Quantum Fisher Information Of Qubits In Non-Markovian Environment

Actual quantum systems interact with its surroundings,resulting in energy dissipation and information attenuation of the quantum system.Therefore,the study of the dynamic evolution of the quantum effects of open quantum systems has become a scientific problem in the field of quantum optics.Among them,how to effectively protect the quantum effects such as quantum Fisher information,quantum coherence and quantum entanglement of open quantum systems has always been the key problem in the field of quantum optics and quantum informatics.With the development of theory and experiment,it is found that using quantum operation such as quantum weak measurement and quantum feedback control can effectively suppress the decoherence of quantum systems.In this paper,the dynamic behavior of quantum Fisher information of qubits in non-Markovian environment is studied,and the scheme of regulating quantum Fisher information by using environmental parameters is put forward.The main research contents of this paper are as follows:The first chapter briefly introduces the background and significance,quantum dynamics process and evolution equation of an open quantum system,and then introduces the basic concepts and measurement methods of quantum Fisher information(QFI),quantum coherence and quantum entanglement.Finally,the basic definition and measurement of non-Markovianity are introduced.In the second chapter,the QFI of a single qubit in non-Markovian environment is studied by using the time deconvolution master equation,and the density matrix of single qubit and the analytic solution of QFI are obtained.The dynamic behavior of QFI in non-Markovian environment in two different initial states is discussed,and the quantum Fisher information flow(QFIL)is used to physically explain theevolution of QFI.The results show that the maintenance and regulation of QFI can be achieved by changing the initial state of the system,adjusting the coupling strength of atomic-cavity and the coupling strength of cavity-environment.And the stronger the coupling strength of atomic-cavity and cavity-environment,the better the maintenance effect of QFI.In the third chapter,the QFI of single qubit in non-equilibrium environment is studied by Liouville-von Neumann equation,and the analytic solutions of single qubit QFI and quantum coherence and their relation are obtained.The non-Markovianity of single qubit is measured by BLP measurement.The results show that when the environment deviates from the equilibrium,the QFI and quantum coherence can be better protected.The smaller the memory attenuation rate of the environment,the better the protection of QFI and quantum coherence.Finally,using the non-Markovian features of the environment to make a reasonable explanation of the quantum dynamics behavior of QFI and coherence.It is found that non-Markovian features also have a good protective effect on QFI and quantum coherence.In the fourth chapter,based on the physical model of the third chapter,the QFI of two qubits in the nonequilibrium environment is studied.The analytic solutions of the QFI and quantum entanglement of the two qubits and the relationship between the QFI and quantum entanglement are obtained.The results show that the maintenance of QFI and the protection of quantum entanglement can be realized by adjusting the equilibrium parameters of the environment,that is,the nonequilibrium of the environment can protect the QFI,and the maximum entanglement value of the initial state can be effectively maintained.The fifth chapter summarizes the work of this paper,and looks forward to the future work.