Cooling limits of coherent refrigerators

TL;DR

This paper establishes fundamental quantum limits on cooling using coherence, introduces protocols to surpass classical bounds, and demonstrates a generalized cooling algorithm outperforming traditional methods.

Contribution

It derives universal quantum cooling limits employing coherence and proposes protocols, including a generalized algorithmic cooling method, that outperform incoherent approaches.

Findings

Quantum coherence enables cooling below classical bounds.

Universal limits for coherent cooling are derived.

A generalized cooling protocol surpasses existing incoherent methods.

Abstract

Refrigeration limits are of fundamental and practical importance. We here show that quantum systems can be cooled below existing incoherent cooling bounds by employing coherent virtual qubits, even if the amount of coherence is incompletely known. Virtual subsystems, that do not necessarily correspond to a natural eigensubspace of a system, are a key conceptual tool in quantum information science and quantum thermodynamics. We derive universal coherent cooling limits and introduce specific protocols to reach them. As an illustration, we propose a generalized algorithmic cooling protocol that outperforms its current incoherent counterpart. Our results provide a general framework to investigate the performance of coherent refrigeration processes.