Theoretical Study On Transmission Of Quantum Information And Quantum Key Ditribution

Quantum information science is a new discipline,which is a combination of quantum mechanics and information science.Quantum mechanics is the foundation of quantum information,which primarily study quantum information processing. When we applied the properties of quantum mechanics to information,classical limit of information theory could be exceeded in many ways,and we can accomplish many unimaginable tasks for classical information processing.In recent years,the significant results of quantum information both in theory and experiment have attracted the interests all over the world.Quantum computation and quantum communication are two important branches of quantum information.As an important part of quantum information,quantum communication provides a new way for transmitting message.Quantum communication mainly includes quantum teleportation,remote state preparation (RSP),quantum key distribution(QKD),quantum secret sharing(QSS)and quantum superdense coding.This thesis involves three areas in quantum communication,i.e., quantum teleportation,remote state preparation and quantum key distribution.In the field of quantum teleportation,a scheme for teleporting a two-particle entangled state is proposed.When the quantum channels are the maximally entangled states,namely the channels are composed of a special two-particle entangled W state which belongs to nonmaximally entangled state and a Bell state which belongs to maximally entangled state,the probability of successful implementation is 66.7%. When the channels are nonmaximally entangled,by introducing an auxiliary qubit and constructing an 4×4 unitary transformation matrix,we solve the problem of the state distortion.RSP has the same goal with the quantum teleportation.The main difference between RSP and teleportation is that in the former the sender is assumed to known fully the transmitted state.In this thesis,a new remote preparation process is proposed.Using the new remote preparation process,the classical communication cost of some RSP schemes which use the two-particle projective measurement can be reduced greatly.Taking the scheme for preparing remotely a three-particle Greenberger-Horne-Zeilinger(GHZ)state as an example,we show how to use this process in detail and present the applicable range of this process.In the field of QKD, a scheme for QKD in a network is proposed.In our scheme,W state,whose entanglement properties are more robust is used as the quantum entangled resource. Bell inequalities for two-particle system and three-particle W state are used to insure the security of the QKD scheme.The situation that exists an eavesdropper(Eve)or Certificate Authority(CA)is unauthentic is discussed.It is proved that our scheme can withstand the attack effectively,and carry out the academic efficiency that three W states can be used to gain two bits key.