Entropy As A Measure Of The Noise Extent In The Quantum Feedback Controlled System And Corresponding Strategy

The quantum informatics is the combination of quantum mechanics and the information theory, which is formalized in the 1980s, and it can solve many information processing problems which cannot be achieved by the classical information theory. As the development of quantum information and computation, quantum information technology will play an important role in the fields of computation, information, national security and commercial. The core of the technology is how to control information, while all the information exist in the physical entity, so the controlling method is the key issue in the realization of quantum information and computation. This paper mainly studied the effect of noise in the quantum feedback controlled system by using Von Neumann entropy, and give a simple systematic approach which can help to make reasonable choice of control strategy to produce ideal results.In chapter 1, the simple overview is presented for the bring history background and the development of quantum feedback control system. We introduced the basic theories,the feasibility of feedback control strategy,recent research trend on this field and the application prospects. All of these lay the foundation for the study of getting a much better feedback control choice.In chapter 2, at first, a simple overview is presented for the bring history background of quantum entropy, and then the basic theories of quantum entropy are explicated. We also give the definion of quantum entropy, and compared with the classical entropy. The physical implementation of manipulation of quantum entropy, which form the theoretical basic of the works in the following chapters, are discussed in detail.In chapter 3, we focused on the investigation of the controlling strategy in the quantum feedback system. By introducing the Von Neumann entropy as a measure of noise extent, we can see to what degree the system was affected by the noise, we studied some different situations of the system's entropy in the process of state's dynamic evolution from an initial state to a target one. The evolution of entropy can provide us with a clear real time noise observation of the system, and a simple systematic approach which can help to make reasonable choice of control strategy to produce ideal results.In chapter 4, we summarized the main content of this paper, and discussed the prospects of quantum feedback controlled system.