Research Single-Photon Acquisition Technique In Free-Space Quantum Communication

Since the first experimental quantum communication is completed, the experimental study of quantum communication gradually developed and becomed more sophisticated, the current main job is to seek the combination between practical applications and quantum communication. Satellite Quantum Key Distribution (QKD) is extremely innovative. Satellite in order to achieve QKD, first of all require the use of satellite optical communication in the target, capture and tracking technologies to set up links in order to capture single-photon. Once the satellite QKD is demonstrated, the global secure satellite communication can be implemented and the applied foundation of the global secure incorporate optical communication networks can be established.Based on the popular encryption technology in the BB84, E91, B92 quantum protocol for a brief introduction, and simulation analysis that 500 randomly generated keys mean and variance and use these points for software distribution Mapping. Fully proved the feasibility of the above agreement, and finally the expected results. According to the probability annotation of quantum mechanics, the theoretical model of the single-photon acquisition probability is analyzed and perfected based on Maxwell equation. Based on the TEM₀₁ Laguerre-Gausssian beams and TEM₂₀ Hermite-Gaussian beams, The theoretical model of single-photon acquisition is analyzed. The single-photon acquisition is analyzed for the laser links between a ground station and a satellite in a low earth orbit. To acquire the single-photon, a bright precursor reference pulse which carries no key information can be used to set a short time window within which to look for the single-photon. The single-photon can be acquired by the receiver at the maximum probability when the Hermite-Gaussian beams and the Laguerre-Gaussian beams are used. The single-photon capture probabilities are in general order of magnitude at 10^-2～10^-4 of two Gaussian beams. Based on the BB84 protocol, set up low-orbit satellite-ground station between the quantum communication system model. Through the capture of single-photon probability, quantum bit-rate and quantum bit error rate's numerically calculating and analyzing. we can know that the communication is feasible between the low-orbit satellites and ground stations.The research work in this paper is the key technology for the realization of satellite quantum communication, provides a theoretical and experimental foundation for the actual satellite quantum communication system design.