# Quantum Coherence in a Quantum Heat Engine

## TL;DR

This paper explores how quantum coherence acts as a resource in a quantum heat engine with a superposed Maxwell's demon, enhancing work output and efficiency through coherence consumption.

## Contribution

It introduces a framework redefining quantum work and heat to include coherence, demonstrating how coherence improves engine performance and discussing a universal coherence-driven information heat engine.

## Key findings

- Quantum coherence enhances heat engine efficiency.
- Coherence consumption increases total quantum work.
- Work extraction is limited by quantum coherence without classical costs.

## Abstract

We identify that quantum coherence is a valuable resource in the quantum heat engine, which is designed in a quantum thermodynamic cycle assisted by a quantum Maxwell's demon. This demon is in a superposed state. The quantum work and heat are redefined as the sum of coherent and incoherent parts in the energy representation. The total quantum work and the corresponding efficiency of the heat engine can be enhanced due to the coherence consumption of the demon. In addition, we discuss an universal information heat engine driven by quantum coherence. The extractable work of this heat engine is limited by the quantum coherence, even if it has no classical thermodynamic cost. This resource-driven viewpoint provides a direct and effective way to clarify the thermodynamic processes where the coherent superposition of states cannot be ignored.