Quasi-autonomous quantum thermal machines and quantum to classical energy flow

TL;DR

This paper explores the thermodynamics of small-scale quantum systems, focusing on autonomous quantum thermal machines, their foundational implications, and how quantum measurements can enhance thermodynamic properties and stability.

Contribution

It introduces a framework using quantum measurements to resolve issues in quantum thermodynamics, demonstrating thermodynamic reversibility and stability in quantum thermal machines.

Findings

Thermodynamic reversibility achieved in a Zeno limit.

Quantum measurements can magnify thermodynamic properties.

Stability of quantum thermal machines can be enhanced through measurement strategies.

Abstract

There are both practical and foundational motivations to consider the thermodynamics of quantum systems at small scales. Here we address the issue of autonomous quantum thermal machines that are tailored to achieve some specific thermodynamic primitive, such as work extraction in the presence of a thermal environment, while having minimal or no control from the macroscopic regime. Beyond experimental implementations, this provides an arena in which to address certain foundational aspects such as the role of coherence in thermodynamics, the use of clock degrees of freedom and the simulation of local time-dependent Hamiltonians in a particular quantum subsystem. For small-scale systems additional issues arise. Firstly, it is not clear to what degree genuine ordered thermodynamic work has been extracted, and secondly non-trivial back-actions on the thermal machine must be accounted for. We find that both these aspects can be resolved through a judicious choice of quantum measurements that magnify thermodynamic properties up the ladder of length-scales, while simultaneously stabilizing the quantum thermal machine. Within this framework we show that thermodynamic reversibility is obtained in a particular Zeno limit, and finally illustrate these concepts with a concrete example involving spin-systems.