Quantum Performance of Thermal Machines over Many Cycles
  The performance of quantum heat engines is generally based on the analysis of a single cycle. We challenge this approach by showing that the total work performed by a quantum engine need not be proportional to the number of cycles. Furthermore, optimizing the engine over multiple cycles leads to the identification of scenarios with a quantum enhancement. We demonstrate our findings with a quantum Otto engine based on a two-level system as the working substance that supplies power to an external oscillator. 
Gentaro Watanabe, B. Prasanna Venkatesh, Peter Talkner, Adolfo del   Campo
cond-mat.stat-mech cond-mat.quant-gas quant-ph