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Entangled Maxwell's Demons Violating Thermodynamical Separability Criteria

Koji Maruyama, Fumiaki Morikoshi, Vlatko Vedral

Published Nov 12, 2003• 0 citations
OpenAlex

Abstract

Quantum correlation, or entanglement, is now believed to be an indispensable physical resource for certain tasks in quantum information processing, for which classically correlated states cannot be useful. Besides information processing, what kind of physical processes can exploit entanglement? In this Letter, we show that there is indeed a more basic relationship between entanglement and its usefulness in thermodynamics by illustrating that we can extract more work out of entangled systems than out of classically correlated ones. Our results suggest a novel connection between entanglement and thermodynamics.

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Quantum correlation, or entanglement, is now believed to be an indispensable physical resource for certain tasks in quantum information processing, for which classically correlated states cannot be useful. Besides information processing, what kind of physical processes can exploit entanglement? In this Letter, we show that there is indeed a more basic relationship between entanglement and its usefulness in thermodynamics by illustrating that we can extract more work out of entangled systems than out of classically correlated ones. Our results suggest a novel connection between entanglement and thermodynamics.
Quantum correlation, or entanglement, is now believed to be an indispensable physical resource for certain tasks in quantum information processing, for which classically correlated states cannot be useful. Besides information processing, what kind of physical processes can exploit entanglement? In this paper, we show that there is indeed a more basic relationship between entanglement and its usefulness in thermodynamics. We derive an inequality showing that we can extract more work out of a heat bath via entangled systems than via classically correlated ones. We also analyze the work balance of the process as a heat engine, in connection with the second law of thermodynamics.
There is ongoing controversy about whether a coherent superposition of the occupied states of two fermionic modes should be regarded entangled or not, that is, whether its intrinsic quantum correlations are operationally accessible and useful as a resource. This has been questioned on the basis that such an entanglement cannot be accessed by local operations on individual modes due to the parity superselection rule which constrains the set of physical observables. In other words, one cannot observe violations of Bell's inequality. Here, we show, however, that entanglement of a two-mode fermionic state can be used as a genuine quantum resource in open-system thermodynamic processes, enabling one to perform tasks forbidden for separable states. We thus demonstrate that quantum thermodynamics can shed light on the nature of fermionic entanglement and the operational meaning of the different notions used to define it.
Within the framework of microscopic thermodynamics, correlations can play a crucial role for energy extraction. Our work sheds light on this connection by demonstrating that entanglement governs the amount of extractable energy in a controllable setting. We experimentally investigate a fundamental link between information, encoded in tunable non-classical correlations and quantified by quantum state tomography, and its utility as fuel for energy extraction. We realize an agent-demon protocol involving two trapped-ion qubits, and show that by implementing an appropriate feedback policy, the demon can optimize the energy extraction process, capitalizing on the correlations between the system's constituents. By quantifying both the concurrence of the two-qubit resource state and the energy extraction gain from applying the feedback policy, we corroborate the connection between information and energy, solidifying the role of non-classical correlations as a resource for thermodynamic processes.
An exponential rise in the demand of secured information processing requires an alternative approach from the conventional classical world, and the present scientific community believes that one of the most distinctive physical resources of the quantum world is quantum entanglement. It is a unique correlation between the components of quantum multipartite systems, which has never been observed in the classical macroscopic world. It is a tool that not only explains the effectiveness and fruitfulness of quantum information processing compared to its classical counterpart but also becomes significant from the security point of view when quantum communication is considered. The most trusted and investigated resource till date is quantum entanglement, for the purpose of secured data communication. Similar to energy, quantum entanglement is a physical resource connected to the odd nonclassical connections that can occur between distant quantum systems. Using a pair of entangled quantum systems, it is feasible to carry out computing operations that are impractical for conventional systems. Quantum information theory is a broad study of the information processing capabilities of quantum systems.
Entanglement, a weird quantum correlation between separate physical systems, is an indispensable resource for quantum information processing. As with other physical resources, the key to understanding its full potential is to quantify it. In this paper, I review our recent insights into the quantification of entanglement based on the operational notion of accessibility between physical states. In particular, I show that the partially ordered structure of mixed entangled states underlies the non-uniqueness of their entanglement measure.
We discuss quantum entanglement in the context of the thermodynamic arrow of time. We review the role of correlations in entropy-decreasing events and prove that the occurrence of a transformation between two thermodynamic states constitutes a new type of entanglement witness, one not defined as a separating plane in state space between separable and entangled states, but as a physical process dependent on the local initial properties of the states. Extending work by Partovi, we consider a general entangled multipartite system that allows large reversals of the thermodynamic arrow of time. We describe a hierarchy of arrows that arises from the different correlations allowed in a quantum state and examine these features in the context of Maxwell's Demon. We examine in detail the case of three qubits, and also propose some simple experimental demonstrations possible with small numbers of qubits.