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 phononlike to photonlike, 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 an 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 ultracold atomic ensemble. Heat engines operating in the quantum regime have attracted much recent attention due to their potential to investigate the quantum limit of classical thermodynamical concepts such as the Carnot efficiency limit-and perhaps overcome that limit, to better understand thermalization in the deep quantum regime, and, on a more applied side, in the quest for the realization of nanoengines of increasingly small size [1][2][3][4][5]. Microscopic scale heat engines have been realized in micro-electro-mechanical systems [6,7], but reaching the quantum regime remains a challenge due to thermal noise in the mechanical elements. Theoretical proposals for quantum heat engines have been advanced involving single ions [8], ultracold bosonic atoms [9], and quantum dots [10], but so far their experimental realization has remained elusive.This Letter proposes and analyzes theoretically a quantum heat engine based on a cavity optomechanical setup. This system presents several attractive features: first, it is a truly mechanical system; second, it has the potential to operate deep in the quantum regime using existing, state-of-the-art equipment; third, it is conceptually extremely simple; and fourth, it offers, in principle at least, the potential to extract work from the 2.7 K blackbody radiation background. Finally, when combined with progress in quantum optics toward the realization of squeezed reservoirs [11], it may provide a route to testing the Carnot efficiency limit in the quantum regime.The key element of a heat engine is a medium that may be used to extract work and that exchanges heat with thermal reservoirs at two different temperatures. Cavity optomechanics provides a conceptually simple way to realize that goal: The radiation pressure force permits the exchange of energy between cavity photons and mechanical phonons, and crucially the cavity and mechanical damping couple the system to both a cold and a hot reservoir. Cavity optomechanics has witnessed spectacular developments in the last decade (s...

Coherent interconversion between optical and mechanical excitations in an optomechanical cavity can be used to engineer a quantum heat engine. This heat engine is based on an Otto cycle between a cold photonic reservoir and a hot phononic reservoir [Phys. Rev. Lett. 112, 150602 (2014)]. Building on our previous work, we (i) develop a detailed theoretical analysis of the work and the efficiency of the engine, and (ii) perform an investigation of the quantum thermodynamics underlying this scheme. In particular, we analyze the thermodynamic performance in both the dressed polariton picture and the original bare photon and phonon picture. Finally, (iii) a numerical simulation is performed to derive the full evolution of the quantum optomechanical system during the Otto cycle, by taking into account all relevant sources of noise.