Mechanical squeezing beyond resolved sideband and weak-coupling limits with frequency modulation

Abstract

It is usually difficult to generate mechanical squeezing in standard optomechanical systems when the decay rate of the cavity or the effective coupling strength of the system is too large. Here we investigate the mechanical squeezing beyond resolved sideband and weak-coupling limits in a standard optomechanical system by using frequency modulation acting on both the cavity field and the mechanical oscillator. It is shown that in the presence of frequency modulation, the beyond 3 dB strong mechanical squeezing can be achieved better than the standard optomechanical system without frequency modulation. Furthermore, the proposed scheme is feasible even in the unstable region of the standard optomechanical system, and a detailed numerical analysis is carried out from the physical essence to illuminate the reason for achieving better mechanical squeezing with frequency modulation. The scheme may open promising perspectives for studying the quantum effect in strong coupling regions without the limitations of system stability and the resolved sideband regime.