Optomechanical entanglement affected by exceptional point in a WGM resonator system

Entanglement of optical mode and mechanical mode plays a significant role for quantum information processing and memory. This type of optomechanical entanglement is always be suppressed by the mechanically dark-mode (DM) effect. However, the reason of the DM generation and how to control the bright-mode (BM) effect flexibly are still not resolved. In this letter, we demonstrate that the DM effect occurs at the exceptional point (EP) and it can be broken by changing the relative phase angle (RPA) between the nano scatters. We find that the optical mode and mechanical mode are separable at EPs but entangled when the RPA is tuned away from the EPs. Remarkably, the DM effect will be broken if the RPA away from EPs, resulting in the ground-state cooling of the mechanical mode. In addition, we prove that the chirality of the system can also influence the optomechanical entanglement. Our scheme can control the entanglement flexible merely depend on the relative phase angle, which is continuously adjustable and experimentally more feasible.