Beyond the Carnot Limit in the Internal Cycles of a Quantum Heat Engine under Finite Heat Reservoirs

TL;DR

This paper analytically demonstrates that microscopic quantum heat engines can surpass the classical Carnot efficiency by utilizing finite heat reservoirs, revealing new insights into quantum thermodynamics and engine performance.

Contribution

It introduces a fully analytical model showing how finite reservoirs enable quantum engines to exceed Carnot limits without extra quantum resources.

Findings

Maximum efficiency depends on reservoir heat capacities.

High performance is due to finite-sized reservoirs.

The model is applicable to various microscopic systems.

Abstract

We investigate, in an analytical fashion, quantum Carnot cycles of a microscopic heat engine coupled to two nite heat reservoirs, whose internal cycles could own higher e ciency than the standard Carnot limit without consuming extra quantum resources, e.g., coherence or squeezing properties. The engine runs time-dependently, involving both the internal and external cycles to collaboratively accomplish a complete Carnot cycle, and the e ciency of the engine depends on the reservoirs heat capacities and the working substance. Our analytical results of the maximum efficiency and the maximum power output clarify the mechanism behind the high performance of the microscopic engines, displaying the key roles played by the nite-sized heat reservoirs. Our proposal is generally valid for any microscopic thermodynamic system and fully feasible under current laboratory conditions.