Optimal linear cyclic quantum heat engines cannot benefit from strong coupling

TL;DR

This paper demonstrates that for optimal linear cyclic quantum heat engines operating under small temperature differences, strong system-bath coupling reduces efficiency, establishing bounds that favor weak coupling for better energy conversion.

Contribution

It analytically proves that strong coupling cannot enhance efficiency in optimal linear cyclic quantum heat engines and provides bounds showing efficiency suppression under strong coupling.

Findings

Efficiency at maximum power is bounded by weak-coupling limits.

Maximum efficiency is upper bounded by weak-coupling efficiency.

Strong coupling causes quadratic suppression of efficiency relative to Carnot limit.

Abstract

Uncovering whether strong system-bath coupling can be an advantageous operation resource for energy conversion can facilitate the development of efficient quantum heat engines (QHEs). Yet, a consensus on this ongoing debate is still lacking owing to challenges arising from treating strong couplings. Here we conclude the debate for optimal linear cyclic QHEs operated under a small temperature difference by revealing the detrimental role of strong system-bath coupling in their optimal operations. We analytically demonstrate that both the efficiency at maximum power and maximum efficiency of strong-coupling linear cyclic QHEs are upper bounded by their weak-coupling counterparts and, particularly, experience a quadratic suppression relative to the Carnot limit under strong time-reversal symmetry breaking.