Alternative experimental ways to access entropy production

TL;DR

This paper compares multiple theoretical and experimental methods to measure entropy production in a quantum feedback process, enhancing understanding of irreversibility in quantum thermodynamics.

Contribution

It introduces and experimentally tests six different approaches to quantify entropy production in a quantum Maxwell's demon setup, unifying various perspectives on irreversibility.

Findings

Six distinct entropy production expressions agree within experimental uncertainties.

The methods reveal different aspects of irreversibility in quantum systems.

Results pave the way for measuring entropy production beyond traditional thermal contexts.

Abstract

We theoretically derive and experimentally compare several different ways to access entropy production in a quantum process under feedback control. We focus on a bipartite quantum system realizing an autonomous Maxwell's demon scheme reported by Najera-Santos et al. [Phys.~Rev.~Research 2, 032025(R) (2020)], where information encoded in a demon is consumed to transfer heat from a cold qubit to a hot cavity. By measuring individual quantum trajectories of the joint demon-cavity-qubit system, we compute the entropy production with six distinct expressions derived from different approaches to the system description and its evolution. Each method uses a specific set of trajectories and data processing. Our results provide a unified view on the various meanings of irreversibility in quantum systems and pave the way to the measurement of entropy production beyond thermal frameworks.