Bulletin of the American Physical Society
49th Annual Meeting of the APS Division of Atomic, Molecular and Optical Physics APS Meeting
Volume 63, Number 5
Monday–Friday, May 28–June 1 2018; Ft. Lauderdale, Florida
Session V07: Quantum Simulation and Thermalization |
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Chair: Tanya Mehlstaeubler, PTB Room: Grand D |
Friday, June 1, 2018 10:30AM - 10:42AM |
V07.00001: Thermalization and Bose-condensation of photons via laser cooling of cold atoms Chiao-Hsuan Wang, Michael Gullans, J. V. Porto, William Phillips, Alexey Gorshkov, Jacob Taylor In high optical depth atomic ensembles, we show that photons reemitted during the laser cooling process can equilibrate with the atomic motion and reach a steady state. We separate a set of long-lived (optically thick) photonic modes and study the atomic photon re-emission and absorption on top of the free-space cooling mechanism. In this regime, we find that a grand canonical ensemble of photons can arise directly via atomic laser cooling in an experimentally accessible regime [1], with a chemical potential controlled by the laser frequency following the general framework of "Floquet thermalization". Moreover, by placing the atoms in a curved cavity, the transverse modes in the cavity can be mapped into 2D massive bosons inside a parabolic well and can lead to 2D Bose-Einstein condensate of light. We consider realization of this regime using two-level atoms in Doppler cooling, and construct a phase diagram in the laser frequency and intensity parameter space showing the gain, condensate, thermal and quasi-thermal regimes for cavity photons with simulated values appropriate for the Yb intercombination transition. Looking forward, our approach will admit various applications such as Rydberg-polariton thermalization with laser-cooled Rydberg atoms. [1] arXiv:1712.08643. [Preview Abstract] |
Friday, June 1, 2018 10:42AM - 10:54AM |
V07.00002: Quantum Simulation of Hyperbolic Systems using Circuit QED Lattices Alicia Kollar, Mattias Fitzpatrick, Andrew Houck The field of circuit QED has emerged as a rich platform for both quantum computation and quantum simulation. The unique deformability of coplanar waveguide microwave resonators enables realization of artificial photonic materials which cannot be made from ordinary atomic or ionic systems. In this talk, we present one such example where we fabricate a two-dimensional periodic lattice in a hyperbolic space of constant negative curvature. This lattice constitutes an artificial material which exists in a region of extreme gravitation or in anti-de Sitter space. Particles in the lattice propagate along geodesics of the hyperbolic metric, rather than along the standard straight lines of flat Euclidean space, and it displays a highly unusual band structure with a gapped flat band. With the addition of high-kinetic-inductance materials or transmon qubits these systems will constitute a table-top simulator of interacting and quantum mechanical particles in strong curvature. [Preview Abstract] |
Friday, June 1, 2018 10:54AM - 11:06AM |
V07.00003: Realization of Gapped Flat Band Models in Circuit QED Mattias Fitzpatrick, Alicia Kollar, Andrew Houck After close to two decades of research and development, superconducting circuits have emerged as a rich platform for both quantum computation and quantum simulation. In this talk, we will explore a novel lattice, called the heptagon-pentagon-kagome (HPK) lattice, created by interspersing pentagons and heptagons in a standard kagome lattice. The HPK lattice is incompatible with other quantum simulators, but readily achievable in circuit QED. In contrast to the well-known kagome lattice, it exhibits a dispersion-less flat band which is gapped from the rest of the spectrum. Because this flat band is spectrally isolated and dispersion-less, interactions are the dominant energy scale, enabling the study of strongly correlated, many-body photon states. We will explore the theoretical origin of this gapped flat band and show experimental results where we introduce effective photon-photon interactions via classical non-linearity using high kinetic-inductance materials such as NbTiN. [Preview Abstract] |
Friday, June 1, 2018 11:06AM - 11:18AM |
V07.00004: Prethermal Dynamics of Trapped Ion Discrete Time Crystals P.W. Hess, P. Becker, A. Kyprianidis, H.B. Kaplan, G. Pagano, W.L. Tan, J. Zhang, C. Monroe, C. Nayak, F. Machado, N. Yao Periodically driving a quantum system can generate phases of matter without analog in stationary systems. Discrete time crystals (DTCs) are one such case, where the spontaneous breaking of a time translational symmetry is forbidden in the time-independent case. Previous observations of this effect relied on strong disorder to stabilize the discrete time crystal's temporal oscillations. Here, we report on the generation of DTC like behavior in a disorderless regime over finite length prethermal timescales. A 1D chain of up to 30 trapped ions is used to simulate a periodically driven long-range interacting spin model, with an individual addressing laser to prepare arbitrary initial spin configurations. The stability of the prethermal time crystal regime is probed by varying the drive frequency and choosing different initial states with varying energy densities. We observe that both low frequency drives and high energy density initial states destroy the periodic time dynamics. Moreover, the single site resolution of this experiment allows us to confirm that the motion of individual domain walls contributes to the decay of the spin order. [Preview Abstract] |
Friday, June 1, 2018 11:18AM - 11:30AM |
V07.00005: Quantum simulations of the Abelian Higgs model with a bosonic ladder Jin Zhang, Judah Unmuth-Yockey, Shan-Wen Tsai, Yannick Meurice We propose to use a physical ladder of bosonic atoms to quantum simulate a lattice gauge theory called the Abelian Higgs model. We use a spin-1 approximation where the 3 spin states are obtained with the three ways two bosons can be placed on a rung. Ladder structures can be realized experimentally, but generating attractive interactions among the nearest neighbor atoms is more challenging. Recent work by J. Zeiher et al. [Phys. Rev. X 7, 041063 (2017)], shows that these interactions can be manufactured by using Rydberg's atoms. A proof of principle would be to start with a single boson per rung which corresponds to the well studied case of the quantum (spin-1/2) Ising model in a transverse field. If relevant at the time of the conference, we comment on recent experimental progress to realize these ideas. [Preview Abstract] |
Friday, June 1, 2018 11:30AM - 11:42AM |
V07.00006: Non-Equilibrium Dynamical Phase Transition with 53 Trapped Ion Qubits P. Becker, J. Zhang, G. Pagano, P. W. Hess, A. Kyprianidis, H. B. Kaplan, A. V. Gorshkov, Z.-X. Gong, C. Monroe Trapped atomic ions are an ideal platform for constructing interesting quantum systems from the ground up. This system features precise laser control, long qubit coherence times, and individual readout, which together satisfy the requirements for a universal quantum computer. We use this toolbox for quantum simulation by engineering interacting many-body systems, with qubits encoded in the hyperfine states of $^{171}\text{Yb}^+$ ions and interactions mediated by motional modes in an RF Paul trap. These interactions create an effective long-range transverse-field Ising model. While the dynamics of a system composed of few spins can be easily calculated, exponentially large Hilbert spaces render classical simulation of 50 or more spins intractable without substantial computing resources. Here we present our observation of a non-equilibrium dynamical phase transition after a quench. The signatures of the phase transition are manifested in low order observables such as magnetization and two-body correlators. We scaled up this experiment to 53 qubits, measuring high order correlators, such as formation probabilities, that are not accessible to classical simulation. [Preview Abstract] |
Friday, June 1, 2018 11:42AM - 11:54AM |
V07.00007: High accuracy many-body calculations on quantum computers James Freericks, Jeffrey Cohn, Khadijeh Najafi, Forest Yang Quantum computers have the potential to revolutionize simulations of many-body physics. But currently available quantum computers are often noisy and subject to rapid decoherence. How can we extract the most accurate result from a digital quantum simulation? In this talk, we describe how to improve the accuracy of current quantum chemistry calculations and of proposed many-body Green's function calculations by employing the quantum computer to directly calculate the many-body self-energy. Then, a conventional computer is employed with an exact noninteracting Green's function, to construct the fully interacting Green's function and extract quantities of physical interest like the ground-state energy. We illustrate how one would perform the measurement in the quantum computer and how one would post-process that data to extract the physical quantities of interest. Since the self-energy is a rather smooth and often small quantity, it is more robust to errors than extracting the full Green's function or the total energy. This allows us, in the spirit of high precision AMO experiments, to greatly improve the accuracy of the quantum computer. We end with a discussion of what the requirements are to implement these types of algorithms on currently available hardware. [Preview Abstract] |
Friday, June 1, 2018 11:54AM - 12:06PM |
V07.00008: K-ETH Algorithm for calculating finte temperature Green's functions of strongly correlated systems. Jeffrey Cohn, Khadijeh Sona Najafi, Forest Yang, James Freericks We illustrate an efficient algorithm for calculating Fermionic many-body Green\^{a}\texteuro \texttrademark s functions at finite temperature, which avoid Gibbs state preparation techniques to initialize the calculation. Instead, by properly invoking the eigenstate thermalization hypothesis (ETH), we are able to initialize the computation rapidly. We show how sum rules guarantee the Green\^{a}\texteuro \texttrademark s functions are correct for short times and we also show how the time at which results begin to fail grows with the system size being simulated. We propose that this algorithm can have applicability to the simulations of a wide range of different strongly correlated systems. [Preview Abstract] |
Friday, June 1, 2018 12:06PM - 12:18PM |
V07.00009: Emergent dynamical phases in non-Markovian open quantum systems Hil Fung Harry Cheung, Yogesh S Patil, Mukund Vengalattore We experimentally realize a parametrically driven two-mode system in the presence of non-Markovian system-reservoir interactions. We show that non-Markovian interactions modify the phase diagram of this system resulting in the emergence of a novel broken symmetry phase in a new universality class that has no counterpart in a Markovian or equilibrium system [1]. We further study the critical dynamics of the transition into this emergent phase by linearly quenching the system from the disordered phase to the ordered phase. We demonstrate that the initial growth of order has a universal behavior conforming to conventional dynamical critical theory. For cyclic quenches across criticality, the system exhibits a dynamical hysteresis due to the divergent relaxation time and non-adiabatic dynamics in the vicinity of the critical point. While the hysteresis area in equilibrium continuous phase transitions scales as a single power law with the quench rate, we observe the scaling exponent in this non-Markovian system depends on the quench rate, suggesting that non-Markovian system-bath interactions may lead to timescale-dependent critical exponents. Such reservoir-engineered systems and dynamical phases can shed light on universal aspects of dynamical phase transitions in non-equilibrium systems, and aid in the robust generation of entanglement and quantum correlations at finite temperatures with potential applications to quantum metrology. \newline [1] H. F. H. Cheung, Y. S. Patil and M. Vengalattore, arXiv: 1707.02622 [Preview Abstract] |
Friday, June 1, 2018 12:18PM - 12:30PM |
V07.00010: Efficiency of thermodynamic processes in the presence of Non-Markovian system-bath interactions Jialun Luo, Hil Fung Harry Cheung, Yogesh S Patil, Mukund Vengalattore In the presence of Markovian system-bath interactions, the efficiency of a thermodynamic or quantum heat engine is bound by established limits such as the Carnot limit and the Curzon-Ahlborn bound. However, it has been theorized that these bounds can be violated in the presence of non-equilibrium or non-Markovian system-bath dynamics. We demonstrate an optomechanical realization of such a non-Markovian heat engine, and describe the performance of this heat engine in various parameter regimes. We also propose an experimental implementation of this concept in the quantum limit in a hybrid quantum system that couples a cavity optomechanical device to an ultracold spin ensemble. These experiments can potentially shed light on generalized quantum thermodynamics bounds for quantum heat engines. [Preview Abstract] |
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