Study On Ground State Cooling Of Mechanical Resonator Based On Optomechanical System

Recently,the mechanical systems have been raised more and more attention and become ideal candidates for studying quantum behavior of macroscopic objects because they resemble a prototype of classical systems.Quantum manipulation of macroscopic mechanical systems is of great interest in both fundamental physics and applications ranging from high-precision metrology to quantum information processing.However,the revelation of the quantum effects for mechanical resonators needs to strongly suppress the uncontrollable thermal fluctuations.It is a prerequisite,therefore,to cool mechanical resonators to their ground state for their potential applications.To this end,numerous significant theoretical and experimental efforts have been made on the ground-state cool-ing of mechanical resonators.Among these schemes,we can roughly classify into two categories,the resolved sideband cooling and the unresolved sideband cooling,according to the decay rate of the optical field(cavity field)is less or larger than the frequency of the mechanical resonator.In the weak coupling regime,the optomechanical cooling can be analyzed using the perturbation theory,where optomechanical coupling is regarded as a perturbation to the optical field.The steady-state final mean phonon number of the mechanical resonator is determined by the difference between the positive and negative frequencies of the fluctuation spectrum of the optical force.In single cavity optpmechani-cal system the profile of the optical fluctuation spectrum has a Lorentzian shape with single peak,the width of the peak is proportional to the decay rate of the cavity.Therefore,the difference between the positive and negative frequencies of the fluctuation spectrum under the condition of unresolvable sidebands is almost zero,so that the mechanical resonator cannot be cooled to the quantum ground state.In this thesis,we devote to the study of the ground state cooling of mechanical resonator under the condition of unresolved sideband,and the main contents are as follows:Based on the hybrid cavity optomechanical system,we propose a scheme for the ground state cooling of mechanical resonator under the condition of unresolved sideband.In the scheme,the fluctuation spectrum of the radiation pressure force can be controlled via the electromagnetically-induced-transparency-like mechanism of the hybrid cavity optomechanical system,this mechanism makes the wide Lorentzian peak split into two narrower peaks with a dip emerging between them.The dip can be used to suppress the Stokes process,whereas one of the peaks can be used to strengthen the anti-Stokes process.The analytical expression of the final mean phonon number under steady state obtained by using the rate equation,the result shows that,mechanical oscillator can be cooled close to its ground state even in the unresolved-sideband regime.Specifically,our scheme works in the unresolved sideband regime with fewer strict limitations for the auxiliary systems,which largely lowers down the experiment cost and provides some reference value for the preparation of mechanical quantum states.