Study On The Enhancement Of Quantum Fisher Information In The Teleportation Processes By Partial Measurements

Quantum teleportation is an important component of quantum network and scalable quantum computation,and attracts widespread attention from the scientific community due to its broad application prospects.The purpose of quantum teleportation is to achieve perfect transmission of quantum information from one site to another distant site via entangled resource and classical communication.Generally,a quantum system is inevitably affected by its surrounding environment,which causes the system to lose its coherence and results in distortion of the transmitted information in quantum teleportation.Quantum Fisher information(QFI)is an important physical quantity in quantum metrology,which can give the optimal value estimating the accuracy of parameters.As we know,QFI is highly susceptible to environmental noise,which can lead to the decrease of measurement accuracy.In this thesis,we mainly investigate how to enhance the QFI of quantum teleportation processes by employing partial measurement operations.We first analyze the effects of depolarization noise,phase-damping noise and amplitude-damping noise on the QFI of the teleportation process through an EPR state as an entangled channel.Subsequently,by generalizing the amplitude damping noise from zero temperature environment to non-zero temperature one,we study how to improve the QFI in the schemes of teleporting a single-qubit state via an EPR state,a GHZ state,and a W state respectively with the technique of partial measurements.Based on different qubit transmission cases of the three quantum teleportation schemes,we consider their respective QFI in detail.After constructing the quantum logic circuits of each quantum teleportation scheme,we examine the variance trends of QFI against the generalized amplitude damping(GAD)noise parameters.Finally,by performing partial measurements on each noise particle and optimizing the related measurement parameters,we explore the corresponding improved QFI,namely,the difference between the QFI with optimal partial measurements and that without partial measurements.We find that optimizing partial measurements can efficiently enhance the QFI of the teleported state in the teleportation processes at finite temperature.Moreover,for the fixed value of ,the lower the environment temperature is,the larger the value of the improved QFI is.Our results could be useful to further understand the application of partial measurements to the quantum communication process and may be shed light on some related quantum parameter estimations and quantum information tasks.