Mechanical squeezing and entanglement in coupled optomechanical system with modulated optical parametric amplifier

We study theoretically the generation of mechanical squeezing and optomechanical entanglement in a double-cavity optomechanical system involving a modulated optical parametric amplifier (OPA). Owing to the cooperation of the modulated OPA and the auxiliary cavity, the mechanical squeezing can be realized in both the resolved-sideband and unresolved-sideband regimes. Particularly, the strong mechanical squeezing can be generated in the resolved-sideband regime with the assistance of the modulated OPA. Moreover, under the joint effect of the auxiliary cavity and the modulated OPA, the optomechanical entanglement can be greatly enhanced in the unresolved-sideband regime. It is noted that both the mechanical squeezing and optomechanical entanglement have strong robustness against the high dissipation of the cavity and thermal noise.