摘要

We theoretically investigate the macroscopic quantum coherence and the mechanical squeezing of a mechanical oscillator in a hybrid optomechanical system consisting of a suspended graphene sheet and an ultracold atomic ensemble trapped inside a Fabry-Perot cavity. In the study the vacuum is used to mediate an effective optomechanical coupling between the graphene oscillator and the cavity field driven by an external laser beam. We find that in the presence of this coupling, the macroscopic quantum coherence and the mechanical squeezing of the graphene sheet can be attained in a certain range of driving power. In particular, the quantum coherence in the optomechanical system can be transferred from the optical field to the mechanical oscillator. We also investigate in detail the spectrum and the squeezing of the output field and the attained results may be used to study the mechanical squeezing of a graphene sheet.