The extraction of work from quantum coherence

TL;DR

This paper investigates how quantum coherence can be converted into work within quantum thermodynamics, demonstrating that ideal machines can extract unlimited work from coherence, while finite-resource machines have limitations but can be reused.

Contribution

It provides a fully quantum-mechanical analysis showing the possibility of extracting unlimited work from coherence with ideal machines and discusses limitations with finite resources.

Findings

Ideal thermal machines can extract arbitrarily large work from coherence.

Finite-resource machines cannot extract all coherence as work.

Bounded machines can be reused infinitely for work extraction.

Abstract

The interplay between quantum-mechanical properties, such as coherence, and classical notions, such as energy, is a subtle topic at the forefront of quantum thermodynamics. The traditional Carnot argument limits the conversion of heat to work; here we critically assess the problem of converting coherence to work. Through a careful account of all resources involved in the thermodynamic transformations within a fully quantum-mechanical treatment, we show that there exist thermal machines extracting work from coherence arbitrarily well. Such machines only need to act on individual copies of a state and can be reused. On the other hand, we show that for any thermal machine with finite resources not all the coherence of a state can be extracted as work. However, even bounded thermal machines can be reused infinitely many times in the process of work extraction from coherence.