Mechanism Research On Continuous-Variable Quantum Key Distribution Based On Quantum Catalysis

Quantum key distribution(QKD)belongs to one of the important branches of quantum cryptography and its unconditional security is rooted in the correctness of quantum theory.Generally speaking,QKD can be implemented by using two groups:discrete-variable(DV)QKD and continuous-variable(CV)QKD.Compared to the former,the latter makes the information encode in the quadratures of the light field,and the coherence detection is finally used to obtain the information.Compared with the DVQKD,additionally,the CVQKD protocol has prominent advantages such as high cipher rate,low-operating cost and easy compatibility with existing optical communication systems,so this protocol plays potential roles from practical values and application prospects.However,due to the limitation of practical technologies,the safe transmission distance of the CVQKD is far less than that of the DVQKD.Therefore,how to improve the performance of the whole continuous variable quantum key distribution system is becoming increasingly prominent,especially in terms of its safe transmission distance.To solve this problem,according to the mechanism differences of CVQKD systems,quantum catalytic operation is adopted in this thesis for in-depth study,and the following innovative achievements are obtained:(1)The multi-photon catalytic operation is proposed to improve the performance of Gaussian modulated(GM)CVQKD.Firstly,the physical essence of quantum catalytic operations is introduced,and then the equivalent operator form of quantum catalysis is derived by using the technique of integration within an ordered product.After discussing the success probability of quantum catalytic operations,the improvement effects of quantum catalysis on the GM CVQKD are theoretically analyzed,and compared to the GM CVQKD protocol with photon subtraction(PS).The results show that both zero-photon quantum catalysis(ZPQC)and single-photon quantum catalysis are used,so the problem of low secret key rates at a short distance can be solved for the PS-GM CVQKD scheme.In addition,compared to other photon catalytic operations,the GM CVQKD with the ZPQC has the best performance,followed by the case of single-photon quantum catalysis.(2)The ZPQC operation is proposed to improve the performance of self-reference GM CVQKD protocol.In order to improve the practicability of quantum catalysis,the ZPQC operation based on switch detector is designed and applied to the self-reference GM CVQKD system.The results show that under the same parameters,the proposed ZPQC self-reference GM CVQKD scheme is superior to the PS self-reference and original self-reference schemes in terms of secret key rate,transmission distance and tolerable excess noise.With the increase of the imperfection of the detector,the performance of both the proposed scheme and the original self-reference one decreases,but the proposed scheme can tolerate more detector imperfections.(3)The ZPQC based on switch detector is proposed for effectively improving the performance of the measurement-device-independent(MDI)GM CVQKD.Firstly,according to the Wigner function and the probability distribution function,it is pointed out that the ZPQC not only has a high probability of success,but also can maintain the Gaussian characteristics of the Wigner function.Then,the improvement effects of quantum catalysis on the performance of the MDI GM CVQKD are theoretically analyzed.The simulation results show that the usage of the ZPQC operation can make the MDI GM CVQKD system greater flexibility and stronger stability.Thus,the performances of the proposed MDI GM CVQKD with quantum catalysis is superior to the original MDI GM CVQKD and the PS MDI GM CVQKD.In particular,when considering the realistic detection situation,although the MDI GM CVQKD system is extremely sensitive to the imperfection of detectors,the applications of the ZPQC operation can further improve the robustness of the whole system.Finally,it is also found that the ZPQC self-reference GM CVQKD scheme in terms of transmission distance can be superior to the MDI GM CVQKD with quantum catalysis,because the transmission distance of the self-reference GM CVQKD scheme excessively depends on the reference pulse amplitudes.(4)The improved performance of the ZPQC-based discrete modulated(DM)CVQKD protocol is explored.Firstly,the main contribution of the ZPQC to the covariance matrix element of the DM CVQKD protocol is analyzed.Then,when given several different parameters,the effects of quantum catalysis on the performance of the DM CVQKD are discussed in detail.Simulation results show that,with the slow increase of modulation variance,the proposed quantum catalytic DM CVQKD scheme can further improve the transmission distance of the original DM CVQKD.In addition,with the decrease of tolerable excess noise,the improved performance of the proposed scheme becomes more and more obvious.Finally,compared with the GM CVQKD protocol,it is found that,without quantum catalytic operations,the DM CVQKD has obvious advantages over the GM one in terms of extending secure communication distance.The thesis contains 41 figures,2 tables,158 references...