Nonequilibrium fluctuations of a quantum heat engine

TL;DR

This paper experimentally investigates the stochastic thermodynamics of a quantum Otto cycle, revealing correlations, efficiency fluctuations, and testing the second law in a quantum heat engine.

Contribution

It provides the first detailed experimental analysis of efficiency and entropy production fluctuations in a quantum heat engine, including joint distributions of work and heat.

Findings

Near perfect anticorrelation between work and heat achieved.

Efficiency distribution peaks at the macroscopic efficiency with suppressed fluctuations.

Second law fluctuation relation verified in the quantum regime.

Abstract

The thermodynamic properties of quantum heat engines are stochastic owing to the presence of thermal and quantum fluctuations. We here experimentally investigate the efficiency and nonequilibrium entropy production statistics of a spin-1/2 quantum Otto cycle. We first study the correlations between work and heat within a cycle by extracting their joint distribution for different driving times. We show that near perfect anticorrelation, corresponding to the tight-coupling condition, can be achieved. In this limit, the reconstructed efficiency distribution is peaked at the macroscopic efficiency and fluctuations are strongly suppressed. We further test the second law in the form of a joint fluctuation relation for work and heat. Our results characterize the statistical features of a small-scale thermal machine in the quantum domain and provide means to control them.