The Research Of Experimental Implement Technology In Free Space Quantum Key Distribution Experiment

Quantum information is the new intercross subject to represent and manipulates information using quantum physics principles as well as the fundamental and method of classical information theory. As a branch of quantum information with good prospect, Quantum secure communication, especially quantum key distribution, is likely to be the first commercial application of quantum information technology at present. According the medium of quantum key distribution (QKD for short), it has two types: QKD in fiber and QKD in free space. Compared with QKD in fiber, QKD in free space won't be affected by the bi-refringent effect, and no additional fiber is needed. When the technology of QKD in free space is mature, it can be used in communication between satellites and ground stations, which will build a global quantum communication network. So the future of QKD in free space is bright. After the comprehensive investigation on the development of QKD experiment abroad and domestically is presented, this article puts the emphasis on the implement technology of QKD in free space. We design and realize the electronic module of the free space QKD system, including six parts: random signal generation, data acquisition, wireless channel setup, online key sift, online key correction, and the encryption and decryption of the bitmap file. In the subsystem of random signal generation and data acquisition, we realize the four random signals generation and acquisition simultaneously. We design data process module of QKD system independently, find the method of sifting and correcting keys on line, realize the comparison and sift of error blocks in batches using the queue structure, make the final key via the discussion on the wireless LAN, and conquer some difficult problems, such as the transmission of synchronous signal, the continuous adjustment of signal duty ratio and the sequence of multi-signals, the transmission of large custom data structure arrays on the networks and so on. The system has been used to complete the QKD experiment in moonlight outdoors. The whole system achieves the expected target, and can complete the task of data generation, acquisition, analyze and processing. The distributed quantum key can be used in the cryptography of the bitmap files, demonstrates the feasibility, validity and practicality of using this system to file encryption. This article further analyses the experiment data, including the average photon number, error ratio and key generation rate, discloses the influent of these result to this system's security and performance, and the mutual relationship of these parameters. The work described in this article provides helpful reference to the implement of quantum secure communication.