Performance bound for quantum absorption refrigerators

TL;DR

This paper analyzes the efficiency limits of quantum absorption refrigerators with three qubits, showing that dissipation effects impose a fundamental bound on performance, and explores how quantum correlations influence operation.

Contribution

It provides a rigorous bound on the coefficient of performance at maximum power for quantum refrigerators considering realistic dissipation effects.

Findings

Efficiency at maximum power is bounded by 3/4 of Carnot efficiency.

Dissipation effects prevent approaching Carnot performance arbitrarily closely.

Quantum correlations may influence the refrigerator's operation.

Abstract

An implementation of quantum absorption chillers with three qubits has been recently proposed, that is ideally able to reach the Carnot performance regime. Here we study the working efficiency of such self-contained refrigerators, adopting a consistent treatment of dissipation effects. We demonstrate that the coefficient of performance at maximum cooling power is upper bounded by 3/4 of the Carnot performance. The result is independent of the details of the system and the equilibrium temperatures of the external baths. We provide design prescriptions that saturate the bound in the limit of a large difference between the operating temperatures. Our study suggests that delocalized dissipation, which must be taken into account for a proper modelling of the machine-baths interaction, is a fundamental source of irreversibility which prevents the refrigerator from approaching the Carnot performance arbitrarily closely in practice. The potential role of quantum correlations in the operation of these machines is also investigated.