Research On High-speed Quantum Key Distribution System

Quantum cryptography describes the use of quantum mechanical effects to perform cryptographic tasks or to break cryptographic systems. It covers mathematics, physics, communications, electronic systems and circuits, computer science, and many other contents. Being full of challenges and hopes, this research not only make us a more accurate understanding and using of the natural world, but also is of great significance to the cause of national defense.Quantum key distribution (QKD) is the core of quantum cryptography. It solves the problem of how to distribute keys securely and secretly. With the one-time pad method, communicating parties can carry out unconditionally secure communications. The current QKD research is towards high speed, low QBER, security, and usability. The ultimate goal is to achieve high-speed and practical secure key rate.This thesis studied QKD protocols and systems to achieve our pre-built set of 200MHz-phase encoding BB84 QKD system extended to the decoy-state protocol. We tested the maximum performance of the system. Through analysis, we think that the bottleneck of the system is the pulse repetition frequency decreasing, the efficiency of the error correction algorithm, USB read speed and basis reconciling speed. In view of this, we designed the control electronics which support 800MHz pulse repetition frequency and PCIe bus data transfer between the electronics and PC.We designed FPGA-based basis reconciling and LDPC error correction implementation, which laid the foundation for the next step to achieve high-speed secure key generation rate. We studied two FPGA chips which support the hard-core CPU to provide practicable solutions for high-speed QKD node system.The original 200MHz QKD system bases on a dedicated SERDES hard IP to generate the high-speed electronics control signals, and to align all signals by delay unit circuit. It achieves high-speed modulation of the light pulse and SPD detection signal reception. In this paper, due to a limited number of dedicated SERDES hard IP of the development board, we using LVDS SERDES to generate the drive voltage of the IM (intensity modulator) which required by decoy states protocol. This program can generate a 1Gbps digital signal, which is completely sufficient for 200MHz system. Besides, we use digital diphase code to encode the IM signal, so as to solve the low-frequency obstacle caused by DC component of the decoy states signal.In this thesis, we developed a QKD system software using client/server architecture and multi-threading technology to achieve high efficient BB84 QKD protocol based on decoy states method. We also designed a set of programs for calculating of electronices parameters.Finally, we achieve a secure key rate of 25km/33kbps without any manual adjustment. The QKD performed stably and maintained the average QBER of signal state within 2.35%. The new control electronics has been tested that it can produce 800Mbps pseudo-random number. The overall and peak transmission speed of PCIe is up to 250MB/s and 1GB/s respectively.Our next work will focus on building a high-speed QKD system based on the new electronics and optical equipment to achieve higher secure key generation rate.