Harmonic quantum heat devices: optimum-performance regimes.

The finite-time performance of a quantum-mechanical heat engine (or refrigerator) with a working fluid consisting of many noninteracting harmonic oscillators is considered in order to analyze three optimum operating regimes: maximum efficiency (maximum coefficient of performance), maximum work output (maximum cooling load) and a third one, Omega criterion, which represents a compromise between them. The reported results extend previous findings for macroscopic and mesoscopic energy converters to quantum heat devices and also endorse the Omega criterion as a unified, optimum working regime for energy converters, independent of their size and nature.