Study Of Some Questions Of The Dissipation Of Open Quantum System

There are over one hundred years since quantum mechanics came into the earth. It has been profoundly involved in almost all the disciplines of nature science, such as all the branches of physics, chemistry, material science, et al. However, the basic principle or theory of quantum mechanics is still on the road of development. Especially in recent twenty years, the theory of open quantum system that came from quantum measurement played an important role in the development of the combination of quantum science and information engineering. First of all, a real quantum system is not an isolated one, which is determined by Schodinger equation plus its initial condition, but is an open one that is influenced by its environment; Secondly, the environment just mentioned should be described in some theoretical model, so that its effect on the system can be quantified; Thirdly, the quantum information science, a research field of great promise, including quantum communication, quantum control and quantum computation, is based on the instruments that are robust against the outer environment, for example, the imagined quantum bits; The last but not least, the key of the above problems is to eliminate or suppress the dissipation effect on the open quantum system imposed by its surrounding environment, such as decoherence and disentanglement.Although physicists have taken great progress in many aspects, some basic theoretical problems, such as the essentials of entanglement and coherence, are still not very clear in the field of open system dissipation. Thus in this thesis, we will made a detailed introduction of our works by tracing the frontier of this field. The whole thesis is consisted of four chapters.In chapter one, we review some classical theoretical methods developed by the dynamics of open quantum system and the definitions of some necessary physical parameters. We look back and sum up important progresses and fruits in the past two...