At least three groups have now achieved cooling of the center-of-mass motion of micromechanical oscillators close to their ground state, with mean phonon numbers substantially less than one. The coherent exchange of excitation between phonons and photons characteristic of the strong coupling regime has also been demonstrated. In a parallel development, Bose-Einstein condensates trapped inside high-Q optical resonators have been shown to behave under appropriate conditions much like optically driven mechanical oscillators, offering an alternative route to study the optomechanical properties of mesoscopic systems. And hybrid systems consisting of mechanical systems operating in the quantum regime coupled to atoms, molecules, or artificial atoms are likely to provide an additional testing ground to address questions ranging from fundamental physics to the development of novel field and force sensors.
Advances past these trailblazing developments will involve a number of additional breakthroughs in what can loosely be called “beyond ground state’’ cavity optomechanics. These include the generation of nonclassical states of the phonon field, and the development of schemes for the characterization of these states, protocols for state transfer between phonon and photon fields. Hybrid systems, which can exploit the exquisite sensitivity of AMO measurements, promise to play an important role in these developments. The talk will review some recent advances in this direction, with particular emphasis on hybrid arrangements comprising coupled mechanical oscillators and quantum degenerate atomic systems.