Nonreciprocal mechanical squeezing in a spinning cavity optomechanical system via pump modulation

We propose a scheme to realize nonreciprocal mechanical squeezing in a spinning optomechanical system, where a spinning resonator is driven by a periodically modulated laser field via a tapered optical fiber. The spinning resonator supports two counterpropagating optical modes and a mechanical breathing mode induced by the radiation pressure. According to the optical Sagnac effect, the two counterpropagating optical modes obtain opposite frequency shifts. By utilizing the modulated pump field with a given frequency, mechanical squeezing can only be achieved by driving the resonator from one direction but not from the other. We analyze the impact of backscattering losses on mechanical squeezing and find that this negative impact can be almost completely avoided by increasing the angular velocity of the resonator. We also show that the presented scheme is robust to mechanical thermal noise and can be realized under the current experimental conditions. Therefore, this work may be meaningful for the study of quantum nonreciprocity and quantum precision measurement.