Power and Efficiency of a Thermal Engine with a Coherent Bath

TL;DR

This paper investigates a quantum thermal engine driven by weak interactions with a coherent three-level atom bath, revealing how ground-state coherence influences thermalisation rate, power output, and efficiency beyond the quasistatic limit.

Contribution

It extends previous models by analyzing the engine out of the quasistatic limit, showing how coherence affects thermalisation rate and enabling power optimization through coherence and stroke duration adjustments.

Findings

Ground-state coherence influences thermalisation rate.

Coherence can increase power and efficiency when thermalisation temperature is lowered.

Engine performance can be optimized by adjusting coherence and stroke durations.

Abstract

We consider a quantum engine driven by repeated weak interactions with a heat bath of identical three-level atoms. This model was first introduced by Scully et al. [Science, 2003], who showed that coherence between the energy-degenerate ground states serves as a thermodynamic resource that allows operation of a thermal cycle with a coherence-dependent thermalisation temperature. We consider a similar engine out of the quasistatic limit and find that the ground-state coherence also determines the rate of thermalisation, therefore increasing the output power and the engine efficiency only when the thermalisation temperature is reduced; revealing a more nuanced perspective of coherence as a resource. This allows us to optimise the output power by adjusting the coherence and relative stroke durations.