Quantum coherence, many-body correlations, and non-thermal effects for autonomous thermal machines

TL;DR

This paper investigates how quantum coherence, many-body correlations, and non-thermal states can enhance the efficiency of autonomous quantum thermal machines, providing a new upper bound based on the quantum battery's apparent temperature.

Contribution

It introduces a generalized model of autonomous thermal machines with quantum batteries and derives a maximal efficiency bound based on apparent temperature, surpassing previous limits.

Findings

Maximal achievable efficiency is always attainable.

Efficiency bound expressed in terms of quantum battery's apparent temperature.

Quantum coherence and many-body correlations can be harnessed to improve machine efficiency.

Abstract

One of the principal objectives of quantum thermodynamics is to explore quantum effects and their potential beneficial role in thermodynamic tasks like work extraction or refrigeration. So far, even though several papers have already shown that quantum effect could indeed bring quantum advantages, a global and deeper understanding is still lacking. Here, we extend previous models of autonomous machines to include quantum batteries made of arbitrary systems of discrete spectrum. We establish their actual efficiency, which allows us to derive an efficiency upper bound, called maximal achievable efficiency, shown to be always achievable, in contrast with previous upper bounds based only on the Second Law. Such maximal achievable efficiency can be expressed simply in term of the it apparent temperature of the quantum battery. This important result appears to be a powerful tool to understand how quantum features like coherence but also many-body correlations and non-thermal population distribution can be harnessed to increase the efficiency of thermal machines.