Research On The Nonclassicality Of New Quantum States Generated In Opto-mechanical System

It is well known that nonclassical states play an important role in quantum optics,quantum computation,quantum information and investigation of fundamental quantum theory.However,with the development of information science,the requirements of the quantum state are correspondingly improved.Some traditional quantum states,such as number states,odd and even coherent states,thermal states,are limited in terms of application.So physicists have been proposed many programs to generate new quantum states.For example,new quantum states is generated to improve stealth transmission,cloning and storage technology in quantum computers.Over the years,much attention has been paid to generate nonclassical states theoretically and experimentally.In addition to the non-Gaussian operation(photon subtraction or photon addition)on classical states and superpositions of well-known basic quantum states(number state,coherent states,and squeezed states,etc.),recent experiments and theoretical studies have shown that opto-mechanical system and conditional measurement can also obtain new nonclassical quantum states.In this paper,some new non-Gaussian quantum states are prepared by opto-mechanical system and conditional measurement,and their nonclassicities are studied.The main contents of this paper are:In Chap.1,theoretical basis of quantum optics will be introduced briefly,including the integral technique of within ordered product of operators(IWOP),main characteristics of common quantum states,the criterion of nonclassical light field.In Chap.2,the model and relevant Hamiltonian of opto-mechanical system are introduced.And the time evolution operator of the light machine system is obtained through IWOP technique.In Chap.3,a entangled state is generated in opto-mechanical system for the initial state composed of four-headed cat state of photonic mode and number state of mechanical mode.Then the linear entropy,nonclassicality and fidelity of the entangled state are discussed.After obtaining the dynamics of the system,we discuss the nonclassical properties of the new generated state through Wigner function(WF)and Negative part volume of WF.We find that the Wigner function of the mechanical mode is composed of finite Wigner functions of displaced number states,which is very useful in quantum information process.Based on the study of the Wigner function,we find that the larger the initial value of the mechanical oscillator,the larger the negative volume of the Wigner function,which indicates that increasing the number of phonons is helpful to improve the nonclassical properties of the mechanical oscillator state.By adjusting the parameters,we can control the nonclassical properties of the quantum states of the light field and its distribution in the phase space.Compared to coherent state and even Schrodinger cat state as the initial state of the optical mode,in the case of four-headed cat states,photonic and mechanical mode will have stronger nonclassicity.And we find that the system state can evolve to a new quantum state only when the light field is strong enough.In Chap.4,the displaced number states and its superposition state are generated by conditional measurement of the optical mode of the opto-mechanical system.After obtaining its normalized constant by IWOP technology,we can prepare various kinds of displacement state and its superposition states by adjusting the parameters x,?,t0,k,g.we find that the larger the value of parameter ? will increase the number of superposition of displaced number states.We derive the analytic expression of its Wigner function,and use it to discuss the negative features of WF and the decoherence of the state in the thermal environment.It is found that the larger the parameter is,the more the number of states of the superposition of quantum states.It is remarkable to notice that the nonclassicality of Wigner function contributed by nondiagonal term of p disappears faster than one contributed by diagonal term of p.The SV time of the sudden disappearance of the nonclassical quantum state is further studied.The displacement state of k? 0 is stronger than that of k=0 on anti-environmental interference ability.In this paper,we provide a new method for the preparation of the superposition states of the number of displacements,which provides a way for the preparation of quantum states.It is expected to provide some useful reference for experimental research.