Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session Z35: Thermodynamics in Quantum Information IIFocus Recordings Available
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Sponsoring Units: DQI GSNP DCMP Chair: Ian Mondragon, Northwestern University Room: McCormick Place W-193B |
Friday, March 18, 2022 11:30AM - 12:06PM |
Z35.00001: Robert E. Marshak Lectureship (2022): Non-Abelian Quantum Transport and Thermosqueezing Effects Invited Speaker: Gabriel Landi Transport usually involves energy and particles, quantities which ultimately commute at the quantum mechanical level. Modern quantum experiments, however, provide examples of transport with noncommuting (also called non-Abelian) quantities. In this talk I discuss recent efforts in putting forth a theory of non-Abelian transport in the linear response regime. Our key insight is to use generalized Gibbs ensembles with noncommuting charges as the basic building blocks. In addition, we describe the dynamics in terms of a collision model where small units interact under a new class of strict charge-preserving interactions. We show that the transport coefficients obey Onsager reciprocity. However, we find that quantum coherence, associated with the noncommutativity, acts so as to reduce the net entropy production, when compared to the case of commuting transport. This therefore provides a clear connection between quantum coherent transport and dissipation. As an example, we study the transport of heat and radiation squeezing in bosonic systems, characterizing a set of thermosqueezing coefficients with potential applications in metrology and heat-to-work conversion in the quantum regime. |
Friday, March 18, 2022 12:06PM - 12:18PM |
Z35.00002: Fast Thermalization from the Eigenstate Thermalization Hypothesis Chi-Fang Chen, Fernando Brandao The Eigenstate Thermalization Hypothesis (ETH) has played a major role in explaining thermodynamic phenomena in quantum systems. However, so far ETH has not been linked to the central question about the timescale of thermalization. In this paper, we rigorously show that ETH does imply that the system thermalizes quickly to the global Gibbs state, whenever it is in contact with an external heat bath. |
Friday, March 18, 2022 12:18PM - 12:30PM |
Z35.00003: Sub-system statistics for out-of-equilibrium qubits Sarah E Shandera Motivated by the thermodynamic evolution of both the homogeneous and inhomogeneous universe, we examine mini-landscapes of qubit systems initialized in inhomogeneous thermal states and evolved with dynamics constrained only by a conservation law. We establish the smallest closed-system size, four qubits, needed to model an increase in extractable work in sub-systems. We then consider larger closed-system qubit landscapes where interactions occur in four-qubit sets and study the evolution of the entropy, concurrence, and non-equilibrium free energy of sub-systems as a function of the inhomogeneity of the initial state. We present requirements, as a function of total system size, for pockets of low entropy and high free energy to persist. |
Friday, March 18, 2022 12:30PM - 12:42PM |
Z35.00004: Dependence of integrated, instantaneous, and fluctuating entropy production on the initial state in quantum and classical processes Artemy Kolchinsky, David H Wolpert We consider the additional entropy production (EP) incurred by a fixed quantum or classical process on some initial state ρ, above the minimum EP incurred by the same process on any initial state. We show that this additional EP, which we term the "mismatch cost of ρ," has a universal information-theoretic form: it is given by the contraction of the relative entropy between ρ and the least-dissipative initial state φ over time. We derive versions of this result for integrated EP incurred over the course of a process, for trajectory-level fluctuating EP, and for instantaneous EP rate. We also show that mismatch cost for fluctuating EP obeys an integral fluctuation theorem. Our results demonstrate a fundamental relationship between thermodynamic irreversibility (generation of EP) and logical irreversibility (inability to know the initial state corresponding to a given final state). We use this relationship to derive quantitative bounds on the thermodynamics of quantum error correction and to propose a thermodynamically operationalized measure of the logical irreversibility of a quantum channel. Our results hold for both finite- and infinite-dimensional systems, and generalize beyond EP to many other thermodynamic costs, including nonadiabatic EP, free-energy loss, and entropy gain. |
Friday, March 18, 2022 12:42PM - 12:54PM |
Z35.00005: Experimental Detection of the Correlation Re ́nyi Entropy Mohamad Niknam, Lea F Santos, David Cory We propose and experimentally measure an entropy that quantifies the volume of correlations among qubits. The experiment is carried out on a nearly isolated quantum system composed of a central spin coupled and initially uncorrelated with 15 other spins. Because of the spin-spin interactions, information flows from the central spin to the surrounding ones forming clusters of multispin correlations that grow in time. We design a nuclear magnetic resonance experiment that directly measures the amplitudes of the multispin correlations and use them to compute the evolution of what we call correlation Re ́nyi entropy. This entropy keeps growing even after the equilibration of the entanglement entropy. We also analyze how the saturation point and the timescale for the equilibration of the correlation Re ́nyi entropy depend on the system size. |
Friday, March 18, 2022 12:54PM - 1:06PM |
Z35.00006: Measurement induced criticality in \texorpdfstring{$\mathbb{Z}_2$}{} symmetric quantum automaton circuits Yiqiu Han, Xiao Chen We study entanglement dynamics in hybrid $\mathbb{Z}_2$ symmetric quantum automaton circuits subject to local composite measurements. We show that there exists an entanglement phase transition from a volume law phase to a critical phase by varying the measurement rate $p$. By analyzing the underlying classical bit string dynamics, we demonstrate that the critical point belongs to parity conserving universality class. We further show that the critical phase with $p>p_c$ is related to the diffusion-annihilation process and is protected by the $\mathbb{Z}_2$ symmetric measurement. We give an interpretation of the entanglement entropy in terms of a two-species particle model and identify the coefficient in front of the critical logarithmic entanglement scaling as the local persistent coefficient. The critical behavior observed at $p\geq p_c$ and the associated dynamical exponents are also confirmed in the purification dynamics. |
Friday, March 18, 2022 1:06PM - 1:18PM |
Z35.00007: Quantum heat statistics with time-evolving matrix product operators Maria Popovic We present a numerically exact method to compute the full counting statistics of heat transfer in non-Markovian open quantum systems, which is based on the time-evolving matrix product operator (TEMPO) algorithm. This approach is applied to the paradigmatic spin-boson model in order to calculate the mean and fluctuations of the heat transferred to the environment during thermal equilibration. We show that system-reservoir correlations make a significant contribution to the heat statistics at low temperature and present a variational theory that quantitatively explains our numerical results. We also demonstrate a fluctuation-dissipation relation connecting the mean and variance of the heat distribution at high temperature. Our results reveal that system-bath interactions make a significant contribution to heat transfer even when the dynamics of the open system is effectively Markovian. The method presented here provides a flexible and general tool to predict the fluctuations of heat transfer in open quantum systems in non-perturbative regimes. |
Friday, March 18, 2022 1:18PM - 1:30PM |
Z35.00008: Thermodynamic uncertainty relation in slowly driven quantum heat engines GIACOMO GUARNIERI Thermodynamic uncertainty relations express a trade-off between precision, defined as the noise-tosignal ratio of a generic current, and the amount of associated entropy production. These results have deep consequences for autonomous heat engines operating at steady state, imposing an upper bound for their efficiency in terms of the power yield and its fluctuations. In the present Letter we analyze a different class of heat engines, namely, those which are operating in the periodic slow-driving regime. We show that an alternative TUR is satisfied, which is less restrictive than that of steady-state engines: it allows for engines that produce finite power, with small power fluctuations, to operate close to reversibility. The bound further incorporates the effect of quantum fluctuations, which reduces engine efficiency relative to the average power and reliability. We finally illustrate our findings in the experimentally relevant model of a single-ion heat engine. |
Friday, March 18, 2022 1:30PM - 1:42PM |
Z35.00009: What Temperature is Schrödinger's Cat? Carolyn E Wood, Harshit Verma, Fabio Costa, Magdalena Zych If thermodynamical quantities can be associated with quantum systems, can temperature have quantum features, similar to how time can exhibit them in association with quantum clocks? |
Friday, March 18, 2022 1:42PM - 1:54PM |
Z35.00010: Equidistant quenches in few-level quantum systems Sreekanth K Manikandan A recent work [Phys. Rev. Lett. 125, 110602] showed that among a pair of \textit{thermodynamically} equidistant quenches from a colder and a hotter initial state at a fixed ambient temperature, the relaxation from the colder initial state (\textit{uphill} relaxation) is always faster, for dynamics close to stable minima. Here we show that this is not generically the case for open quantum systems with two or three energy levels. We find that both faster uphill and faster downhill relaxation and symmetric thermal relaxation can be observed in equidistant quenches, depending on the transition rates and the choice of the distance measure used. Furthermore, we obtain a phase diagram in the parameter space for the three-level system corresponding to different thermalization behaviours. |
Friday, March 18, 2022 1:54PM - 2:06PM |
Z35.00011: Work statistics and symmetry breaking in an excited-state quantum phase transition Zakaria Mzaouali, Ricardo Puebla, John Goold, Morad El Baz, Steve Campbell We examine how the presence of an excited state quantum phase transition manifests in the dynamics of a many-body system subject to a sudden quench. Focusing on the Lipkin-Meshkov-Glick model initialized in the ground state of the ferromagnetic phase, we demonstrate that the work probability distribution displays non-Gaussian behavior for quenches in the vicinity of the excited state critical point. Furthermore, we show that the entropy of the diagonal ensemble is highly susceptible to critical regions, making it a robust and practical indicator of the associated spectral characteristics. We assess the role that symmetry breaking has on the ensuing dynamics, highlighting that its effect is only present for quenches beyond the critical point. Finally, we show that similar features persist when the system is initialized in an excited state and briefly explore the behavior for initial states in the paramagnetic phase. |
Friday, March 18, 2022 2:06PM - 2:18PM |
Z35.00012: Resource theory of quantum uncomplexity Nicole Yunger Halpern, Naga B. T. Kothakonda, Jonas Haferkamp, Anthony Munson, Jens Eisert, Philippe Faist Quantum complexity is emerging as a key property of many-body systems, including black holes, topological materials, and early quantum computers. A state's complexity quantifies the number of computational gates required to prepare the state from a simple tensor product. The greater a state's distance from maximal complexity, or "uncomplexity," the more useful the state is as input to a quantum computation. Separately, resource theories—simple models for agents subject to constraints—are burgeoning in quantum information theory. We construct a resource theory of uncomplexity in which the allowed operations, fuzzy operations, are slightly random implementations of two-qubit gates. We formalize two operational tasks, uncomplexity extraction and expenditure. Their optimal efficiencies depend on an entropy, the complexity entropy, that we engineer to reflect complexity. We also present two monotones, uncomplexity measures that decline monotonically under fuzzy operations, in certain regimes. We draw connections to data compression and thermodynamic information erasure under computational limitations, giving a physical interpretation to the complexity entropy. This work unleashes on many-body quantum chaotic systems the resource-theory toolkit from quantum information theory. |
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