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Open AccessArticle

Implications of Coupling in Quantum Thermodynamic Machines

Optics and Quantum Information Group, The Institute of Mathematical Sciences, HBNI, C. I. T. Campus, Taramani, Chennai 600113, India
Author to whom correspondence should be addressed.
Entropy 2017, 19(9), 442;
Received: 5 July 2017 / Revised: 13 August 2017 / Accepted: 17 August 2017 / Published: 8 September 2017
(This article belongs to the Special Issue Quantum Thermodynamics)
We study coupled quantum systems as the working media of thermodynamic machines. Under a suitable phase-space transformation, the coupled systems can be expressed as a composition of independent subsystems. We find that for the coupled systems, the figures of merit, that is the efficiency for engine and the coefficient of performance for refrigerator, are bounded (both from above and from below) by the corresponding figures of merit of the independent subsystems. We also show that the optimum work extractable from a coupled system is upper bounded by the optimum work obtained from the uncoupled system, thereby showing that the quantum correlations do not help in optimal work extraction. Further, we study two explicit examples; coupled spin- 1 / 2 systems and coupled quantum oscillators with analogous interactions. Interestingly, for particular kind of interactions, the efficiency of the coupled oscillators outperforms that of the coupled spin- 1 / 2 systems when they work as heat engines. However, for the same interaction, the coefficient of performance behaves in a reverse manner, while the systems work as the refrigerator. Thus, the same coupling can cause opposite effects in the figures of merit of heat engine and refrigerator. View Full-Text
Keywords: quantum heat engines; quantum refrigerators; coupled oscillators; coupled spins quantum heat engines; quantum refrigerators; coupled oscillators; coupled spins
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Thomas, G.; Banik, M.; Ghosh, S. Implications of Coupling in Quantum Thermodynamic Machines. Entropy 2017, 19, 442.

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