Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session V27: Driven and Dissipative AMO Systems IILive
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Sponsoring Units: DAMOP Chair: Yariv Yanay, Laboratory for Physical Sciences |
Thursday, March 18, 2021 3:00PM - 3:12PM Live |
V27.00001: Universal dynamics in the expansion of vortex clusters in a dissipative two-dimensional superfluid Oliver Stockdale, Matthew Reeves, Xiaoquan Yu, Guillaume Gauthier, Kwan Goddard-Lee, Warwick Bowen, Tyler W Neely, Matthew Davis A large ensemble of quantum vortices in a superfluid may itself be treated as a novel kind of fluid that exhibits anomalous hydrodynamics [1]. In this talk, I’ll consider the dynamics of vortex clusters under thermal friction and present an analytic solution that uncovers a new universality class in the out-of-equilibrium dynamics of dissipative superfluids. The long-time dynamics of the vorticity distribution is universal in the form of an expanding Rankine vortex (i.e., top-hat distribution) independent of initial conditions. This highlights a fundamentally different decay process to classical fluids, where the Rankine vortex is forbidden by viscous diffusion. Experimental results of expanding vortex clusters in a quasi-two-dimensional Bose-Einstein condensate are in excellent agreement with the vortex fluid theory predictions. Our theoretical, numerical, and experimental results establish the validity of the vortex fluid theory for superfluid systems [2]. |
Thursday, March 18, 2021 3:12PM - 3:24PM Live |
V27.00002: Entanglement Entropy of Fermionic Open Quantum Systems from Wigner Characteristics Saranyo Moitra, Rajdeep Sensarma We formulate a new "Wigner characteristics'' based method to calculate entanglement entropies of subsystems of Fermions using Keldysh field theory. This bypasses the requirements of working with complicated manifolds to calculate Rényi entropies for many body systems. We provide an exact analytic formula for Rényi and von-Neumann entanglement entropies in non-interacting open quantum systems, which are initialised in arbitrary Fock states. We use this formalism to look at entanglement entropies of momentum Fock states of one-dimensional Fermions. We show that the entanglement entropy of a Fock state can scale either logarithmically or linearly with subsystem size, depending on whether the number of discontinuities in the momentum distribution is smaller or larger than the subsystem size. We also use this formalism to describe entanglement dynamics of an open quantum system starting with a single domain wall at the center of the system. Using entanglement entropy and mutual information, we understand the dynamics in terms of coherent motion of the domain wall wavefronts, creation and annihilation of domain walls, and incoherent exchange of particles with the bath. |
Thursday, March 18, 2021 3:24PM - 3:36PM Live |
V27.00003: Fluctuations effects in many body self-organization in a cavity Catalin-Mihai Halati, Ameneh Sheikhan, Alla Bezvershenko, Achim Rosch, Ritsch Helmut, Corinna Kollath We investigate the full quantum evolution of ultracold interacting bosonic atoms on a chain and coupled to an optical cavity. Extending the time-dependent matrix product state techniques and the many-body adiabatic elimination technique to capture the global coupling to the cavity mode and the open nature of the cavity, we examine the long time behavior of the system beyond the mean-field elimination of the cavity field. We show that the fluctuations beyond the mean-field state give a mixed state character to the dissipative phase transition and self-organized steady states. Thus, beside the mean-field predicted density wave also excited states play an important role at long time. |
Thursday, March 18, 2021 3:36PM - 3:48PM Live |
V27.00004: Measuring the time atoms spend in the excited state due to a photon they don’t absorb Josiah Sinclair, Daniela Angulo Murcillo, Kyle Thompson, Kent AG Bonsma-Fisher, Aharon Brodutch, Aephraim M Steinberg When a resonant photon traverses a sample of absorbing atoms, how much time do atoms spend in the excited state? Does the answer depend on whether the photon is ultimately absorbed or transmitted? In an experiment with ultra-cold Rubidium atoms, we simultaneously record whether atoms are excited by incident photons and whether those photons are transmitted. We measure the time spent by atoms in the excited state by using a separate laser to monitor the index of refraction of the sample and use direct detection to isolate the effect of single transmitted photons. We find that the average time atoms spend in the excited state due to one transmitted photon is not zero, but rather (77 +/- 16)% of the time the average incident photon causes them to spend in the excited state. We attribute this observation of "excitation without loss'' to coherent forward emission, which happens naturally when a broadband pulse propagates through an optically thick medium. These results unambiguously reveal the history of photons as they propagate through an absorbing medium and illustrate the power of utilizing post-selection to experimentally investigate the past of observed quantum systems. |
Thursday, March 18, 2021 3:48PM - 4:00PM Live |
V27.00005: Modelling non-Markovian and non-perturbative environments with unphysical modes Neill Lambert, Shahnawaz Ahmed, Mauro Cirio, Franco Nori Pseudo-modes are discrete effective modes used to model the effect of continuum environments on open quantum systems. Here we develop a new approach to pseudomodes to deal with a quantum system ultra-strongly-coupled to a bosonic continuum even at zero temperature [1]. This is made possible by defining pseudomodes which have a non-Hermitian interaction with the system, and which in isolation are unphysical. We show how they successfully describe the appearance of virtual excitations in the zero-temperature steady-state, which we analyze and bench-mark with the hierarchy-equations-of-motion and the reaction-coordinate approaches. We also discuss new applications of our approach to other types of environments and to error mitigation. |
Thursday, March 18, 2021 4:00PM - 4:12PM Live |
V27.00006: Simulating infinite baths using finite baths with periodic refreshing Archak Purkayastha, Giacomo Guarnieri, Steve Campbell, Javier Prior, John Goold A large part of research in quantum physics, biology, chemistry and engineering revolves around understanding quantum many-body systems connected to multiple baths which can all have different temperatures and chemical potentials. However, a general approach for the numerically exact description of the dynamics of such open quantum many-body systems has remained an outstanding problem. The main difficulty in simulating such set-ups stems from the baths having infinite degrees of freedom. Here we show that it is possible to accurately simulate the dynamics of a wide class of such open quantum many-body systems using finite and rather small-sized baths, when the baths are refreshed to their original initial states periodically after a carefully chosen time interval. This tremendously simplifies obtaining the dynamics of such set-ups, albeit in discrete time steps. When combined with existing tensor network approaches, this provides an extremely efficient and general technique to obtain numerically exact dynamics of a large class of interacting open quantum many-body systems beyond all other state-of-the-art techniques. |
Thursday, March 18, 2021 4:12PM - 4:24PM Live |
V27.00007: Work and heat in conventional and measurement powered quantum heat engines Katérina Verteletsky, Klaus Molmer We constructed a simple autonomous thermoelectric engine operated out of thermal equilibrium composed of two superconducting qubits coupled to separate heat baths and connected by a Josephson junction. |
Thursday, March 18, 2021 4:24PM - 4:36PM Live |
V27.00008: Work statistics in effective non-Hermitian systems Zheng-Yang Zhou, Ze-Liang Xiang, Jianqiang You, Franco Nori Non-Hermitian systems with specific forms of Hamiltonians can exhibit novel phenomena, but often such systems are hard to realize, especially in the quantum regime. A proper description of these difficulties can help to introduce optimizing methods. Thermodynamic quantities can be potential choices, but the present thermodynamics theory does not work well in non-Hermitian systems. We treat non-Hermitian systems as effective processes generated from Hermitian systems, so that the free energy cost of these processes can be studied from the work statistics. A way to define the work statistics in such non-Hermitian systems is also provided. Based on these results, we further show an example of optimized process to generate a non-Hermitian system. |
Thursday, March 18, 2021 4:36PM - 4:48PM Live |
V27.00009: Classical Simulability of Dissipative Interactions of Fermions Oles Shtanko, Abhinav Deshpande, P S Julienne, Alexey V Gorshkov It is widely accepted that the efficient classical simulability of free-fermion dynamics is not robust under elastic interactions. We examine how the classical simulability of fermions that are initially noninteracting changes in the presence of purely dissipative Markovian interactions described by quadratic Lindblad jump operators, including, for example, incoherent transitions or pair losses. On the one hand, we establish three broad classes of Markovian dynamics that are efficiently simulable classically, by devising efficient algorithms. On the other hand, we demonstrate that, in the worst case, simulating Markovian dynamics with quadratic Lindblad jump operators is at least as hard as simulating universal quantum circuits. To prove this result, we propose a practical scheme for universal quantum computation in cold atom systems using natural pair loss, which is of independent interest. Our proposed scheme of dissipation-assisted quantum computing might have significant advantages in the speed of two-qubit gates and, therefore, in error tolerance. |
Thursday, March 18, 2021 4:48PM - 5:00PM Live |
V27.00010: Dynamical scaling at critical exceptional points Shuoguang Liu, Ryo Hanai, Peter Littlewood In conventional critical phenomena, the slow and long-distance fluctuations are provided by the softening of a massive mode. Recently, a new class of critical phenomena driven instead by the coalescence of the collective modes to the Goldstone mode were found to occur in the steady state of open binary condensates [1] and in non-reciprocally interacting many-body systems [2]. Surprisingly, at this “critical exceptional point (CEP)”, it was shown that the critical fluctuations become anomalous giant (which diverges at d≤4) compared to the conventional case (which diverges at d≤2) [1]. However, it was difficult to determine the scaling exponents in realistic spatial dimensions with standard analytical techniques, due to the anomalously enhanced many-body effects. In this work, we perform a direct numerical study on the one-dimensional binary condensates described by the noisy driven-dissipative Gross-Pitaevskii equations. We found a strong evidence of anomalous large fluctuations near the CEP, as well as a surprisingly large many-body correction to the roughening exponent that strongly suppress these fluctuations. |
Thursday, March 18, 2021 5:00PM - 5:12PM Live |
V27.00011: Keldysh Approach to Driven-Dissipative Phase Transition in a Kerr Oscillator Xin H. H. Zhang, Harold U Baranger We study open quantum many-body physics using a minimal model, namely a Kerr non-linear oscillator subject to two-photon driving and single-photon dissipation. Exact solutions are provided by coherently tying together several methods such as mean field theory, exact diagonalization, and Keldysh field theory. Spectral properties are given analytically using the Keldysh formalism (both the spectral function of the oscillator and the power-spectrum of the emitted photons). Then using the quantum Langevin equation, finite-size scaling is calculated exactly. |
Thursday, March 18, 2021 5:12PM - 5:24PM Live |
V27.00012: Observation of an Exceptional Point Associated With Coupled Rb Atomic Oscillators Sehyun Park, J. Gary Eden Exceptional points (EPs) arise in open quantum systems for which the Hamiltonian is non-Hermitian and have been observed previously in photonic resonators, plasmonics, and Feshbach resonances. Theory has predicted that a phase shift occurs in the proximity of an EP [1] and the present work confirms this prediction for coupled atomic Rb oscillators. Quantum beating in the vicinity of the Rb (5d5/2-5p3/2)-(5p3/2-5s1/2) resonance at 70.4 cm-1 (~2.1 THz) is observed through one- and two-photon excitation of the atom with 50-200 fs laser pulses, and parametric four-wave mixing. The Fano lineshape for this oscillator is tuned by varying the mean Rb-Rb distance (<R>) and a phase shift of ~π/4 is observed in the <R>=80-90 nm interval. The transformation of the Fano profile and the phase shift are signatures of an EP, and the ability to tune both is attributed to the impact of the dipole-dipole interaction (C3R-3) on the interatomic potential. Data has also been obtained for Rb-Ar and Rb-Cs mixtures. |
Thursday, March 18, 2021 5:24PM - 5:36PM Live |
V27.00013: Tavis-Cummings open quantum system modeling on a commercial quantum computer Marina Krstic Marinkovic, Marina Radulaski Recent progress in experimental control of light-matter interaction has sparked renewed interest in simulations of large-Hilbert-space open quantum systems. An interesting playground for understanding a wide range of quantum phenomena exhibited by the open quantum systems is the Tavis-Cummings model, which reduces QED to an ensemble of N two-level systems interacting with an optical cavity. Full numerical treatment of these systems on a classical computer is limited to ensembles with a handful of emitters. In an attempt to overcome this limitation, we use Qiskit open source framework and IBM Q Experience quantum computers to model open Tavis-Cummings systems, exploring their energy ladder complexities and quantum state evolution. Finally, we discuss approaches toward optimal scaling. |
Thursday, March 18, 2021 5:36PM - 5:48PM On Demand |
V27.00014: Coexistence of exceptional ring and exceptional surface in a doped molecular chain Savannah Garmon, Yujin Dunham, Kazuki Kanki, Gonzalo Ordonez, Satoshi Tanaka In recent years, the spectral features and topological properties associated with coalescing eigenstates at exceptional points have been studied in a wide range of physical contexts. In this work, we reveal the occurrence of higher-dimensional exceptional manifolds in the spectrum of a magnetized donor atom at the endpoint of a molecular chain. We demonstrate the presence of both an exceptional ring and an exceptional surface in the parameter space of an externally applied magnetic field, which reflect underlying symmetries in the model. We propose electron spin resonance (ESR) as a method to observe these exceptional manifolds in experiment. We emphasize that the exceptional manifolds arise in our system due to the influence of the microscopic degrees of freedom ascribed to the molecular chain. This is as opposed to treatments in which explicit non-Hermitian elements are introduced to represent macroscopic approximations over such degrees of freedom. |
Thursday, March 18, 2021 5:48PM - 6:00PM On Demand |
V27.00015: Asymptotic phase function for quantum nonlinear oscillators reveals signatures of quantum synchronization Yuzuru Kato, Hiroya Nakao We propose the asymptotic phase function for quantum nonlinear oscillators. We introduce the asymptotic phase function of the system in terms of the eigenoperator of the adjoint Liouville superoperator associated with the fundamental frequency. This quantum asymptotic phase function yields appropriate phase values of the system even in the strong quantum regime and reproducing the conventional asymptotic phase in the semiclassical regime. We analyze a quantum van der Pol oscillator with Kerr effect and show that there are several dominant eigenoperators with different fundamental frequencies in the strong quantum regime. The quantum asymptotic phase functions with respective fundamental frequencies reveal that the multiple phase locking of the system with a harmonic drive at several different frequencies, an explicit quantum signature observed only in the strong quantum regime, can be interpreted as synchronization on a torus rather than a simple limit cycle. |
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