Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session T33: Open Quantum Systems IIFocus Recordings Available
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Sponsoring Units: DAMOP Chair: Edwin Ng, NTT Research, Inc. Room: McCormick Place W-192C |
Thursday, March 17, 2022 11:30AM - 11:42AM |
T33.00001: Efficient sampling of low-energy Ising spin configurations in a coherent Ising machine using quantum noise dynamics Edwin Ng, Tatsuhiro Onodera, Satoshi Kako, Peter L McMahon, Hideo Mabuchi, Yoshihisa Yamamoto Coherent Ising machines (CIMs) are an emerging class of intermediate- to large-scale experimental systems that embed and solve hard combinatorial optimization problems using engineered networks of nonlinear optical oscillators. We show how quantum noise can drive nonlinear stochastic dynamics in CIMs and how these dynamics can be exploited to efficiently sample many degenerate low-energy spin configurations of the Ising problem. Our numerical results are based on a discrete-time Gaussian-state model which overcomes previous limitations of both mean-field models, which neglect quantum noise, and continuous-time quantum models based on Lindblad master equations, which require high-finesse oscillators. In addition to opening up new application areas and operational modalities for the CIM, these results also shed light on the dynamical and computational roles of quantum effects in coupled oscillator networks more generally. |
Thursday, March 17, 2022 11:42AM - 11:54AM |
T33.00002: Real-time optimal quantum control of mechanical motion at room temperature Lorenzo Magrini The ability to accurately control the dynamics of physical systems by measurement and feedback is a pillar of modern engineering. Today, the increasing demand for applied quantum technologies requires to adapt this level of control to individual quantum systems. Achieving this in an optimal way is a challenging task that relies on both quantum-limited measurements and specifically tailored algorithms for state estimation and feedback. In this talk I will describe how the quantum trajectory of a glass sphere -- the size of a virus -- can be tracked and controlled in real time at the quantum limit. We combine confocal position sensing close to the Heisenberg limit with optimal state estimation via Kalman filtering to track the particle motion in phase space in real time with a position uncertainty of 1.3 times the zero point fluctuation. Optimal feedback allows us to stabilize the quantum harmonic oscillator to a mean occupation of n=0.56±0.02 quanta, realizing quantum ground state cooling from room temperature. Our work establishes quantum Kalman filtering as a method to achieve quantum control of mechanical motion, with potential implications for sensing on all scales. In combination with levitation, this paves the way to full-scale control over the wavepacket dynamics of solid-state macroscopic quantum objects in linear and nonlinear systems. |
Thursday, March 17, 2022 11:54AM - 12:06PM |
T33.00003: Operator size and error propagation: the Loschmidt echo in many-body open quantum systems Thomas Schuster, Norman Y Yao The dispersal of quantum information in many-body systems---i.e. quantum information scrambling---is a hallmark feature of many-body quantum dynamics. In recent years, quantum simulators have enabled direct experimental measurements of scrambling, motivating an essential open question: What is the effect of experimental error and decoherence, i.e. open quantum dynamics, on information scrambling? In this work, we provide a universal framework for the effect of local errors on scrambling, in which we predict that error propagation is determined nearly entirely by the scrambling dynamics themselves, not the specific form of error. We apply our framework numerically and analytically to a range of examples, and find that scrambling can be unaffected, slowed, stopped, or even reversed by error, depending on the dimensionality, integrability, and conservation laws of the system under study. Finally, within our framework, we demonstrate that this interplay between scrambling and error is responsible for the time profile of the Loschmidt echo decay in many-body systems, which provides a potential theoretical underpinning to recent nuclear magnetic resonance experiments. |
Thursday, March 17, 2022 12:06PM - 12:18PM |
T33.00004: Dissipation in a polariton superfluid beyond the Landau criterion Shouvik Mukherjee, David W Snoke, Ashton Bradley Polariton superfluids have a finite lifetime and are often created under a constant optical pumping in a semiconductor microcavity. The balance between the gain and loss of the particles in the superfluid generates a steady-state current. In this steady-state condition, the polariton superfluid experiences energy damping and is slowed down due to the collisions with the particles in a stationary reservoir that is comprised of free thermal electrons. When the reservoir is in relative motion with respect to the superfluid these collisions give rise to either an upward or a downward shift in the chemical potential of the superfluid depending on the direction of the relative motion. This phenomenon has been observed in recent experiments described in https://arxiv.org/abs/1808.07866. |
Thursday, March 17, 2022 12:18PM - 12:30PM |
T33.00005: Exact Solution of Interacting Dissipative Systems via Weak Symemtries Alexander McDonald, Aashish Clerk In open quatnum systems, the tight connection between symmetries and conserved quantities no longer holds due to dissipation. Nevertheless, here we demonstrate how the presence of continuous weak symmetry can be used to analytically diagonalize the Liouvillian of a class Markovian dissipative systems with arbitrary strong interactions or nonlinearity. This enables an exact description of the full dynamics and dissipative spectrum. Our method can be viewed as implementing an exact, sector-dependent mean-field decoupling, or alternatively, as a kind of quantum-to-classical mapping. Although our method is general, we focus on two canonical examples: a nonlinear bosonic mode subject to incoherent loss and pumping, and an inhomogeneous quantum Ising model with arbitrary connectivity and local dissipation.We also discuss how our method provides a useful starting point to study systems where the weak symmetry is broken. |
Thursday, March 17, 2022 12:30PM - 12:42PM |
T33.00006: Dicke superradiance in atomic arrays: Part 1 Stuart J Masson, Eric Sierra Garzo, Ana Asenjo-Garcia We investigate the physics of collective decay in ordered arrays. The decay of a fully inverted ensemble of atoms at a single point is well known: the emitted light initially grows in intensity and photons are emitted in a short burst, so-called Dicke superradiance. However, atoms separated by large distances act independently and their decay is exponential, monotonically decreasing in time. In the intermediate regime, where atoms have finite separation but still behave collectively, calculating the emission requires evolution in a Hilbert space that grows exponentially with atom number. However, the nature of the decay can be characterized from the statistics of the first two photons. This reduces the problem to a concise and exact inequality - which is applicable to arrays of any dimensionality and topology - that can be evaluated in linear time. This can be used to find the critical interatomic distance beyond which superradiance disappears. |
Thursday, March 17, 2022 12:42PM - 12:54PM |
T33.00007: Dicke superradiance in atomic arrays: Part 2 Eric Sierra Garzo, Stuart J Masson, Ana Asenjo-Garcia In previous work, we derived an inequality which can be used to characterize the emission from fully excited arrays of atoms. Here, we investigate the role of dimensionality and geometry on the collective decay of large atomic arrays. We show that for 1D arrays, Dicke superradiance is bounded and cannot occur for any atom number above a particular distance. In 2D, the maximum interatomic distance for Dicke superradiance scales sub-logarithmically with atom number, and faster than that for 3D arrays. In contrast to Dicke's original work, which assumes that all atoms are confined to a volume of dimensions much smaller than the transition wavelength, we show that superradiance survives in arrays where the smallest interparticle distance is larger than a wavelength. Our results provide a guide to explore this many-body phenomenon in state-of-the-art experimental setups. |
Thursday, March 17, 2022 12:54PM - 1:06PM |
T33.00008: Kramers' degeneracy for open systems in thermal equilibrium Simon Lieu, Max McGinley, Oles Shtanko, Nigel R Cooper, Alexey V Gorshkov Kramers' degeneracy theorem underpins many interesting effects in quantum systems with time-reversal symmetry. We show that the generator of dynamics for Markovian open fermionic systems can exhibit an analogous degeneracy, protected by a combination of time-reversal symmetry and the microreversibility property of systems at thermal equilibrium—the degeneracy is lifted if either condition is not met. We provide simple examples of this phenomenon and show that the degeneracy is reflected in the standard Green's functions. Furthermore, we show that certain experimental signatures of topological edge modes in open many-body systems can be protected by microreversibility in the same way. Our results suggest that time-reversal symmetry of the system-bath Hamiltonian can affect open system dynamics only if the bath is in thermal equilibrium. |
Thursday, March 17, 2022 1:06PM - 1:18PM |
T33.00009: Exact solutions of many-body driven-dissipative systems using hidden time-reversal symmetry David Roberts, Aashish Clerk Recent work has shown that the ability to analytically solve for the steady state of several canonical quantum optics models (e.g. a driven-damped nonlinear bosonic mode [1]) is related to a surprising “hidden time reversal symmetry” [2]. These previous solutions were limited to systems with at most one or two modes. Here, we show that the same approach can be used to derive analytic descriptions of truly many-body driven dissipative models, including variants of coherently driven Bose-Hubbard models subject to Markovian dissipation. These models were not previously known to be solvable. Our exact solutions let one transcend the limitations of standard approximation methods such as Gurtzwiller mean-field theory or semiclassical approximations, and reveal a wealth of new physical phenomena, including new subtle kinds of pairing correlations. The models we describe are directly relevant to a number of experimental platforms, in particular realizations using superconducting circuits [3]. |
Thursday, March 17, 2022 1:18PM - 1:54PM |
T33.00010: Multimode Open Quantum Systems Invited Speaker: Vittorio Peano
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Thursday, March 17, 2022 1:54PM - 2:06PM |
T33.00011: Stabilizing volume-law entangled states of fermions and qubits using local dissipation Andrew Pocklington, Yuxin Wang, Yariv Yanay, Aashish Clerk It has long been appreciated that suitably tailored dissipation can be used to stabilize many-body entangled states [1,2]. Unfortunately, the required resources are often extremely daunting (i.e. control of non-trivial dissipation on every site of a large lattice, or the ability to prepare the system initially in a highly non-trivial state). Here, we analyze a surprisingly simple scheme that stabilizes both qubit and fermionic lattices using only a single dissipative pairing process applied to two adjacent lattice sites [3]. The resulting entanglement stabilization is insensitive to the initial state, and is robust to lattice disorder. The qubit version of our setup is not integrable, mapping onto an interacting fermionic problem. Nonetheless, we are able to analytically describe the existence of a unique, pure entangled steady state. We outline how our technique could be physically realized on a number of experimental platforms, including superconducting circuits and trapped ions. |
Thursday, March 17, 2022 2:06PM - 2:18PM |
T33.00012: Universal Lindblad equation for open quantum systems Frederik S Nathan, Mark Rudner We develop a Markovian master equation in the Lindblad form that enables the efficient study of a wide range of open quantum many-body systems that would be inaccessible with existingmethods. The validity of themaster equation is based entirely on properties of the bath and the system-bath coupling, without any requirements on the level structure within the system itself. The master equation is derived using a Markov approximation that is distinct from that used in earlier approaches. We provide a rigorous bound for the error induced by this Markov approximation; the error is controlled by a dimensionless combination of intrinsic correlation and relaxation timescales of the bath. Our master equation is accurate on the same level of approximation as the Bloch-Redfield equation. In contrast to the Bloch-Redfield approach, our approach ensures preservation of the positivity of the density matrix. As a result, our method is robust, and can be solved efficiently using stochastic evolution of pure states (rather than density matrices). We discuss how our method can be applied to static or driven quantum many-body systems, and illustrate its power through numerical simulation of a spin chain that would be challenging to treat by existing methods. |
Thursday, March 17, 2022 2:18PM - 2:30PM |
T33.00013: History is the best guide to the future: propagating non-Markovian memory effects across spacetime with long-range tensor network models for open quantum systems Thibaut Lacroix A number of biological structures have the ability to coordinate optically induced electronic processes and operate in a regime where the usual assumptions of a Markovian bath do not hold. |
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