How to make an atom emit sound?

With Michele Cotrufo and Andrea Fiore from TU Eindhoven, we published new theory work in Physical Review Letters. We present a new way to realize a strong and controllable interaction between a natural (or artificial) atom and a macroscopic mechanical resonator. This has been a long-sought aim in quantum physics, as it would allow using the nonlinearities of the atom to  create nonclassical states (e.g., superposition states) of a macroscopic object, which are of extreme interest for fundamental studies in quantum mechanics. We show how such an interaction can be readily obtained via an intermediate light field, an effect that we termed “mode field coupling”: if the mechanical displacement modulates the light amplitude at the atom’s position, a coherent interaction between the atom and the mechanical resonator is obtained. Importantly, the coupling rate scales with the light amplitude. Therefore, by simply modulating an external optical pumping, it is possible to control in time and to enhance at will the coupling between the atom and the mechanical resonator. Arbitrary mechanical states can be created with this method, by transferring the excitation from the atom to the resonator with properly timed optical pulses. Even accounting for realistic losses, the coupling rate of this interaction is strong enough to generate  several nonclassical mechanical states, including superposition states,  with large fidelities. The proposed optically-controlled atom-phonon interaction paves the way for future developments such as control of spontaneous phonon emission, creation of nonclassical states of motion and phonon lasing.