Nonclassical Effects Of Open Qubit System Under Quantum Weak Measurement

Nonclassical effects is a kind of peculiar quantum effects, which is induced by the interaction between the quantum systems, it is different from classical physics characteristics. In recent years, nonclassical effects have attracted more and more attention of people because it is an effective resources to realize several tasks in quantum information processing and quantum computation. Pructical quantum systems inevitably interact with the environment around it, which results in destroying coherence of quantum systems and decreasing even disappearing nonclassical effects of quantum system. Therefore, how to effectively control effect of ambient noise environment on coherence of quantum system and enhance or protect the nonclassical effects of quantum system is an important subject in the research of quantum optics field. In recent years, people made a lot of theoretical studies and empirical inquiry about quantum weak measurement and measurement feedback and found that it can effectively inhibited decoherence is induced by the interaction between quantum system and its environment. Then, whether nonclassical effects of quantum systems can be improved by quantum weak measurement and measurement feedback? In this paper, nonclassical effects of open qubit systems are studied by using the basic theories of quantum weak measurement and some innovative results are obtained. The main research contents and innovations are as follows:In the first chapter, the basic theory of weak measurement and quantum measurement and definitions of the specific quantum measurement are introduced, then several typical quantum measurement are presented. Finally, the basic concept of quantum weak measurement and measurement feedback is described.In the second chapter, several typical nonclassical effects of quantum systems are described, such as quantum coherence of quantum system and its measure method, quantum entanglement, the atomic operator squeezing effect.In the third chapter, the basic theory of open quantum system is briefly introduced. Firstly, the definitions of closed quantum system and open quantum systemare given. Then, master-equation method of open quantum system is solved. Lastly, several kinds of the quantum channel and their operators are described.In the fourth chapter, nonclassical effects are studied by using quantum weak measurement and measurement feedback, include the coherence of open single qubit system, two qubit system and two-level atomic operator squeezing effect.what is more, the influence of quantum weak measurement and measurement feedback on nonclassical effects of open qubit system is discussed. The results show that it can protect the nonclassical effects of quantum system from amplitudedamping decoherence using quantum weak measurement and measurement feedback.In the fifth chapter, summary and outlook of the full text are presented.