Mechanical squeezing of the tripod-type four-level atom-assisted optomechanical system

Quadrature squeezing of a mesoscopic mechanical oscillator is investigated in a driven hybrid optomechanical system with a membrane-in-middle configuration containing a tripod-type four-level atom on either side of the membrane. We analyze in detail the influence of the coupling constant between cavity field and atom, amplitude of pump field, cavity pump detuning and Rabi frequency of classical field on the squeezing of the position quadrature of the vibrating membrane. The results show that the mechanical squeezing can be controlled by choosing the evolved parameters and initial state of atom, appropriately. Also, it is shown that a noticeable amount of squeezing can be obtained by increasing the amplitude of the classical pump field and therefore effective coupling constant. More over, we investigate that such a system can lead to a larger squeezing than the case with A-type three-level atom.