Nonequilibrium quantum absorption refrigerator

TL;DR

This paper investigates a quantum absorption refrigerator with a focus on the role of quantum coherence in its efficiency and cooling performance, revealing that coherence can both aid and hinder different operational aspects.

Contribution

It introduces a model with strong internal coupling and analyzes how quantum coherence affects the refrigerator's cooling ability and efficiency metrics.

Findings

Quantum coherence benefits the nonequilibrium fridge's operation.

Coherence is detrimental to maximum COP and COP at maximum power.

The COP is defined based on heat currents from the tripartite interaction.

Abstract

We study a quantum absorption refrigerator, in which a target qubit is cooled by two machine qubits in a nonequilibrium steady state. It is realized by a strong internal coupling in the two-qubit fridge and a vanishing tripartite interaction among the whole system. The coherence of a \emph{machine virtual qubit} is investigated as quantumness of the fridge. A necessary condition for cooling shows that the quantum coherence is beneficial to the nonequilibrium fridge, while it is detrimental as far as the maximum coefficient of performance (COP) and the COP at maximum power are concerned. Here, the COP is defined only in terms of heat currents caused by the tripartite interaction, with the one maintaining the two-qubit nonequilibrium state being excluded. The later can be considered to have no direct involvement in extracting heat from the target, as it is not affected by the tripartite interaction.