Study On Scheme And Protocol Of Multi-user Quantum Communication

According to the quantum indeterminate principle, superposition principle of quantumstates and quantum no-cloning theorem, quantum communication based on quantummechanics has incomparable characteristics on high security and highly efficient incomparison with classical communication theory, so it becomes a highlight area studied atpresent. Quantum communication includes the quantum key distribution, quantum securedirect communication, quantum secret sharing, quantum identification and quantumteleportation etc. In1993, Bennett et al. presented a scheme of quantum teleportation. Duringthe teleportation, an initial photon which carries the polarization is transferred and one of apair of entangled photons is subjected to a measurement such that the second photon of theentangled pair acquires the polarization of the initial photon. From the point of view ofcommunication, quantum teleportation actually carries out the process of quantum signaltransmission, signal modulation and demodulation and is point to-point communication. Withthe development of quantum communication, Quantum Communication Network (QCN) will come intobeing. An integrated system of quantum communication consists of two parts, namely classicalcommunication network and quantum transmission network.This dissertation is focused on multi-user quantum key distribution protocol, quantumrouting scheme, quantum wireless communication and quantum time-division multi-channelcommunication. The main contributions and innovation of this work can be summarized asfollows:A Multi-user Quantum Key Distribution (MQKD) protocol is proposed. It only needs nquantum channels for a communication system of n users to realize the protocol withentangled states and entanglement swapping. By the quantum mediator, any two among nusers of the system can communicate with each other, even though there is no direct quantumchannel between them. Furthermore, the quantum mediator, who performs entanglementswapping, has many Bell state measurement units and makes it possible that several userscommunicate with each other at the same time. Based on the traffic theory, we present arelationship formula of the number of user n and the number of Bell state measurement unit m.Because entanglement swapping entangles the quantum states of the two users, the quantummediator has no way to fraudulently intervene in or eavesdrop on the communication.A quantum swapping routing scheme, based on quantum teleportation and entanglementswapping, is proposed to teleports a quantum state from one quantum device to anotherwirelessly even though the two devices which do not share EPR pairs mutually. By thequantum swapping routing scheme, the model of quantum wireless communication network is presented. In order to be compatible with the present conventional wireless communicationnetwork, the network architecture of a two-tier database structure and correlativecommunication protocol are proposed. Performance analysis results show that the proposedscheme is superior to quantum relay routing scheme in qubit transmission time and security.The scheme has high practicability and scalability.Based on multistage quantum teleportation, a quantum routing scheme is propose. By thequantum routing scheme, the model of quantum wireless wide-area networks is presented. Interms of time complexity, the proposed scheme transports a quantum bit in time almost thesame as the quantum teleportation does regardless of the number of hops between the sourceand destination node. From this point of view, the quantum routing scheme is close to optimalin data transmission time. The characteristics of scheme and the correlative routing processare proposed. The scheme may play an important role in establishment of quantum wirelesscommunication networks in a large scale in the future.Based on the classical time division multi-channel communication theory, a scheme ofquantum time division multi-channel communication (QTDMC) is presented. Moreover, themodel of quantum time division switch (QTDS) and correlative protocol of QTDMC areproposed. The quantum bit error rate (QBER) is analyzed and the QBER simulation test isperformed. The scheme shows that the QTDS can carry out multi-user communicationthrough quantum channel, the QBER can also reach the reliability requirement ofcommunication, and the protocol of QTDMC has high practicability and transplantable. Thescheme of QTDS may play an important role in establishment of quantum communication ina large scale in the future.