Stage‐Dependent Quantum Correlations in a Three‐Qubit Stirling Heat Engine

We investigate a quantum Stirling engine whose working medium is a three‐qubit Heisenberg XXZ spin chain incorporating the Dzyaloshinskii‐Moriya interaction. The integration of a regenerator, which recovers internal energy during the isochoric processes, significantly enhances the efficiency of the engine, allowing it to approach the Carnot efficiency under appropriate parameters. Our analysis reveals a pronounced stage dependence of quantum correlations: at the end of the isothermal expansion, quantum entanglement and coherence of the thermal equilibrium state are positively correlated with the cycle efficiency, whereas at the end of the isothermal compression, they are negatively correlated with the efficiency. Furthermore, we demonstrate how external magnetic fields and coupling coefficients regulate these quantum correlations and the engine performance, including the work output and efficiency. This work provides a systematic comparison of the stage‐dependent roles of entanglement and coherence in a three‐qubit Stirling cycle, offering insights for designing high‐performance regenerative quantum thermal devices.