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Open AccessArticle

Thermodynamics of Quantum Feedback Cooling

School of Mathematical Sciences, The University of Nottingham, University Park, Nottingham NG7 2RD, UK
Unitat de Física Teòrica: Informació i Fenòmens Quàntics, Departament de Física, Universitat Autònoma de Barcelona, Bellaterra 08193, Spain
Centre for Quantum Engineering, Department of Applied Physics, Aalto University School of Science, P.O.Box 11100, Aalto 00076, Finland
Centre of Excellence in Computational Nanoscience, Department of Applied Physics, Aalto University School of Science, P.O.Box 11100, Aalto 00076, Finland
Turku Centre for Quantum Physics, Department of Physics and Astronomy, University of Turku, Turun Yliopisto FI-20014, Finland
Author to whom correspondence should be addressed.
Academic Editor: Ronnie Kosloff
Entropy 2016, 18(2), 48;
Received: 24 November 2015 / Revised: 27 January 2016 / Accepted: 28 January 2016 / Published: 4 February 2016
(This article belongs to the Special Issue Quantum Thermodynamics)
The ability to initialize quantum registers in pure states lies at the core of many applications of quantum technologies, from sensing to quantum information processing and computation. In this paper, we tackle the problem of increasing the polarization bias of an ensemble of two-level register spins by means of joint coherent manipulations, involving a second ensemble of ancillary spins and energy dissipation into an external heat bath. We formulate this spin refrigeration protocol, akin to algorithmic cooling, in the general language of quantum feedback control, and identify the relevant thermodynamic variables involved. Our analysis is two-fold: on the one hand, we assess the optimality of the protocol by means of suitable figures of merit, accounting for both its work cost and effectiveness; on the other hand, we characterise the nature of correlations built up between the register and the ancilla. In particular, we observe that neither the amount of classical correlations nor the quantum entanglement seem to be key ingredients fuelling our spin refrigeration protocol. We report instead that a more general indicator of quantumness beyond entanglement, the so-called quantum discord, is closely related to the cooling performance. View Full-Text
Keywords: feedback cooling; quantum thermodynamics; quantum correlations feedback cooling; quantum thermodynamics; quantum correlations
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Liuzzo-Scorpo, P.; Correa, L.A.; Schmidt, R.; Adesso, G. Thermodynamics of Quantum Feedback Cooling. Entropy 2016, 18, 48.

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