Research On Quantum Key Distribution Protocol With Passive Light Source Monitoring

The security of quantum key distribution(QKD)is based on the laws of quantum physics and information theory,supported by theoretical proofs in several ways over the past decades.Contrary to theory,practical QKD applications can lead to safety risks in QKD systems due to unsafe measurement equipment and non-trusted signal sources.With the high development of QKD,the measurement device-independent quantum key distribution protocol(MDI-QKD)proposed by Lo et al.can perfectly solve the security leakage at the detection side and reduce the requirement of measurement devices in the QKD system.However,it cannot solve the problem of untrustworthy light sources,and when the QKD system is flawed in its light sources,there is a risk that the coded state information can be accessed by the eavesdropper Eve without being detected by legitimate users.For resolving the problem of unreliable light sources,this paper proposes a passive light source monitoring scheme to improve the light source resistance of the decoy state QKD system,which can effectively avoid the modulation error problem of the active light source monitoring scheme,and the main research results are as follows:1.To solve the light source unreliability problem,this paper proposes a passive light source monitoring(PLSM)scheme,which mainly consists of a beam splitter(BS)and two single-photon detectors.In this paper,the PLSM module is placed at the local side to monitor the photon number distribution of the signal light in real time,and the bounds of the light source distribution can be accurately estimated by the four different response events measured by the two single photon detectors.In this paper,the BB84 protocol is used as an example for simulation analysis,and the global optimization as well as the three-intensity decoy state method are used for model construction and parameter optimization under the condition of considering the finite length effect,and then the actual safety performance of the QKD system is improved.The theoretical simulation results show that this scheme can improve the performance of the QKD system compared with the original BB84 protocol when considering the fluctuation of the light source distribution,and the performance advantage becomes more obvious as the fluctuation of the light source distribution increases.2.In this paper,a BB84-QKD system with passive light source monitoring function is built to verify relevant theories.A narrow-line-width pulsed wave laser with a repetition frequency of 20 MHz and a central wavelength of 1550 nm is used at the sending end.In the experiment,a variable attenuator is used to modulate signal light into different intensities to obtain different decoy states and signal light.Meanwhile,Mach-Zehnder interference ring is used for phase encoding.Signal light pulses of different intensities are decoded by the corresponding Mach-Zehnder interference ring after passing through the quantum channel.Finally,a single photon superconducting detector is connected for detection.The idle light is monitored in real time by the PLSM module.Finally,combined with the strict statistical fluctuation analysis,the quantum key distribution experiment is realized respectively at the transmission distance of 75 km and 150 km.The key rate at 75 km is and the key rate at 150 km is,and the measured results are basically consistent with the theoretical simulation results.3.In this paper,the PLSM module is extended to the reference system independent quantum key distribution protocol(RFI-QKD)and the send-or-go-no-send two-field quantum key distribution protocol(SNS-TFQKD).The simulation results show that the PLSM-RFIQKD scheme outperforms the original RFI-QKD protocol in the presence of high pulses and light source fluctuations.In addition,the PLSM-RFIQKD scheme has a significant advantage over the original RFI-QKD protocol in terms of security key rate in the case of non-ideal light sources and the presence of deviation angles.For example,the maximum transmission distance of the original protocol decreases by 35 km when the light source distribution undulation size σ increases by 0.01,while the corresponding PLSMRFIQKD scheme can almost maintain the original performance,indicating that the protocol has better robustness in the presence of fluctuating light sources.Further,this paper proposes the SNS-TFQKD protocol with passive monitoring module and compares it with the corresponding active light source monitoring protocol and the original protocol.The simulation results show that the PLSM SNSTFQKD scheme outperforms the corresponding active light source monitoring scheme and the original protocol without light source monitoring module in the presence of both modulation errors and light source fluctuations.