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

%8 6/3/2020 %G eng %U https://arxiv.org/abs/2006.02486 %0 Journal Article %D 2020 %T Frustration-induced anomalous transport and strong photon decay in waveguide QED %A Ron Belyansky %A Seth Whitsitt %A Rex Lundgren %A Yidan Wang %A Andrei Vrajitoarea %A Andrew A. Houck %A Alexey V. Gorshkov %XWe study the propagation of photons in a one-dimensional environment consisting of two non-interacting species of photons frustratingly coupled to a single spin-1/2. The ultrastrong frustrated coupling leads to an extreme mixing of the light and matter degrees of freedom, resulting in the disintegration of the spin and a breakdown of the "dressed-spin", or polaron, description. Using a combination of numerical and analytical methods, we show that the elastic response becomes increasingly weak at the effective spin frequency, showing instead an increasingly strong and broadband response at higher energies. We also show that the photons can decay into multiple photons of smaller energies. The total probability of these inelastic processes can be as large as the total elastic scattering rate, or half of the total scattering rate, which is as large as it can be. The frustrated spin induces strong anisotropic photon-photon interactions that are dominated by inter-species interactions. Our results are relevant to state-of-the-art circuit and cavity quantum electrodynamics experiments.

%8 7/7/2020 %G eng %U https://arxiv.org/abs/2007.03690 %0 Journal Article %J Phys. Rev. Lett. %D 2020 %T Minimal model for fast scrambling %A Ron Belyansky %A Przemyslaw Bienias %A Yaroslav A. Kharkov %A Alexey V. Gorshkov %A Brian Swingle %XWe study quantum information scrambling in spin models with both long-range all-to-all and short-range interactions. We argue that a simple global, spatially homogeneous interaction together with local chaotic dynamics is sufficient to give rise to fast scrambling, which describes the spread of quantum information over the entire system in a time that is logarithmic in the system size. This is illustrated in two exactly solvable models: (1) a random circuit with Haar random local unitaries and a global interaction and (2) a classical model of globally coupled non-linear oscillators. We use exact numerics to provide further evidence by studying the time evolution of an out-of-time-order correlator and entanglement entropy in spin chains of intermediate sizes. Our results can be verified with state-of-the-art quantum simulators.

%B Phys. Rev. Lett. %V 125 %8 9/22/2020 %G eng %U https://arxiv.org/abs/2005.05362 %N 130601 %R https://doi.org/10.1103/PhysRevLett.125.130601 %0 Journal Article %J Phys. Rev. A %D 2020 %T Quantum Simulation of Hyperbolic Space with Circuit Quantum Electrodynamics: From Graphs to Geometry %A Igor Boettcher %A Przemyslaw Bienias %A Ron Belyansky %A Alicia J. KollĂˇr %A Alexey V. Gorshkov %XWe show how quantum many-body systems on hyperbolic lattices with nearest-neighbor hopping and local interactions can be mapped onto quantum field theories in continuous negatively curved space. The underlying lattices have recently been realized experimentally with superconducting resonators and therefore allow for a table-top quantum simulation of quantum physics in curved background. Our mapping provides a computational tool to determine observables of the discrete system even for large lattices, where exact diagonalization fails. As an application and proof of principle we quantitatively reproduce the ground state energy, spectral gap, and correlation functions of the noninteracting lattice system by means of analytic formulas on the PoincarĂ© disk, and show how conformal symmetry emerges for large lattices. This sets the stage for studying interactions and disorder on hyperbolic graphs in the future. Our analysis also reveals in which sense discrete hyperbolic lattices emulate the continuous geometry of negatively curved space and thus can be used to resolve fundamental open problems at the interface of interacting many-body systems, quantum field theory in curved space, and quantum gravity.

%B Phys. Rev. A %V 102 %8 9/11/2020 %G eng %U https://arxiv.org/abs/1910.12318 %N 032208 %R https://doi.org/10.1103/PhysRevA.102.032208 %0 Journal Article %D 2020 %T Quench Dynamics of a Fermi Gas with Strong Long-Range Interactions %A Elmer Guardado-Sanchez %A Benjamin M. Spar %A Peter Schauss %A Ron Belyansky %A Jeremy T. Young %A Przemyslaw Bienias %A Alexey V. Gorshkov %A Thomas Iadecola %A Waseem S. Bakr %XWe induce strong non-local interactions in a 2D Fermi gas in an optical lattice using Rydberg dressing. The system is approximately described by a t−V model on a square lattice where the fermions experience isotropic nearest-neighbor interactions and are free to hop only along one direction. We measure the interactions using many-body Ramsey interferometry and study the lifetime of the gas in the presence of tunneling, finding that tunneling does not reduce the lifetime. To probe the interplay of non-local interactions with tunneling, we investigate the short-time relaxation dynamics of charge density waves in the gas. We find that strong nearest-neighbor interactions slow down the relaxation. Our work opens the door for quantum simulations of systems with strong non-local interactions such as extended Fermi-Hubbard models.

%8 10/12/2020 %G eng %U https://arxiv.org/abs/2010.05871 %0 Journal Article %D 2020 %T Symmetry breaking and error correction in open quantum systems %A Simon Lieu %A Ron Belyansky %A Jeremy T. Young %A Rex Lundgren %A Victor V. Albert %A Alexey V. Gorshkov %XSymmetry-breaking transitions are a well-understood phenomenon of closed quantum systems in quantum optics, condensed matter, and high energy physics. However, symmetry breaking in open systems is less thoroughly understood, in part due to the richer steady-state and symmetry structure that such systems possess. For the prototypical open system---a Lindbladian---a unitary symmetry can be imposed in a "weak" or a "strong" way. We characterize the possible Zn symmetry breaking transitions for both cases. In the case of Z2, a weak-symmetry-broken phase guarantees at most a classical bit steady-state structure, while a strong-symmetry-broken phase admits a partially-protected steady-state qubit. Viewing photonic cat qubits through the lens of strong-symmetry breaking, we show how to dynamically recover the logical information after any gap-preserving strong-symmetric error; such recovery becomes perfect exponentially quickly in the number of photons. Our study forges a connection between driven-dissipative phase transitions and error correctio

%8 8/6/2020 %G eng %U https://arxiv.org/abs/2008.02816 %0 Journal Article %D 2020 %T Transport and dynamics in the frustrated two-bath spin-boson model %A Ron Belyansky %A Seth Whitsitt %A Rex Lundgren %A Yidan Wang %A Andrei Vrajitoarea %A Andrew A. Houck %A Alexey V. Gorshkov %XWe study the strong coupling dynamics as well as transport properties of photons in the two-bath spin-boson model, in which a spin-1/2 particle is frustratingly coupled to two independent Ohmic bosonic baths. Using a combination of numerical and analytical methods, we show that the frustration in this model gives rise to rich physics in a very wide range of energies. This is in contrast to the one-bath spin-boson model, where the non-trivial physics occurs at an energy scale close to the renormalized spin frequency. The renormalized spin frequency in the two-bath spin-boson model is still important, featuring in different observables, including the non-equiblirum dynamics of both the spin and the baths along with the elastic transport properties of a photon. The latter however reveals a much more complex structure. The elastic scattering displays non-monotonic behavior at high frequencies, and is very different in the two channels: intra- and inter-bath scattering. The photon can also be inelastically scattered, a process in which it is split into several photons of smaller energies. We show that such inelastic processes are highly anisotropic, with the outgoing particles being preferentially emitted into only one of the baths. Moreover, the inelastic scattering rate is parameterically larger than in the one-bath case, and can even exceed the total elastic rate. Our results can be verified with state-of-the-art circuit and cavity quantum electrodynamics experiments.

%8 7/7/2020 %G eng %U https://arxiv.org/abs/2007.03690 %0 Journal Article %D 2019 %T Nondestructive cooling of an atomic quantum register via state-insensitive Rydberg interactions %A Ron Belyansky %A Jeremy T. Young %A Przemyslaw Bienias %A Zachary Eldredge %A Adam M. Kaufman %A Peter Zoller %A Alexey V. Gorshkov %XWe propose a protocol for sympathetically cooling neutral atoms without destroying the quantum information stored in their internal states. This is achieved by designing state-insensitive Rydberg interactions between the data-carrying atoms and cold auxiliary atoms. The resulting interactions give rise to an effective phonon coupling, which leads to the transfer of heat from the data atoms to the auxiliary atoms, where the latter can be cooled by conventional methods. This can be used to extend the lifetime of quantum storage based on neutral atoms and can have applications for long quantum computations. The protocol can also be modified to realize state-insensitive interactions between the data and the auxiliary atoms but tunable and non-trivial interactions among the data atoms, allowing one to simultaneously cool and simulate a quantum spin-model.

%8 7/28/2019 %G eng %U https://arxiv.org/abs/1907.11156