Exploiting coherence for quantum thermodynamic advantage

TL;DR

This paper explores how quantum coherence can enhance thermal machines, enabling them to surpass classical efficiency limits and exhibit unconventional behaviors like hybrid refrigeration and work generation.

Contribution

It demonstrates the advantages of quantum coherence in thermal machines, including surpassing Carnot efficiency and creating hybrid operational modes.

Findings

Machines can operate as hybrid refrigerators and engines.

Quantum coherence allows efficiencies beyond Carnot bounds.

An upper bound on efficiency in coherent reservoirs is established.

Abstract

The introduction of the quantum analogue of a Carnot engine based on a bath comprising of particles with a small amount of coherence initiated an active line of research on the harnessing of different quantum resources for the enhancement of thermal machines beyond the standard reversible limit, with an emphasis on non-thermal baths containing quantum coherence. In our work, we investigate the impact of coherence on the thermodynamic tasks of a collision model which is composed of a system interacting, in the continuous time limit, with a series of coherent ancillas of two baths at different temperatures. Our results show the advantages of utilising coherence as a resource in the operation of the machine, and allows it: (i) to exhibit unconventional behaviour such as the appearance of a hybrid refrigerator, capable of simultaneous refrigeration and generation of work, and (ii) to function as an engine or a refrigerator with efficiencies larger than the Carnot bound. Moreover, we find an effective upper bound to the efficiency of the thermal machine operating as an engine in the presence of a coherent reservoir.