Research On Quantum Communication Algorithm Based On Free-space

Quantum communication is a new field that combination with quantum physics and classicinformation science. It is most rapidly developing recently because of the unique advantages ofabsolute security. Generally, quantum communication utilizes free-space channel or optical fiberchannel. Due to the bottleneck of current technology, the distance of fiber-optic quantumcommunication has reached the limit. While free-space quantum communication has theexcellence of high stability, low losses, and make use of the space platform, which makes it to begenerally considered as the most feasible option for the global quantum communication.However, in practice, quantum communication is not secure due to the imperfect devices, suchas single photon sources and detectors, which cause the key leakage. In order to solve this problem,quantum algorithm will be used to extract the key after quantum key distribution.This paper first describes the classic encryption and physics theories that can ensure theabsolute security for the quantum communication. The next part is the security analysis. With asmall adjustment of the hardware, we improve that the decoy state method can close this loopholeand substantially improve the QKD performance in the field of transmission distance and final keyrate.In the fourth chapter, we introduced the quantum communication algorithms, including thebasis verification, reconciliation and privacy amplification. Basis verification is mainly used BB84protocol to extract the original key. We use the synchronous light in the experiment to reduce thedark count and time measurement module impact on the bit error rate, eventually upgrade the finalkey rate. Reconciliation protocol is aimed to reverse the error bits in quantum key distribution. Weintroduce four algorithms, improve the Winnow, do the performance and find the Cascade andLDPC are approached to the Shannon entropy. The final step is privacy amplification. It useduniversal hash function to compress the leaded information that the eavesdropper may obtain. Byquantum communication algorithm, we can get the absolutely safe key.Finally, we conclude this paper. With the development of quantum communication, thealgorithms will be more important in the future.