Strong coupling of an optomechanical system to an anomalously dispersive atomic medium

We investigate a hybrid optomechanical system in which a membrane oscillator is coupled to a collective spin of ground states of an intracavity Λ-type three-level atomic medium. The cavity field response is greatly modified by atomic coherence and the anomalous dispersion generated by two Raman pumping beams near two-photon resonance. The optomechanical interaction, therefore radiation pressure force, is substantially enhanced due to superluminal propagation of light pulse in the cavity. Such improvement facilitates ground-state cooling of the mechanical oscillator with room temperature as the thermal environment. Moreover, it can greatly improve the sensitivity and bandwidth of displacement measurement. In such a system, optically-controlled strong-coupling interaction between the mechanical oscillator and cavity field could be implemented on small intracavity photon number, even at the single quanta level, which is important for weak-light nonlinear photonics and the generation of nonclassical quantum states in the mechanical field.