Studies On Exact Dissipative Dynamics Of Hybrid Quantum System

When modeling realistic physics systems,it is necessary to take the coupling between concerned system and external environment into account.However,the study on exact dynamics is always a nontrivial problem due to the infinite numbers of environmental degrees of freedom.In the past decades,researchers have proposed many theoretical methods to deal with the open quantum systems,including quantum trajectory,Monte-Carlo numerical simulation,Kraus operator,etc.Nowadays,the Lindblad master equation based on the Born-Markov approximation is still the most popular method in most scenarios.But more and more investigations indicate that the coupling strength between realistic systems and environments is so strong as to break the Markovian approximation.Thus the solution of the non-Markovian dynamics is significant in recent works in both theory and experiment.Quantum-state-diffusion(QSD)equation is a kind of effective method to solve the non-Markovian dynamics.By transforming the environmental modes into the Gaussian noise,the exact dynamics of system can be obtained with the statistical property of the environmental noise.By treating the cavity modes as noises rather than operators,a recent work extended the QSD method to a more general situation.Now it can be used to describe the hybrid quantum system where the atomic system interacts with the lossy cavities.The hybrid quantum systems have a wide range of application in quantum computation and quantum information.The exact solution of dynamics can be used to investigate the strategy that might prolong the coherence time of concerned system,and then offer suggestions for the realization of realistic systems.In this paper,we will discuss the application of QSD in a hybrid quantum system in details.Based on the exact non-Markovian dynamics derived from the QSD method,we can exploit the features of dissipative hybrid quantum system to conserve the quantumness of the open systems.This thesis is organized as following.In Chapter 1,we introduce the investigation background of this thesis,which involves with the basic concepts of a hybrid quantum system.We will describe the features of the preceding hybrid systems.We will give a brief review of the non-Markovian dynamics and then explain the advantages of our theoretical method,the QSD equation,in dealing with hybrid quantum systems.Then we derive a QSD equation in a novel form that is suitable to deal with the quantum hybrid systems.In Chapter 2,we solve the dynamics of quantum bits embedded in the lossy cavity array with the exact master equation derived from the QSD equation.By defining the combination of cavity and reservoir as a double-layer hierarchical environment,we can discuss the influence of parameters and the structure of the hierarchical environment on the coherence and entanglement of qubit system.Then we present the strategies that can prolong the coherence time of system.In addition,through a unitary transformation,we show the underlying physics behind the dynamics.In Chapter 3,we study a driven three-level hybrid system.Based on the master equation,we track the adiabatic evolution of atom that is driven by continuous or pulse lasers.Our results justify the validity of adiabatic approximation.The coherent driving of laser and cavity modes can form a closed-loop interaction.In this case,we discuss the fundamental influence of relative phase of laser on the population dynamics of the three-level atom.In Chapter 4,we summarize the main part of the works and innovations of this thesis and then put forward the future research plan.