Research On Quantum Secure Direct Communication And Quantum Time Division Multiuser Communication

Quantum information science, a new field combining quantum mechanics with information science, provides a new approach to the development of information science. Quantum communication is not only an important branch of quantum information science but also is expected to be the first application field of quantum technology. A lot of important achievement has been obtained in theory and practice in recent years. This thesis focuses on quantum communication scheme and quantum multiuser communication.First of all, the theoretical principle and basic form of quantum communication is introduced in this thesis.Secondly, based on the analysis of the standard quantum teleportation schemes and probabilistic quantum teleportation schemes, a probabilistic quantum teleportation scheme based on POVM is proposed. This scheme can achieve the best success probability. The POVM optimal operators are also presented. Furthermore, the quantum state of EPR pairs transmitted via a channel with special quantum noise is estimated. The performance of the estimation and fidelity of the quantum teleportation is simulated and analyzed. The results show that mean square error of the estimation tends to 0 and the fidelity of the transmission state tends to 1 with the increase in the number of the sample.Thirdly, Ping-Pong protocol and its security are investigated, and the largest amount of information leakage is analyzed with Holevo theorem. The simulation and analysis are also to be carried out. A quantum secure direct communication protocol using EPR pairs and single photon is proposed. Analysis results show that the protocol is secure. The proposed protocol overcomes the shortcomings of Ping-Pong protocol and improves the utilization efficiency of the security channel.Fourthly, Primary study of quantum multiuser communication is presented in this thesis. Based on the Quantum channel time division multiplexing scheme and the quantum switch scheme, a quantum time division multiuser communication scheme and communication protocol are proposed. By analyzing the bit error rate, the results show that the major factor causing quantum bit errors is quantum noise.Finally, a summarization is given, and the future work is prospected.