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We consider a quasi-static quantum Otto cycle using two effectively two-levelsystems with degeneracy in the excited state. The systems are coupled throughisotropic exchange interaction of strength $J>0$, in the presence of anexternal magnetic field $B$ which is varied during the cycle. We prove thepositive work condition, and show that level-degeneracy can act as athermodynamic resource, so that a larger amount of work can be extracted thanfrom the non-degenerate case, both with and without coupling. We also derive anupper bound for the efficiency of the cycle. This bound is the same as derivedfor 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 onthe control parameters of the Hamiltonian, but is independent of the leveldegeneracy and the reservoir temperatures.

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