Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session C27: Quantum Thermodynamics and Resource TheoriesFocus

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Sponsoring Units: DQI Chair: Bo Sun, HRL Laboratories Room: BCEC 160C 
Monday, March 4, 2019 2:30PM  2:42PM 
C27.00001: Quantum to ‘classical’ behaviour in closedsystems thermodynamics: an analysis of the quantum work distribution in driven fermionic chains Krissia Zawadzki, Marcela Herrera, Roberto Menezes Serra, Irene D'Amico The role of manybody interactions in work and entropy production at nanoscales has become a trend topic mainly boosted by increasing interest of probing the laws of thermodynamics for few particle systems. When we turn to the case of strongly correlated systems, one might be interested in probing phase transitions by means of thermodynamical quantities and their statistics, as, for instance, the moments of the socalled quantum work distribution P(W). We propose to examine this question in the context of outofequilibrium Hubbard chains by inspecting the extracted work 〈W〉 and the first four central moments 〈W  〈W〉〉^{k }, (k=1,2,3,4)$ of P(W). Our analysis inspects the interplay between coupling and dynamical regimes, i.e., we analyse the thermodynamical quantities from noninteracting to the strongly coupled limits when the driving external field is turned on adiabatically or as a sudden quench. Our results indicate a high sensibility of the third momentum (skewness) to the Mott insulator transition and we discuss how it could be used as an order parameter to probe quantum phase transitions in experimental nanoscopic strongly correlated systems. 
Monday, March 4, 2019 2:42PM  2:54PM 
C27.00002: Local superfluid distillation of Bose liquids Tyler Volkoff, Yongkyung Kwon By introducing a localized resource theory of quantum coherence, we discuss limits to local distillation of complete superfluidity from imperfect superfluid states. To define the local maximal superfluid resource, we develop a theory of local superfluidity from first principles using local Galilei transformations, and demonstrate the framework in effective and microscopic models of Bose liquids. The combined theoretical framework of local superfluidity and localized resource theory of quantum coherence allows quantum informationbased design and analyses of spatially structured superfluid quantum devices. 
Monday, March 4, 2019 2:54PM  3:06PM 
C27.00003: Work Extraction from a Single Energy Eigenstate Kazuya Kaneko, Eiki Iyoda, Takahiro Sagawa Work extraction from the Gibbs ensemble by a cyclic operation is impossible, as represented by the second law of thermodynamics. On the other hand, recent studies revealed that a thermal equilibrium state can be represented not only by the Gibbs state, but also by a single energy eigenstate. This is referred to as the eigenstate thermalization hypothesis (ETH). We attempt to unify these two perspectives by examining the possibility of extracting work from a single energy eigenstate. Specifically, we performed numerical exact diagonalization of a quench protocol of local Hamiltonians and evaluated the number of workextractable energy eigenstates. We found that it becomes exactly zero in a finite system size, implying that a positive amount of work cannot be extracted from any energy eigenstate, if one or both of the pre and the postquench Hamiltonians are nonintegrable. This result suggests that the second law of thermodynamics is true even at the level of individual energy eigenstates if the system is nonintegrable (i.e., quantum chaotic), which is analogous to the ETH. 
Monday, March 4, 2019 3:06PM  3:18PM 
C27.00004: DFT protocols for quantum thermodynamics of outofequilibrium systems Amy Skelt, Krissia Zawadzki, Marcela Herrera, Irene D'Amico Quantum thermodynamics strives to understand quantum fluctuations at the nanoscale, with an emphasis on the determination of thermodynamic properties of outofequilibrium quantum systems. This already challenging task becomes significantly more complex when manybody interactions give rise to strongly correlated systems. Inspired by the KohnSham approach to Density Functional Theory (DFT), we propose to tackle this problem in a framework where the system is effectively described by noninteracting particles, and extend the protocol introduced in M. Herrera, R.M. Serra, I. D’Amico, Scientific Reports 7, 4655 (2017). Considering all dynamic regimes, from adiabatic to sudden quench, we study the work extraction and entropy production in finite Hubbard chains up to 8 sites, and compare results from various driving potentials. We examine the competition between the evolution time, interaction strength, and thermal regimes, benchmarking approximate results against the exact ones. Our results reveal that the DFTinspired protocol performs well, with deviation of less than 10%, compared to the exact results up to moderate coupling regimes and, surprisingly for a ground state DFT protocol, up to intermediate temperatures of KT~23 J, J the hopping parameter. 
Monday, March 4, 2019 3:18PM  3:30PM 
C27.00005: Absolute irreversibility and continuous quantum measurement: a fluctuation theorem perspective Sreenath Kizhakkumpurath Manikandan, Cyril Elouard, Andrew N Jordan The outofequilibrium fluctuations of thermodynamic quantities like entropy production for a small system in contact with a thermal reservoir are constrained beyond the second law using relations known as fluctuation theorems. Here we show that, in the absence of a thermal reservoir, the dynamics of continuously measured quantum systems can also be described by a fluctuation theorem, where the fluctuations originate from inherently probabilistic quantum measurement dynamics. This theorem captures the emergence of an arrow of time in the measurement process, from microscopically reversible quantum state dynamics in continuous quantum measurements. We also demonstrate that the measurementinduced wavefunction collapse exhibits absolute irreversibility, such that Jarzynski and Crookslike equalities are violated. We apply our results to different continuous measurement schemes on a qubit: dispersive measurement, homodyne and heterodyne detection of qubit's fluorescence. 
Monday, March 4, 2019 3:30PM  3:42PM 
C27.00006: Thermodynamics of fast quantum gates Cyril Elouard, Massimiliano Esposito, Alexia Auffèves, Andrew N Jordan Quantum computation gates rely on the possibility to perform qubit rotations in the Bloch sphere faster than decoherence. Strikingly, a thermodynamic description analyzing the coherent energy exchanges between the qubit and the driven field is still missing. Previous studies have focused on long timescales [12], much larger than one Rabi period, blurring out any coherent phenomenon, and are therefore inadequate to study e.g. the work cost of fast gates. Here we propose a thermodynamic description that is valid at short timescales, where the dynamics is captured by the Optical Bloch Equations, featuring coherent excitation exchanges between qubit and the field. We identify the first and second law and their quantum components. The derivation of an integral and a detailed Crooks quantum fluctuation theorems ensures the thermodynamic consistency of our theory. Predictions from earlier Floquetbased (long timescale) approaches are recovered in relevant regimes. Our results contribute to bridge the gap between quantum thermodynamics on the one hand, and quantum optics and quantum computation on the other hand. 
Monday, March 4, 2019 3:42PM  4:18PM 
C27.00007: Quantum of information and its fluctuations in a conductor heat current Invited Speaker: Yasuhiro Utsumi Mesoscopic quantum conductors have been tools to investigate thermodynamics in the quantum regime [1]. They also offer a playground to think about entanglement and information transmission. In a quantum conductor, by applying a sourcedrain bias voltage, entangled electronhole pairs can be created [2]. Moreover one bit of information content can be conveyed by the arrival or nonarrival of an electron [3]. We revisit this problem by analyzing a novel quantity, the distribution of fluctuating information, particle and heat currents, which is closely related to the `Rényi entanglement entropy’ [4]. Our approach is the fullcounting statistics based on the multicontour Keldysh Green function developed recently [4,5]. 
Monday, March 4, 2019 4:18PM  4:30PM 
C27.00008: Work extraction and Landauer's principle in a quantum spin Hall device Inanc Adagideli, Ahmet Mert Bozkurt, Baris Pekerten Landauer's principle states that erasure of each bit of information in a system requires at least a unit of energy kBTln2 to be dissipated. In return, the blank bit may possibly be utilized to extract usable work of the amount kBTln2, in keeping with the second law of thermodynamics. While in principle any collection of spins can be utilized as information storage, work extraction by utilizing this resource in principle requires specialized engines that are capable of using this resource. In this work, we focus on heat and charge transport in a quantum spin Hall device in the presence of a spin bath. We show how a properly initialized nuclear spin subsystem can be used as a memory resource for a Maxwell's Demon to harvest available heat energy from the reservoirs to induce charge current that can power an external electrical load. We also show how to initialize the nuclear spin subsystem using applied bias currents which necessarily dissipate energy, hence demonstrating Landauer's principle. This provides an alternative method of "energy storage" in an allelectrical device. We finally propose a realistic setup to experimentally observe a Landauer erasure/work extraction cycle. 
Monday, March 4, 2019 4:30PM  4:42PM 
C27.00009: The dramatic impact of nonenergetic coherences on heat flows Camille Lombard Latune, Ilya Sinayskiy, Francesco Petruccione We show that the heat flow between a system and a stationary reservoir (under BornMarkov approximation) is dramatically affected by coherences between degenerate levels of the system. To assess the resulting effects of coherences on heat flows we introduce a concept of apparent temperature [1] which crucially takes into account coherences, by contrast with the virtual temperature [2]. It provides an intuitive picture in which nonenergetic coherences behave as populations, enabling one to recover seminal results on phaseonium, thermally entangled atoms, and lasing without inversion. Moreover, we predict new effects like the dramatic increase of apparent temperature due to delocalised excitations. One of its manifestations, testable experimentally, is the “apparent thermalization”, where an ensemble of indistinguishable subsystems equilibrates at a much lower (or higher) energy than when interacting separately (or distinguishably) with the bath. Such phenomena stem from the mixture of the dynamics of the populations and coherences, which happens only in presence of degeneracy and is unique to quantum thermodynamics. 
Monday, March 4, 2019 4:42PM  4:54PM 
C27.00010: Quantum thermalization and optimal control are compatible in a manybody system Ferney Rodriguez, Fernando GómezRuiz, Luis Quiroga, Neil F Johnson We propose a novel protocol for characterizing and ultimately controlling collective matterradiation effects that emerge when a manybody quantum system is driven through a critical value of the interaction coupling strength. There are many possible ways to use our scheme to achieve quantum computing and information processing, including controlling superconducting qubits or color defects in diamond by means of quantum light in cavities. We show that apparently disparate phenomena such as thermalization, excited state quantum phase transitions and orthogonality catastrophes can be present in the system when subject to a finite pulsed coupling with the light field. In particular, we demonstrate a connection between the thermalization through entanglement of the global quantum pure system reached at the middle of the pulse, and the controlled production of an orthogonal global state at the end of the pulse. Our results should prove useful in a variety of contexts including the preparation of phases of condensed matter in quantum simulators and the engineering of states in quantum protocols. 
Monday, March 4, 2019 4:54PM  5:06PM 
C27.00011: Critical point behaviour of a measurementbased quantum heat engine Suman Chand, Asoka Biswas At the critical point (CP), pertaining to quantum phase transition (QPT), the longrange quantum correlation (e.g., entanglement) becomes dominant. We show, in case of an ionbased quantum Otto engine, that such correlation does not necessarily enhance the efficiency of the engine, in the neighborhood of the CP. We choose two trapped ions as the working system, subject to a magnetic field and an internal energyexchange coupling J_{1}. During the expansion stage of the engine cycle, the adiabatic decrease of the magnetic field from B_{H} to B_{L} leads to certain work. The cooling of the system during the exhaust stage is mimicked by a projective measurement of the system into the ground state. During the compression stage, the magnetic field is adiabatically restored to B_{H}. We find that the critical point B_{L}=J_{1}/2 poses as a minimum threshold for the system to work as a heat engine. Further, the efficiency of the engine increases with increase of the interaction strength J_{1}. On the contrary, the coupling to any ancillary system deteriorates the efficiency at the critical point, though such coupling enhances entanglement into the system. Our result suggests that longrange correlation may not be beneficial for an efficient quantum heat engine in the realm of QPT. 
Monday, March 4, 2019 5:06PM  5:18PM 
C27.00012: Topological work in nonequilibrium quantum thermodynamics Charles Stafford, Abhay Shastry, Yiheng Xu, Marco Antonio Jimenez Valencia As a model open quantum system out of equilibrium, we consider a system of electrons coupled to multiple (typically 3) macroscopic electron reservoirs and threaded by an AharonovBohm flux φ. For the noninteracting case, we determine the exact nonequilibrium steadystate density matrix and entropy. We prove that the Nernst theorem (3rd law of thermodynamics) holds without exception for an open quantum system, even for the nonequilibrium case. The general principles are illustrated for the case of a quantum thermocouple. Both the chemical work due to electron exchange between the reservoirs and the topological work due to the AharonovBohm effect must be included in applying the 1st law. The effect of electronelectron interactions on the thermoelectric device performance beyond linear response are investigated. 
Monday, March 4, 2019 5:18PM  5:30PM 
C27.00013: Observable Thermalization Fabio Anza To understand under which conditions thermodynamics emerges from the microscopic dynamics is the ultimate goal of statistical mechanics. Despite the fact that the theory is more than 100 years old, we are still discussing its foundations and its regime of applicability. A point of crucial importance is the definition of the notion of thermal equilibrium, which is given as the state that maximises the von Neumann entropy. Here we argue that it is necessary to propose a new way of describing thermal equilibrium, focused on observables rather than on the full state of the quantum system. We characterise the notion of thermal equilibrium, for a given observable, via the maximisation of its Shannon entropy and highlight the thermal properties that such a principle heralds. Eventually, we bring to light an intimate connection with the Eigenstate Thermalisation Hypothesis. 
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