# Quantum Otto engine with exchange coupling in the presence of level degeneracy

## TL;DR

This paper analyzes a quantum Otto cycle with degenerate energy levels and exchange coupling, demonstrating how degeneracy enhances work output and deriving an efficiency bound based on system parameters.

## Contribution

It introduces a model of a quantum Otto engine with degenerate levels and exchange coupling, showing degeneracy as a thermodynamic resource and establishing an efficiency bound.

## Key findings

- Degeneracy increases the maximum extractable work.
- The efficiency bound depends only on Hamiltonian parameters.
- Degeneracy acts as a resource for improved thermodynamic performance.

## Abstract

We consider a quasi-static quantum Otto cycle using two effectively two-level systems with degeneracy in the excited state. The systems are coupled through isotropic exchange interaction of strength $J>0$, in the presence of an external magnetic field $B$ which is varied during the cycle. We prove the positive work condition, and show that level-degeneracy can act as a thermodynamic resource, so that a larger amount of work can be extracted than from the non-degenerate case, both with and without coupling. We also derive an upper bound for the efficiency of the cycle. This bound is the same as derived for a system of coupled spin-1/2 particles [G. Thomas and R. S. Johal, Phys. Rev. E {\bf 83}, 031135 (2011)] i.e. without degeneracy, and depends only on the control parameters of the Hamiltonian, but is independent of the level degeneracy and the reservoir temperatures.