  We investigate theoretically a quantum optomechanical realization of a heat
engine. In a generic optomechanical arrangement the optomechanical coupling
between the cavity field and the oscillating end-mirror results in polariton
normal mode excitations whose character depends on the pump detuning and the
coupling strength. By varying that detuning it is possible to transform their
character from phonon-like to photon-like, so that they are predominantly
coupled to the thermal reservoir of phonons or photons, respectively. We
exploit the fact that the effective temperatures of these two reservoirs are
different to produce a Otto cycle along one of the polariton branches. We
discuss the basic properties of the system in two different regimes: in the
optical domain it is possible to extract work from the thermal energy of a
mechanical resonator at finite temperature, while in the microwave range one
can in principle exploit the cycle to extract work from the blackbody radiation
background coupled to an ultra-cold atomic ensemble.
