Nonadiabatic coupled-qubit Otto cycle with bidirectional operation and efficiency gains

TL;DR

This paper explores a quantum Otto cycle with a two-qubit system that operates under nonadiabatic conditions, revealing resilience in certain cycle features and efficiency behaviors despite quantum nonadiabaticity.

Contribution

It introduces a detailed analysis of a nonadiabatic two-qubit quantum Otto cycle, highlighting the effects of finite-time operations on cycle performance and efficiency.

Findings

Counter-rotating cycles can operate as heat engines.

Cycle efficiency can increase as temperature difference decreases.

Efficiency remains above standard Otto value for small nonadiabaticity.

Abstract

We study a quantum Otto cycle that uses a 2-qubit working substance whose Hamiltonian does not commute with itself at different times during unitary strokes. We investigate how the cycle responds to the loss of quantum adiabaticity when these strokes are operated with a finite duration. We find that qualitative features such as the possibility of counter-rotating cycles operating as heat engines, or a cycle efficiency that can increase with a decrease in the temperature difference between the baths, are resilient even to highly nonadiabatic strokes. However, cycle efficiency rapidly decreases, although it can still remain above the standard Otto value for small degrees of quantum nonadiabaticity.