| Quantum secure communication is an emerging interdisciplinary subject derived from the combination of quantum mechanics and information science.Its core is quantum key dis-tribution.Fundamentals of quantum mechanics enable hackers to be discovered immedi-ately by both communication parties once eavesdropping,thus unshackled by computational complexity assumptions.Although QKD has been proved to have unconditional security in theory,the non-ideality of actual physical devices makes security loopholes still exist in prac-tical QKD systems.Because of these security loopholes,eavesdroppers will launch various quantum attacks.The measurement-device-independent（MDI）QKD protocol can resist all quantum attacks initiated by eavesdroppers on the measurement setup,effectively enhancing the security of the QKD system,and at the same time improving the protocol’s bit rate and safe transmission distance.In addition,the unique structure of the MDI-QKD system makes it very suitable for building a star network.It is expected to become a key technology for building a quantum secure communication network in the future.In recent years,quantum secure communication technology has been gradually moving from theory and experiment to commercialization.The realization of the high code rate and the long-distance quantum key distribution is the key to the commercialization of quantum communication.At the same time,with the increasing demand for multi-party group communication such as video con-ferencing,multi-party key distribution technology becomes particularly important.In this paper,we focus on the multi-party MDI-QKD protocol based on the W-state.The main con-tributions are as follows:First,a pulse/vacuum coding scheme is proposed based on the deep learning of the existing coding methods of the MDI-QKD protocol.When this coding scheme is adopted,the exist-ing four-particle W-state analyzer can distinguish a set of W4 states∣W4,c（?）、∣W4,d（?）、∣W4,e（?）、∣W4,f（?）.And the identification probability of this group ofW4states reaches 0.25,then the total probability of successful recognition of the 16W4eigenstates is 0.0625.Compared with the one using a time-bin encoding scheme,the total probability of successful identification of the set ofW4states by the W-state analyzer is increased by a factor of seven.Second,a new four-party MDI-QKD protocol based on W-state using a pulse/vacuum coding scheme is proposed,which can realize key distribution among four legal users.In addition,it is not necessary to align the time instants when the four optical pulses reach the measure-ment end,which reduces the complexity of implementation.After analysis,the proposed protocol is unconditionally secure.The numerical analysis results show that,compared with the existing four-party MDI-QKD protocol,the proposed protocol has a higher key rate over longer distances.Third,the performance of the new four-party MDI-QKD protocol in the case of channel asymmetry and the quantum network scheme based on this protocol is studied.Aiming at the problem of channel asymmetry in the actual network environment,an improved proto-col is proposed.In this protocol,the measuring setup modulates the sending time of the synchronous optical pulse according to the arrival time difference of the synchronous opti-cal pulse,realizes the calibration of the synchronous optical pulse,and solves the problem that the clocks of the optical pulses arriving at the measuring end are not synchronized due to channel asymmetry.Numerical simulation analysis shows that the influence of channel asymmetry on the performance of the protocol can be reduced by optimizing the value of the probability of four communication users sending single-photon pulses in the Z basis.This paper proposes a quantum network scheme constructed by a new four-party MDI-QKD protocol based on W-state,which consists of quantum switches,four-particle W-state ana-lyzers,and legitimate communication users.Increases the number of users who concurrently distribute keys,and allows multiple groups of users to communicate at the same time.In ad-dition,an optimization scheme for further extending the network to a larger network is also proposed. |
