Bulletin of the American Physical Society
APS March Meeting 2021
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session J34: Quantum Thermodynamics IIFocus Live

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Sponsoring Units: DQI Chair: Ruichao Ma, Purdue University 
Tuesday, March 16, 2021 3:00PM  3:36PM Live 
J34.00001: Autonomous entanglement engines Invited Speaker: Geraldine Haack Generating and stabilizing entangled states is one of the upmost taks for achieving quantum information processing. Engineering, controlling and implementing feedback protocols between the quantum system and its environments have becoming stateoftheart experimental techniques, at the heart of the development of quantum technologies. In this talk, I would like to take a step back, and simply discuss the possibility of exploiting outofequilibrium thermal environments, without any control, to generate quantum correlations among two or more qubits or higherdimensional quantum systems. Remarkably, these setups can be viewed as thermal machines (the temperature bias between the environments acts as the thermodynamic force), operating exclusively in the quantum regime as their product is quantum correlations. Hence, they do not have a classical counterpart. Their dynamics and steadystate properties can be understood with theoretical tools appropriate for open quantum systems. I will review some of the most important results we obtained, with the goal of triggering new exciting experiments towards quantum thermal machines: the steadystate generation of multipartite entangled states, the existence of a critical heat current for certifying the presence of entanglement, and the control of the transient dynamics of these entanglement engines, with signatures of nonHermitian physics in energybased observables. 
Tuesday, March 16, 2021 3:36PM  3:48PM Live 
J34.00002: Measuring entanglement in a quantum heat engine Alwin van Steensel, Mohammad Ansari We study how entanglement in a quantum heat engine can impact its nonequilibrium thermodynamics. For this purpose we consider a network of qubits whose state can be fully controlled by entangling gates and rotation gates. We weakly couple the network to a number of heat reservoirs, each kept at a different temperature. Heat flows between the reservoirs run via the network and are studied for different entangled states of this network. Some entangled states reveal interesting properties in the heat flow thereby furthering our understanding of the quantum nature of such thermodynamical systems. 
Tuesday, March 16, 2021 3:48PM  4:00PM Live 
J34.00003: Quantum Process Inference for a Single Qubit Maxwell’s demon Xingrui Song, Mahdi Naghiloo, Kater Murch In a quantum Maxwell’s demon experiment, two major quantities are commonly investigated  the average work extraction 〈W〉 and the efficacy γ which measures the violation of Jarzynski’s equality when extracted information and feedback are not accounted for. Here, we carefully analyze the relation between these two quantities and find that they are not maximized simultaneously, requiring different feedback protocols. Using the tool of quantum process matrix, we are able to investigate and experimentally implement these feedback protocols. 
Tuesday, March 16, 2021 4:00PM  4:12PM Live 
J34.00004: TensorNetwork Method to Simulate Strongly Interacting Quantum Thermal Machines Juan MendozaArenas, Marlon Brenes, Archak Purkayastha, Mark Mitchison, Stephen Clark, John Goold We present a methodology to simulate the quantum thermodynamics of thermal machines which are built from an interacting working medium in contact with fermionic reservoirs at a fixed temperature and chemical potential. Our method works at a finite temperature, beyond linear response and weak systemreservoir coupling, and allows for nonquadratic interactions in the working medium. The method uses mesoscopic reservoirs, continuously damped toward thermal equilibrium, in order to represent continuum baths, and a novel tensornetwork algorithm to simulate the steadystate thermodynamics. Using the example of a quantumdot heat engine, we demonstrate that our technique replicates the wellknown LandauerBüttiker theory for efficiency and power. We then simulate a threesite machine with nonquadratic interactions; remarkably, these lead to power enhancement without being detrimental to the efficiency. Finally, we demonstrate the capability of our method to tackle complex manybody systems by extracting the superdiffusive exponent for hightemperature transport in the isotropic Heisenberg model. 
Tuesday, March 16, 2021 4:12PM  4:24PM 
J34.00005: Information scrambling vs. decoherence  two competing sinks for entropy Akram Touil, Sebastian Deffner A possible solution of the information paradox can be sought in quantum information scrambling. In this paradigm, it is postulated that all information entering a black hole is rapidly and chaotically distributed across the event horizon making it impossible to reconstruct the information by means of any local measurement. However, in this scenario the effects of decoherence are typically ignored, which may render information scrambling moot in cosmological settings. In this work, we develop key steps towards a thermodynamic description of information scrambling in open quantum systems. In particular, we separate the entropy production into contributions arising from scrambling and decoherence, for which we derive statements of the second law. This is complemented with a numerical study of the SachdevYeKitaev, MaldacenaQi, XXX, mixed field Ising, LipkinMeshkovGlick models in the presence of decoherence in energy or computational basis. 
Tuesday, March 16, 2021 4:24PM  4:36PM Live 
J34.00006: HilbertSpace Fragmentation of an Embedded Fredkin Spin Chain Christopher Langlett, Shenglong Xu As a result of emerging constraints, we show that the Hilbert space fragments into many disconnected sectors in an embedded Fredkin model. Closely related to the frustrationfree Fredkin model with spin moves given by the controlSWAP operation. The model we study embeds the zeroenergy ground into the middle of the spectrum resulting in a dramatic effect on the Hilbert space structure. This embedding induces a spectralreflection symmetry that accompanies the U(1) charge and domain wall conservation. The rich structure is developed through an effective model which is a constrained 1D FermiHubbard model at infiniteU. Using this formalism we show that certain emergent subsectors display nontrivial dynamics including chaotic with manybody scarring, as well as, Betheansatz solvable. The structure of the initial state is shown to result in a wide class of dynamics. 
Tuesday, March 16, 2021 4:36PM  4:48PM Live 
J34.00007: Quantum Symmetry Detection Using an Anyonic Plasmon Engine Nathan Myers, Fabian Menges, Sebastian Deffner Understanding quantum statistics and its impact on the performance of quantum devices is an essential step in the development of quantum technologies. To this end, we propose an experimental implementation of a continuous quantum engine utilizing a working medium of anyonic plasmons. Such surface plasmons are generated on a gold nanowire through the coupling of entangled Bellstate photons. Based on the statistical mixture of the Bellstate symmetry of incident photons, anyonic statistics are encoded in the surface plasmons. Work is extracted via the emission of electrons into a uniform electric field. We show that the average work extracted is independent of the particle statistics, but that higher moments of the work distribution are sensitive to the anyonic phase. Utilizing the GreenKubo relations we demonstrate that measurements of electronic transport coefficients can yield information about the statistics encoded in the plasmons. We conclude with a short perspective on how a quantum plasmonic nanowire tip with anyonic phase control might be used to probe exotic quasiparticles in topological matter. 
Tuesday, March 16, 2021 4:48PM  5:00PM Live 
J34.00008: Information driven double quantumdot engine fueled by entanglement between electron spins Martin Josefsson, Martin Leijnse The laws of thermodynamics allow work extraction from a single heat bath provided that the entropy decrease of the bath is compensated for by another part of the system. We propose a thermodynamic quantum engine that exploits this principle and consists of two electrons on a double quantum dot (QD) [1]. The engine is fueled by providing it with singlet spin states, where the electron spins on different QDs are maximally entangled, and its operation involves only changing the tunnel coupling between the QDs. Work can be extracted since the entropy of an entangled singlet is lower than that of a thermal (mixed) state, although they look identical when measuring on a single QD. We show that the engine is an optimal thermodynamic engine in the longtime limit. In addition, we include a microscopic description of the thermal bath and analyze the engine’s finitetime performance using experimentally relevant parameters. 
Tuesday, March 16, 2021 5:00PM  5:12PM Live 
J34.00009: Work Estimation and Work Fluctuations in the Presence of NonIdeal Measurements Tiago Debarba, Gonzalo Manzano, Yelena Guryanova, Marcus Huber, Nicolai Friis From the perspective of quantum thermodynamics, realizable measurements cost work, and result in measurement devices that are not perfectly correlated with the measured systems. We investigate the consequences for the estimation of work in nonequilibrium processes and the fundamental structure of the fluctuations when one assumes that the measurements are nonideal. We show that obtaining work estimates and their statistical moments at finite work cost implies an imperfection of the estimates themselves: more accurate estimates incur higher costs. We revisit these concepts and investigate the consequences for these quantities when one does not assume ideal measurements. We explicitly show how the average work is modified and discuss the operational meaning of the corresponding estimates. We show that while Jarzynski’s equality can be maintained exactly at the expense of a correction that only depends on the system’s Hamiltonian, the more general relation due to Crooks (as well as related results linking irreversibility and dissipation) no longer hold in the presence of nonideal measurements. Our results provide a quantification of the cost of obtaining information about work as well as the trustworthiness of it. 
Tuesday, March 16, 2021 5:12PM  5:24PM Live 
J34.00010: Topological effects on the thermodynamics of open quantum systems Charles Stafford, Yiheng Xu, Ferdinand Evers The thermodynamics of open quantum systems coupled to topological fields is analyzed. Thermodynamic state functions of an open quantum system are defined based on a partition of Hilbert/Fock space, rather than a partition of the corresponding operators. This distinction is crucial, not only due to longrange interactions, but also due to uniquely quantum mechanical action at a distance. Both the AharonovBohm effect for systems of charged particles and the AharonovCasher effect for systems of neutral spin1/2 particles are considered. A proper treatment of the work done by the topological fields is necessary to ensure that the entropy and internal energy of the system are state functions, and to avoid thermodynamic paradoxes. 
Tuesday, March 16, 2021 5:24PM  5:36PM Live 
J34.00011: Andreev reflecting black holes: a black hole analogy in solid state. Sreenath Kizhakkumpurath Manikandan, Andrew N Jordan We present a microscopic quantum description for Hawking radiation as analogous to Andreev mode conversions from a superconductor/normal metal interface. Our approach, extending our previous proposals [PRD 96, 124011 (2017), PRD 98, 124043 (2018)], provides a manifestly unitary description for a black hole in its late stages of the evaporation process, where it accepts collapsing matter by pairing them with the infalling Hawking quantum into a BardeenCooperSchrieffer like quantum ground state. The quantum information encoded in the collapsing matter is Andreev reflected in the outgoing modes, resolving the quantum information paradox. Our resolution is similar to the HorowitzMaldacena black hole final state proposal, where the quantum information is preserved by the black hole applying a final boundary condition at its singularity. The microscopic details we present suggests a possible mechanism by which the quantum final state proposal may emerge, devoid of possibly unphysical computational enhancements resulting from a final state projection. 
Tuesday, March 16, 2021 5:36PM  5:48PM Live 
J34.00012: Heat transport in overdamped quantum systems Sadeq. S Kadijani, Thomas L Schmidt, Massimiliano Esposito, Nahuel Freitas In classical and statistical physics, the overdamped limit of systems interacting with their environments is a very useful approximation allowing for the simplification of the FokkerPlank equation in phase space to the Smoluchowski equation for the position variable alone. For 
Tuesday, March 16, 2021 5:48PM  6:00PM Live 
J34.00013: Measuring OutofTimeOrder Correlators with Projected Revivability Brittany Richman, Minh Tran, Jacob Taylor The outoftimeorder correlator (OTOC) has emerged as an important indicator for quantum chaos. However, it remains a major challenge in many systems to measure the OTOC due to the required implementation of timereversal in the system. We propose a protocol to measure the OTOC using an auxillary quantum bit. Our approach is focused on systems that contain an island of revivabilitya subspace within which the systems' dynamics exhibit quasiperiodic revivals. This allows approximate timereversal in this subspace, and enables a qubitbased measurement of the OTOC. We provide an approach to find the island of revivability by showing that, in the classical limit, this subspace corresponds to an island of stability, i.e., a subspace within which the system is periodic. We demonstrate the effectiveness of this concept in a simple system of two coupled oscillators, and show that it is able to probe the nonrevivable region nearby, enabling observation of OTOC growth consistent with quantum chaos. 
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