Description
Quantum heat engines operate through quasistatic transformations, and a common assumption is that the working medium is in instantaneous thermal equilibrium. However, several many-body systems offer long-lived prethermal states: can we use them to operate quantum engines with enhanced efficiency? This work considers the quantum Otto cycle, which consists of two adiabatic strokes and two thermalizations with a reservoir. The adiabatic strokes are performed in isolation from the environment, so prethermal systems move along generalized Gibbs states rather than canonical equilibrium states. We provide how to construct prethermal cycles, and we build a comparison with the standard thermal case. We present analytical results on infinitesimal cycles and numerical results on cycles over finite regions in the parameter space. We found temperature as the crucial parameter: the prethermal cycle displays advantage for negative temperature, regardless of the model and the initial data. Negative temperature can be realized in models with bounded energy, like spin chains. Hence, we focused on the integrable XXZ chain displaying prethermal states.
