Research On Several Practical Problems In Quantum Networks

Information security has always been the focus of people's attention in all ages.With the development of society and the Internet,people have higher and higher requirements for information encryption,especially after the emergence of quantum communication and quantum computing,people's cognition of information security has reached a new height.In terms of quantum communication,quantum key distribution is an important encryption method of quantum communication system.Bennet and Brassard proposed the BB84 quantum key distribution protocol in 1984,whose unconditional security is guaranteed by quantum mechanics theory.After nearly 40 years of development,quantum key distribution has broken through the bottlenecks of imperfect equipment(such as decoy-state method,measurement device independent quantum key distribution protocol)and limited transmission distance(twin-field quantum key distribution protocol).In terms of quantum computing,blind quantum computation(BQC)complements and develops quantum computing,which is mainly used to solve the current situation of lack of quantum resources.However,the research on it is not perfect yet.This dissertation improves and supplements the practicability and security of the current quantum network based on the above contents,mainly including the following two aspects:1.Passive blind quantum computation with heralded single-photon sources.Blind quantum computing is mainly used to solve the problem of insufficient quantum computer resources.In this case,the client can deliver its quantum computation task to the server,and in this process,the client will not disclose its computation task and the calculation results.However,in most reported studies on decoy-state BQC,the source intensities are actively modulated,unfortunately,resulting in side-channel leakage and reducing system security.In this dissertation,we present a scheme on the passive decoy-state BQC,which circumvents this problem skillfully and improves the system security.In addition,the heralded single-photon source is used in this dissertation to solve the problem of a large proportion of vacuum pulses of the weak coherent source.Simulation results show that our present work can exceed those active schemes with the improvement of the detection efficiency of the local detectors.And it thus seems very a promising candidate in practical implementations of BQC in the near future.2.A passive light source monitoring scheme is proposed based on twin-field quantum key distribution.Untrusted source is always an important factor affecting the security of quantum key system,which results in the sender unknowing the photon number distribution of the light source.At present,the solution to this problem is to add a light source monitoring module.This method requires adjusting variable optical attenuators many times,which inevitably leads to adjustment errors,thus reducing the security of the system.Therefore,this dissertation proposes a passive light source monitoring scheme that can be applied to the twin-field protocol to solve the problem of untrusted light sources without changing the security of the original protocol.In this scheme,the passive setup is added into the twin-field protocol.Based on the different clicks of the local detectors,we use these events to carry out linear programming for the photon number distribution and then get the secure key rate.Through simulation,it is proved that the method proposed in this dissertation can show superior performance in terms of key generation rate and transmission distance.