Fluctuations and stability of a fast driven Otto cycle

TL;DR

This paper explores how quantum coherence influences fluctuations and stability in a fast-driven Otto cycle, revealing conditions under which classical thermodynamic bounds are violated and how coherence affects cycle performance.

Contribution

It demonstrates the impact of system coherences on fluctuations and stability in a stochastic Otto cycle, including violations of classical thermodynamic uncertainty bounds.

Findings

Coherences increase system instabilities with the cold bath.

Cycle precision improves with the hot bath, reducing fluctuations below classical bounds.

Dephasing does not prevent the violation of classical thermodynamic bounds.

Abstract

We investigate the stochastic dynamics of a thermal machine realized by a fast-driven Otto cycle. By employing a stochastic approach, we find that system coherences strongly affect fluctuations depending on the thermodynamic current. Specifically, we observe an increment in the system instabilities when considering the heat exchanged with the cold bath. On the contrary, the cycle precision improves when the system couples with the hot bath, where thermodynamic fluctuations reduce below the classical Thermodynamic Uncertainty Relation bound. Violation of the classical bound holds even when a dephasing source couples with the system. We also find that coherence suppression not only restores the cycle cooling but also enhances the convergence of fluctuation relations by increasing the entropy production of the reversed process. An additional analysis unveiled that the stochastic sampling required to ensure good statistics increases for the cooling cycle while downsizes for the other protocols. Despite the simplicity of our model, our results provide further insight into thermodynamic relations at the stochastic level.