Engineering a heat engine purely driven by quantum coherence

TL;DR

This paper investigates a quantum heat engine driven solely by quantum coherence, demonstrating optimal work extraction and efficiency depend on coherence levels, system-bath interactions, and temperature, without heat flow during the cycle.

Contribution

It introduces a coherence-only quantum heat engine model, analyzing how coherence charging and system parameters affect work and efficiency, highlighting optimal conditions.

Findings

Maximum extractable work occurs with four charged qubits.

Optimal coherence is achieved at intermediate bath coherence levels.

Highest efficiency is found at lower temperatures and weaker system-bath coupling.

Abstract

The question of whether quantum coherence is a resource beneficial or detrimental to the performance of quantum heat engines has been thoroughly studied but remains undecided. To isolate the contribution of coherence, we analyze the performance of a purely coherence-driven quantum heat engine, a device that does not include any heat flow during the thermodynamic cycle. The engine is powered by the coherence of a multiqubit system, where each qubit is charged via interaction with a coherence bath using the Jaynes-Cummings model. We demonstrate that optimal coherence charging and hence extractable work is achieved when the coherence bath has an intermediate degree of coherence. In our model, the extractable work is maximized when four copies of the charged qubits are used. Meanwhile, the efficiency of the engine, given by the extractable work per input coherence flow, is optimized by avoiding the coherence being stored in the system-bath correlations that is inaccessible to work. We numerically find that the highest efficiency is obtained for slightly lower temperatures and weaker system-bath coupling than those for optimal coherence charging.