Research On Twin-field Quantum Key Distribution Protocol Based On Non-ideal Light Source

Based on the fundamental principles of quantum mechanics,quantum cryptography(QC)enables legitimate users Alice and Bob to a secure key in the case of Eve eavesdropping.Its security has been rigorously demonstrated and QC has been a practical quantum technique.Photon is a common information carrier in the process of quantum cryptography,resulting in the key-rate bound,called PLOB bound,existing in the quantum cryptography due to the loss of channel noise during the distribution.However,the twin-field quantum key distribution(TF-QKD)protocol has broken through the PLOB bound without quantum relays and both the phase-matching quantum key distribution(PM-QKD)protocol and the simple of twin-field quantum key distribution(Simple-TFQKD)protocol are the variants of the TF-QKD protocol.The TF-QKD protocol and its derivative protocols have become one of the hot topics in quantum cryptography.We study the PM-QKD protocol and Simple-TF-QKD protocol in this paper.The main works are the following:(1)In order to solve the problem of non-ideal light source in PM-QKD protocol,we propose a PM-QKD protocol based on light source monitoring(LSM),which is called PM-QKD-LSM protocol.By adding a light source detection device to the non-ideal light source,the upper and lower bounds of the photon number probability distribution of the non-ideal light source can be estimated accurately,and the key rate of the PM-QKD-LSM protocol can be derived from the upper and lower bounds.The key rate of the protocol is analyzed when the light intensity is fluctuated,the transmission channel is symmetric or the transmission channel is asymmetric.The numerical results show that the PM-QKDLSM protocol has similar key rate with PM-QKD protocol under the ideal light source,and the maximum transmission distance is 504 km(non-ideal)and 507 km(ideal),respectively.When the communication distance is more than 212 km,the key rate of PM-QKD-LSM protocol will exceed the PLOB bound.The intensity fluctuation has little effect on the performance of PM-QKD-LSM protocol,and the key rate of PM-QKD-LSM protocol is not affected by the non-ideal light source when the quantum cryptography system is asymmetric.(2)In order to ensure the implementation of Simple-TF-QKD protocol in the case of actual light source,we study the Simple-TF-QKD protocol with light source error.In Simple-TF-QKD protocol,the local phase randomization and pre-selected global phase(0 or π)are used to avoid the postselection of phase in general TF-QKD protocol to match the global phase of Alice and Bob,then the quantum key rate is effectively increased by an order of magnitude.Considering the asymmetry of both channels and the errors of light source(such as light source intensity fluctuation),we analyze the influence of light source intensity fluctuation and dark count on the performance of Simple-TFQKD protocol.The simulation results show that the small fluctuation of the light source intensity will cause a large decrease of key rate.When the fluctuation rate reaches a certain value,the key rate will reach a certain limit,and the key rate will not decrease greatly.At the same time,when the dark count rate is high,the key rate of the protocol will decrease.