Theoretical Study Of Quantum Communication Process Based On Weak Measurements

The thesis is contributed to the study of the quantum fidelity and quantum Fisher information when the quantum communication process go across the decoherence channel.We focus on studying the effect of weak measurement for quantum state in the deterministic remote state preparation protocol and the teleportation protocol.Generally,a realistic quantum system is unavoidably coupled with the external environment,which causes the system to lose its coherence.The quantum fidelity is a physical quantity to measure the similar degree between the final state with the initial state.Thus enhancing the fidelity of quantum state transmission in the presence of noise is a significant subject in the field of quantum communication.In this theies,improving the fidelity of a deterministic remote state preparation(RSP)protocol under decoherence is investigated with the technique of weak measurement(WM)and weak measurement reversal(WMR).We first construct the quantum circuit of the deterministic remote preparation for a single-qubit state through an EPR state.Then we analytically derive the average fidelity of the deterministic RSP protocol under the influence of generalized amplitude damping noises acting on the EPR state.Our results show that when only qubit 2 undergoes the decoherence channel,the average fidelity of the RSP subject to generalized amplitude damping noise is the same as that subject to amplitude damping noise.It is found that the application of WM and a subsequent reversal operation could lead to the remarkable improvement of the average fidelity for most values of the decoherence parameters.We also study the effect of environmental noise for the quantum qubit in the remote state preparation and quantum teleportation,and optimize the quantum fisher information of the quantum protocols with the weak measurement a subsequent reversal operation.Through the numerical analysis of the result,the weak measurement and the reversal operation indeed contribute to the optimizing of the quantum state's quantum Fisher information.Furthermore,we found that the weak measurement and the measurement reversal are asymmetric and the measurement reversal plays a more important role in the optimal protocols.