Driven quantum harmonic oscillators: A working medium for thermal machines

The study of quantum thermodynamics is key to the development of quantum thermal machines. In contrast to most of the previousproposals based on discrete strokes, here we consider a working substance that is permanently coupled to two or more baths at differenttemperatures and continuously driven. To this end, we investigate parametrically driven quantum harmonic oscillators coupled to heat bathsvia a collision model. Using a thermodynamically consistent local master equation, we derive the heat flows and power of the workingdevice, which can operate as an engine, refrigerator, or accelerator, and analyze the instantaneous and average efficiencies and coefficients ofperformance. Studying the regimes of both slow and fast driving of the system, we find that an increased driving frequency can lead to achange of functioning to a dissipator. Finally, we investigate the effect of squeezing one of the thermal baths: it leads to an apparent higherefficiency compared to the corresponding Carnot value of an equilibrium bath with the same temperature and to sustained entanglementbetween the working substance oscillators in the limit cycle