The Study Of Entanglement Characteristics Between Optical Modes In Optomechanical System

Quantum entanglement is a physical phenomenon and one of the most obvious characteristics of quantum physics.When a pair or a group of particles generate or interact,the quantum state of each particle cannot be independent of the description of other states.The quantum state must be described as the entire system.The preparation of entangled state and its wide applications in the distrinct filed have attracted people’s attention.Based on the existing experimental conditions and techniques,the preparation of strong and stable entanglement source has become a hot topic.In fact,different physical systems usually have different resonant frequencies,which requires that the interacting multipartite entangled light fields need to have a matching resonant frequency,further,this can realize efficient quantum information processing.As one of the effective platforms for realizing this kind of process,the optomechanical system has the outstanding advantage that it can use mechanical vibrators to entanglement different subsystems.Optomechanics study the interaction between optical field and mechanical oscillator in optical microcavity.In recent years,cavity optomechanics has developed rapidly.Here,we propose a new theoretical scheme to enhance the interaction between optical modes and improve the degree of entanglement mainly.In addition,we also studied another method of generating quantum entangled states,such as four-wave-mixing process.Based on the phase-sensitive cascaded four-wave-mixing system,we focused on the control of the relative phase of the pump on the entanglement.This has potential application value in quantum manipulation.The main work of this paper is as follows:(1)In the first chapter,we introduce the concept of quantum optics.Optomechanics is a more active research content in quantum optics.Cavityoptomechanics study the interaction between optical field and mechanical oscillator in optical microcavity,and then introduce the concept of optical microcavity.Then the research and application of cavity optomechanical system are introduced.At last,two type classical cavity optomechanical systems,the basic theory and entanglement criterion of optomechanics are given.(2)In the second chapter,we put forward a theoretical scheme for increasing the entanglement of the two optical fields effectively by placing a degenerate optical parameter amplifier(DOPA)in the optomechanical cavity.The two cavity modes of the system are respectively pumped with the red and blue detuned pump lights.When the detuning is equal to the frequency of the mechanical oscillator and is far greater than the attenuation rate of the cavity field,the two cavity modes are entangled by the mechanic oscillator as an intermediary.The DOPA squeezes the two cavity modes in the cavity simultaneously(amplitude squeeze and phase squeeze,respectively).We adopt the logarithmic negativity to quantify the entanglement.The results show that the squeeze effect can increase the entanglement of the two cavity modes significantly,and the entanglement improvement is more obvious at cryogenic temperature.(3)In the third chapter,we introduce the concept of the four-wave-mixing.And a phase-sensitive cascaded four-wave-mixing system is studied.The Hamiltonian of the system is given,then the quadrature fluctuation equations of each field can be obtained.The bipartite entanglement criterion is used to determine the entanglement characteristics of the generated beams.And we focus on discussing the manipulation of pump phase on entanglement.(4)The fourth chapter is the summary and outlook,we summarie the major work of this thesis,and propose the next plan.