Improving Research On Continuous Variable Quantum Key Distribution Based On Optical Fiber Communication

Quantum cryptography is an important research branch of quantum information,which uses the physical principles of quantum mechanics—the Quantum Non-Cloning Theorem and Uncertainty Principle to realize the unconditional secure communication in theory.With the development of current Internet information,the importance of information security has become increasingly prominent,which makes quantum cryptography highly concerned by all parties and becomes a hot issue in the current society.Currently,there are two major types of quantum key distribution(QKD): Quantum key distribution based on discrete variables(DV)and quantum key distribution based on continuous variables(CV).Although the discrete variable technology based on the single-photon detection protocol has gradually matured over several decades,it has made great progress,but because of the great technical problems in the preparation and detection of single photon states.Meanwhile,the continuous variable quantum key distribution(CV-QKD)encodes information on the quadratures of the optical field,and the carrier of information is continuous variable.This solves the technical problem of the discrete variable protocol in single photon,which makes the continuous variable protocol become a more effective alternative.In this paper,we take the coherent state continuous variable quantum key distribution as the research point,which mainly includes three aspects:1.Improving the transmission distance of the CV-QKD with entanglement in the middle in the presence of device noise by using the optical parametric amplifier.In order to improve the secret key rate and transmission distance of system when the device is not ideal,we propose added the optical amplifier before the receiver end to amplify the signal state,and derived the expression of secret key rate under collective attacks with revers reconciliation.Simulation results based on practical system parameters demonstrate that using the optical amplifier can improve the maximal transmission distance with appropriate parameters.2.The effects of optical amplifier on phase noise of self-referenced continuous variable quantum key distribution protocol is analyzed.Due to the mismatching between the reference pulse and phase pulse,the self-referenced continuous variable quantum key distribution protocol will introduce some phase noise and reduce the performance of system.We propose add the optical amplifier at the Bob side,analyze the amplifier's effect on the phase noise in detail.Based on practical parameters demonstrate that amplifier can compensate the phase noise under the appropriate parameters,in terms of extend the maximum transmission distance effectively.3.Propose a scheme that combines quantum key distribution and private classical communication through continuous variables.To realize parallel transmission of quantum communication and classical communication,we propose to utilize the quadratures of coherent state to encode the classical bits and Gaussian random numbers,and realize the simultaneous transmission by a certain contract method.Through the security analysis of CV-QKD and BER of classical communication,simulation results show that under realistic parameters,this method can achieve the parallel transmission of the QKD and classical communication safely.