Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session K50: Thermodynamics of Open Quantum SystemsRecordings Available

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Sponsoring Units: DCMP Chair: Peizhi Mai, Oak Ridge National Lab Room: McCormick Place W474A 
Tuesday, March 15, 2022 3:00PM  3:12PM 
K50.00001: Dynamics of a Single Spin in Markovian and nonMarkovian Environments Naushad Ahamad Kamar, Daniel A. Paz, Mohammad F. Maghrebi The spinboson model, describing a twolevel system strongly coupled to a thermal bath, is extensively well studied in the context of dissipative quantum systems. This model exhibits rich behavior and even a localization transition in the strong coupling regime. Here, we investigate the consequence of Markovian dissipation (on top of the nonMarkovian bath) due to coupling to a noisy environment. For moderate values of coupling, we develop a nonperturbative method to characterize the dynamics of the spin. We show that the Markovian dissipation renormalizes the frequency and the decay rate of the spin evolution. Our findings are relevant to the strong coupling regime in circuit QED systems among others. 
Tuesday, March 15, 2022 3:12PM  3:24PM 
K50.00002: On the First Law of Thermodynamics in TimeDependent Open Quantum Systems Parth Kumar, Charles A Stafford An unambiguous operator is established for the internal energy of an interacting timedependent open quantum system, shedding light on a longstanding debate about how exactly the First Law of Thermodynamics should be formulated for such systems. We arrive at this using a key insight from Mesoscopics: infinitely far away from the local driving and coupling of an open quantum system, reservoirs are only infinitesimally perturbed from equilibrium, allowing one to unambiguously define Heat in strongly driven systems. Fully general expressions for the quantumstatistical averages of the heat current and the power delivered by various agents to the system are derived using NonEquilibrium Green's Functions, establishing an experimentally meaningful and quantum mechanically consistent division of the energy of the system under consideration into Heat flowing from and Work done on the system. Motivated by previous work^{1}, we apply our formalism to analyze the thermodynamic performance of a model quantum machine: a pulsed twolevel quantum system strongly coupled to two metallic reservoirs, which can operate in several configurationsas a chemical pump/engine or a heat pump/engine. 
Tuesday, March 15, 2022 3:24PM  3:36PM 
K50.00003: Open system dynamics in interacting quantum field theories Brenden M Bowen, Nishant Agarwal, Archana Kamal A quantum system that interacts with its environment, in general, undergoes nonunitary evolution. The resulting dynamics can further be nonMarkovian or Markovian based on properties of the interaction and environment. I will first discuss the construction of a nonMarkovian master equation in a relativistic setting for different interacting quantum field theories in flat spacetime. I will next present a method to calculate resummed equaltime correlations with the master equation and discuss how this compares to a regular loop correction. I will discuss how the rotating wave and Markovian approximations manifest in our result and compare the evolution under these approximations to nonMarkovian evolution for different choices of interaction and initial state for the environment. Lastly, I will briefly discuss how our results can be generalized for curved spacetimes. 
Tuesday, March 15, 2022 3:36PM  3:48PM 
K50.00004: Topological gauge theory for mixed Dirac stationary states in all dimensions ZeMin Huang, XiaoQi Sun, Sebastian Diehl We derive the universal real time $U(1)$ topological gauge field action for mixed quantum states in all dimensions, and demonstrate its independence of the underlying equilibrium or nonequilibrium nature of dynamics. The only prerequisites are charge quantization and charge conservation. The gauge action encodes nonquantized linear responses as expected for mixed states, but also quantized nonlinear responses, associated with mixed state topology and accessible in experiment. Our construction furthermore demonstrates how the physical pictures of anomaly inflow and bulkboundary correspondence extend to nonequilibrium systems. 
Tuesday, March 15, 2022 3:48PM  4:00PM 
K50.00005: Entropy density and flux in topological and nonequilibrium quantum systems Charles A Stafford, Marco A Jimenez Valencia, Caleb M Webb, Ferdinand Evers We consider the flow of entropy and heat in quantum systems induced by topological fields and/or nonequilibrium bias conditions. A new solenoidal (divergencefree) contribution to the flow of entropy and heat is uncovered, which is missing from standard formulas for the heat current. This new term is shown to occur generically in such systems and to be large in magnitude in comparison to the conventional formulas. Although entropy is a nonlocal property in quantum mechanics, we show how to construct explicit expressions for the entropy density and entropy current density for systems of independent identical quantum particles, and apply these results to compute the flow of entropy in various model noninteracting systems, illustrating the importance of the new solenoidal contribution. Possible implications for the exchange of quantum information are discussed. 
Tuesday, March 15, 2022 4:00PM  4:12PM 
K50.00006: SignProblemFree RealTime Quantum Monte Carlo Simulations of Open Interacting Electron Systems Martin Claassen Nonequilibrium quantum manybody systems and quantum circuits have recently garnered much attention due to applications ranging from engineering nonequilibrium states of matter in materials to quantum computing. However, simulating the realtime dynamics of quantum systems remains a fundamental challenge – here, the exponential complexity in system size and time is commonly disguised as entanglement growth in tensor network algorithms or a dynamical sign problem in quantum Monte Carlo methods, limiting numerical studies to small or lowdimensional systems. In contrast, we show that dissipation due to coupling to the environment can dramatically ameliorate this situation and "cure" the dynamical sign problem in a realtime auxiliaryfield quantum Monte Carlo formulation of interacting electrons coupled to a bath. In this picture, simulations of the realtime evolution of interacting electron systems admit a rigorous lower bound for the average fermion sign as a function of dissipation rates and interactions, while remaining signproblemfree with polynomial simulation complexity beyond a critical dissipation strength. To illustrate the utility of this approach, we investigate the Floquet dynamics of periodicallydriven interacting electron systems with Markovian dissipation, characterize the computational complexity of simple dissipative lattice models with interactions, and chart extensions to Majorana fermions. Our results establish a new tool to simulate the realtime dynamics of stronglyinteracting dissipative fermionic systems in two or three dimensions. 
Tuesday, March 15, 2022 4:12PM  4:24PM 
K50.00007: Steady state formulation of Inchworm Monte Carlo Andre Erpenbeck, Emanuel C Gull, Guy Cohen We present an Inchworm method directly formulated in the steady state. Until now, numerically exact real time Monte Carlo methods have simulated steady state dynamics by propagating from a tractable initial condition to long times. The computational cost for accessing nonequilibrium steady states in these methods was often prohibitive. We demonstrate the performance of our steady state method by comparison with analytical results and other numerically exact techniques and showcase its usage within dynamical mean field simulations. The steady state formulation of the Inchworm method closes the gap between shorttime dynamics and the long time behavior and extends the applicability of nonequilibrium Monte Carlo methods as impurity solvers within quantum embedding schemes. 
Tuesday, March 15, 2022 4:24PM  4:36PM 
K50.00008: Continuous measurement boosted adiabatic quantum thermal machiens Bibek Bhandari, Andrew N Jordan We study continuous measurement based quantum thermal machines in static as well as adiabatically driven systems. In the adiabatically driven case, we show how measurement based thermodynamic quantities can be attributed geometric characteristics. We illustrate the aforementioned ideas and study the phenomena of refrigeration in two different paradigmatic examples: a coupled quantum dot and a coupled qubit system. In the timeindependent case, we observe that nonlinear coupling (in the coupled qubit case) produces cooling effects in certain regime where otherwise heating is expected. We also observe that quantum coherence can improve the performance of measurement based thermal machines. In the adiabatically driven case, we observe that quantum measurement can provide significant boost to the power of adiabatic quantum refrigerators. The measurement based refrigerators can have similar or better coefficient of performance in the driven case compared to the static one in the regime where heat extraction is maximum. Our results have potential significance for future application in devices ranging from measurement based quantum thermal machines to refrigeration in quantum processing networks. 
Tuesday, March 15, 2022 4:36PM  4:48PM 
K50.00009: Thermal control across a chain of electronic nanocavities Etienne Jussiau, Sreenath K Manikandan, Bibek Bhandari, Andrew N Jordan We study a chain of alternating hot and cold electronic nanocavities—connected to one another via resonanttunneling quantum dots—with the intent of achieving precise thermal control across the chain. This is accomplished by positioning the dots' energy levels such that a predetermined distribution of heat currents is realized across the chain in the steady state. The number of electrons in each cavity must be conserved in the steady state which constrains the cavities' chemical potentials. Determining these chemical potentials is a challenging task, but can be performed analytically in the linear response regime where the energy differences between the dots' resonant levels and the neighboring chemical potentials are much smaller than the thermal energy. In this regime, the thermal control problem can then be solved exactly. 
Tuesday, March 15, 2022 4:48PM  5:00PM 
K50.00010: Extractable work in quantum electromechanics. Oisín P Culhane, Mark T Mitchison, John Goold We investigate quantum electromechanics from the perspective of work extraction. Our work draws inspiration from recent experiments which have coupled a vibrational mode of a suspended carbonnanotube to a single electron transistor. In one such experiment a threshold voltage has been observed for the onset of selfsustained oscillations in analogy to the theory of the laser. This is suggestive that the vibrational degree of freedom can serve as a flywheel or quantum battery for work deposition. In this paper we derive a microscopic model that qualitatively matches the experimental finding. We use our model to calculate the Wigner function of the quantum vibrational mode in the non equilibrium steady state and study the phonon lasing threshold. We characterise the threshold by means of a concept routinely used in the thermodynamics of quantum systems called the ergotropy. This set an upperbound for extractable work from the quantum state by means of a cyclical unitary operation. We find ergotropy serves as an order parameter for the phonon lasing threshold. 
Tuesday, March 15, 2022 5:00PM  5:12PM 
K50.00011: Heat flux in chiral and nonchiral quasionedimensional systems with intrinsic dissipation Florian Stäbler In this talk we explore a onedimensional chiral system with an intrinsic mechanism of dissipation. Measurements of the energy relaxation in the integer quantum hall edge at filling factor \nu =2 show the breakdown of heat current quantization [H. le Sueur et al., Phys. Rev. Lett. 105, 056803]. It was shown that dissipative neutral modes contributing less than a quantum of heat can be an explanation for the missing heat flux [A Goremykina et al., arXiv preprint arXiv:1908.01213]. In the previous analysis, using a hydrodynamic approach, it was necessary to introduce a UV cutoff given by the transverse size of the neutral modes. In this work we present an effective model of a dissipative quantum hall edge, which takes into account the full range of momenta. We mapped the QHE to a transmission line by analogy and used the Langevin method to extract the heat current in the presence of weak and strong dissipation. We proceed to generalize our results to nonchiral systems. 
Tuesday, March 15, 2022 5:12PM  5:24PM 
K50.00012: Symmetryprotected quantization of complex Berry phases in nonHermitian manybody systems Shoichi Tsubota, Hong Yang, Yutaka Akagi, Hosho Katsura We investigate the quantization of the complexvalued Berry phases in nonHermitian quantum systems with certain generalized symmetries. In Hermitian quantum systems, the realvalued Berry phase is known to be quantized in the presence of certain symmetries, and this quantized Berry phase can be regarded as a topological order parameter for gapped quantum systems. We establish that the complex Berry phase is also quantized in the systems described by a family of nonHermitian Hamiltonians in the presence of certain generalized symmetries. Specifically, we discuss two classes of nonHermitian Hamiltonians with such generalized symmetries described by unitary and Hermitian operators. In one class, the complex Berry phase γ is quantized to 0 or π. In the other class, γ is not necessarily real, but its real part is shown to be quantized. Our results are quite general and apply to both interacting and noninteracting systems. We also argue that the quantized complex Berry phase can classify nonHermitian topological phases and demonstrate this in onedimensional manybody systems with and without interactions. 
Tuesday, March 15, 2022 5:24PM  5:36PM 
K50.00013: Universal quantum work statistics in chaotic Fermi liquids András Grabarits, Izabella Lovas, Marton Kormos, Gergely Zarand We present a theory of work statistics in generic chaotic, disordered Fermi liquid systems within a driven random matrix formalism. We extend Phil Anderson’s orthogonality determinant formula [1] to compute the full distribution of quantum work at arbitrary temperature [2]. The evolution of quantum work distribution is found to be universal, and characterized by just two parameters: the temperature in units of mean level spacing, and a dimensionless average work [3]. The average work is growing linearly in time, independently of the temperature. For low temperatures fluctuations exhibit superdiffusive behavior [3] and a nonGaussian work statistics is observed [4], while in the opposite limit the distribution of work becomes Gaussian with diffusive fluctuations. 
Tuesday, March 15, 2022 5:36PM  5:48PM 
K50.00014: Quantised topological invariants and topological pumping in onedimensional open quantum systems Paolo Molignini, Nigel R Cooper We employ the Ensemble Geometric Phase (EGP)  a generalisation of the Zak phase to mixed states  to analyse the topology of an open SuSchriefferHeeger model involving both unitary Hamiltonian dynamics and dissipative coupling. For dissipation described by the Lindblad formalism, we discover regimes where the EGP is quantised to zero or pi, and relate the quantisation to the existence of an inversion symmetry. Furthermore, we devise topological charge pumping protocols by sequentially tuning hopping and systembath couplings and realising an interplay between unitary dynamics and dissipation. We investigate the fate of this quantisation to situations of finite temperature through the Redfield master equation. 
Tuesday, March 15, 2022 5:48PM  6:00PM 
K50.00015: Fractional Josephson effect induced by weak measurement Mohammad Atif Javed, RomanPascal Riwar, Jakob Schwibbert The fractional Josephson effect is commonly directly linked to the presence of Majorana and parafermions, which are important candidates to implement (universally) protected quantum gates in superconducting quantum hardware. However, these exotic particles still seem notoriously challenging to realize in experiment, and difficult to unambiguously identify via transport measurements. Moreover, a proper understanding of the topological transport properties requires a generalization to an open quantum system context. 
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