Post-selection Von Neumann Measurement And Its Quantum State Optimization Problems

Quantum mechanics is arguably one of the greatest achievements in the physical world in the last century,and leading us into the microscopic world of macroscopic matter and driving the progress of human society and the development of science and technology.Quantum optics is a sub-discipline developed with it,and research in this area has expanded the practical applications of various types of light beams.In quantum optics,the information carried by different radiated light fields can be represented by different state functions and studied analytically.Therefore,the analysis and optimization of the corresponding state functions of the optical fields have become a hot research topic in the physics community.The measurement problem,as a core problem in quantum mechanics,can obtain the required information in any state and is closely related to the preparation and optimization of quantum states,which is essential for quantum information processing.Therefore,finding better measurement methods and studying the effect of measurement on quantum states are of profound importance in the basic research of quantum optics and in its related applications.This thesis focused on the post-selection von Neumann measurement theory and its applications in quantum state optimization problems.In the Chapter one,the development of quantum mechanics and quantum optics is briefly reviewed,the concept of measurement including the post-selection von Neumann measurement theory and its research status also introduced,and finally the chapter arrangement of this thesis is given.In Chapter 2,the basic elements of quantum measurement theory are first introduced,followed by a comparative description of strong and weak measurements,and finally an overview of post-selection von Neumann measurement theory and its applications.In the third chapter,the related contents of orthogonal squeezing effect and amplitude squared squeezing effect in quantum states are given,the concepts and some basic properties of coherent state and Schr(?)dinger cat state are described,and the effects of postselection von Neumann measurements on the amplitude squared squeezing effect and phase space distribution of Schr(?)dinger cat states are studied and discussed in detail.The results show that a significant amplitude squared squeezing effect appears in the Schr(?)dinger cat states after the measurement,and the analysis results combined with its phase space distribution show that the post-selection von Neumann measurement method improves the non-classical properties of the Schr(?)dinger cat states.In Chapter 4,the non-classical properties of the superposition of the coherent state and the single photon added coherent state are studied from the optimization problem of the quantum state,including the photon number statistics,the second-order correlation function,the Mandel factor,the squeezing effect and the Wigner function.The results show that the superimposed states exhibit better non-classical properties than the coherent states and the single photon added coherent states alone.Finally,the whole paper is concluded and an outlook is presented.