Quantum correlated heat engine with nonlinear spin-spin interactions
  We propose a four level quantum heat engine in Otto cycle with a working substance of two spins subject to an external magnetic field and coupled to each other by a one-axis twisting spin squeezing nonlinear interaction. We calculate the positive work and the efficiency of the engine for different parameter regimes. In particular, we investigate the effects of quantum correlations at the end of the two isochoric processes of the Otto cycle, as measured by the entanglement of formation and quantum discord, on the work extraction and efficiency. The regimes where the quantum correlations could enhance the efficiency and work extraction are characterized. 
Ferdi Altintas, Ali \"U. C. Hardal and \"Ozg\"ur E.   M\"ustecapl{\i}o\u{g}lu
quant-ph cond-mat.stat-mech