CN114448621B

CN114448621B - A multi-party dual-field quantum key distribution protocol implementation method and system

Info

Publication number: CN114448621B
Application number: CN202210070718.2A
Authority: CN
Inventors: 朱畅华; 徐宁; 权东晓; 何先灯; 赵楠; 易运晖; 陈南
Original assignee: Xidian University
Current assignee: Xidian University
Priority date: 2022-01-21
Filing date: 2022-01-21
Publication date: 2024-04-23
Anticipated expiration: 2042-01-21
Also published as: CN114448621A

Abstract

The present invention belongs to the field of quantum information communication technology, and discloses a multi-party dual-field quantum key distribution protocol implementation method and system, uses a W state analyzer at a measurement end to perform W ₄ state measurement on a coded light pulse, and the input signal state will be projected to the W ₄ state. According to the response result of a single-photon detector in the W state analyzer, a group of W ₄ states is uniquely distinguished, and the communication user obtains the key through screening; the dual-field quantum key distribution protocol and the W state analyzer are combined to realize communication between four users, and when the detection response result announced by the untrusted measurement end is a valid detection response, any two of the four participants disclose their information bits, and the remaining two participants can obtain the key bits. The total probability of successful detection corresponding to the present invention is 6.25%, which is eight times higher than the existing W state analyzer based on two-photon interference.

Description

Multi-party double-field quantum key distribution protocol implementation method and system

Technical Field

The invention belongs to the technical field of quantum information communication, and particularly relates to a multiparty double-field quantum key distribution protocol realization method and system.

Background

At present, classical cryptography, which introduces mathematical theory, makes cryptography a discipline of rigorous and systematic. However, the security of classical cryptography is based on the computational complexity of mathematical problems, which only guarantee computational security for a period of time. With the increase of the computation level, if a quantum computer is implemented, the existing encryption algorithm based on the computation complexity will be overwhelming. Unlike classical cryptography, where security relies on mathematical computational complexity, the security of quantum cryptography relies on physical means, i.e. the key used for encryption theoretically has true randomness and can guarantee secure distribution of sufficiently long quantum keys. Quantum secret communication is based on quantum cryptography, and the security of the quantum secret communication is based on the physical law of quantum mechanics, rather than on mathematical computational complexity. Quantum Key Distribution (QKD) is the core of quantum secret communications, and is currently the most important and mainstream quantum communication technology. QKD is a key distribution method in which two parties of communication use a quantum state as a carrier of information and transmit the information through a quantum channel, thereby negotiating a key between the two parties of communication. The quantum state transmission in the QKD process is realized by means of encoding, transmission and measurement of photons, so that the key negotiation process of the QKD protocol mainly comprises the processes of emitting light pulses by a light source, encoding the light pulses, measuring the light pulses by a measuring end, publishing a measuring result, generating a key by a communication user and the like.

Quantum key distribution is the use of quantum mechanical properties to secure communications, which enable two parties to a communication to generate and share a random, secure key to encrypt and decrypt messages. QKD is theoretically unconditionally secure, allowing both parties in a long distance and legitimate communication to generate secure keys in the presence of eavesdropping. Since the first quantum key distribution protocol BB84 protocol was proposed in 1984, a number of particularly executable QKD protocols have been proposed, and various quantum secret communication system implementations based on the QKD protocols have been demonstrated and implemented. The measurement device independent quantum key distribution (MDI-QKD) protocol proposed in 2012 can resist all attacks against the probe side and can be implemented using prior art, the security of which has been proven and experimentally verified on a real network. However, QKD systems under lossy channels based on point-to-point unrepeatered also face a key rate-distance limitation, referred to as the key capacity (SERECT KEY CAPACITY, SKC) limitation of the quantum channel, and MDI-QKD and its previously proposed QKD protocols cannot break through SKC limitations, and thus communication transmission distances are relatively close. At present, a method for overcoming the limit of the SKC mainly uses quantum relay, but quantum relay is difficult to realize in the prior art. In 2018, the double field (TF) quantum key distribution protocol proposed by m.lucamaini et al effectively breaks through SKC limitations. The double-field quantum key distribution protocol effectively inherits the advantage that the MDI-QKD protocol can resist attacks against holes of measuring equipment, meanwhile, the characteristic of single photon interference is utilized, the coding distance far exceeding a common quantum key distribution scheme can be obtained, the coding rate far exceeding the common quantum key distribution scheme can be obtained theoretically, and a new direction is provided for remote and high-performance quantum key distribution. Whether a higher bit-rate and a longer transmission distance are available is an important indicator for evaluating the quality of a quantum key distribution protocol.

A series of QKD protocols, such as MDI-QKD protocol, two-field quantum key distribution protocol TF-QKD protocol, were originally proposed for two-party users. Until now, most of the theoretical research and experimental work of quantum communication has focused on two-party protocols, aiming at solving the security hole existing in the existing two-party protocols and increasing the distance of two legal users for quantum communication. Multi-party quantum communication protocols have been proposed in succession, and significant progress has been made in view of the fact that there may be multiple participants communicating in an actual communication scenario. Such as multi-party QKD based on cluster state as proposed by Zhiwei Sun et al in 2015, multi-party MDI-QKD based on W state as proposed by Zhu Changhua et al in 2015, QKD employing the new Bell state coding mode as proposed by Xiyuan Ma et al in 2021, etc. One key weakness of QKD protocols over the multi-party communication protocols that have been proposed so far is that the measurement device is assumed to be authentic, however, imperfections in the physical devices in actual QKD systems make many quantum hacking attacks, such as time-shift attacks, phase remapping attacks, etc., possible, which makes this assumption very unrealistic. The MDI-QKD protocol and the TF-QKD protocol can resist the attack possibly existing at the detector end, and the harsh requirements on trusted measuring equipment are eliminated.

In summary, the appropriate entanglement and its analyzer are another key factor in the design of a multi-party QKD protocol. The entanglement states which can be used for realizing the multiparty QKD protocol at present mainly comprise a GHZ state, a cluster state, a W state and the like, and the corresponding proposed analyzers comprise a GHZ state analyzer, a cluster state analyzer and a W state analyzer. The GHZ state is the maximum entanglement of three photons, but once one bit of them is detected, the other bits lose entanglement characteristics, with poor robustness; and the GHZ state analyzer is mainly limited to the case of three participants, and in the case of having more participants, the key generation rate may be reduced. The cluster state is the maximum entangled state of four photons, and although the entangled characteristic is not lost because a certain bit is detected, the robustness is strong, the existing cluster state analyzer is only applicable to a single photon and can not be applied to a weak coherent light source, and the application range is limited. The W state is not the maximum entanglement state of four photons, but does not interfere entanglement of other photons because a certain bit is detected, so that the W state has stronger robustness; and the W-state analyzer can be applied to the situation with more participants communicating, both to the scene of a single photon source and to the scene of a weak coherent light source. Therefore, in order to make the designed multiparty QKD protocol have a higher key rate, the usage scenario is wider, and it is sensible to select a W-state analyzer.

Through the above analysis, the problems and defects existing in the prior art are as follows: the communication transmission distance in the current multiparty quantum communication protocol is lower.

The difficulty of solving the problems and the defects is as follows: how to extend the two-field quantum key distribution protocol with a longer transmission distance in the two-party quantum key distribution protocol to the situation that a plurality of participants participate in communication, a proper entanglement state and a corresponding analyzer need to be found. How to combine the two-party double-field quantum key distribution protocol with the W-state analyzer and extend the two-party double-field quantum key distribution protocol to the multi-party double-field quantum key distribution protocol is a great difficulty, and under the condition that how to take the coding mode into consideration, the coded light pulse can be successfully measured by the W-state analyzer, and a unique group of W ₄ states are identified; how to obtain the key through screening needs to be considered, and which conditions are required to be met by the key obtained through screening; it is also necessary to consider whether the obtained key is secure.

The meaning of solving the problems and the defects is as follows: the two-field quantum key distribution protocol with a longer transmission distance in the current two-party quantum key distribution protocol is combined with the W-state analyzer with good performance, and the multi-party two-field quantum key distribution protocol implementation method is provided, so that the defect of lower communication transmission distance in the current multi-party quantum communication protocol is overcome, and the development of multi-party quantum communication and quantum networks is facilitated.

Disclosure of Invention

Aiming at the problems existing in the prior art, the invention provides a multipartite double-field quantum key distribution protocol realization method and a multipartite double-field quantum key distribution protocol realization system.

The invention is realized in such a way, a multipartite double-field quantum key distribution protocol realization method is realized, the multipartite double-field quantum key distribution protocol realization method is based on measuring light pulse by a measuring end, W ₄ state measurement is carried out on the coded light pulse by using a W state analyzer, the input signal state is projected to W ₄ state, a group of W ₄ states are uniquely distinguished according to the response result of a single photon detector in the W state analyzer, and a communication user obtains a key through screening; the two-field quantum key distribution protocol and the W-state analyzer are combined to realize communication among four users, when the detection response result published by the unreliable measuring end is effective detection response, any two of the four participants disclose own information bits, and the other two participants can obtain key bits.

The existing W-state analyzer is based on two-photon interference, and is further optimized, so that the W-state analyzer is applicable to single-photon interference at the same time, and the detection efficiency is improved; based on optimizing the W-state analyzer as single photon interference, the method for realizing multipartite (tetragonal) double-field quantum key distribution protocol is provided, and the transmission distance of multipartite communication is increased. The user screening to obtain the key needs to satisfy the condition simultaneously: the detection response result published by the unreliable measuring end is effective detection response; the four participant-encoded light pulses are all encoded at the encoding base Z.

Further, the multiparty double-field quantum key distribution protocol implementation method comprises the following steps:

firstly, constructing a multipartite double-field quantum key distribution system based on a W-state analyzer;

second, the light source emits light pulse

Thirdly, coding the light pulse emitted by the light source;

Fourthly, measuring coded light pulses by using an Emma at a measuring end and publishing a measuring result;

Fifthly, the communication user obtains the secret key through screening;

Sixthly, the communication user carries out parameter estimation on the secret key obtained by screening;

And seventh, the communication user carries out post-processing on the key.

Further, the first step includes: constructing a double-field quantum key distribution system comprising four legal communication user branches Bob, alice, charlie and David with the same structure and an untrusted measurement end Emma comprising a W-state analyzer; any one of the four communication users is a sender and a receiver of other users; the unreliable measuring end Emma comprises a W-state analyzer consisting of an interferometer group and four single photon detectors, wherein the W-state analyzer is provided with four input ends; each legal communication user branch comprises an ideal single photon source SPS, an intensity modulator IM connected with a random number generator RNG1 and a phase modulator PM connected with a random number generator RNG2 which are connected in sequence, wherein the intensity modulator IM and the phase modulator PM are connected with a random number generator RNG3 together; the four communication user branches with identical structures are connected to the four input ends of the W-state analyzer at the measuring end Emma through quantum channels.

Further, the second step includes: the single photon source SPS of each branch of Bob, alice, charlie and David continuously emits N optical pulses S_B＝{S_B1,S_B2,…,S_BN}、S_A＝{S_A1,S_A2,…,S_AN}、S_C＝{S_C1,S_C2,…,S_CN} and S _D＝{S_D1,S_D2,…,S_DN with random phases of theta _B、θ_A、θ_C and theta _D respectively according to a certain time interval tau, wherein N is more than 1024; s _Bi、S_Ai、S_Ci and S _Di represent the ith light pulse from the single photon source SPS of each of the branches Bob, alice, charlie and David, respectively, where i=1, 2, …, N.

Further, the third step includes:

(1) the optical pulses S _Bi、S_Ai、S_Ci and S _Di emitted by the ideal single photon source SPS of each user branch can execute corresponding coding operation according to the binary random number generated by the random number generator RNG3, the intensity modulator IM and the phase modulator PM judge whether the value of the binary random number generated by the random number generator RNG3 is 1, if 1, the optical pulses are coded under the coding base Z, and (2) otherwise, the optical pulses are coded under the coding base X, and (3);

(2) Encoding the light pulses at an encoding base Z: the intensity modulator IM judges whether the value of the binary random number generated by the random number generator RNG1 is 1, if the value is 1, the intensity modulator IM does not play a role equivalent to a passage, the light pulse passes through normally, otherwise, the intensity modulator IM modulates the intensity of the light pulse to 0; the random number generator RNG2 and the phase modulator PM do not play a role equivalent to a passage, and the light pulse modulated by the intensity modulator IM normally passes through;

(3) Encoding the light pulses at an encoding base X: the intensity modulator IM judges whether the value of the binary random number generated by the random number generator RNG1 is 1, if the value is 1, the intensity modulator IM does not play a role equivalent to a passage, the light pulse passes through normally, otherwise, the intensity modulator IM modulates the intensity of the light pulse to 0; the phase modulator PM modulates the light pulse modulated by the intensity modulator IM according to the binary random number generated by the random number generator RNG2, and judges whether the value of the binary random number generated by the random number generator RNG2 is 1 or not, if yes, the phase modulator PM modulates the light pulse by a phase pi, otherwise, the phase modulator PM modulates the light pulse by a phase 0;

(4) Finally, N light pulses emitted by the light source in each of Bob, alice, charlie and David branches are encoded under different encoding bases, so that N encoded light pulses are S′_B＝{S′_B1,S′_B2,…,S′_BN}、S′_A＝{S′_A1,S′_A2,…,S′_AN}、S′_C＝{S′_C1,S′_C2,…,S′_CN}, S '_D＝{S′_D1,S′_D2,…,S′_DN};S′_Bi、S′_Ai、S′_Ci, and S' _Di, respectively, to represent the i-th light pulse encoded in each of Bob, alice, charlie and David branches, where i=1, 2, …, N; each communication user branch transmits the encoded N optical pulses to the Emma of the measuring end through the quantum channel in sequence.

Further, the fourth step includes:

(1) The coded light pulses in each communication user branch sequentially pass through the quantum channel to reach the input end of the W-state analyzer; the coded light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di in each user branch are regarded as a group, and after single photon interference is carried out through a group of interferometers in the W-state analyzer, a group of detection responses are generated at four single photon detectors in the W-state analyzer, and N groups of detection responses are obtained altogether; each set of probe responses may be different, there may be M modes of probe response, M > 32, where 32 modes of probe response are valid; when the coded set of light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di has a probe response of any one of the 32 modes, the set of probe responses is considered a valid probe event;

(2) Emma publishes the results of N groups of detection responses through classical channels authenticated between communication users; users participating in communication publish coding base information and phase fragment information of N light pulses through classical channels respectively; the phase fragment information needs to be published, the Z base for generating the secret key does not need to be matched with the phase fragment information, and the X base needs to be matched with the phase fragment information;

The fifth step includes: when the detection response result of the group of light pulses published by the measurement end Emma is any one of detection responses of 32 modes, and the coded group of light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di are coded by adopting a coding base Z, original key bits can be successfully obtained among users participating in communication; wherein any two participants publish own information bits, and if the published information bits are 11, the rest two participants obtain keys by turning over the information bits of any one participant;

the sixth step includes: all communication users randomly extract a part of key bits from the obtained original key bit data to calculate gain and quantum bit error rate, and if the quantum bit error rate QBER is smaller than a threshold value, the rest quantum key bits serve as initial key bits, and a seventh step is executed; if the quantum bit error rate QBER is larger than the threshold value, an eavesdropper Eve possibly exists, the secret key is discarded, and the secret key distribution is finished;

the seventh step includes: after obtaining the screened initial key bits, all communication users execute error correction and confidentiality amplification on the screened initial key bits; and finally, generating an unconditional security key, and completing the execution of the one-time complete multiparty double-field quantum key distribution protocol.

Further, the measuring the coded light pulse by the measuring end Emma in the fourth step includes:

1) The coded light pulses in each communication user branch sequentially pass through the quantum channel to reach the input end of the W-state analyzer; the input end of the W-state analyzer is divided into four paths corresponding to the spatial modes b, a, c and d; the spatial modes b, a, c and d correspond to the four communication subscriber branches Bob, alice, charlie and David, respectively;

2) The coded light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di in each user leg are considered a group; assuming that the time when a group of light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di reach the spatial modes b, a, c and d of the input end of the W-state analyzer is t ₀, when the light pulses reach four single-photon detectors after single-photon interference by a group of interferometers, the situation that photons exist at all three times t ₀,t₁,t₂ can occur, wherein τ is the delay brought by the interferometers, t ₁＝t₀+τ,t₂＝t₁+τ;t₀,t₁,t₂ is the detection time corresponding to each single-photon detector, and the responses of the same detector at different detection times are regarded as different detection responses;

3) After a group of light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di simultaneously interfere by a group of interferometers in the W-state analyzer, a group of detection responses are generated at four single photon detectors in the W-state analyzer, and N groups of detection responses are obtained altogether; each set of probe responses may be different, there may be M modes of probe response, M > 32, where 32 modes of probe response are valid; a coded set of light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di is considered a valid detection event when its detection response is any one of the 32 modes of detection response.

It is a further object of the present invention to provide a computer device comprising a memory and a processor, the memory storing a computer program which, when executed by the processor, causes the processor to perform the steps of the multiparty two-field quantum key distribution protocol implementation method.

Another object of the present invention is to provide a multiparty two-field quantum key distribution protocol implementation system for implementing the multiparty two-field quantum key distribution protocol implementation method, the multiparty two-field quantum key distribution protocol implementation system comprising:

the system construction module is used for constructing a multipartite double-field quantum key distribution system based on a W-state analyzer;

the optical pulse coding module is used for realizing the optical pulse emitted by the light source and coding the optical pulse emitted by the light source;

The measuring result publishing module is used for measuring the coded light pulse by the measuring end Emma and publishing the measuring result;

the key processing module is used for generating a key by a communication user; the communication user carries out parameter estimation on the key obtained by screening: the communication user performs key post-processing.

Another object of the present invention is to provide a quantum information communication application of the multiparty double-field quantum key distribution protocol implementation method.

By combining all the technical schemes, the invention has the advantages and positive effects that: the invention provides a multiparty double-field quantum key distribution protocol implementation method based on a W-state analyzer, which can realize communication among four participants and is used for solving the problem that more than two participants communicate in an actual communication scene, and meanwhile, the invention can realize communication at a longer distance under a plurality of participants communication scenes.

The core of the invention is based on measuring the light pulse by the measuring end, the W ₄ state measurement is carried out on the coded light pulse by using the W state analyzer, the input signal state can be projected to the W ₄ state, and a group of W ₄ states can be uniquely distinguished according to the response result of the single photon detector in the W state analyzer, so that a communication user can obtain a key through screening. The steps of the protocol of the present invention mainly include four phases: encoding the light pulse emitted by the light source, measuring the light pulse by the measuring end, publishing the measuring result, screening the generated key and performing post-treatment. The invention combines the two-field quantum key distribution protocol with the W-state analyzer, can realize the communication among four users, after the untrusted measuring end publishes the detection response result of the light pulse, four participants obtain the key through screening, and under the condition that the screening condition is satisfied, any two of the four participants disclose own information bits, and the other two participants can obtain the key bits. The invention solves the problem of lower communication transmission distance in the multiparty quantum communication protocol, and compared with other multiparty quantum communication protocols, the multiparty quantum communication protocol has longer transmission distance under the condition of ensuring the security of the secret key, thereby greatly improving the transmission distance of quantum communication.

The invention discloses a key distribution realization process of a multipartite double-field quantum key distribution protocol based on a W-state analyzer. Conceptually, tetragonal TF-QKD can be thought of as a W ₄ -state protocol implementation based on a time reversal. In this protocol, each of the four users can prepare an entangled EPR photon pair, reserve one photon of each photon pair, and send the other photon to the measurement end. The state of the photon is projected and measured by the measuring end, and if the state is projected to the W ₄ state by the measuring end, the states of the remaining four photons in the hand of the user are also projected to the same W ₄ state.

The invention improves the original W-state analyzer based on time-bin coding and two-photon interference, so that the original W-state analyzer limited to two-photon interference is simultaneously applicable to single-photon interference. Meanwhile, a double-field quantum key distribution protocol is used for an improved W-state analyzer, and a square double-field quantum key distribution protocol is provided.

Compared with the prior art, the invention has the following advantages:

The invention improves the W-state analyzer based on time-bin coding and two-photon interference, so that the W-state analyzer is simultaneously suitable for single-photon interference, and the probability of successful detection of a measuring end is greatly improved. The W state analyzer proposed in the paper of W-state Analyzer and Multi-party Measurement-device-INDEPENDENT QUANTUM KEY DISTRIBUTION published by Zhu Changhua et al in month 2015 12 is based on time-bin coding and two-photon interference, and finally four W ₄ states can be successfully detected and identified after passing through the analyzer, and the total probability of the corresponding detection success is 0.78%. The coding mode of the W-state analyzer is based on phase coding, four W ₄ states can be successfully detected after the W-state analyzer passes through the analyzer, the total probability of the corresponding detection success is 6.25%, and compared with the existing W-state analyzer based on two-photon interference, the detection success probability is improved by eight times.

Compared with other multiparty quantum communication protocols, the invention greatly improves the transmission distance of quantum communication. The invention distributes TF-QKD protocol based on four-way double-field quantum key of W-state analyzer, which greatly increases the transmission distance of quantum communication. From the first quantum communication protocol BB84 protocol to the later-implemented measuring device-independent quantum key distribution (MDI-QKD) protocol, the quantum communication field has made a great breakthrough. However, neither the BB84 protocol nor the MDI-QKD protocol breaks through the SKC limit, and the communication transmission distance is limited. For the TF class QKD protocol, the measuring equipment is irrelevant, and the method can resist the attack of all detector ends like the MDI-QKD protocol, and meanwhile, the distance from a communication user to the measuring end is half of that in the BB84 protocol. And the carrier used by the TF-class QKD protocol to encode key information is a |01> or |10> photon pair, where 0 represents a vacuum state and 1 represents a single photon. The vacuum state is not affected by channel attenuation, and the measuring end can measure an effective event as long as the single photon pulse emitted by the communication user is received by the measuring end. Unlike the MDI-QKD protocol, the information carrier used to encode the key is a single photon pair, in which a measurement end cannot detect a valid event as long as one photon is absorbed by the channel. Therefore, the TF DKD protocol has the greatest advantages of breaking through the limit of SKC and greatly improving the communication transmission distance.

The invention provides the TF-QKD protocol based on the W-state analyzer by means of the advantages of the TF-QKD protocol, compared with the W-state-based multiparty measurement device independent quantum key distribution (MDI-QKD) protocol and other multiparty quantum key distribution protocols which are proposed in Zhu Changhua and the like, the advantages that the MDI-QKD protocol can resist attacks of all detector ends and the advantages that the TF-QKD protocol can break through the SKC limit are reserved, and the transmission distance of quantum communication is greatly improved.

Drawings

Fig. 1 is a flowchart of a method for implementing a multiparty double-field quantum key distribution protocol according to an embodiment of the present invention.

Fig. 2 is a schematic structural diagram of a multiparty two-field quantum key distribution protocol implementation system according to an embodiment of the present invention.

Fig. 3 is a flowchart of an implementation method of the multiparty double-field quantum key distribution protocol according to an embodiment of the present invention.

Fig. 4 is a basic schematic diagram of a two-field quantum key distribution system based on a W-state analyzer according to an embodiment of the present invention.

Fig. 5 is a schematic diagram of a W-state analyzer according to an embodiment of the present invention.

Fig. 6 is a diagram of a temporal and spatial pattern before a single photon detector in a W-state analyzer according to an embodiment of the present invention.

Fig. 7 is a phase slice provided in an embodiment of the present invention.

Fig. 8 is a schematic diagram of comparison of a multiparty measurement device independent quantum key distribution protocol and a multiparty double-field quantum key distribution protocol key rate with distance change based on a W-state analyzer according to an embodiment of the present invention.

In the figure: 1. a system construction module; 2. an optical pulse coding module; 3. a measurement result publishing module; 4. and a key processing module.

Detailed Description

The present invention will be described in further detail with reference to the following examples in order to make the objects, technical solutions and advantages of the present invention more apparent. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.

Aiming at the problems existing in the prior art, the invention provides a multiparty double-field quantum key distribution protocol realization method and a multiparty double-field quantum key distribution protocol realization system, and the invention is described in detail below with reference to the accompanying drawings.

As shown in fig. 1, the implementation method of the multiparty double-field quantum key distribution protocol provided by the invention comprises the following steps:

s101: constructing a multipartite double-field quantum key distribution system based on a W-state analyzer;

S102: the light source emits light pulses, and the light pulses emitted by the light source are encoded;

s103: measuring the coded light pulse by using an Emma at a measuring end and publishing a measuring result;

S104: generating a secret key by a communication user; the communication user carries out parameter estimation on the key obtained by screening: the communication user performs key post-processing.

The method for realizing the multipartite double-field quantum key distribution protocol provided by the invention comprises the following steps:

(1) Constructing a multipartite double-field quantum key distribution system based on a W-state analyzer:

Constructing a double-field quantum key distribution system comprising four legal communication user branches Bob, alice, charlie and David with the same structure and an untrusted measurement end Emma comprising a W-state analyzer; any one of the four communication users is a sender and a receiver of other users; the unreliable measuring end Emma comprises a W-state analyzer consisting of an interferometer group and four single photon detectors, wherein the W-state analyzer is provided with four input ends; each legal communication user branch comprises an ideal single photon source SPS, an intensity modulator IM connected with a random number generator RNG1 and a phase modulator PM connected with a random number generator RNG2 which are connected in sequence, wherein the intensity modulator IM and the phase modulator PM are connected with a random number generator RNG3 together; the four communication user branches with the identical structures are connected to four input ends of the W-state analyzer at the measuring end Emma through quantum channels;

(2) The light source emits light pulses

The single photon source SPS of each branch of Bob, alice, charlie and David continuously emits N optical pulses S_B＝{S_B1,S_B2,…,S_BN}、S_A＝{S_A1,S_A2,…,S_AN}、S_C＝{S_C1,S_C2,…,S_CN} and S _D＝{S_D1,S_D2,…,S_DN with random phases of theta _B、θ_A、θ_C and theta _D respectively according to a certain time interval tau, wherein N is more than 1024; s _Bi、S_Ai、S_Ci and S _Di represent the ith light pulse from the single photon source SPS of each of the branches Bob, alice, charlie and David, respectively, where i=1, 2, …, N;

(3) Encoding the light pulses emitted by the light source:

(3a) The optical pulses S _Bi、S_Ai、S_Ci and S _Di sent by the ideal single photon source SPS of each user branch can execute corresponding coding operation according to the binary random number generated by the random number generator RNG3, the intensity modulator IM and the phase modulator PM judge whether the value of the binary random number generated by the random number generator RNG3 is 1, if 1, the optical pulses are coded under the coding base Z, the operation is executed (3 b), otherwise, the optical pulses are coded under the coding base X, and the operation is executed (3 c);

(3b) Encoding the light pulses at an encoding base Z: the intensity modulator IM judges whether the value of the binary random number generated by the random number generator RNG1 is 1, if the value is 1, the intensity modulator IM does not play a role equivalent to a passage, the light pulse passes through normally, otherwise, the intensity modulator IM modulates the intensity of the light pulse to 0; the random number generator RNG2 and the phase modulator PM do not play a role equivalent to a passage, and the light pulse modulated by the intensity modulator IM normally passes through;

(3c) Encoding the light pulses at an encoding base X: the intensity modulator IM judges whether the value of the binary random number generated by the random number generator RNG1 is 1, if the value is 1, the intensity modulator IM does not play a role equivalent to a passage, the light pulse passes through normally, otherwise, the intensity modulator IM modulates the intensity of the light pulse to 0; the phase modulator PM modulates the light pulse modulated by the intensity modulator IM according to the binary random number generated by the random number generator RNG2, and judges whether the value of the binary random number generated by the random number generator RNG2 is 1 or not, if yes, the phase modulator PM modulates the light pulse by a phase pi, otherwise, the phase modulator PM modulates the light pulse by a phase 0;

(3d) Finally, N light pulses emitted by the light source in each of Bob, alice, charlie and David branches are encoded under different encoding bases, so that N encoded light pulses are S′_B＝{S′_B1,S′_B2,…,S′_BN}、S′_A＝{S′_A1,S′_A2,…,S′_AN}、S′_C＝{S′_C1,S′_C2,…,S′_CN}, S '_D＝{S′_D1,S′_D2,…,S′_DN};S′_Bi、S′_Ai、S′_Ci, and S' _Di, respectively, to represent the i-th light pulse encoded in each of Bob, alice, charlie and David branches, where i=1, 2, …, N; each communication user branch sequentially transmits the encoded N optical pulses to a measuring end Emma through a quantum channel;

(4) The measuring end Emma measures the coded light pulse and publishes the measuring result:

(4a) The coded light pulses in each communication user branch sequentially pass through the quantum channel to reach the input end of the W-state analyzer; the coded light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di in each user branch are regarded as a group, and after single photon interference is carried out through a group of interferometers in the W-state analyzer, a group of detection responses are generated at four single photon detectors in the W-state analyzer, and N groups of detection responses are obtained altogether; each set of probe responses may be different, there may be M modes of probe response, M > 32, where 32 modes of probe response are valid; when the coded set of light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di has a probe response of any one of the 32 modes, the set of probe responses is considered a valid probe event;

(4b) Emma publishes the results of N groups of detection responses through classical channels authenticated between communication users; users participating in communication publish coding base information and phase fragment information of N light pulses through classical channels respectively; the phase fragment information needs to be published, the Z base for generating the secret key does not need to be matched with the phase fragment information, and the X base needs to be matched with the phase fragment information;

(5) The communication user generates a key:

When the detection response result of the group of light pulses published by the measurement end Emma is any one of detection responses of 32 modes, and the coded group of light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di are coded by adopting a coding base Z, original key bits can be successfully obtained among users participating in communication; wherein any two participants publish own information bits, and if the published information bits are 11, the rest two participants can obtain keys by turning over the information bits of any one participant;

(6) The communication user carries out parameter estimation on the key obtained by screening:

All communication users randomly extract a part of key bits from the obtained original key bit data to calculate gain and quantum bit error rate, and if the quantum bit error rate QBER is smaller than a threshold value, the rest quantum key bits serve as initial key bits, and the step (7) is executed; if the quantum bit error rate QBER is larger than the threshold value, an eavesdropper Eve possibly exists, the secret key is discarded, and the secret key distribution is finished;

(7) Communication user post-processes the key:

After successfully obtaining the screened initial key bits, all communication users execute error correction and confidentiality amplification on the screened initial key bits; and finally, generating an unconditional security key, and completing the execution of the one-time complete multiparty double-field quantum key distribution protocol.

Other steps may be adopted by those skilled in the art to implement the multiparty double-field quantum key distribution protocol implementation method provided by the present invention, and the multiparty double-field quantum key distribution protocol implementation method provided by the present invention of fig. 1 is merely a specific embodiment.

As shown in fig. 2, the multiparty double-field quantum key distribution protocol implementation system provided by the present invention includes:

the system construction module 1 is used for constructing a multipartite double-field quantum key distribution system based on a W-state analyzer;

The optical pulse coding module 2 is used for realizing the optical pulse emitted by the light source and coding the optical pulse emitted by the light source;

the measurement result publishing module 3 is used for measuring the coded light pulse by the measurement end Emma and publishing the measurement result;

A key processing module 4, configured to generate a key by a communication user; the communication user carries out parameter estimation on the key obtained by screening: the communication user performs key post-processing.

The technical scheme of the invention is further described below with reference to the accompanying drawings.

Example 1

Quantum key distribution protocols occupy an important role in communication networks, and as research continues, TF-class QKD protocols that can break through SKC limitations have been proposed successively. However, the current research on TF QKD protocols is mostly based on the situation of two-party communication users, and the problem that the transmission distance of the existing multiparty quantum key distribution protocol is limited due to the fact that a plurality of participant communication scenes possibly exist in an actual communication scene is considered. The invention is based on the ideal single photon source and the W state of four quantum bits, namely W ₄ state, and can realize the communication between four users. The invention is beneficial to constructing the quantum network, is mainly applied to the application fields such as national defense, finance, government affairs, energy, business and the like with high safety requirements, and can fundamentally solve the problem of secret information transmission.

The invention relates to a method for realizing a multiparty double-field quantum key distribution protocol based on a W-state analyzer, which relates to four legal communication users Bob, alice, charlie and David and an untrusted measurement end Emma, and is shown in fig. 3 and 4, and comprises the following steps:

(1) Constructing a square double-field quantum key distribution system:

The implementation method of the multipartite double-field quantum key distribution protocol based on the W-state analyzer is implemented on the quantum key distribution QKD system, and four communication users carry quantum key bit information in the optical pulses after coding in the respective optical branches, and one photon carries a key bit information. The key formed in the invention is a string of quantum key bit information strings, which is obtained by continuously emitting N light pulses through the system according to a certain time interval tau by light sources in respective branches of four communication users.

(2) The light source emits light pulses

The single photon source SPS of each branch of Bob, alice, charlie and David continuously emits N optical pulses S_B＝{S_B1,S_B2,…,S_BN}、S_A＝{S_A1,S_A2,…,S_AN}、S_C＝{S_C1,S_C2,…,S_CN} and S _D＝{S_D1,S_D2,…,S_DN with random phases of theta _B、θ_A、θ_C and theta _D respectively according to a certain time interval tau, wherein N is more than 24; s _Bi、S_Ai、S_Ci and S _Di represent the ith light pulse from the single photon source SPS of each of the branches Bob, alice, charlie and David, respectively, where i=1, 2, …, N;

(3) Encoding the light pulses emitted by the light source:

(3b) Encoding the light pulses at an encoding base Z: the intensity modulator IM judges whether the value of the binary random number generated by the random number generator RNG1 is 1, if the value is 1, the intensity modulator IM does not play a role equivalent to a passage, the light pulse normally passes through, the coded quantum state is |1 > to represent the information bit 1, otherwise, the intensity modulator IM modulates the intensity of the light pulse to 0, and the coded quantum state is |0> to represent the information bit 0; the random number generator RNG2 and the phase modulator PM do not play a role equivalent to a passage, and the light pulse modulated by the intensity modulator IM normally passes through;

(3c) Encoding the light pulses at an encoding base X: the intensity modulator IM judges whether the value of the binary random number generated by the random number generator RNG1 is 1, if the value is 1, the intensity modulator IM does not play a role equivalent to a passage, the light pulse passes through normally, otherwise, the intensity modulator IM modulates the intensity of the light pulse to 0; the phase modulator PM modulates the light pulse modulated by the intensity modulator IM according to the binary random number generated by the random number generator RNG2, and judges whether the value of the binary random number generated by the random number generator RNG2 is 1, if so, the phase modulator PM modulates the phase pi of the light pulse, and the coded quantum state is Representing information bit 1, otherwise the phase modulator PM modulates the optical pulse to phase 0, and the coded quantum state isRepresenting information bit 0;

(4a) The coded light pulses in each communication user branch sequentially pass through the quantum channel to reach the input end of the W-state analyzer, see fig. 4; the coded light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di in each user branch are considered as a group, and after single photon interference is performed by a group of interferometers in the W-state analyzer, a group of detection responses are generated at four single photon detectors in the W-state analyzer, and N groups of detection responses are obtained altogether, see fig. 5; each set of probe responses may be different, there may be M modes of probe response, M > 32, where 32 modes of probe response are valid, table 1; when the coded set of light pulses S '_Ai、S′_Bi、S′_Ci and S' _Di has a probe response of any one of 32 patterns, the set of probe responses is considered to be a valid probe event, meaning that a set of W ₄ states |w _4,c>、|W_4,d>、|W_4,e > and |w _4,f > can be uniquely identified;

TABLE 1

(4B) Emma publishes the results of N groups of detection responses through classical channels authenticated between communication users; users participating in communication publish coding base information and phase fragment information of N light pulses through classical channels respectively; the users participating in communication do not need to publish own random phases, and the random phases are divided into M parts with equal intervals by adopting a phase slicing method, which is shown in fig. 7The phase value falls in any slice randomly, and only the serial number of the phase slice is required to be published;

(5) The communication user generates a key:

When the following three conditions are satisfied at the same time, the key bits can be successfully obtained among the four communication users; wherein any two participants publish own information bits, and if the published information bits are 11, the rest two participants can obtain original key bits by turning over the information bits of any one participant, and the specific operation is shown in table 2;

TABLE 2

Condition 1: the detection response result of the group of light pulses published by the measuring end Emma is any one of detection responses of 32 modes;

Condition 2: the coded group of light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di are coded by a coding base Z;

The coded group of light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di generate a group of detection responses at a single photon detector after single photon interference is carried out by an interferometer in a W-state analyzer, four communication users generate quantum key bits, and Bob, alice, charlie and David screen all the generated quantum key bits to generate original quantum key bits;

(7) Communication user post-processes the key:

After successfully obtaining the screened initial key bits, all communication users perform error correction and confidentiality amplification on the screened initial key bits. Error correction is necessary because the keys ultimately established by the communicating parties are consistent. Confidentiality amplification is a very important step in the key post-processing by which the effect of an eavesdropper Eve, if present, on the key rate can be estimated; finally, generating an unconditional security key, and completing execution of a multi-party double-field quantum key distribution protocol with once complete key distribution;

The invention discloses a multipartite double-field quantum key distribution protocol based on a W-state analyzer, which is realized based on a W state of four-quantum bits, namely a W ₄ state, wherein the W ₄ state is shown as a formula (1), and 16W ₄ states are all obtained. Conceptually, tetragonal TF-QKD can be thought of as an implementation of a W ₄ -state protocol based on time-reversal, with each of the four users preparing an entangled EPR photon pair, retaining one photon of each photon pair, and sending the other photon to the measurement end. The state of the photon is projected and measured through the measuring end, if the state is projected to the W ₄ state through the measuring end, the states of the four remaining photons in the hand of the user are also projected to the same W ₄ state, and therefore four communication users can acquire key bits according to the W ₄ state in the hand.

The invention integrates the advantages of the prior multiparty quantum key distribution protocol, improves the prior multiparty quantum key distribution protocol, breaks through the SKC limit by utilizing the TF-QKD protocol, has the advantage of longer communication transmission distance, provides the multiparty double-field quantum key distribution TF-QKD protocol based on a W-state analyzer, and provides more possibility for multiparty quantum communication and development of a quantum network.

Example 2

The method for realizing the square double-field quantum key distribution protocol based on the W-state analyzer is the same as that of the embodiment 1, the measurement end Emma in the step (3) measures the coded light pulse, see fig. 5, 6 and table 1, and comprises the following contents:

(4a) The coded light pulses in each communication user branch sequentially pass through the quantum channel to reach the input end of the W-state analyzer; the input end of the W-state analyzer is divided into four paths corresponding to the spatial modes b, a, c and d; the spatial modes b, a, c and d correspond to the four communication subscriber branches Bob, alice, charlie and David, respectively;

(4b) The coded light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di in each user leg are considered a group; assuming that the times when a group of light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di reach the spatial modes b, a, c and D of the input end of the W-state analyzer are t ₀, when the light pulses reach four single-photon detectors after single-photon interference by a group of interferometers, the situation that photons exist at all three times t ₀,t₁,t₂ can occur, wherein τ is the delay brought by the interferometers, t ₁＝t₀+τ,t₂＝t₁+τ;t₀,t₁,t₂ is the detection time corresponding to each single-photon detector, the single-photon detectors D ₁、D₂、D₃ and D ₄ respectively correspond to the spatial modes S, u, v and W, see fig. 6, and the responses of the same detector at different detection times are regarded as different detection responses; for a specific meaning of the detection mode in table 1, see fig. 6, s ₀s₁u₁,s₀s₁ in table 1 indicates that the single-photon detector D ₁ generates detection responses at the spatial mode s at the detection times t ₀ and t ₁, and u ₁ indicates that the single-photon detector D ₂ generates detection responses at the spatial mode u at the detection time t ₁, respectively;

(4c) After a group of light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di simultaneously interfere by a group of interferometers in the W-state analyzer, a group of detection responses are generated at four single photon detectors in the W-state analyzer, and N groups of detection responses are obtained altogether; each set of probe responses may be different, there may be M modes of probe response, M > 32, where 32 modes of probe response are valid, see table 1; when the coded set of light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di has a probe response of any one of the 32 modes, the set of probe responses is considered a valid probe event;

The measurement of the existing W-state analyzer aims at time-bin coding and two-photon interference, and the invention is improved on the basis of the original W-state analyzer, so that the invention is simultaneously applicable to single-photon interference, and the probability of successful detection is improved from 0.78% to 6.25%.

Example 3

The implementation method of the square double-field quantum key distribution protocol based on the W-state analyzer is the same as that of the embodiment 1-2, and the two communication users in the step (4) screen the keys, and the method comprises the following steps:

When the detection response result of the group of light pulses published by the measurement end Emma is any one of the detection responses of 32 modes, and the coded group of light pulses S '_Bi、S′_Ai、S′_Ci and S' _Di are coded by adopting the coding base Z, the original key bits can be obtained between communication users. When any two of the participants publish their own information bits, if the published information bits are "11", the remaining two participants can obtain key bits by flipping the information bits of any one of the participants, and the specific operation is shown in table 2. For example, if Charlie and David publish that their own information bits are "11", either Alice or Bob in Alice or Bob toggles the information bits in their own hands to obtain the original key bits.

The technical effects of the present invention will be described in detail with reference to the test.

When the measurement end W-state analyzer is used for measuring based on two-photon interference and single-photon interference, the detection success rate is compared with that shown in Table 3:

TABLE 3 Table 3

	Two-photon interference	Single photon interference
			Probability of success of detection of W _4,c	0.0469	0.25
Probability of success of detection of W _4,d	0.0156	0.25
			Total probability of successful detection	0.78％	6.25％

The comparison diagram of the key rate of the multiparty measurement device independent quantum key distribution protocol and the multiparty double-field quantum key distribution protocol based on the W-state analyzer along with the distance is shown in fig. 8.

Fig. 8 is a simulation of two multiparty quantum key distribution protocols with all required parameters being the same, and it can be observed that the secure transmission distance of the multiparty measurement device independent quantum key distribution protocol (MDI-QKD) is about 220km, whereas the secure transmission distance of the multiparty double-field quantum key distribution protocol (TF-QKD) of the present invention can reach about 250 km.

It should be noted that the embodiments of the present invention can be realized in hardware, software, or a combination of software and hardware. The hardware portion may be implemented using dedicated logic; the software portions may be stored in a memory and executed by a suitable instruction execution system, such as a microprocessor or special purpose design hardware. Those of ordinary skill in the art will appreciate that the apparatus and methods described above may be implemented using computer executable instructions and/or embodied in processor control code, such as provided on a carrier medium such as a magnetic disk, CD or DVD-ROM, a programmable memory such as read only memory (firmware), or a data carrier such as an optical or electronic signal carrier. The device of the present invention and its modules may be implemented by hardware circuitry, such as very large scale integrated circuits or gate arrays, semiconductors such as logic chips, transistors, etc., or programmable hardware devices such as field programmable gate arrays, programmable logic devices, etc., as well as software executed by various types of processors, or by a combination of the above hardware circuitry and software, such as firmware.

The foregoing is merely illustrative of specific embodiments of the present invention, and the scope of the invention is not limited thereto, but any modifications, equivalents, improvements and alternatives falling within the spirit and principles of the present invention will be apparent to those skilled in the art within the scope of the present invention.

Claims

1. A multipartite double-field quantum key distribution protocol implementation method is characterized in that the multipartite double-field quantum key distribution protocol implementation method is based on a coding mode of a two-party double-field quantum key distribution protocol and measurement of light pulses by a W-state analyzer at a measurement end, and the W-state analyzer is used by the measurement end to carry out single-photon interference-based on the coded light pulsesThe state measurement, the input signal state is projected toA state uniquely separating a group according to the response result of the single photon detector in the W state analyzerIn a state, a communication user obtains a secret key through screening; combining the two-field quantum key distribution protocol with the W-state analyzer to realize communication among four users, when an unreliable measuring end publishes an effective detection response of the light pulse, any two of the four participants disclose own information bits, and the other two participants can obtain key bits;

The multipartite double-field quantum key distribution protocol implementation method comprises the following steps:

second, the light source emits light pulse

Thirdly, coding the light pulse emitted by the light source;

Fifthly, the communication user obtains the secret key through screening;

Seventh, the communication user carries out post-processing on the secret key;

The first step comprises: constructing a double-field quantum key distribution system comprising four legal communication user branches Bob, alice, charlie and David with the same structure and an untrusted measurement end Emma comprising a W-state analyzer; any one of the four communication users is a sender and a receiver of other users; the unreliable measuring end Emma comprises a W-state analyzer consisting of an interferometer group and four single photon detectors, wherein the W-state analyzer is provided with four input ends; each legal communication user branch comprises an ideal single photon source SPS, an intensity modulator IM connected with a random number generator RNG1 and a phase modulator PM connected with a random number generator RNG2 which are connected in sequence, wherein the intensity modulator IM and the phase modulator PM are connected with a random number generator RNG3 together; the four communication user branches with the identical structures are connected to four input ends of the W-state analyzer at the measuring end Emma through quantum channels;

the third step comprises:

(1) Light pulses emitted by an ideal single photon source SPS for each subscriber branch AndThe corresponding coding operation can be executed according to the binary random number generated by the random number generator RNG3, the intensity modulator IM and the phase modulator PM judge whether the value of the binary random number generated by the random number generator RNG3 is 1, if 1, the optical pulse is coded under the coding base Z, the coding operation is executed (2), otherwise, the optical pulse is coded under the coding base X, the coding operation is executed (3);

(3) Encoding the light pulses at an encoding base X: the intensity modulator IM judges whether the value of the binary random number generated by the random number generator RNG1 is 1, if the value is 1, the intensity modulator IM does not play a role equivalent to a passage, the light pulse passes through normally, otherwise, the intensity modulator IM modulates the intensity of the light pulse to 0; the phase modulator PM modulates the light pulse modulated by the intensity modulator IM according to the binary random number generated by the random number generator RNG2, and the phase modulator PM judges whether the value of the binary random number generated by the random number generator RNG2 is 1, if so, the phase modulator PM modulates the phase of the light pulse Otherwise, the phase modulator PM modulates the phase 0 of the optical pulse;

(4) Finally, N coded light pulses are obtained by coding N light pulses emitted by a light source in each branch of Bob, alice, charlie and David under different coding bases, wherein the N coded light pulses are respectively And；Representing the i-th light pulse encoded in each of the Bob, alice, charlie and David branches, whereEach communication user branch sequentially transmits the encoded N optical pulses to a measuring end Emma through a quantum channel;

the fourth step includes:

(1) The coded light pulses in each communication user branch sequentially pass through the quantum channel to reach the input end of the W-state analyzer; coded light pulses in each subscriber leg Regarding as a group, after single photon interference is carried out through a group of interferometers in the W-state analyzer, a group of detection responses are generated at four single photon detectors in the W-state analyzer, and N groups of detection responses are obtained altogether; each set of probe responses may be different, and there may beDetection response of seed pattern,Of which 32 modes of probe response are valid; when a set of coded light pulsesWhen the probe response of (a) is any one of the 32 modes of probe response, the set of probe responses is considered to be a valid probe event;

(2) Emma publishes the results of N groups of detection responses through classical channels authenticated between communication users; users participating in communication publish coding base information and phase fragment information of N light pulses through classical channels respectively;

the fifth step includes: when the detection response result of the group of light pulses published by the measurement end Emma is any one of the detection responses of 32 modes, a group of coded light pulses When the coding base Z is adopted for coding, the original key bits can be successfully obtained among users participating in communication; wherein any two participants publish own information bits, and if the published information bits are 11, the rest two participants obtain keys by turning over the information bits of any one participant;

2. The method for implementing the multiparty two-field quantum key distribution protocol according to claim 1, wherein the second step comprises: single photon source SPS of Bob, alice, charlie and David branches respectively according to a certain time intervalContinuously emitting N random phases respectively asIs of (1)AndWherein,The ith light pulse from the single photon source SPS of each leg Bob, alice, charlie and David are shown separately, where。

3. The method for implementing the multipartite double-field quantum key distribution protocol according to claim 1, wherein the measuring end Emma of the fourth step measures the coded light pulse, comprising:

2) Coded light pulses in each subscriber leg Considered as a group; assuming a set of light pulsesThe moment of arrival at the W-state analyzer input spatial modes b, a, c and d isWhen the four single photon detectors are reached after single photon interference by a group of interferometers, the/>, appearsThere may be photon cases at all three moments, whereTime delay for interferometer,,;The response of the same detector at different detection moments is regarded as different detection responses at the detection moments corresponding to each single photon detector;

3) A set of light pulses Meanwhile, after single photon interference is carried out by a group of interferometers in the W-state analyzer, a group of detection responses are generated at four single photon detectors in the W-state analyzer, and N groups of detection responses are obtained altogether; each set of probe responses may be different, and there may beDetection response of seed pattern,Of which 32 modes of probe response are valid; when a set of coded light pulsesWhen the probe response of (2) is any of the 32 modes of probe response, the set of probe responses is considered a valid probe event.

4. A computer device, characterized in that the computer device comprises a memory and a processor, the memory storing a computer program, which when executed by the processor causes the processor to execute the steps of the method for implementing a multiparty two-field quantum key distribution protocol according to any of claims 1-3.

5. A multiparty double-field quantum key distribution protocol implementation system implementing the multiparty double-field quantum key distribution protocol implementation method according to any one of claims 1-3, wherein the multiparty double-field quantum key distribution protocol implementation system comprises: