A Study For The Key Technology Of Quantum Networks Based On Entanglement

Quantum communication is a combination of quantum mechanics and classical information technology. It has broken the limit of classical communications in information security, commumcation capacity and information transmission rate et al. In recent years, quantum communication has gradually been developed from theory to practice and from point to point communication to networking communication. At present, some quantum secure communication networks based on quantum key distribution have already been built and put into use. However, quantum communication networks based on entanglement properties are still in the stage of theory and experiment. In this paper, we mainly studied the key technologies of quantum communication network that based on entanglement, including its network model, relay strategy and routing strategy.The first two chapters introduced some basic knowledge of the development status of quantum communication at home and abroad, including the properties of quantum bits, the quantum gates, the dense coding, the quantum teleportation, the entanglement swapping, the network architecture and a typical quantum relay strategy.In the third chapter, a network model based on entanglement was proposed. Firstly, the entanglement channel was built between the sender and the receiver. Then, the entanglement resource was distributed according to the need of subsequent protocols. Finally, the protocol was executed. This chapter used teleportation as an example to analyze the transmission success rate and the throughput under the ideal and non-ideal circumstance. The calculation and simulation was made. This chapter was trying to realize the separation of channel establishment and information transmission, such properties could make the network relatively flexible and adaptable.In the fourth chapter, a quantum relay strategy based on entanglement swapping was proposed. It achieved entanglement swapping by means of quantum gate and quantum measurement. In the strategy, multiple nodes could simultaneously execute entanglement swapping and entanglement purification. We used link state matrix to express the distribution of entanglement in different stages of link construction. We also proposed a control method based on this link state matrix. In this way, the time delay could be reduced. By partitioning relay parameters and relay series of links, node number either for integral power of 2 or non integer power of 2 could be available. At the end of this chapter, we analyzed the link performance of the strategy. Results showed that the proposed strategy was more effective than the past step by step strategy, and the higher the relay series, the more obvious the improvement effect.In the fifth chapter, in order to solve the problem of routing, Bell state evolution under the three typical noise channel model was studied. Firstly, the partial entropy of entanglement after the three evolutions was calculated respectively. Then, the chapter discussed the node function of quantum communication network based on entanglement. In this chapter, we referred to the classical shortest path first routing algorithm and took the amplitude damping channel as an example. Finally a distributed node routing method which has preference for link with smaller node number and higher entanglement was proposed.In the case of using quantum packet transmission protocol, the performance of the link was calculated and analyzed. The strategy might be a reference for the routing operation in chapter three and chapter four before the entanglement channel was constructed.In the last chapter, the full text was summarized and prospected. The next-step research direction was proposed, and some questions that need to be solved were indicated.