Research On Quantum Secure Direct Communication And Network Technology

Quantum Information is a young cross discipline, which is improved based on the basic principle of information technology and quantum mechanics, and has been developed rapidly in recent years. Since the unconditional security of quantum information system is ensured by the Heisenberg uncertainty principle and quantum no-cloning theory in quantum mechanics, the technology of quantum information came to world-wide attention recently. As the most mature and practicable application in quantum information field, the technology of quantum communication has been progressed quickly. From the proposition of the quamtum key distribution protocol to the experimental realization of the quantum key distribution system, the quamtum communication system got many research findings in theory and experiment. As a research branch of quantum communication system, quantum secure direct communication (QSDC) system is characterized by transmitting secret messeage directly and safely, doesn’t need quantum key. However, the research of QSDC system mainly focused on the design of specific communication protocol, which are all based on the ideal communication environment, makes the research of practical applicability insufficiency.The major research target of this thesis is to improve the engineering and practical applicability of QSDC system, focusing on the problems of noise and networking. The work is launches from the following three aspects.(1) The influence of quantum noise on the quantum communication system is analzyed. In consideration of the security requirement of quantum secure direct communication, the tranditional encoding method is combined with the quantum system, and a model of quantum secure direct communication based on decoherce free subspace is presented. The proposed model decreases quantum noise evidently, whic is caused by collective dephasing coherence. The communication procedure and the security problem of the model are studied in detail, results in solved noise problem and improved safety of the quantum secure direct communication.(2) Based on the existing fundamental theory of quantum network, a quantum secure direct commucation system is presented using the basic idea of quantum repeater. Firstly, the concept of quantum repeater is introduced to peer to peer quantum secure direct communication system, and a bidirectional qubit transmission system based on decoy quantum state is proposed. Then, the quantum secure direct communication network structure using double communication rings connecting with quantum repeater is designed. This structure can increased the communication distance of quantum secure direct communication system. Finally, the quantum secure direct communication network structure using multi communication rings is discussed, by which the enhancement of the quantum system’s flexibility and practicability is improved. The security of this system is discussed, and the quantum repeater as a quantum network node is simulated.(3) The multiplexing problem of quantum secure direct communication is researched. The space multiplexing division model of quantum secure direct communicatin based on the transmission in free space is presented. The receiving and transmitting parts of this model are designed in detail. The basic communication procedure of this model is discussed. When the transmission channel is free space, the influence of various factors in this channel is analyzed. The communication capacity and flexibility of quantum secure direct communication system are improved.