Enhanced entanglement between two movable mirrors in an optomechanical system with nonlinear media

We investigate the entanglement between two movable mirrors in an optomechanical cavity, in which a Kerr-down-conversion crystal consisting of a Kerr nonlinear medium and an optical parametric amplifier (OPA) is placed. The effects of the nonlinear media on the entanglement have been analyzed. It is shown that the Kerr nonlinear medium makes the perfect entanglement in some discrete frequency regions. Furthermore, when the input vacuum field is squeezed, the frequency range for producing the entanglement can be effectively extended and the reachable maximal entanglement can be enhanced by the Kerr nonlinear medium, while the OPA medium reduces the degree of the entanglement and necks the frequency range for generating the entanglement. These results suggest that nonlinear media could serve as a new handle to coherently control the entanglement between the vibrational modes of the micromirrors in the optomechanical cavity system.