Comment on "Extending the Laws of Thermodynamics for Arbitrary Autonomous Quantum Systems"

TL;DR

The paper critically analyzes recent claims of extending thermodynamics to quantum systems, highlighting fundamental issues with the proposed definitions of entropy and temperature, and compares alternative frameworks.

Contribution

It identifies conflicts in the new definitions with classical thermodynamics and proposes a unifying approach for quantum thermodynamic frameworks.

Findings

The new definitions violate the zeroth law of thermodynamics.

They significantly misestimate entropy production.

An alternative framework avoids these issues.

Abstract

Recently, Elouard and Lombard Latune [PRX Quantum 4, 020309 (2023)] claimed to extend the laws of thermodynamics to "arbitrary quantum systems" valid "at any scale" using "consistent" definitions allowing them to "recover known results" from the literature. I show that their definitions are in conflict with textbook thermodynamics and over- or underestimate the real entropy production by orders of magnitude. The cause of this problem is traced back to problematic definitions of entropy and temperature, the latter, for instance, violates the zeroth law. It is pointed out that another framework presented in PRX Quantum 2, 030202 (2021) does not suffer from these problems, while Elouard and Lombard Latune falsely claim that it only provides a positive entropy production for a smaller class of initial states. A simple way to unify both approaches is also presented.