The extraction of work from quantum coherence

TLDR

The interplay between quantum coherence and classical energy concepts remains a subtle frontier in quantum thermodynamics. The study critically examines whether quantum coherence can be converted into work, challenging the traditional Carnot limit. We demonstrate that quantum thermal machines can extract work from coherence arbitrarily efficiently, requiring only single‑copy operations and allowing infinite reuse, though finite‑resource machines cannot harvest all coherence.

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.