results from the change to particles with distinguishable momentum states in the thermal gas. We compare this theory to the measured spin population evolution after times up to a few hundreds of ms, finding quantitative agreement with the amplitude and period. We also measure the damping time of the oscillations as a function of magnetic field. 1 aPechkis, Hyewon, K.1 aWrubel, Jonathan, P.1 aSchwettmann, Arne1 aGriffin, Paul, F.1 aBarnett, Ryan1 aTiesinga, Eite1 aLett, Paul, D. uhttp://arxiv.org/abs/1306.4255v101318nas 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/1203.4172v100871nas a2200157 4500008004100000245006300041210006200104260001500166490000700181520037400188100001900562700002200581700002100603700001900624856007000643 2012 eng d00aNon-Recursively Constructible Recursive Families of Graphs0 aNonRecursively Constructible Recursive Families of Graphs c2012/04/160 v193 aIn a publication by Noy and Ribó, it was shown that recursively constructible families of graphs are recursive. The authors also conjecture that the converse holds; that is, recursive families are also recursively constructible. In this paper, we provide two specific counterexamples to this conjecture, which we then extend to an infinite family of counterexamples.1 aBouey, Colleen1 aGraves, Christina1 aOstrander, Aaron1 aPalma, Gregory uhttp://www.combinatorics.org/ojs/index.php/eljc/article/view/221101068nas a2200157 4500008004100000245005000041210005000091260001500141300001600156490000800172520062800180100002400808700002200832700001900854856003700873 2012 eng d00aQuantum Algorithms for Quantum Field Theories0 aQuantum Algorithms for Quantum Field Theories c2012/05/31 a1130 - 11330 v3363 a Quantum field theory reconciles quantum mechanics and special relativity, and plays a central role in many areas of physics. We develop a quantum algorithm to compute relativistic scattering probabilities in a massive quantum field theory with quartic self-interactions (phi-fourth theory) in spacetime of four and fewer dimensions. Its run time is polynomial in the number of particles, their energy, and the desired precision, and applies at both weak and strong coupling. In the strong-coupling and high-precision regimes, our quantum algorithm achieves exponential speedup over the fastest known classical algorithm. 1 aJordan, Stephen, P.1 aLee, Keith, S. M.1 aPreskill, John uhttp://arxiv.org/abs/1111.3633v200654nas a2200193 4500008004100000245008700041210006900128300000700197490000800204100002300212700002200235700001700257700002700274700002500301700001700326700002300343700002000366856007400386 2012 eng d00aQuantum nonlinear optics with single photons enabled by strongly interacting atoms0 aQuantum nonlinear optics with single photons enabled by strongly a570 v4881 aPeyronel, Thibault1 aFirstenberg, Ofer1 aLiang, Qi-Yu1 aHofferberth, Sebastian1 aGorshkov, Alexey, V.1 aPohl, Thomas1 aLukin, Mikhail, D.1 aVuletic, Vladan uhttp://www.nature.com/nature/journal/v488/n7409/full/nature11361.html01053nas a2200157 4500008004100000245008200041210006900123260001500192490000800207520056400215100001900779700002200798700001900820700001900839856003700858 2011 eng d00aLaser cooling and optical detection of excitations in a LC electrical circuit0 aLaser cooling and optical detection of excitations in a LC elect c2011/12/270 v1073 aWe explore a method for laser cooling and optical detection of excitations in a LC electrical circuit. Our approach uses a nanomechanical oscillator as a transducer between optical and electronic excitations. An experimentally feasible system with the oscillator capacitively coupled to the LC and at the same time interacting with light via an optomechanical force is shown to provide strong electro-mechanical coupling. Conditions for improved sensitivity and quantum limited readout of electrical signals with such an "optical loud speaker" are outlined. 1 aTaylor, J., M.1 aSørensen, A., S.1 aMarcus, C., M.1 aPolzik, E., S. uhttp://arxiv.org/abs/1108.2035v101416nas a2200145 4500008004100000245014100041210006900182260001400251490000700265520088800272100002801160700002501188700002001213856003701233 2011 eng d00aLight storage in an optically thick atomic ensemble under conditions of electromagnetically induced transparency and four-wave mixing 0 aLight storage in an optically thick atomic ensemble under condit c2011/6/200 v833 a We study the modification of a traditional electromagnetically induced transparency (EIT) stored light technique that includes both EIT and four-wave mixing (FWM) in an ensemble of hot Rb atoms. The standard treatment of light storage involves the coherent and reversible mapping of one photonic mode onto a collective spin coherence. It has been shown that unwanted, competing processes such as four-wave mixing are enhanced by EIT and can significantly modify the signal optical pulse propagation. We present theoretical and experimental evidence to indicate that while a Stokes field is indeed detected upon retrieval of the signal field, any information originally encoded in a seeded Stokes field is not independently preserved during the storage process. We present a simple model that describes the propagation dynamics of the fields and the impact of FWM on the spin wave. 1 aPhillips, Nathaniel, B.1 aGorshkov, Alexey, V.1 aNovikova, Irina uhttp://arxiv.org/abs/1103.2131v101088nas a2200169 4500008004100000245005200041210005100093260001400144490000800158520060000166100002500766700002400791700002600815700001700841700002300858856003700881 2011 eng d00aPhoton-Photon Interactions via Rydberg Blockade0 aPhotonPhoton Interactions via Rydberg Blockade c2011/9/220 v1073 a We develop the theory of light propagation under the conditions of electromagnetically induced transparency (EIT) in systems involving strongly interacting Rydberg states. Taking into account the quantum nature and the spatial propagation of light, we analyze interactions involving few-photon pulses. We demonstrate that this system can be used for the generation of nonclassical states of light including trains of single photons with an avoided volume between them, for implementing photon-photon quantum gates, as well as for studying many-body phenomena with strongly correlated photons. 1 aGorshkov, Alexey, V.1 aOtterbach, Johannes1 aFleischhauer, Michael1 aPohl, Thomas1 aLukin, Mikhail, D. uhttp://arxiv.org/abs/1103.3700v101036nas a2200181 4500008004100000245006600041210006500107260001400172490000700186520050100193100002500694700001700719700002100736700001800757700002300775700001900798856003700817 2010 eng d00aAdiabatic preparation of many-body states in optical lattices0 aAdiabatic preparation of manybody states in optical lattices c2010/6/220 v813 a We analyze a technique for the preparation of low entropy many body states of atoms in optical lattices based on adiabatic passage. In particular, we show that this method allows preparation of strongly correlated states as stable highest energy states of Hamiltonians that have trivial ground states. As an example, we analyze the generation of antiferromagnetically ordered states by adiabatic change of a staggered field acting on the spins of bosonic atoms with ferromagnetic interactions. 1 aSorensen, Anders, S.1 aAltman, Ehud1 aGullans, Michael1 aPorto, J., V.1 aLukin, Mikhail, D.1 aDemler, Eugene uhttp://arxiv.org/abs/0906.2567v301192nas a2200133 4500008004100000245005800041210005800099260001500157520078600172100002900958700001600987700001801003856003701021 2010 eng d00aEfficient Direct Tomography for Matrix Product States0 aEfficient Direct Tomography for Matrix Product States c2010/02/243 a In this note, we describe a method for reconstructing matrix product states from a small number of efficiently-implementable measurements. Our method is exponentially faster than standard tomography, and it can also be used to certify that the unknown state is an MPS. The basic idea is to use local unitary operations to measure in the Schmidt basis, giving direct access to the MPS representation. This compares favorably with recently and independently proposed methods that recover the MPS tensors by performing a variational minimization, which is computationally intractable in certain cases. Our method also has the advantage of recovering any MPS, while other approaches were limited to special classes of states that exclude important examples such as GHZ and W states. 1 aLandon-Cardinal, Olivier1 aLiu, Yi-Kai1 aPoulin, David uhttp://arxiv.org/abs/1002.4632v101775nas a2200229 4500008004100000245003900041210003900080260001500119300000800134490000600142520116900148100001901317700002301336700002401359700001701383700002601400700001901426700002901445700001601474700001801490856003701508 2010 eng d00aEfficient quantum state tomography0 aEfficient quantum state tomography c2010/12/21 a1490 v13 a Quantum state tomography, the ability to deduce the state of a quantum system from measured data, is the gold standard for verification and benchmarking of quantum devices. It has been realized in systems with few components, but for larger systems it becomes infeasible because the number of quantum measurements and the amount of computation required to process them grows exponentially in the system size. Here we show that we can do exponentially better than direct state tomography for a wide range of quantum states, in particular those that are well approximated by a matrix product state ansatz. We present two schemes for tomography in 1-D quantum systems and touch on generalizations. One scheme requires unitary operations on a constant number of subsystems, while the other requires only local measurements together with more elaborate post-processing. Both schemes rely only on a linear number of experimental operations and classical postprocessing that is polynomial in the system size. A further strength of the methods is that the accuracy of the reconstructed states can be rigorously certified without any a priori assumptions. 1 aCramer, Marcus1 aPlenio, Martin, B.1 aFlammia, Steven, T.1 aGross, David1 aBartlett, Stephen, D.1 aSomma, Rolando1 aLandon-Cardinal, Olivier1 aLiu, Yi-Kai1 aPoulin, David uhttp://arxiv.org/abs/1101.4366v101343nas a2200193 4500008004100000245007300041210006900114260001300183490000700196520075700203100001400960700002500974700002100999700002601020700002001046700002301066700002301089856003701112 2009 eng d00aRealization of Coherent Optically Dense Media via Buffer-Gas Cooling0 aRealization of Coherent Optically Dense Media via BufferGas Cool c2009/1/60 v793 a We demonstrate that buffer-gas cooling combined with laser ablation can be used to create coherent optical media with high optical depth and low Doppler broadening that offers metastable states with low collisional and motional decoherence. Demonstration of this generic technique opens pathways to coherent optics with a large variety of atoms and molecules. We use helium buffer gas to cool 87Rb atoms to below 7 K and slow atom diffusion to the walls. Electromagnetically induced transparency (EIT) in this medium allows for 50% transmission in a medium with initial OD >70 and for slow pulse propagation with large delay-bandwidth products. In the high-OD regime, we observe high-contrast spectrum oscillations due to efficient four-wave mixing. 1 aHong, Tao1 aGorshkov, Alexey, V.1 aPatterson, David1 aZibrov, Alexander, S.1 aDoyle, John, M.1 aLukin, Mikhail, D.1 aPrentiss, Mara, G. uhttp://arxiv.org/abs/0805.1416v200539nas a2200133 4500008004100000245014600041210006900187300000900256490000700265100001900272700002500291700001600316856007300332 2009 eng d00aSlow light propagation and amplification via electromagnetically induced transparency and four-wave mixing in an optically dense atomic vapor0 aSlow light propagation and amplification via electromagnetically a19160 v561 aPhillips, N, B1 aGorshkov, Alexey, V.1 aNovikova, I uhttp://www.informaworld.com/smpp/content db=all content=a91354540501777nas a2200241 4500008004100000245007500041210006900116260001400185490000700199520107300206100001801279700002701297700001801324700001901342700001701361700002101378700001901399700002101418700002001439700001701459700002201476856003701498 2008 eng d00aMultilevel effects in the Rabi oscillations of a Josephson phase qubit0 aMultilevel effects in the Rabi oscillations of a Josephson phase c2008/9/150 v783 a We present Rabi oscillation measurements of a Nb/AlOx/Nb dc superconducting quantum interference device (SQUID) phase qubit with a 100 um^2 area junction acquired over a range of microwave drive power and frequency detuning. Given the slightly anharmonic level structure of the device, several excited states play an important role in the qubit dynamics, particularly at high power. To investigate the effects of these levels, multiphoton Rabi oscillations were monitored by measuring the tunneling escape rate of the device to the voltage state, which is particularly sensitive to excited state population. We compare the observed oscillation frequencies with a simplified model constructed from the full phase qubit Hamiltonian and also compare time-dependent escape rate measurements with a more complete density-matrix simulation. Good quantitative agreement is found between the data and simulations, allowing us to identify a shift in resonance (analogous to the ac Stark effect), a suppression of the Rabi frequency, and leakage to the higher excited states. 1 aDutta, S., K.1 aStrauch, Frederick, W.1 aLewis, R., M.1 aMitra, Kaushik1 aPaik, Hanhee1 aPalomaki, T., A.1 aTiesinga, Eite1 aAnderson, J., R.1 aDragt, Alex, J.1 aLobb, C., J.1 aWellstood, F., C. uhttp://arxiv.org/abs/0806.4711v201341nas a2200145 4500008004100000245004200041210004200083260001300125490000700138520094000145100002801085700002501113700002001138856003701158 2008 eng d00aOptimal light storage in atomic vapor0 aOptimal light storage in atomic vapor c2008/8/10 v783 a We study procedures for the optimization of efficiency of light storage and retrieval based on the dynamic form of electromagnetically induced transparency (EIT) in warm Rb vapor. We present a detailed analysis of two recently demonstrated optimization protocols: a time-reversal-based iteration procedure, which finds the optimal input signal pulse shape for any given control field, and a procedure based on the calculation of an optimal control field for any given signal pulse shape. We verify that the two procedures are consistent with each other, and that they both independently achieve the maximum memory efficiency for any given optical depth. We observe good agreement with theoretical predictions for moderate optical depths (<25), while at higher optical depths the experimental efficiency falls below the theoretically predicted values. We identify possible effects responsible for this reduction in memory efficiency. 1 aPhillips, Nathaniel, B.1 aGorshkov, Alexey, V.1 aNovikova, Irina uhttp://arxiv.org/abs/0805.3348v100956nas a2200145 4500008004100000245005600041210005600097260001400153490000700167520052600174100002000700700002800720700002500748856003700773 2008 eng d00aOptimal light storage with full pulse shape control0 aOptimal light storage with full pulse shape control c2008/8/200 v783 a We experimentally demonstrate optimal storage and retrieval of light pulses of arbitrary shape in atomic ensembles. By shaping auxiliary control pulses, we attain efficiencies approaching the fundamental limit and achieve precise retrieval into any predetermined temporal profile. Our techniques, demonstrated in warm Rb vapor, are applicable to a wide range of systems and protocols. As an example, we present their potential application to the creation of optical time-bin qubits and to controlled partial retrieval. 1 aNovikova, Irina1 aPhillips, Nathaniel, B.1 aGorshkov, Alexey, V. uhttp://arxiv.org/abs/0805.1927v100417nas a2200133 4500008004100000245005600041210005500097300001400152490000700166100001600173700001900189700002500208856005000233 2008 eng d00aOptimal light storage with full pulse-shape control0 aOptimal light storage with full pulseshape control a021802(R)0 v781 aNovikova, I1 aPhillips, N, B1 aGorshkov, Alexey, V. uhttp://link.aps.org/abstract/PRA/v78/e021802/00824nas 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://s00566nas a2200181 4500008004100000245008800041210006900129300001100198490000800209100002500217700001200242700001500254700001500269700001400284700001600298700001900314856005100333 2008 eng d00aSuppression of Inelastic Collisions Between Polar Molecules With a Repulsive Shield0 aSuppression of Inelastic Collisions Between Polar Molecules With a0732010 v1011 aGorshkov, Alexey, V.1 aRabl, P1 aPupillo, G1 aMicheli, A1 aZoller, P1 aLukin, M, D1 aBüchler, H, P uhttp://link.aps.org/abstract/PRL/v101/e073201/01273nas a2200145 4500008004100000245009500041210006900136260001400205490000700219520078700226100002301013700002401036700002301060856004401083 2007 eng d00aImproved quantum algorithms for the ordered search problem via semidefinite programming 0 aImproved quantum algorithms for the ordered search problem via s c2007/3/260 v753 a One of the most basic computational problems is the task of finding a desired item in an ordered list of N items. While the best classical algorithm for this problem uses log_2 N queries to the list, a quantum computer can solve the problem using a constant factor fewer queries. However, the precise value of this constant is unknown. By characterizing a class of quantum query algorithms for ordered search in terms of a semidefinite program, we find new quantum algorithms for small instances of the ordered search problem. Extending these algorithms to arbitrarily large instances using recursion, we show that there is an exact quantum ordered search algorithm using 4 log_{605} N \approx 0.433 log_2 N queries, which improves upon the previously best known exact algorithm. 1 aChilds, Andrew, M.1 aLandahl, Andrew, J.1 aParrilo, Pablo, A. uhttp://arxiv.org/abs/quant-ph/0608161v100984nas a2200181 4500008004100000245005700041210005700098260001400155490000700169520043900176100002000615700002500635700002400660700002500684700002300709700002600732856004400758 2007 eng d00aOptimal control of light pulse storage and retrieval0 aOptimal control of light pulse storage and retrieval c2007/6/150 v983 a We demonstrate experimentally a procedure to obtain the maximum efficiency for the storage and retrieval of light pulses in atomic media. The procedure uses time reversal to obtain optimal input signal pulse-shapes. Experimental results in warm Rb vapor are in good agreement with theoretical predictions and demonstrate a substantial improvement of efficiency. This optimization procedure is applicable to a wide range of systems. 1 aNovikova, Irina1 aGorshkov, Alexey, V.1 aPhillips, David, F.1 aSorensen, Anders, S.1 aLukin, Mikhail, D.1 aWalsworth, Ronald, L. uhttp://arxiv.org/abs/quant-ph/0702266v100624nas 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-%20649901375nas a2200181 4500008004100000245008800041210006900129260001400198490000700212520082100219100001901040700001801059700002001077700001501097700001901112700001801131856004401149 2007 eng d00aRelaxation, dephasing, and quantum control of electron spins in double quantum dots0 aRelaxation dephasing and quantum control of electron spins in do c2007/7/130 v763 aRecent experiments have demonstrated quantum manipulation of two-electron spin states in double quantum dots using electrically controlled exchange interactions. Here, we present a detailed theory for electron spin dynamics in two-electron double dot systems that was used to guide these experiments and analyze experimental results. The theory treats both charge and spin degrees of freedom on an equal basis. Specifically, we analyze the relaxation and dephasing mechanisms that are relevant to experiments and discuss practical approaches for quantum control of two-electron system. We show that both charge and spin dephasing play important roles in the dynamics of the two-spin system, but neither represents a fundamental limit for electrical control of spin degrees of freedom in semiconductor quantum bits. 1 aTaylor, J., M.1 aPetta, J., R.1 aJohnson, A., C.1 aYacoby, A.1 aMarcus, C., M.1 aLukin, M., D. uhttp://arxiv.org/abs/cond-mat/0602470v202123nas a2200121 4500008004100000245003900041210003900080260001500119520179200134100001701926700002101943856003701964 2007 eng d00aTwo dogmas about quantum mechanics0 aTwo dogmas about quantum mechanics c2007/12/273 a We argue that the intractable part of the measurement problem -- the 'big' measurement problem -- is a pseudo-problem that depends for its legitimacy on the acceptance of two dogmas. The first dogma is John Bell's assertion that measurement should never be introduced as a primitive process in a fundamental mechanical theory like classical or quantum mechanics, but should always be open to a complete analysis, in principle, of how the individual outcomes come about dynamically. The second dogma is the view that the quantum state has an ontological significance analogous to the significance of the classical state as the 'truthmaker' for propositions about the occurrence and non-occurrence of events, i.e., that the quantum state is a representation of physical reality. We show how both dogmas can be rejected in a realist information-theoretic interpretation of quantum mechanics as an alternative to the Everett interpretation. The Everettian, too, regards the 'big' measurement problem as a pseudo-problem, because the Everettian rejects the assumption that measurements have definite outcomes, in the sense that one particular outcome, as opposed to other possible outcomes, actually occurs in a quantum measurement process. By contrast with the Everettians, we accept that measurements have definite outcomes. By contrast with the Bohmians and the GRW 'collapse' theorists who add structure to the theory and propose dynamical solutions to the 'big' measurement problem, we take the problem to arise from the failure to see the significance of Hilbert space as a new kinematic framework for the physics of an indeterministic universe, in the sense that Hilbert space imposes kinematic (i.e., pre-dynamic) objective probabilistic constraints on correlations between events. 1 aBub, Jeffrey1 aPitowsky, Itamar uhttp://arxiv.org/abs/0712.4258v201078nas a2200145 4500008004100000245006200041210006200103260001400165490000700179520063300186100001900819700002300838700002700861856004400888 2006 eng d00aEffects of finite temperature on the Mott insulator state0 aEffects of finite temperature on the Mott insulator state c2006/1/200 v733 a We investigate the effects of finite temperature on ultracold Bose atoms confined in an optical lattice plus a parabolic potential in the Mott insulator state. In particular, we analyze the temperature dependence of the density distribution of atomic pairs in the lattice, by means of exact Monte-Carlo simulations. We introduce a simple model that quantitatively accounts for the computed pair density distributions at low enough temperatures. We suggest that the temperature dependence of the atomic pair statistics may be used to estimate the system's temperature at energies of the order of the atoms' interaction energy. 1 aPupillo, Guido1 aWilliams, Carl, J.1 aProkof'ev, Nikolay, V. uhttp://arxiv.org/abs/cond-mat/0407075v301812nas a2200169 4500008004100000245010200041210006900143260001300212490000700225520125500232100002601487700002001513700001901533700002301552700002301575856004401598 2006 eng d00aMean-field treatment of the damping of the oscillations of a 1D Bose gas in an optical lattice 0 aMeanfield treatment of the damping of the oscillations of a 1D B c2006/1/90 v733 a We present a theoretical treatment of the surprisingly large damping observed recently in one-dimensional Bose-Einstein atomic condensates in optical lattices. We show that time-dependent Hartree-Fock-Bogoliubov (HFB) calculations can describe qualitatively the main features of the damping observed over a range of lattice depths. We also derive a formula of the fluctuation-dissipation type for the damping, based on a picture in which the coherent motion of the condensate atoms is disrupted as they try to flow through the random local potential created by the irregular motion of noncondensate atoms. We expect this irregular motion to result from the well-known dynamical instability exhibited by the mean-field theory for these systems. When parameters for the characteristic strength and correlation times of the fluctuations, obtained from the HFB calculations, are substituted in the damping formula, we find very good agreement with the experimentally-observed damping, as long as the lattice is shallow enough for the fraction of atoms in the Mott insulator phase to be negligible. We also include, for completeness, the results of other calculations based on the Gutzwiller ansatz, which appear to work better for the deeper lattices. 1 aGea-Banacloche, Julio1 aRey, Ana, Maria1 aPupillo, Guido1 aWilliams, Carl, J.1 aClark, Charles, W. uhttp://arxiv.org/abs/cond-mat/0410677v401217nas a2200169 4500008004100000245006000041210005800101260001500159300001400174490000600188520072400194100001900918700002000937700002300957700002300980856004401003 2006 eng d00aPseudo-fermionization of 1-D bosons in optical lattices0 aPseudofermionization of 1D bosons in optical lattices c2006/08/30 a161 - 1610 v83 a We present a model that generalizes the Bose-Fermi mapping for strongly correlated 1D bosons in an optical lattice, to cases in which the average number of atoms per site is larger than one. This model gives an accurate account of equilibrium properties of such systems, in parameter regimes relevant to current experiments. The application of this model to non-equilibrium phenomena is explored by a study of the dynamics of an atom cloud subject to a sudden displacement of the confining potential. Good agreement is found with results of recent experiments. The simplicity and intuitive appeal of this model make it attractive as a general tool for understanding bosonic systems in the strongly correlated regime. 1 aPupillo, Guido1 aRey, Ana, Maria1 aWilliams, Carl, J.1 aClark, Charles, W. uhttp://arxiv.org/abs/cond-mat/0505325v201431nas a2200169 4500008004100000245007100041210006900112260001400181490000700195520091200202100002001114700001801134700001901152700002301171700002301194856004401217 2005 eng d00aBragg Spectroscopy of ultracold atoms loaded in an optical lattice0 aBragg Spectroscopy of ultracold atoms loaded in an optical latti c2005/8/120 v723 a We study Bragg spectroscopy of ultra-cold atoms in one-dimensional optical lattices as a method for probing the excitation spectrum in the Mott insulator phase, in particular the one particle-hole excitation band. Within the framework of perturbation theory we obtain an analytical expression for the dynamic structure factor $S(q,\omega)$ and use it to calculate the imparted energy which has shown to be a relevant observable in recent experiments. We test the accuracy of our approximations by comparing them with numerically exact solutions of the Bose-Hubbard model in restricted cases and establish the limits of validity of our linear response analysis. Finally we show that when the system is deep in the Mott insulator regime, its response to the Bragg perturbation is temperature dependent. We suggest that this dependence might be used as a tool to probe temperatures of order of the Mott gap. 1 aRey, Ana, Maria1 aBlakie, Blair1 aPupillo, Guido1 aWilliams, Carl, J.1 aClark, Charles, W. uhttp://arxiv.org/abs/cond-mat/0406552v201428nas a2200181 4500008004100000245008400041210006900125260001500194300001600209490000700225520086200232100002301094700001901117700002001136700002301156700002301179856004401202 2005 eng d00aScalable register initialization for quantum computing in an optical lattice 0 aScalable register initialization for quantum computing in an opt c2005/06/14 a1687 - 16940 v383 a The Mott insulator state created by loading an atomic Bose-Einstein condensate (BEC) into an optical lattice may be used as a means to prepare a register of atomic qubits in a quantum computer. Such architecture requires a lattice commensurately filled with atoms, which corresponds to the insulator state only in the limit of zero inter-well tunneling. We show that a lattice with spatial inhomogeneity created by a quadratic magnetic trapping potential can be used to isolate a subspace in the center which is impervious to hole-hoping. Components of the wavefunction with more than one atom in any well can be projected out by selective measurement on a molecular photo-associative transition. Maintaining the molecular coupling induces a quantum Zeno effect that can sustain a commensurately filled register for the duration of a quantum computation. 1 aBrennen, Gavin, K.1 aPupillo, Guido1 aRey, Ana, Maria1 aClark, Charles, W.1 aWilliams, Carl, J. uhttp://arxiv.org/abs/quant-ph/0312069v101494nas a2200157 4500008004100000245010300041210006900144260001400213490000700227520097300234100002001207700001901227700002301246700002301269856004401292 2005 eng d00aUltracold atoms confined in an optical lattice plus parabolic potential: a closed-form approach 0 aUltracold atoms confined in an optical lattice plus parabolic po c2005/9/220 v723 a We discuss interacting and non-interacting one dimensional atomic systems trapped in an optical lattice plus a parabolic potential. We show that, in the tight-binding approximation, the non-interacting problem is exactly solvable in terms of Mathieu functions. We use the analytic solutions to study the collective oscillations of ideal bosonic and fermionic ensembles induced by small displacements of the parabolic potential. We treat the interacting boson problem by numerical diagonalization of the Bose-Hubbard Hamiltonian. From analysis of the dependence upon lattice depth of the low-energy excitation spectrum of the interacting system, we consider the problems of "fermionization" of a Bose gas, and the superfluid-Mott insulator transition. The spectrum of the noninteracting system turns out to provide a useful guide to understanding the collective oscillations of the interacting system, throughout a large and experimentally relevant parameter regime. 1 aRey, Ana, Maria1 aPupillo, Guido1 aClark, Charles, W.1 aWilliams, Carl, J. uhttp://arxiv.org/abs/cond-mat/0503477v201230nas a2200193 4500008004100000245007800041210006900119260001500188520065600203100001900859700001500878700001500893700001600908700001800924700001500942700001800957700001700975856004400992 2004 eng d00aQuantum information processing using localized ensembles of nuclear spins0 aQuantum information processing using localized ensembles of nucl c2004/07/233 aWe describe a technique for quantum information processing based on localized en sembles of nuclear spins. A qubit is identified as the presence or absence of a collective excitation of a mesoscopic ensemble of nuclear spins surrounding a single quantum dot. All single and two-qubit operations can be effected using hyperfine interactions and single-electron spin rotations, hence the proposed scheme avoids gate errors arising from entanglement between spin and orbital degrees of freedom. Ultra-long coherence times of nuclear spins suggest that this scheme could be particularly well suited for applications where long lived memory is essential. 1 aTaylor, J., M.1 aGiedke, G.1 aChrist, H.1 aParedes, B.1 aCirac, J., I.1 aZoller, P.1 aLukin, M., D.1 aImamoglu, A. uhttp://arxiv.org/abs/cond-mat/0407640v201546nas a2200181 4500008004100000245007100041210006900112260001500181300001600196490000700212520099700219100001901216700002001235700001901255700002301274700002301297856004401320 2004 eng d00aScalable quantum computation in systems with Bose-Hubbard dynamics0 aScalable quantum computation in systems with BoseHubbard dynamic c2004/02/15 a2395 - 24040 v513 a Several proposals for quantum computation utilize a lattice type architecture with qubits trapped by a periodic potential. For systems undergoing many body interactions described by the Bose-Hubbard Hamiltonian, the ground state of the system carries number fluctuations that scale with the number of qubits. This process degrades the initialization of the quantum computer register and can introduce errors during error correction. In an earlier manuscript we proposed a solution to this problem tailored to the loading of cold atoms into an optical lattice via the Mott Insulator phase transition. It was shown that by adding an inhomogeneity to the lattice and performing a continuous measurement, the unit filled state suitable for a quantum computer register can be maintained. Here, we give a more rigorous derivation of the register fidelity in homogeneous and inhomogeneous lattices and provide evidence that the protocol is effective in the finite temperature regime. 1 aPupillo, Guido1 aRey, Ana, Maria1 aBrennen, Gavin1 aWilliams, Carl, J.1 aClark, Charles, W. uhttp://arxiv.org/abs/quant-ph/0403052v201322nas 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/0210076v101212nas a2200145 4500008004100000245007400041210006900115260001400184490000700198520074500205100002300950700002400973700002500997856004401022 2001 eng d00aExact sampling from non-attractive distributions using summary states0 aExact sampling from nonattractive distributions using summary st c2001/2/220 v633 a Propp and Wilson's method of coupling from the past allows one to efficiently generate exact samples from attractive statistical distributions (e.g., the ferromagnetic Ising model). This method may be generalized to non-attractive distributions by the use of summary states, as first described by Huber. Using this method, we present exact samples from a frustrated antiferromagnetic triangular Ising model and the antiferromagnetic q=3 Potts model. We discuss the advantages and limitations of the method of summary states for practical sampling, paying particular attention to the slowing down of the algorithm at low temperature. In particular, we show that such a slowing down can occur in the absence of a physical phase transition. 1 aChilds, Andrew, M.1 aPatterson, Ryan, B.1 aMacKay, David, J. C. uhttp://arxiv.org/abs/cond-mat/0005132v100767nas a2200145 4500008004100000245004800041210004800089260001500137490000700152520035800159100002300517700001800540700001900558856004400577 2001 eng d00aRobustness of adiabatic quantum computation0 aRobustness of adiabatic quantum computation c2001/12/140 v653 a We study the fault tolerance of quantum computation by adiabatic evolution, a quantum algorithm for solving various combinatorial search problems. We describe an inherent robustness of adiabatic computation against two kinds of errors, unitary control errors and decoherence, and we study this robustness using numerical simulations of the algorithm. 1 aChilds, Andrew, M.1 aFarhi, Edward1 aPreskill, John uhttp://arxiv.org/abs/quant-ph/0108048v101129nas a2200157 4500008004100000245005000041210005000091260001500141300001400156490000700170520069000177100002300867700001900890700001800909856004400927 2000 eng d00aQuantum information and precision measurement0 aQuantum information and precision measurement c1999/04/07 a155 - 1760 v473 a We describe some applications of quantum information theory to the analysis of quantum limits on measurement sensitivity. A measurement of a weak force acting on a quantum system is a determination of a classical parameter appearing in the master equation that governs the evolution of the system; limitations on measurement accuracy arise because it is not possible to distinguish perfectly among the different possible values of this parameter. Tools developed in the study of quantum information and computation can be exploited to improve the precision of physics experiments; examples include superdense coding, fast database search, and the quantum Fourier transform. 1 aChilds, Andrew, M.1 aPreskill, John1 aRenes, Joseph uhttp://arxiv.org/abs/quant-ph/9904021v2