Effects of Magnetic Anisotropy on 3-Qubit Antiferromagnetic Thermal Machines

TL;DR

This paper examines how magnetic anisotropy influences the performance of 3-qubit antiferromagnetic thermal machines, revealing that easy-axis anisotropy improves efficiency and that different cycles exhibit unique operational regimes.

Contribution

It demonstrates the significant impact of magnetic anisotropy on quantum thermal machine efficiency and compares the operational regimes of Stirling and Otto cycles in this context.

Findings

Easy-axis anisotropy enhances engine efficiency.

Ring topology outperforms chain at low temperatures.

Stirling cycle achieves Carnot efficiency with finite work.

Abstract

This study investigates the anisotropic effects on a system of three qubits with chain and ring topology, described by the antiferromagnetic Heisenberg XXX model subjected to a homogeneous magnetic field. We explore the Stirling and Otto cycles and find that easy-axis anisotropy significantly enhances engine efficiency across all cases. At low temperatures, the ring configuration outperforms the chain on both work and efficiency during the Stirling cycle. Additionally, in both topologies, the Stirling cycle achieves Carnot efficiency with finite work at quantum critical points. In contrast, the quasistatic Otto engine also reaches Carnot efficiency at these points but yields no useful work. Notably, the Stirling cycle exhibits all thermal operational regimes engine, refrigerator, heater, and accelerator unlike the quasistatic Otto cycle, which functions only as an engine or refrigerator.