Quantum optomechanics of a multimode system coupled via a photothermal and a radiation pressure force

We provide a full quantum description of the optomechanical system formed by a Fabry-Perot cavity with a movable micromechanical mirror whose center-of-mass and internal elastic modes are coupled to the driven cavity mode by both radiation pressure and photothermal force. Adopting a quantum Langevin description, we investigate simultaneous cooling of the micromirror elastic and center-of-mass modes, and also the entanglement properties of the optomechanical multipartite system in its steady state.