The Theoretical Research Of Quantum Fisher Information And Dynamical Decoupling Pulses

Over the past several decades, quantum information science has attracted extensive attention and become a fast developing discipline. One of the most important part of quantum information is quantum metrology which combines the quantum mechanics and parameter estimation theory. However, the unavoidable interaction between the quantum systems of interest and surrounding environment will lead to decoherence which plays a destructive role for the the precision of parameter estimation. Thus, how to suppress decoherence is a challenging problem in quantum metrology. In this paper, we investigate how to suppress decoherence and enhance the precision of parameter estimation by employing dynamical decoupling pulses.In Chapter 1, we gives a brief introduction on the quantum information science. As the basis of this paper, we mainly outline the definition as well as the general formalism of quantum Fisher information in Chapter 2. Quantum Fisher information plays an very important role in parameter estimation theory due to the fact that the inverse of quantum Fisher information provides the lower bound of the error of the parameter estimation.In Chapter 3, we introduce a theoretical model which describes the decoherence dynamics behavior of N qubits independently interact with their own thermal reservoirs.In Chapter 4, we firstly study the influence of dynamical decoupling pulses on the precision of the initial state parameters of one single qubit and two qubits cases in this mode. It is shown that the dynamical decoupling pulses can effectively enhance the precision of the initial state parameters regardless of single qubit or two qubits case. Moreover, we investigate the dynamics of Entanglement of formation and Concurrence between two qubits in this model with dynamical decoupling pulses for two different initial states. It is found that the dynamical decoupling pulses is able to increase the value of Entanglement of formation and Concurrence. Finally, we conclude our works.