Froehlich condensate of Phonons and heat control

Different from Bose-Einstein Condensate (BEC) that occurs at equilibrium, phonon condensate happens in the condition of out of equilibrium[1]. In this work, we will present that the Fröhlich condensate of phonons can be realized in optomechanical systems [2] as well as in a self-feedback classical mechanical system [3]. Our optomechanical system consists of a one-dimensional array of membranes coupled to the cavity field via a quadratic interaction, and the cavity is pumped by an external laser. Analytical and numerical results demonstrate that the high phonon occupancy of the lowest or highest mechanical mode is achievable depending on the detuning of the driving laser, the optomechanical strength, and the temperature. The feasibility of experimental implementation is discussed. Our results shed light on energy conversion and transfer, heat control, and multimode cooling using optomechanical systems.