Study On Mechanical Squeezing And Entanglement Based On Cavity Optomechanical System

Cavity optomechanics,as an emerging discipline,provides many promising plat-forms for testing the quantum properties of macroscopic objects,for instance,mechanical entanglement,quantum steering,quantum state superposition,quantum state transfer,the cooling of mechanical oscillators,and mechanical squeezing.As two important parts of the macroscopic quantum effect,mechanical squeezing and mechanical-mechanical entanglement have been widely studied.Mechanical squeezing plays an important role in fundamental physics research and practical applications,such as the high-precision measurement of weak force and the quantum-classical boundary.Some schemes have been proposed to achieve mechanical squeezing both theoretically and experimentally via mechanical parametric amplification.However,the stationary squeezing is limited by3 d B due to the instability of the system arranging from the parametric amplification pro-cess.The squeezing beyond 3 d B is beneficial to high-precision measurements.Breaking3d B is the challenge we have to overcome.In this thesis,we investigate the stationary two-mode squeezing and mechanical-mechanical entanglement in the disipative cavity optomechanical system via frequency modulation of cavity modes and the main contents are as follows:Initially,we propose a scheme for realization of strong and robust two-mode mechan-ical squeezing in the disipative cavity optomechanical system via frequency modulation of cavity modes.The system parameters are a set of typically practical parameters in experiments.We numerically simulate the squeezing logarithmic negativity by choosing the feasible parameters experimentally.The numerical simulation result shows that for the full Hamiltonian,the squeezing direction which changes continually in a period is controlled by modulation amplitude.The numerical result indicates that,based on RWA method,the information of the squeezing direction will be erased.By a redefined relative squeezing degree,we investigate the dynamic squeezing conveniently when the squeezing direction is unfixed.We show that the strong mechanical squeezing,which is highly robust against the thermal noise.The generated maximal squeezing can exceed 20 d B by resorting to the cavity dissipation.In the following,we study stationary macroscopic mechanlcal-mechanical entangle-ment in the disipative cavity optomechanical system via frequency modulation of cavity modes.Via numerically simulating the entanglement logarithmic negativity,we find that the mechanical-mechanical entanglement is a nonmonotonic function of the effective op-tomechanical coupling sidebands.With the increase ofλ₁₊,the mechanical-mechanical entanglement first becomes more and more stronger.However,with the further increase of the effective optomechanical coupling sidebands,the mechanical-mechanical entangle-ment is significantly reduced whenλ₁₊/λ_1-approaching to 1.