Sensing of mechanical motion at the quantum level via a hybrid atom-optomechanical setup

We consider a hybrid quantum system in which an optomechanical cavity is coupled to a Fabry-P\'erot cavity containing a trapped cold atomic ensemble. We show that it is possible to cool the mechanics to the ground state from room temperature outside the resolved-sideband regime by optically coupling it to the internal levels of the atoms. We also find that while in the familiar homodyne detection of small displacements this system exhibits the same standard quantum limit as traditional cavity optomechanics, it is possible to engineer the optical response of the atoms so as to realize a back-action evading measurement scheme.