Enhanced efficiency of a quantum Otto engine based on an XX spin chain near its dynamical phase transition


Implementation of heat engines in the nanoscale must consider quantum effects. In this study, a quantum Otto engine with an XX spin chain as a working substance was investigated near its dynamical phase transition for its efficiency enhancement. We used two isothermal and two isomagnetic branches for the thermodynamic cycle of the quantum Otto engine. The working substance was operated at the ground state and at a thermal state. The isothermal branches were implemented at zero temperature and inverse temperature βJ ≥ 1, while the isomagnetic branches at constant |λ/J| < 2. The quantum heat engine was found to achieve a 100% peak efficiency near the ground state curve in the chemical potential diagram and operates at constant 100% efficiency for extended regions when the system undergoes dynamical phase transition.