Controllable optical bistability and cooling of a mechanical oscillator in a hybrid optomechanical system

We investigate theoretically the effect of optical feedback from a cavity containing an ultracold two level atomic ensemble, on the bistable behavior shown by mean intracavity optical field in an optomechanical cavity resonator. It turns out that the optical bistability can be controlled by tuning the frequency and power of the driving laser and is largely affected by the presence of the atomic ensemble in the feedback cavity. In essence, our work emphasizes the possibility of realization of a controllable optical switch depending on the hybrid interaction, commanding lower threshold power than a single optomechanical cavity. Further, we study the aspect of optomechanical cooling of the mechanical oscillator in this hybrid system and the time evolution of the mean phonon number indicates ground-state cooling of the oscillator in the unresolved sideband regime.