Enhancing optomechanically induced entanglement via coherent feedback

We investigate the enhancement of optomechanically induced entanglement in a single-cavity optomechanical system via three coherent feedback configurations (pump-only, probe-only, and dual feedback configurations). Without feedback, the pump-probe entanglement is weak and exists in a narrow range of detuning. The feedback enhances the entanglement and broadens the entangled range of detuning for the three configurations. The dual feedback shows stronger entanglement than the pump-only/probe-only feedback. With moderate feedback coefficient, the entanglement degree between two beams reaches ∼6dB, much higher than ∼0.3dB without feedback. The entanglement exists mainly in the positive feedback region. Furthermore, two criteria are used, Duan-Giedke-Cirac-Zoller (DGCZ) and logarithmic negativity (LN). The entanglement region with the LN criterion is broader than the DGCZ criterion, which is consistent with the previous theory.