Anisotropy-assisted thermodynamic advantage of a local-spin thermal machine

TL;DR

This paper explores how anisotropy in a two-spin quantum Otto engine can enhance efficiency and power, surpassing standard limits through quantum interference effects, especially when using a local spin as the working system.

Contribution

It reveals the fundamental role of anisotropy in improving quantum Otto engine performance and demonstrates surpassing the standard quantum limit with local-spin configurations.

Findings

Efficiency increases with anisotropy in quasistatic cycles.

Quantum interference enables surpassing the standard quantum Otto limit.

Anisotropy enhances performance in finite-time operations.

Abstract

We study quantum Otto thermal machines with a two-spin working system coupled by anisotropic interaction. Depending on the choice of different parameters, the quantum Otto cycle can function as different thermal machines, including a heat engine, refrigerator, accelerator and heater. We aim to investigate how the anisotropy plays a fundamental role in the performance of the quantum Otto engine operating in different time scales. We find that while the efficiency of the engine efficiency increases with the increase in anisotropy for the quasistatic operation, quantum internal friction and incomplete thermalization degrade the performance in a finite time cycle. Further, we study the QOE with one of the spins, the local spin, as the working system. We show that the efficiency of such an engine can surpass the standard quantum Otto limit, along with maximum power, thanks to the anisotropy. This can be attributed to quantum interference effects. We demonstrate that the enhanced performance of a local-spin QOE originates from the same interference effects, as in a measurement-based QOE for their finite time operation.