02 Mar 2021-Vol. 2, Iss: 1, pp 010336

Abstract: A framework for deriving tight, and therefore more predictive, bounds on the evolution of quantum devices is presented within the body of quantum thermodynamics.

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Topics: Quantum thermodynamics (70%), Quantum (57%), Deformation (meteorology) (53%)

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12 results found

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Topics: Open quantum system (90%), Quantum technology (89%), Quantum process (83%) ... show more

1,008 Citations

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Mark T. Mitchison^{1}, Mark T. Mitchison^{2}, Mischa P. Woods^{3}, Mischa P. Woods^{4} +2 more•Institutions (6)

Abstract: The extension of thermodynamics into the quantum regime has received much attention in recent years. A primary objective of current research is to find thermodynamic tasks which can be enhanced by quantum mechanical effects. With this goal in mind, we explore the finite-time dynamics of absorption refrigerators composed of three qubits. The aim of this finite-time cooling is to reach low temperatures as fast as possible and subsequently extract the cold particle to exploit it for information processing purposes. We show that the coherent oscillations inherent to quantum dynamics can be harnessed to reach temperatures that are colder than the steady state in orders of magnitude less time, thereby providing a fast source of low-entropy qubits. This effect demonstrates that quantum thermal machines can surpass classical ones, reminiscent of quantum advantages in other fields, and is applicable to a broad range of technologically important scenarios.

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Topics: Quantum dynamics (62%), Qubit (59%), Quantum (53%) ... show more

75 Citations

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Abstract: In many real-world situations, there are constraints on the ways in which a physical system can be manipulated. We investigate the entropy production (EP) and extractable work involved in bringing a system from some initial distribution $p$ to some final distribution $p'$, given that the set of master equations available to the driving protocol obeys some constraints. We first derive general bounds on EP and extractable work, as well as a decomposition of the nonequilibrium free energy into an "accessible free energy" (which can be extracted as work, given a set of constraints) and "inaccessible free energy" (which must be dissipated as EP). In a similar vein, we consider the thermodynamics of information in the presence of constraints, and decompose the information acquired in a measurement into "accessible" and "inaccessible" components. This decomposition allows us to consider the thermodynamic efficiency of different measurements of the same system, given a set of constraints. We use our framework to analyze protocols subject to symmetry, modularity, and coarse-grained constraints, and consider various examples including the Szilard box, the 2D Ising model, and a multi-particle flashing ratchet.

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Topics: Entropy production (51%), Non-equilibrium thermodynamics (51%), Physical system (50%)

7 Citations

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Abstract: The laws of thermodynamics are usually formulated under the assumption of infinitely large environments. While this idealization facilitates theoretical treatments, real physical systems are always finite and their interaction range is limited. These constraints have consequences on important tasks such as cooling, not directly captured by the second law of thermodynamics. Here, we study catalytic transformations that cannot be achieved when a system exclusively interacts with a finite environment. Our core result consists of constructive conditions for these transformations, which include the corresponding global unitary operation and the explicit states of all the systems involved. From this result we present various findings regarding the use of catalysts for cooling. First, we show that catalytic cooling is always possible if the dimension of the catalyst is sufficiently large. In particular, the cooling of a qubit using a hot qubit can be maximized with a catalyst as small as a three-level system. We also identify catalytic enhancements for tasks whose implementation is possible without a catalyst. For example, we find that in a multiqubit setup catalytic cooling based on a three-body interaction outperforms standard (non-catalytic) cooling using higher order interactions. Another advantage is illustrated in a thermometry scenario, where a qubit is employed to probe the temperature of the environment. In this case, we show that a catalyst allows to surpass the optimal temperature estimation attained only with the probe.

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Topics: Qubit (52%), Physical system (51%)

6 Citations

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Abstract: A thermodynamic framework provides new bounds on how much work can be extracted from a system under nonidealized, real-world conditions.

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Topics: Entropy production (55%), Work (thermodynamics) (55%)

5 Citations

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47 results found

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Abstract: The usual laws of thermodynamics that are valid for macroscopic systems do not necessarily apply to the nanoscale, where quantum effects become important. Here, the authors develop a theoretical framework based on quantum information theory to properly treat thermodynamics at the nanoscale.

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Topics: Quantum thermodynamics (68%), Quantum information (65%), Laws of thermodynamics (62%) ... show more

648 Citations

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Fernando G. S. L. Brandão^{1}, Michał Horodecki^{2}, Nelly Huei Ying Ng^{3}, Jonathan Oppenheim^{3} +2 more•Institutions (3)

Abstract: The second law of thermodynamics places constraints on state transformations. It applies to systems composed of many particles, however, we are seeing that one can formulate laws of thermodynamics when only a small number of particles are interacting with a heat bath. Is there a second law of thermodynamics in this regime? Here, we find that for processes which are approximately cyclic, the second law for microscopic systems takes on a different form compared to the macroscopic scale, imposing not just one constraint on state transformations, but an entire family of constraints. We find a family of free energies which generalize the traditional one, and show that they can never increase. The ordinary second law relates to one of these, with the remainder imposing additional constraints on thermodynamic transitions. We find three regimes which determine which family of second laws govern state transitions, depending on how cyclic the process is. In one regime one can cause an apparent violation of the usual second law, through a process of embezzling work from a large system which remains arbitrarily close to its original state. These second laws are relevant for small systems, and also apply to individual macroscopic systems interacting via long-range interactions. By making precise the definition of thermal operations, the laws of thermodynamics are unified in this framework, with the first law defining the class of operations, the zeroth law emerging as an equivalence relation between thermal states, and the remaining laws being monotonicity of our generalized free energies.

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Topics: Laws of thermodynamics (68%), Zeroth law of thermodynamics (63%), Quantum thermodynamics (59%) ... show more

600 Citations

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Abstract: This topical review article gives an overview of the interplay between quantum information theory and thermodynamics of quantum systems. We focus on several trending topics including the foundations of statistical mechanics, resource theories, entanglement in thermodynamic settings, fluctuation theorems and thermal machines. This is not a comprehensive review of the diverse field of quantum thermodynamics; rather, it is a convenient entry point for the thermo-curious information theorist. Furthermore this review should facilitate the unification and understanding of different interdisciplinary approaches emerging in research groups around the world.

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Topics: Quantum thermodynamics (58%), Quantum information (55%), Quantum entanglement (51%)

584 Citations

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Description of quantum coherence in thermodynamic processes requires constraints beyond free energy.

Abstract: Recent studies have developed fundamental limitations on nanoscale thermodynamics, in terms of a set of independent free energy relations. Here we show that free energy relations cannot properly describe quantum coherence in thermodynamic processes. By casting time-asymmetry as a quantifiable, fundamental resource of a quantum state, we arrive at an additional, independent set of thermodynamic constraints that naturally extend the existing ones. These asymmetry relations reveal that the traditional Szilard engine argument does not extend automatically to quantum coherences, but instead only relational coherences in a multipartite scenario can contribute to thermodynamic work. We find that coherence transformations are always irreversible. Our results also reveal additional structural parallels between thermodynamics and the theory of entanglement. The statistical nature of standard thermodynamics provides an incomplete picture for individual processes at the nanoscale, and new relations have been developed to extend it. Here, the authors show that by quantifying time-asymmetry it is also possible to characterize how quantum coherence is modified in such processes.

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Topics: Quantum state (56%), Quantum entanglement (55%), Coherence (physics) (55%) ... show more

546 Citations