Steady And Optimal Entropy Squeezing And Quantum Entanglement For Three-level Atomic Systems

In the process of quantum information processing and transmission,there are many limitations.On the one hand,the existence of quantum noise seriously affects the precise measurement of physical variables in the experiment,the preparation of high-quality quantum resources,the correctness of quantum computer operation and the fidelity and efficiency of quantum information transmission.In order to break through this limitation and realize ultra-low noise or even noisefree quantum information processing environment,it is the earnest expectation of workers in quantum information field.The entropy squeezing theory of atom and light field can be used to measure the magnitude of quantum resource noise,and has important application value in many aspects,such as quantum precision measurement,quantum key distribution,entanglement witness and so on,which has attracted extensive attention in recent years.On the other hand,as the basis of quantum information processing,quantum entanglement has always attracted the attention of many people.Due to the quantum system will inevitably interact with the surrounding environment,quantum entanglement will decay or even suddenly death.Since entanglement needs to be prevented from disappearing for a period of time until the quantum task can be completed in the process of quantum information processing,how to prepare sustained and stable entangled resources in a dissipative environment is one of the most concerned problems in quantum information field.So far,most previous studies have focused on two-level atomic systems,but it is the trend to study the quantum effects of higher dimensional systems in quantum optics and quantum information fields,because there are more superior quantum properties.Therefore,this paper studies the dynamic evolution of three-level atoms in different quantum systems.The specific content and innovative results are as follows:The basic entropy squeezing theory of atom and quantum entanglement are explained in the first chapter.The entropy squeezing of a two-level atom is emphasized.The steady and optimal entropy squeezing of three different types of threelevel atoms interacting with a single-mode field are studied in chapter 2.A stationary three-level atom cannot obtain a steady entropy squeezing whatever initial conditions are chosen,while a moving three-level atom can achieve a steady and optimal entropy squeezing through choosing higher velocity and appropriate initial state of the three-level atom.The direction and depth of entropy squeezing of moving three-level atom can be regulated by selecting appropriate initial state of the three-level atom.In chapter 3,the protection of the entanglement between two ?-atoms(EBTVA)in a multi-cavity coupling system is studied.The whole system consists of two Vatoms which are initially in the maximum entangled state and interacts locally with its own dissipative cavity which is coupled to external cavities with high quality factor(ECWHQF).The results show that,when there is no ECWHQF,the EBTVA can be protected effectively in the case where the ?-atom and the dissipative cavity are weak coupled in large detuning,while when there are different numbers n of ECWHQF coupled to two dissipative cavities,by adjusting the parameters of the number n of ECWHQF and the coupling strength k between cavities,the EBTVA can be protected perfectly and continuously.In Chapter 4,conclusions and prospects are presented.