Research On Afterpulse In Reference-Frame-Independent Type Quantum Key Distribution Systems

Cryptography plays an important role in today’s information society.However,as quantum computing technology advances,the security of traditional cryptography based on computational complexity can be threatened.Fortunately,based on the fundamental principles of quantum physics,quantum key distribution(QKD)can share unconditionally secure key between two remote parties,Alice and Bob,even under an eavesdrop Eve.QKD has attracted widespread attention from researchers due to its information-theoretic unconditional security.Since the proposal of QKD protocol,researchers have made significant efforts to improve the performance and security of practical QKD systems.However,in most QKD systems,Alice and Bob need to calibrate their reference frames in real time,which increases the cost and complexity of the QKD system and reduces the efficiency of the entire communication process.Fortunately,researchers have proposed the reference-frame-independent QKD(RFI-QKD)protocol,which can generate secure keys in the presence of slow drifts of the reference frame,solving the problem of active reference frame calibration.Meanwhile,in practical systems,Eve can still obtain the key information of communication parties by attacking the measurement devices due to defects in the measurement devices.The reference-frame-independent measurement-device-independent QKD(RFI-MDI-QKD)protocol can effectively solve the problem of side-channel attacks on measurement devices and slow drifts of the reference frame.Subsequently,researchers proposed the improved RFI-QKD and RFI-MDI-QKD protocols to enhance the performance of the RFI type QKD protocols.This thesis focuses on the influence of RFI type(RFI-QKD and RFI-MDI-QKD)systems.The main work is as follows:(1)The influence of the afterpulse effect on two RFI-QKD systems was investigated.In most RFI-QKD systems,the afterpulse inherent in single-photon avalanche detectors at the receiver’s side is always ignored,which will lead to a large deviation from the data obtained by the existing analytical models.Therefore,it is necessary to establish an afterpulse-compatible analytical model to fix this deviation.Simulation results show that the secret key rate is overestimated when the afterpulse is ignored.Furthermore,based on the afterpulse-compatible model,the impact of the intensity fluctuation of the source at the transmitter’s side was investigated.Simulation results show that both the afterpulse and the intensity fluctuation have an impact on system performance,which should be carefully considered in practical RFI-QKD systems.(2)The influence of the afterpulse effect on two RFI-MDI-QKD systems was investigated.By analyzing the afterpulse effect of single-photon avalanche detectors,an afterpulse compatible model was established for RFI-MDI-QKD system.In particular,as the system frequency increases,the afterpulse effect will be further aggravate.Based on this afterpulse-compatible analysis model,a numerical analysis was conducted on practical RFI-MDI-QKD systems.Simulation results show that the secret key rate is overestimated when afterpulse is ignored,and as the afterpulse increases,the secret key rate is further overestimated.Therefore,the existence of afterpulse cannot be ignored in practical systems.