Practical Security Analysis Of Twin-field Quantum Key Distribution

With the development of science and technology,secure communication is beconing increasingly important.Modern cryptography ensures the secure transmission of information based on the complexity of eomputations.However,the emergence of quantum algorithms and the research of quantum computers pose a serious threat to the security of modern cryptography.Using quantum physics,researchers have proposed a quantum key distribution whose security is based on quantum mechanics rather than computational complexity.The quantum key distribution thus has information-theoretic security that is provable.Combining it with the one-time pad encryption method,legimate parties can perform secure communication.To improve the performance of quantum key distribution,researchers have proposed several types of quantum key distribution protocols.Among these protocols,the twin-field protocol is in the spotlight.The twin-field protocol uses single-photon interference to generate a secure key.Therefore,it can break the linear bound and has a longer communication distance than other protocols.Although the properties of the twin-field protocol have been verified by experiments,the research on the twin-field protocol is still incomplete,e.g.,how can the finite key analysis of the twin field protocol be improved?how can the post-processing process of the twin-field protocol be optimized?How can the finite-key effects of the twin-field protocol be analyzed with discrete phase randomization?Based on the research work in the PhD phase,this paper summarizes the practical security analysis of the twin-field protocol,which is briefly summarized as follows.1.An improved finite-key analysis of the twin-field protocol without phase postselection is proposed.With the aim of solving the problem that the computation of the information leakage of the original finite-key analysis is not dense,an improved operator inequality is proposed.By combining this new operator inequality with the concentration inequality,a tighter upper bound on the number of phase errors is calculated,which ensures a higher secure key rate of this protocol.Moreover,this improved inequality is applied to the finite-key analysis of the twin-field protocol without phase post-selection,which contains more decoy states.2.A finite-key analysis of the four-phase twin-field protocol is proposed.By combining the operator inequality with the entanglement-equivalent protocol,a tight upper bound on the number of phase errors is calculated.The secure key rate of the practical quantum key distribution system is calculated.The result shows that this protocol has the advantage of communication distance even in the case of finite-key.3.A finite-key analysis of the discrete-phase randomized twin-field protocol is proposed.In view of the problem that the coherent states in the protocol are in practice discrete-phase randomized instead of continuous-phase randomized,an analytical expression for the number of phase errors is derived using the entanglement-equivalent protocol.Also,a new lemma is proposed to derive the analytical expression for the upper bound on the number of phase errors.This analytical expression is used to calculate the secret key rate of this protocol in the case of eight discrete phases.The result shows that by this lemma a high secure key rate is given even in the case of a finite key.Moreover,this lemma is also applied to the finite key analysis of other protocols in the case of discrete phase randomization.4.An improved post-processing of the twin-field protocol is proposed.By using the advantage distillation method,an improved phase-matching protocol is proposed,which has a higher secure key rate and a longer communication distance than the original phase-matching protocol.Moreover,by combining the advantage distillation method with the Actively Odd-Parity Pairing(AOPP)method,the performance of sending or not sending twin-field protocol is immensely improved.