Research On Key Technologies Of Signal Processing Of Continuous-variable Quantum Key Distribution

Quantum cryptography is a revolutionary comprehensive new frontier interdisciplinary.Quantum cryptography is the fusion of Quantum Key Distribution(QKD)technology in "one-time pad" communication system.The uncertainty principle and non-cloning theorem are used to integrate the modern cryptographic information encryption and transmission methods,to break through the relatively secure of traditional encryption relying on the assumption that the eavesdropper’s limited computing ability.It realizes the information theory security of information transmission network space and opens up the theoretical and experimental research field of quantum information security science in cyberscience.Continuous variable Quantum Key Distribution(CV-QKD)technology uses continuous variables represented in infinite dimensional Hilbert space to encode key information.A single pulse of CV-QKD can encode multi-bit information,which has potential to generate a large security code rate.The CV-QKD technology based on optical fiber can better integrate the classical communication network,and c n easily connect to thousands of households in the metropolitan area.The security key rate of CV-QKD system is limited by the coherent state preparation rate,the data sampling rate and data post-processing rate of the probe system,and the security distance of the system is limited by the efficiency of reconciliation.We plan to develop a prototype of CV-QKD experimental system with an operating frequency of 20 MHz and transmission distance of 25 km.The main work of this paper focuses on the design and development of electronics system of prototype,which including three modules:Data Acquisition(DAQ)of detection system,generator of coherent state modulation and post-processing of the key.The high-speed DAQ module is mainly responsible for collecting,uploading,and recovering the output signal of the detector.This paper designs a system platform of 1 Gsps DAQ printed circuit board.The test results show that the effective number of bits of the DAQ card is about 9 bits and has good integral nonlinearity and differential nonlinearity.Meanwhile,this paper completes the joint test related to optics and the detector system.This paper completes a hardware design of Gaussian Random Numbers(GRN)generator based on mathematical transformation method,which can generate GRN with the highest frequency of 40 MHz and precision of 16 bits.The voltage modulation is realized through the output of the digital-to-analog converter(DAC).Aiming at the key error correction part of key post-processing,this paper adopts a method of extending lifting size of low density parity check codes(LDPC)in 5G protocol.Through mathematical analysis of the decoding and encoding algorithm process,the structure and hardware resources of the algorithms on Field Programmable Gate Array(FPGA)chips can achieve better performance and lower complexity.The results show that when the code rate is 22/68 and the Ratio of Signal to Noise(RSN)threshold of Gaussian white noise channel is 0.7,the theoretical efficiency of reconciliation is 85%,the theoretical safe distance can reach 30 km,and the theoretical safe code rate is 200 kbps.The coding and decoding throughput is 125 Gbps and 472 kbps with 200 MHz system clock.This paper has the following innovations in key technologies of signal processing of CV-QKD:1.This paper developed a DAQ system with high precision,high sampling rate and large cache depth for detection system of prototype of CV-QKD experimental system.This paper developed a set of high-speed DAQ hardware,digital logic,and computer software of high-speed DAQ.The DAQ can collect,receive,transfer,upload and analyze data from detector.Extendable hardware based on daughter-mother structure can reduce the difficulty of design,shorten cycle of the experiment,and reduce the cost of hardware implementation.2.This paper proposed a hardware structure for Gaussian modulation to meet the demand of Gaussian modulated coherent state CV-QKD system.The hardware structure can convert the external uniform random source into GRN.This paper realized the conversion of random number to generate higher speed GRN in FPGA,which can further improve the repetition frequency of CV-QKD system.GRN has better independence,which can enhance the security of key of CV-QKD experimental system.3.This paper proposed a coding algorithm and decoding algorithm for LDPC using FPGA.The algorithm structure and hardware resources are optimized by mathematical derivation to realize high-speed parallel processing.This paper completed a hardware design of error correction code in the post-processing of prototype of CV-QKD.It completes error correction away from the computer and establishes physical isolation from potential eavesdroppers.