Some Applications Of Master Equation In The Dynamics Of Open Quantum System

To apply the quantum technology in reality,the researches of open quantum system are attracting more and more attention in both of academia and industry.The microscopic quantum system inevitably interacts with the surrounding environment,which leads to the leaking of energy and quantum information from the system into the environment.This interaction results in quantum decoherence,which is a major obstacle in the practical application of quantum technology.How to suppress quantum decoherence is still a problem to be solved.Quantum master equation is one of the effective methods to describe dissipative dynamics of an open quantum system.By tracing over the irrelevant degrees of freedom,we can derive the quantum master equation which only involves with the degrees of freedom of the open system.In this thesis,we mainly employ the quantum master equation to study the dynamics of open system.After brief recalling the basic theory of open quantum system,we focus on the Jaynes-Cummings(JC)model with or without cavity losses.The collapse and revival phenomenon of the atomic population inversion occurs in JC model.It is found that the revival of atomic population inversion can be destroyed by spontaneous emission of an atom and the dissipation of the cavity.Moreover the latter presents more influence on the system than the former.To capture the real dynamics of an open quantum system,one should choose a proper quantum master equation according to the particular model.We make a comparative study on the concurrence dynamics between two two-level systems calculated by the phenomenological and microscopic master equations.In this model,only one of the two two-level systems coupled to a local bath.With a zero-temperature bath,we get the same results obtained by the two master equations.However,in a finite temperature bath,the result is dramatic different.We investigate the steady state of two coupled two-level atoms interacting with a non-equilibrium environment that consists of two heat baths at different temperatures.When employing the master equation with no secular approximation,we find that coherence of the system in our model survives after a long-time decoherence.The absolute value of quantum coherence decreases in the presence of additional atombath interaction channels.Quantum master equation is a useful method to solve the dynamics of open quantum systems.It is obtained by skillfully tracing the degree of freedom of environment.Thus it is limited by the approximation taking in the tracing procedure.We hope that this thesis sheds new light on the application of the master equation in the field of open quantum system.