Cooling of mechanical resonator in a double-cavity system with two-level atomic ensemble

Abstract

We propose a hybrid optomechanical system to achieve the ground state cooling of mechanical resonator by an electromagnetically-induced transparency (EIT)-like cooling mechanism. This system is composed of a mechanical resonator and two coupled single-mode cavities, and a two-level atomic ensemble simultaneously trapped in a standard optomechanical cavity. It is found that in the presence of a two-level atomic ensemble, the optical noise spectrum is split into an EIT-like spectrum. In particular, we investigate the effect of the atomic ensemble coupling strength on the EIT-like spectrum, indicating that the atomic ensemble coupling strength greatly increases the asymmetry of the EIT spectrum. Furthermore, we analyze the optimal conditions for achieving the maximum difference between cooling and heating processes in detail. In addition, we demonstrate that even in regions with unresolved sideband, the ground state cooling of mechanical resonator can be achieved by adjusting the coupling strength of the atomic ensemble. This research opens up the possibility for the application of cavity quantum optomechanics beyond the resolved sideband regime.