A spin heat engine coupled to a harmonic-oscillator flywheel

TL;DR

This paper demonstrates a microscopic heat engine using a single electron spin in a trapped ion, coupled to a harmonic oscillator flywheel, and analyzes its energetics and fluctuations during operation.

Contribution

It introduces a spin-based heat engine coupled to a harmonic oscillator flywheel, with detailed characterization of energy storage and fluctuations, advancing understanding of microscopic thermodynamics.

Findings

The engine operates starting from the oscillator ground state.

The energy and fluctuations of the flywheel are reconstructed via Husimi Q function.

Intrinsic fluctuations limit the engine's performance.

Abstract

We realize a heat engine using a single electron spin as a working medium. The spin pertains to the valence electron of a trapped $^{40}$Ca$^+$ ion, and heat reservoirs are emulated by controlling the spin polarization via optical pumping. The engine is coupled to the ion's harmonic-oscillator degree of freedom via spin-dependent optical forces. The oscillator stores the work produced by the heat engine and therefore acts as a flywheel. We characterize the state of the flywheel by reconstructing the Husimi $\mathcal{Q}$ function of the oscillator after different engine runtimes. This allows us to infer both the deposited energy and the corresponding fluctuations throughout the onset of operation, starting in the oscillator ground state. In order to understand the energetics of the flywheel, we determine its ergotropy, i.e. the maximum amount of work which can be further extracted from it. Our results demonstrate how the intrinsic fluctuations of a microscopic heat engine fundamentally limit performance.