Steady‐State Nonreciprocal Strong Mechanical Squeezing Against Thermal Noise via Periodic Driving

ABSTRACT Based on the Sagnac effect, we propose how to achieve nonreciprocal strong mechanical squeezing via periodic driving in a spinning microdisk optomechanical system. We find that the strong nonreciprocal squeezing effect happens when the system is driven by a periodically modulated pump in a chosen port but not in the other. By appropriately choosing the ratio of the optomechanical coupling sidebands, the squeezing degree in the steady state can far surpass the 3‐dB limit. We provide a detailed analysis of the underlying nonreciprocal squeezing mechanism by introducing the Bogoliubov mode and demonstrate that cooling it into ground state is the decisive factor to generate the nonreciprocal squeezing effect. We show that the proposed scheme has strong robustness against thermal noise and even for high thermal phonon occupation number , the 3‐dB squeezing limit still can be broken. Specifically, by utilizing the technique of adiabatic elimination of cavity mode, we obtain the analytical result of nonreciprocal squeezing, which matches very well with the numerical simulation. We also demonstrate that the generated nonreciprocal squeezing can be effectively measured by the output field in the experiment. Our scheme provides a potential path to manipulate nonreciprocal mechanical squeezing and also has significant applications ranging from nonreciprocal quantum metrology to directional quantum communication.