Theoretical Study Of Nonclassical Effect And Weak Force Sensing In Cavity Optomechanical System

Cavity optomechanics is a new field that has emerged in recent years,focusing on the study of mechanical motions induced by the radiation pressure of a cavity field,from which a series of non-classical effects are generated.With the rise of micro-nano technology,the physical realization of optomechanical systems makes it possible and thus becomes an important experimental platform,which has attracted widespread interest.Cavity optomechanical systems are unique in revealing the quantum properties of macroscopic objects and weak force sensing.In this paper,we take the cavity optomechanical system as the research object and focus on the realization of the squeezed-cat-state of the macroscopic oscillator and the quantum measurement of weak signals due to the sensitivity of mechanical oscillators for weak electromagnetic fields,weak forces,and tiny masses.Firstly,The research background of cavity optical system is introduced,and the current status of related research as well as the research motivation is also included.Then the basic concepts and theory methods which need to be used,such as the quantization of electromagnetic field,Wigner function,quantum detection,and the standard quantum limit are involved.The following works have been carried out on the basis of this work:(1)The study of squeezed-cat-states of mechanical oscillator.Since Schrodinger cat states were proposed,the quantum properties of macroscopic objects are difficult to observe due to their large number of degrees of freedom and inevitable decoherence.But with the development of cavity optomechanics and micro-nano technology,the macroscopic oscillators within the system exhibiting quantum properties can be achieved.We consider a hybrid optomechanical system to realize the squeezed-cat-state of mechanical mode.The system is composed of two coupled optical cavities with modulation time-dependent jumping rates,which share a common movable mirror with linear and quadratic coupling respectively.The optimized squeezed parameter and average phonon number are obtained by adjusting other parameters,and finally,the Wigner function shows the distinguishable cat states with different squeezed directions.(2)High-sensitivity weak force sensing in a dual-cavity system with modulation timedependent jumping rateIn the scheme of weak force detection,on the one hand,the optomechanical interactions sense the signal and transform it into optical information which can be measured.On the other hand,optomechanical couplings result in back-action noise,while cavity field fluctuation causes shot noise,so the two kinds of noise compete with each other leading to the standard quantum limit.Due to the positive demand of optomechanical couplings,generally,the back-action noise needs to be eliminated,so there are many proposals to reduce or evade the back-action noise,for example,the introduction of nonlinearity,negative mass,two-tone driving of the cavity field,and coherent noise cancellation.We propose linear and quadratic optomechanical coupling and dual-cavity with modulation time-dependent jumping rate to achieve high-sensitivity weak force detection.The importance of the quadratic coupling in the system is analyzed,and the additional noise can be greatly suppressed with experimentally feasible parameters.(3)Weak force measurement for suppressing thermal noise in optomechanical system with frequency modulated in cavity fieldBreaking the standard quantum limit and lowering the thermal noise of the mechanical oscillator become the main obstacle for precision measurements.At present,many weak force measurements are still focused on reducing the additional noise,ignoring the effect of mechanical thermal noise.In order to suppress the thermal noise of the mechanical oscillator,we have studied the weak force sensing in the optomechanical system consisting of the cavity field with modulated frequency and mechanical mode with a parametric term by Coulomb coupling between the oscillator and a charged body.By introducing the frequency modulation of the cavity field,the system can achieve the quantum non-demolition measurement interaction so that the back-action evading can be achieved.With the help of a parametric term,the mechanical mode exhibits squeezed effect.Thus combining quantum non-demolition measurement with mechanical squeezing,the weak force signal can be amplified,which is equivalent to amplifying the mechanical response function,reducing additional noise as well as thermal noise of the mechanical oscillator.So the scheme improves the detection sensitivity.These works are meaningful for the fundamental physics of cavity optomechanical systems and potential applications for weak force measurements.