Design And Implementation Of New Quantum Cryptographic Schemes

For a century,with the emergence and rapid development of computer and Internet technology,secure communication has become an indispensable part of the current information society.At present,the security for our daily life communication is guaranteed by classical cryptography,whose security is based on the computational complexity of the algorithm.However,in recent years,with the rise of supercomputing technology and quantum computer,the ability to crack classical codes has been constantly improved,hence the current communication network is facing severe threats.At the same time,the need for more secure communication technologies is becoming more urgent and intense.Quantum communication,especially quantum cryptography,provides a new solution for secure communication.Unlike classical cryptography,quantum cryptography can provide unconditional security based on fundamental principles of quantum mechanics.Quantum key distribution,as a core research direction of quantum cryptography,allows to share real-time secure keys among users located at different positions,realizing the secure communication by combining with the one-time pad algorithm.Since the first quantum key distribution protocol(BB84 protocol)was proposed by Bennet and Brassard in 1984,quantum cryptography has been moving from theory to practical applications.However,its practical performances,such as security,key rate and transmission distance,are still limited by the practical conditions.In this dissertation,the main works during my doctoral study focused on improving the performance of practical quantum cryptography have been introduced,which can be divided into three parts as following:1.Design and realization of BB84 protocol-based quantum cryptography.Present decoy-state BB84 protocols mostly adopt three-intensity active decoy-state scheme based on weak coherent states.It contains a large proportion of vacuum state components in the weak coherent states,resulting in limited transmission distance,and the active decoy-state modulation may introduce additional sidechannel loopholes,further deteriorating the practical security.According to those shortcomings,a new passive decoy-state scheme based on the heralded single-photon sources was designed,and corresponding experimental demonstration was realized.Moreover,the passive decoy-state method was proposed to implement quantum digital signatures,and a proof-of-principle demonstration of passive decoy-state quantum digital signatures over 200 km was accomplished.2.Design new schemes of measurement-device-independent quantum key distributions.Since the measurement-device-independent quantum key distribution was proposed in 2012,most practical systems adopt the unbiased-basis-choice active decoy-state scheme.In this dissertation,the traditional three-intensity unbiased-basis-choice decoy-state scheme was improved to three-intensity biased-basis-choice scheme,and combined with collective constraint and joint estimation techniques,greatly increasing the key rates and the secure transmission distances.3.Design a new scheme of the twin-field quantum key distribution.Before the twin-field protocol was proposed,the key rate of the quantum key distribution system was linearly dependent on channel loss without quantum repeater.Twin-field protocol overcomes this rate-distance limit and turns the relation into square-root dependence,which is a major breakthrough in the development of quantum cryptography.Based on an original sending-or-not-sending twin-field quantum key distribution scheme,the modified coherent states was proposed to replace the weak coherent states as light sources,achieving substantially improved key rates and secure transmission distances.