Quantum Fisher Information And Quantum Speed Limit For Open System

With the development of quantum information theory,the requirements for the accuracy of quantum measurement are also increasing these years.Therefore,the Parameter Estimation Theory has become particularly important nowadays.While the Quantum Fisher Information(QFI)also plays an important role in the field of parameter estimation,hence it is vitally significant to study the QFI both in theory and in experiment.The evolution speed of the quantum system involves a most all fields of quantum physics,and one of the fundamental problems in all these fields.Quantum speed limit(QSL)means the shortest time for a system to evolve from a given initial quantum state to a distinguishable target state,and it also indicates the maximum evolution speed of the system.The study of closed systems is time-honored,but the decoherence caused by the interaction between realistic quantum systems and environment is inevitable.So it is a very important subject in the field of quantum optics and quantum information to study the QSL of open quantum system so as to find the method of accelerating quantum evolution.The purpose of this thesis is to study the QFI,quantum coherence(QC)and the acceleration effects of quantum evolution by using static qubits.At the same time,this thesis utilizes the moving qubits driven by classical field to analyze the QSL and non-Markovianity of open systems.The main innovation points are as follows:1.The damped J-C model is studied by solving the master equation.And in this way,the analytical solution of the qubits in the model is obtained.Meanwhile,this present thesis analyzes the QFI,QC and their relationships in detail,which are all based on the Ohmicand Lorentzian reservoir.The results show that both the atom-cavity coupling and the cavity-environment coupling can efficaciously protect the QFI and the QC.Especially when the atom-cavity coupling or the cavity-environment coupling goes beyond a certain critical value,both the QFI and the QC tend to be stable.The effective enhancement of QFI and improvement of quantum metrology caused by QC is also indicated by the further researches.Finally,dynamic changes of the QFI and QC can be explained by the decoherence rate.2.The QSL and the non-Markovianity of the qubit in the damped J-C model are studied by solving the master equation.The results show that the QSL and the non-Markovianity can be effectively controlled by atom-cavity coupling and environmental parameters.The evolution from Markovian dynamics to non-Markovian dynamics can be caused by the coupling and detuning of atom and cavity,which is also the main physical reason for the quantum acceleration.3.The method of solving the Schr?dinger equation can be used to study the moving qubit driven by the classical field.By this approach,the analytical solution of the qubit density operator is obtained.The impact of the classical field,moving velocity of the qubit,environmental parameters on the QSL and non-Markovianity is analyzed in detail,as well as the relationship between the between non-Markovianity and QSL.The results show that the quantum acceleration is internally caused by the evolution from Markovian to non-Markovian dynamics.Whether the driven field or the strong coupling can promote the non-Markovianity of the dynamic process and accelerate the dynamic evolution process.While the velocity of the qubit can weaken the non-Markovian of the dynamic process and slow down the evolution of the dynamic process.To some extent,the influence of the moving velocity of the qubit on the quantum evolution can be controlled by the classical field.