Efficiencies and Work Losses for Cycles Interacting with Reservoirs of Apparent Negative Temperatures

Inverted quantum states of apparent negative temperature store the work required for their creation [Struchtrup. Phys. Rev. Lett. 2018, 120, 250602]. Thermodynamic cycles operating between a classical reservoir and an inverted state reservoir seem to have thermal efficiencies at or even above unity. These high efficiencies result from inappropriate definition adopted from classical heat engines. A properly defined efficiency compares the work produced in the cycle to the work expended in creating the reservoir. Due to work loss to irreversible processes, this work storage based efficiency always has values below unity.