A measurement device-independent quantum dialogue method based on entanglement swapping

Abstract

The present invention belongs to the field of quantum communication technology and discloses a measurement device-independent quantum dialogue method based on entanglement exchange, in which user B first loads the information to be transmitted into an entangled photon pair through phase encoding. Users A and B establish a long-distance entangled channel through two Bell state measurements at one end of the detection party. User A then performs phase encoding to load the information to be transmitted into its own photon. Both parties then send the photons in their hands to the detection party for a third Bell state measurement. Based on the results of the three Bell state measurements and their respective operations, the two parties can decode the information transmitted by the other party and complete the dialogue. The present invention can effectively resist all attacks from the measurement end and ensure the security of quantum dialogue under the actual conditions of imperfect detection equipment. The present invention uses all linear optical devices, which can be implemented under current experimental conditions and can effectively promote the practical application of MDI-QD.

Description

Technical Field

[0001] The present invention belongs to the technical field of quantum communication, and in particular relates to a measurement device-independent quantum dialogue method based on entanglement exchange. Background Art

[0002] The purpose of quantum secure communication is to protect information security. Quantum secure communication can detect eavesdropping and is absolutely secure. Quantum secure direct communication (QSDC) is an important branch of quantum secure communication. QSDC can transmit secret information directly through quantum channels, and the communicating parties do not need to share a key in advance. QSDC was first proposed by Professor Long Guilu of Tsinghua University in 2000. In 2003, Long Guilu, Liu Xiaoshu, Deng Fuguo and others clarified the definition and construction principles of QSDC, and proposed a two-step QSDC scheme based on EPR entangled photon pairs with a more complete structural meaning. In 2004, Deng Fuguo and Long Guilu proposed a single-photon-based QSDC scheme (DL04 scheme), clarified its physical mechanism and gave the conditions that QSDC needs to meet. The two typical schemes in the early stage gave the construction principles and security criteria of quantum secure direct communication, laying a solid theoretical foundation for the further development of QSDC.

[0003] In recent years, QSDC has made significant progress both experimentally and theoretically. In 2016, Xiao Liantuan and others from Shanxi University implemented the DL04 scheme using frequency coding experiments. In June 2017, the University of Science and Technology of China and Nanjing University of Posts and Telecommunications collaborated to experimentally implement a two-step entanglement-based QSDC scheme for the first time using quantum storage. In November 2017, Tsinghua University and Nanjing University of Posts and Telecommunications collaborated to experimentally implement long-distance QSDC in optical fiber for the first time. In 2019 and 2020, the research teams of Long Guilu and Sheng Yubo first proposed device-independent (DI) and measurement-device-independent (MDI) QSDC schemes.

[0004] In 2004, Nguyen and others from the Korea Advanced Institute proposed the first QSDC scheme that can achieve two-way communication, named the quantum dialogue (QD) scheme. In 2008, Gao Feng and others discovered that from the perspective of information theory and cryptography, the above-mentioned quantum dialogue scheme would cause half of the information to be leaked due to the public discussion of the measurement results, and there is a vulnerability of "secret information leakage". In order to eliminate the information leakage vulnerability, Arpita and Maitra proposed the MDI-QD scheme in 2017, which combines the BB84 protocol to perform quantum key distribution first. In 2020, Das et al. proposed two MDI-QD protocols with different encoding methods. In 2021, Basak et al. proposed a reference frame-independent MDI-QD protocol. However, the above-mentioned MDI-QD schemes all added a quantum key distribution (QKD) step before the dialogue, and this pre-quantum key distribution step is not independent of the measurement device, so there are still vulnerabilities. Summary of the Invention

[0005] Like QKD and QSDC, quantum dialogue is subject to attacks from the detector side. Furthermore, early quantum dialogues suffered from secret leakage issues due to inherent protocol flaws. To protect against detector-side attacks while enabling quantum dialogue, this paper proposes a measurement-device-independent quantum dialogue method based on entanglement swapping. This method enables bidirectional quantum secure communication between two communicators, resisting all attacks from the detector side while eliminating the "secret leakage" vulnerability.

[0006] The measurement device-independent quantum dialogue method based on entanglement exchange described in the present invention comprises the following steps:

[0007] Step 1: User A and User B prepare entangled photon pairs respectively, where User A prepares 2n pairs in the same entangled state |ψ + > photon pairs, user B prepares n pairs in the same entangled state |ψ + > photon pairs;

[0008] Step 2: User B pairs n pairs of + >Phase encoding operation of photons U MB , encode the information to be transmitted onto the entangled photon pair;

[0009] Step 3: User A takes out one photon from each of the n pairs of entangled photons he prepared and forms S in sequence T sequence, the remaining photons form S in sequence A Sequence: Take one photon from each of the other n pairs of entangled photons and form S in sequence T 'sequence, the remaining photons form S in sequence A 'Sequence; User A in S T and S T 'M single photons randomly prepared in X-based or Z-based conditions are randomly inserted into the sequence. After the single photons are inserted, S T and S T 'The sequence becomes P with n+m photons respectively T and P T 'sequence; User B takes out one photon from each of the n pairs of entangled photons he prepared and forms S in sequence B sequence, the remaining n photons form S in sequence B ' sequence, then Bob in S B and S B 'M single photons randomly prepared in X-based or Z-based conditions are randomly inserted into the sequence. After the single photons are inserted, S B and S B 'The sequence becomes P with n+m photons each B and PB 'sequence;

[0010] Step 4: User A and User B will P T Sequence and P B The sequence of photons is sent to the detector C through the quantum channel, and the detector C receives P T and P B After the photons of the sequence are detected, Bell state measurement (BSM) is performed on each photon pair and the measurement results are announced;

[0011] Step 5: User A and User B disclose P through the classical channel T and P B The position and quantum state of single photons in the sequence are determined, and the BSM results are subjected to a first round of security checks. After the security check is completed, if the error rate is higher than the set threshold, the first round of photon transmission is considered unsafe and communication is terminated. If the error rate is lower than the set threshold, the next step is continued.

[0012] Step 6: User A and User B will P T 'Sequence and P B 'The sequence of photons is sent to the detector Charlie, who performs BSM on each photon pair and publishes the measurement results;

[0013] Step 7: User A and User B disclose P through the classical channel T ' and P B 'The position and quantum state of the single photon in the sequence; and perform a second round of security testing on the BSM results; after the second round of security testing is completed, if the error rate is higher than the set threshold, the second round of photon transmission is considered unsafe and communication is terminated; if the error rate is lower than the set threshold, proceed to the next step;

[0014] Step 8: User A uses the unitary operation U T S A and S A The entangled photon pairs formed in the sequence are converted into the quantum state encoded by Bob, and then user A transmits the information pair S according to the need. A The photons in the sequence perform operations encoding U MA ;

[0015] Step 9: User A in S A Q single photons randomly encoded in the X basis or Z basis are randomly inserted into the sequence. A q random single photons encoded in the X or Z basis are also inserted at the corresponding position of the sequence to form P A and P A 'Sequence; then user A puts P A and P AThe sequence is sent to the detection party C for Bell state measurement and the measurement results are announced;

[0016] Step 10: User A publishes P A and P A 'Safety check of the position of single photon pairs in the sequence; User A uses the measurement results of single photon pairs for safety check. If the bit error rate is higher than the set threshold, communication is terminated. If the bit error rate is lower than the set threshold, the third round of photon transmission is confirmed to be safe and the next step is carried out.

[0017] Step 11: For the coded photon pair in step 8, user A infers the quantum photon state after encoding by user B based on the results of three rounds of BSM and its own encoding operation, thereby obtaining the encoding information of user B; user B infers the encoding operation of user A based on the results of three rounds of BSM and its own encoding operation in step 2, thereby obtaining the encoding of user A, and the quantum dialogue is completed.

[0018] Furthermore, in step 1, both dialogue participants user A and user B are prepared to be in the maximum entangled state |ψ + > entangled photon pairs, user A prepares 2n pairs all in |ψ + >, user B prepares n pairs of entangled photons all in |ψ + > entangled photon pairs; where |ψ + > belongs to the following four polarization Bell states:

[0019]

[0020]

[0021] H and V represent the horizontal and vertical polarization of the photon, respectively.

[0022] Furthermore, in step 5, if the two photons undergoing BSM are both single photons and have the same preparation basis, user A and user B perform the first round of security checks based on the BSM results and the quantum state of the photons. If the preparation basis of the two single photons is different, the BSM result is discarded; if the two photons undergoing BSM are both derived from entangled photon pairs, then their security in S A and P B 'The corresponding photons in the sequence are entangled through entanglement exchange; if the two photons undergoing BSM are one single photon and the other comes from an entangled photon pair, then the BSM result and S A or P B 'The remaining photons in the sequence are discarded.

[0023] Further, in step 7, if both photons for BSM are single photons and have the same preparation basis, user A and user B perform a second round of security detection based on the BSM result and the quantum state of the photons. If the preparation bases of the two single photons are different, the BSM result is discarded; if both photons for BSM are from an entangled photon pair, their corresponding photons in the S A and S A ’ sequences establish entanglement through entanglement swapping; if one of the two photons for BSM is a single photon and the other is from an entangled photon pair, the BSM result and the remaining photons in the S A or S A ’ sequences are all discarded.

[0024] Further, the single photons used in steps 3, step 5 and step 9 are randomly prepared in the Z basis and the X basis, and the Z basis and the X basis are respectively represented as

[0025] Z = {|H>, |V>};

[0026]

[0027] Therefore, the single photon is any one of the four quantum states |H>, |V>, |+>, |->.

[0028] Further, in steps 2 and step 8, both parties in the conversation use the phase encoding method to load information onto the entangled photon pair, and their encoding operations U MA and U MB both include two unitary operations {I, σ z}; I = |H><H| + |V><V| (identity operation) represents the classical information 0, and σ z = |H><H| - |V><V| (phase flip operation) represents the classical information 1.

[0029] Further, the BSM used in steps 4, step 6 and step 9 is all based on linear optics and can only distinguish between the two Bell states |ψ + > and |ψ - >, and cannot distinguish between |φ + > and |φ - >;

[0030] During the three rounds of security detection, if both single photons are in the Z basis, that is, |H>|V> or |V>|H>, then if the photon pair is in |H>|H> or |V>|V>, then

[0031] when the measurement result of |H>|V> or |V>|H> shows |φ ±>, or the measurement result of |H>|H> or |V>|V> appears |ψ ± >, both parties can determine that an error has occurred; therefore, using BSM under linear optical conditions does not affect security;

[0032] If both single photons are X-based, i.e. |+>|+> and |+>|->, the theoretical result is:

[0033]

[0034]

[0035] In BSM, it is impossible to distinguish |φ ± >, it is possible that both parties will make misjudgments and affect security; therefore, in order to avoid misjudgments, if BSM obtains |ψ + > or |ψ - >, both parties use BSM results to perform security checks, if BSM obtains |φ ± >, both parties will discard the results of BSM;

[0036] If the two single photons have different bases, that is, |+>|H>, the theoretical measurement results are as follows:

[0037] In this case, it is impossible to determine whether an error has occurred based on the BSM results. Therefore, both parties will discard the BSM results in this case.

[0038] Furthermore, in step 8, user A chooses whether to apply a phase flip operation to S according to the results of the first two rounds of BSM. A and S A 'The corresponding entangled photon pair in the sequence is restored to the quantum state encoded by user B;

[0039] If the results of the first two BSMs are |ψ + >||ψ + > or |ψ - >||ψ - >, S A and S A The entangled photon state generated in the sequence is the same as the encoded quantum state of user B, and the unitary operation applied by user A is U T =I; if the results of the first two BSMs are |ψ + >||ψ - > or |ψ - >||ψ + >, S A and S A The entangled photon state generated in the sequence is opposite to the phase of the encoded quantum state of user B, and the unitary operation applied by user A is UT =σ Z .

[0040] Furthermore, in step 11, after the detection party C announces the Bell state measurement result of the entangled photon pair, user A knows the encoding operation U that he has performed. MA , inversely deduce the state of user B after encoding, and decode the encoding operation U performed by user B MB , thus knowing the information that user B wants to transmit; for user B, it knows the quantum state of user A before and after encoding, and can infer the encoding operation U of user A. MA , we know the information that user A wants to transmit, specifically:

[0041] User B transmits information 0, and user A transmits information 1: User B first executes U MB =I, after encoding we get |ψ + > bb' ; Assume that the results of the first two BSMs performed by the detection party C are |ψ + >||ψ - >, then user A has S in his hand A ,S A 'Sequence of entangled photons to perform operation U T =σ Z get Then, by A Sequence of photons applying operation U MA =σ z Encode to get User A sends the encoded photon pair to the detection party C for the third BSM. The detection party C announces the BSM result as |ψ - > aa' ; User A according to U MA =σ z It can be determined that the state after Bob's encoding is |ψ + > bb' , combined with the encoding rules, we can know that the information transmitted by user B is 0. Similarly, user B knows the state of user A before encoding, and knowing the state after encoding, we can infer that user A used U MA =σ z Encode and then know that the information transmitted by user A is 1.

[0042] Furthermore, the detecting party C may be dishonest and even be completely controlled by the eavesdropper E. In steps 4, 6, and 9, although the detecting party C or the eavesdropper E knows the results of the three rounds of BSM, since the detecting party C or the eavesdropper E does not know the encoding operation of user B, it cannot obtain the information transmitted between users A and B.

[0043] The beneficial effects described in the present invention are as follows: the method described in the present invention is expanded on the basis of the previous MDI-QSDC unidirectional communication, and the unidirectional communication of MDI-QSDC is expanded to bidirectional communication, which completely eliminates the problems of vulnerability of the measuring equipment to attack and "secret information leakage" in the original quantum dialogue scheme, and only two Bell states need to be identified during the measurement process, which can be achieved using the BSM under existing linear optical conditions; at the same time, the entangled state preparation, phase encoding operation and quantum memory involved in the present invention have been realized in existing experiments, so the present invention is feasible under existing experimental conditions, and promotes the practical application of MDI-QD. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] Figure 1 It is a communication flow diagram of the present invention;

[0045] Figure 2 It is a schematic diagram of the principle of the present invention. DETAILED DESCRIPTION

[0046] In order to make the contents of the present invention more clearly understood, the present invention is further described in detail below based on specific embodiments in conjunction with the accompanying drawings.

[0047] like Figure 1 and Figure 2 As shown, the present invention provides an entanglement-based measurement device-independent quantum dialogue solution, comprising the following steps:

[0048] The process of the present invention is analyzed below with reference to a specific example, where user A is Alice and user B is Bob;

[0049] First, as Figure 2 As shown in the small figure (1), Alice prepares 2n pairs of initial states |ψ + > at The entangled photon pairs (a1, t1), (a1', t1'), (a2, t2), (a2', t2')... (a n ,t n )、(a n ',t n '), Bob prepares n pairs of initial states |ψ + > bb, The photon pairs (b1,b1'),(b2,b2')...(b n ,b n '). Then Figure 2 As shown in the small figure (2), Bob sends the information to (b i ,b i ') to perform operation encoding, the encoding rules are After encoding (b i ,bi ') changes to one of the following two states: {|ψ + > bb ,,|ψ - > bb ,}.

[0050] like Figure 2 As shown in the small figure (3), Alice starts with n pairs of entangled photons (a i ,t i )(i=1,2,…,n) and take out t1,t2...t n These n photons form S in sequence T sequence, the remaining photons form S in sequence A sequence; from another n pairs of entangled photons (a i ',t i ')(i=1,2,…,n) take out t1',t2'...t n 'These n photons form S in sequence T 'sequence, the remaining photons form S in sequence A 'Sequence. Alice in S T and S T 'M random single photons encoded in the X basis or Z basis for security detection are randomly inserted into each sequence. After the single photon is inserted, S T and S T 'The sequence becomes P with n+m photons each T and P T 'sequence. Bob takes out one photon from each of the n pairs of entangled photons and forms S in sequence B sequence, the remaining n photons form S in sequence B ' sequence. Then Bob in S B and S B 'M random single photons encoded in X basis or Z basis for security detection are randomly inserted into each sequence. After the single photon is inserted, S B and S B 'The sequence becomes P with n+m photons each B and P B 'sequence.

[0051] like Figure 2 As shown in the small figure (4), Alice sets P T sequence, Bob will P B The sequence of photons is sent to the detector Charlie, who detects the photon pairs (t i ,b i )(i=1,2,3,…,n+m) perform Bell state measurement and publish the measurement results. Alice and Bob publish P through the classical channel T and PB The position and quantum state of a single photon in the sequence. Depending on the source of the photon, these measurements correspond to four scenarios:

[0052] (1) When t i and b i When all are single photons and the preparation base is the same, the corresponding measurement results will be used for safety testing;

[0053] (2) When t i and b i When both are single photons and the preparation bases are different, both parties discard the corresponding measurement results;

[0054] (3) When t i and b i When both are derived from entangled photon pairs, the two entangled photon pairs involved will produce entanglement exchange when measuring in Bell state, S A and P B 'The corresponding photons in the sequence establish a long-distance entangled channel;

[0055] (4) When t i and b i When one side is a single photon and the other side is an entangled photon, both sides discard the measurement results and S A or P B 'The corresponding photon in the sequence.

[0056] Since the BSM used in this scheme is based on linear optics, it can only distinguish |ψ + > and |ψ - >These two Bell states cannot distinguish |φ + > and |φ - >. Figure 2 As shown in the small figure (5), during the safety detection process, if both single photons are Z-based, such as |H>|V> or |V>|H>, then If the photon pair is in |H>|H> or |V>|V>, then Although BSM cannot distinguish |φ + > and |φ - >, but it is still possible to determine whether an error has occurred. For example, if the measurement result of |H>|V> or |V>|H> shows |φ ± >, or the measurement result of |H>|H> or |V>|V> appears |ψ ± >, both parties can determine whether an error has occurred. Therefore, using BSM under linear optical conditions does not affect safety.

[0057] If both single photons are X-based, such as |+>|+> and |+>|->, the theoretical result is:

[0058]

[0059]

[0060] In BSM, it is impossible to distinguish |φ ± >, it is possible that both parties will make misjudgments and affect security. Therefore, in order to avoid misjudgments, if BSM obtains |ψ + > or |ψ - >, both parties use BSM results to perform security checks, if BSM obtains |φ ± >, both parties will discard the results of BSM.

[0061] After the security check is completed, when the detected error rate exceeds the threshold, both parties consider the communication unsafe and terminate the communication; otherwise, they continue to communicate.

[0062] like Figure 2 As shown in the small figure (6), Alice sets P T 'Sequence, Bob will P B 'The sequence is sent to the detection party Charlie, Charlie responds to (t i ',b i ') performs Bell state measurement and announces the measurement result. After Charlie announces the measurement result, Alice and Bob publish P through the classical channel. T ' and P B 'The position and quantum state of single photons in the sequence are used for security detection. Figure 2 As shown in the small figure (7), the safety detection process is the same as above.

[0063] After the first BSM, S A and P B 'The corresponding photons in the sequence establish entanglement through entanglement exchange; after the second BSM, S A With S A 'The corresponding photons in the sequence are entangled through entanglement exchange, and Alice's new (a1, a1'), (a2, a2')... (a n ,a n ') The quantum state of the entangled pair can be transformed by a unitary operation U T ({I,σ z}) is converted into Bob's encoded form (b1,b1'),(b2,b2')...(b n ,b n ') quantum state. Which specific U T It is necessary to judge based on the results of the previous two Bell state measurements. Assume that Bob's second information bit is encoded as Then the two entanglement exchange processes are as follows:

[0064] In the first BSM,

[0065]

[0066] Because Charlie can only recognize |ψ + > and |ψ - >, so only the measurement results are kept and And their corresponding entanglement exchange results and

[0067] In the second BSM, there are two situations according to the result of the first BSM.

[0068] (1) The result of the first measurement is

[0069]

[0070] The result of the first measurement is

[0071]

[0072] After the above two entanglement exchanges, S A a2 photons and S in the sequence A The photon a2 in the sequence forms an entangled photon pair, and the state conversion operation U T The connection with the two Bell state measurement results is as follows:

[0073]

[0074]

[0075] like Figure 2 As shown in the small figure (8), the entangled photon pair (a i ,a i ') After completing the state conversion, Alice uses it according to the information she wants to transmit. Operations are encoded, such as Figure 2 As shown in the small figure (9), after the encoding is completed, Alice randomly A Insert q randomly prepared single photons into the sequence, and at the same time, A 'q randomly prepared single photons are also inserted at the same position of the sequence. After the single photons are inserted, S A and S A 'The sequence becomes P A and P A ' sequence. Then Figure 2 As shown in the small figure (10), Alice puts P Aand P A 'The sequence is sent to the detection party Charlie, such as Figure 2 As shown in the small figure (11), Charlie performs BSM and publishes the measurement results. Alice uses the measurement results of the single photon position to perform security analysis, calculates the bit error rate, and determines whether the channel is secure based on whether the bit error rate is higher than the threshold.

[0076] Under the premise of confirming the security of the channel, Alice and Bob can infer each other’s coding operations based on the measurement results published by Charlie. For example, Alice knows that she has T The encoding operation U performed by the entangled pair of operations MA , when the Bell state measurement result of the entangled pair is known, the quantum state of the photon corresponding to Bob’s encoding can be inferred, and then compared with the initial state to obtain Bob’s encoding operation, thereby obtaining the information Bob wants to transmit. For Bob, he knows the quantum state of his entangled pair after encoding, that is, the corresponding Alice has completed U T The quantum state of the entangled pair after the operation, when the Bell state measurement result of the entangled pair is known, the operation U used by Alice can be deduced. MA , thus knowing the information Alice wants to transmit, and the conversation is completed.

[0077] For example, if the information Bob needs to transmit is 0 and the information Alice needs to transmit is 1: Bob first executes U MB =I, after encoding we get Suppose Charlie executes BSM twice and the result is Then Alice applies U to the entangled pair (a2, a2') in her hand T =σ Z Perform phase flip to obtain Then through U MA =σ z Encode to get Charlie announced the third BSM results as follows: After that, Alice uses U MA =σ z It can be determined that Bob's encoded state is Combined with the encoding rules, we can know that Bob's transmission information is 0. Similarly, Bob knows the state before Alice's encoding, and knowing the state after encoding, we can infer that Alice used U MA =σ z Encode and then know that the information transmitted by Alice is 1.

[0078] The security of this scheme is guaranteed by three rounds of security checks. Furthermore, in this scheme, the testing party, Charlie, can be dishonest or even completely controlled by the eavesdropper (Eve). In steps 4, 6, and 9, although Charlie (Eve) knows the results of the three rounds of BSM, since Charlie (Eve) is unaware of Bob's encoding operations, he cannot obtain the information exchanged between Alice and Bob.

[0079] The above description is only a preferred embodiment of the present invention and is not intended to further limit the present invention. All equivalent changes made using the contents of the present invention description and drawings are within the scope of protection of the present invention.

Claims

1. A measurement device-independent quantum dialogue method based on entanglement exchange, characterized in that: The method steps are as follows: Step 1: User A and User B prepare entangled photon pairs respectively, where User A prepares 2n pairs in the same entangled state |ψ + > photon pairs, user B prepares n pairs in the same entangled state |ψ + > photon pairs; Step 2: User B pairs n pairs of + >Phase encoding operation of photons U MB , encode the information to be transmitted onto the entangled photon pair; Step 3: User A takes out one photon from each of the n pairs of entangled photons he prepared and forms S in sequence T sequence, the remaining photons form S in sequence A Sequence: Take one photon from each of the other n pairs of entangled photons and form S in sequence T 'sequence, the remaining photons form S in sequence A 'Sequence; User A in S T and S T 'M single photons randomly prepared in X-based or Z-based conditions are randomly inserted into the sequence. After the single photons are inserted, S T and S T 'The sequence becomes P with n+m photons respectively T and P T 'sequence; User B takes out one photon from each of the n pairs of entangled photons he prepared and forms S in sequence B sequence, the remaining n photons form S in sequence B ' sequence, then Bob in S B and S B 'M single photons randomly prepared in X-based or Z-based conditions are randomly inserted into the sequence. After the single photons are inserted, S B and S B 'The sequence becomes P with n+m photons each B and P B 'sequence; Step 4: User A and User B will P T Sequence and P B The sequence of photons is sent to the detector C through the quantum channel, and the detector C receives P T and P B After the photons of the sequence are detected, Bell state measurement (BSM) is performed on each photon pair and the measurement results are announced; Step 5: User A and User B disclose P through the classical channel T and P B The position and quantum state of single photons in the sequence are determined, and the BSM results are subjected to a first round of security checks. After the security check is completed, if the error rate is higher than the set threshold, the first round of photon transmission is considered unsafe and communication is terminated. If the error rate is lower than the set threshold, the next step is continued. Step 6: User A and User B will P T 'Sequence and P B 'The sequence of photons is sent to the detector Charlie, who performs BSM on each photon pair and publishes the measurement results; Step 7: User A and User B disclose P through the classical channel T ' and P B 'The position and quantum state of the single photon in the sequence; and perform a second round of security testing on the BSM results; after the second round of security testing is completed, if the error rate is higher than the set threshold, the second round of photon transmission is considered unsafe and communication is terminated; if the error rate is lower than the set threshold, proceed to the next step; Step 8: User A uses the unitary operation U T S A and S A The entangled photon pairs formed in the sequence are converted into the quantum state encoded by Bob, and then user A transmits the information pair S according to the need. A The photons in the sequence perform operations encoding U MA ; Step 9: User A in S A Q single photons randomly encoded in the X basis or Z basis are randomly inserted into the sequence. A q random single photons encoded in the X or Z basis are also inserted at the corresponding position of the sequence to form P A and P A 'Sequence; then user A puts P A and P A The sequence is sent to the detection party C for Bell state measurement and the measurement results are announced; Step 10: User A publishes P A and P A 'Safety check of the position of single photon pairs in the sequence; User A uses the measurement results of single photon pairs for safety check. If the bit error rate is higher than the set threshold, communication is terminated. If the bit error rate is lower than the set threshold, the third round of photon transmission is confirmed to be safe and the next step is carried out. Step 11: For the coded photon pair in step 8, user A infers the quantum photon state after encoding by user B based on the results of three rounds of BSM and its own encoding operation, thereby obtaining the encoded information of user B; user B infers the encoding operation of user A based on the results of three rounds of BSM and its own encoding operation in step 2, thereby knowing the information that user A wants to transmit, and the quantum dialogue is completed.

2. The measurement device-independent quantum dialogue method based on entanglement exchange according to claim 1, characterized in that: In step 1, both dialogue participants user A and user B are prepared to be in the maximum entangled state |ψ + > entangled photon pairs, user A prepares 2n pairs all in |ψ + >, user B prepares n pairs of entangled photons all in |ψ + > entangled photon pairs; where |ψ + > belongs to the following four polarization Bell states: H and V represent the horizontal and vertical polarization of the photon, respectively.

3. The measurement device-independent quantum dialogue method based on entanglement exchange according to claim 1, characterized in that: In step 5, if the two photons undergoing BSM are both single photons and have the same preparation basis, user A and user B perform the first round of security checks based on the BSM results and the quantum state of the photons. If the preparation basis of the two single photons is different, the BSM result is discarded; if the two photons undergoing BSM are both derived from entangled photon pairs, then their security in S A and P B 'The corresponding photons in the sequence are entangled through entanglement exchange; if the two photons undergoing BSM are one single photon and the other comes from an entangled photon pair, then the BSM result and S A or P B 'The remaining photons in the sequence are discarded.

4. The measurement device-independent quantum dialogue method based on entanglement exchange according to claim 1, characterized in that: In step 7, if the two photons undergoing BSM are both single photons and have the same preparation basis, user A and user B perform a second round of security checks based on the BSM results and the quantum state of the photons. If the preparation basis of the two single photons is different, the BSM result is discarded; if the two photons undergoing BSM are both derived from entangled photon pairs, then their S A and S A 'The corresponding photons in the sequence are entangled through entanglement exchange; if the two photons undergoing BSM are one single photon and the other comes from an entangled photon pair, then the BSM result and S A or S A 'The remaining photons in the sequence are discarded.

5. The measurement device-independent quantum dialogue method based on entanglement exchange according to claim 1, characterized in that: The single photons used in steps 3, 5, and 9 are randomly prepared in the Z-basis and X-basis, which are represented by Z={|H>,|V>}; Therefore, a single photon is any one of the four quantum states |H>, |V>, |+>, |->.

6. The measurement device-independent quantum dialogue method based on entanglement exchange according to claim 1, characterized in that: In the said Step 2 and Step 8, both parties in the conversation adopt the phase encoding method to load information onto the entangled photon pairs, and the encoding operations U MA and U MB both contain two unitary operations {I, σ z}; I = |H><H| + |V><V| represents the classical information 0, and σ z = |H><H| - |V><V| represents the classical information 1.

7. The measurement device-independent quantum dialogue method based on entanglement exchange according to claim 1, characterized in that: The BSM used in steps 4, 6, and 9 is based on linear optics and can only distinguish |ψ + > and |ψ - >These two Bell states cannot distinguish |φ + > and |φ - > During the three rounds of safety testing, if both single photons are Z-based, i.e., |H>|V> or |V>|H>, then If the photon pair is in |H>|H> or |V>|V>, then When the measurement result of |H>|V> or |V>|H> appears |φ ± >, or the measurement result of |H>|H> or |V>|V> appears |ψ ± >, both parties can determine that an error has occurred; therefore, using BSM under linear optical conditions does not affect security; If both single photons are X-based, i.e. |+>|+> and |+>|->, the theoretical result is: In BSM, it is impossible to distinguish |φ ± >, it is possible that both parties will make misjudgments and affect security; therefore, in order to avoid misjudgments, if BSM obtains |ψ + > or |ψ - >, both parties use BSM results to perform security checks, if BSM obtains |φ ± >, both parties will discard the results of BSM; If the two single photons have different bases, that is, |+>|H>, the theoretical measurement results are as follows: In this case, it is impossible to determine whether an error has occurred based on the BSM results. Therefore, both parties will discard the BSM results in this case.

8. The measurement device-independent quantum dialogue method based on entanglement exchange according to claim 1, characterized in that: In step 8, user A chooses whether to apply a phase flip operation to S according to the results of the first two rounds of BSM. A and S A 'The corresponding entangled photon pair in the sequence is restored to the quantum state encoded by user B; If the results of the first two BSMs are |ψ + >|ψ + > or |ψ - >|ψ - >, S A and S A The entangled photon state generated in the sequence is the same as the encoded quantum state of user B, and the unitary operation applied by user A is U T =I; if the results of the first two BSMs are |ψ + >|ψ - > or |ψ - >|ψ + >, S A and S A The entangled photon state generated in the sequence is opposite to the phase of the encoded quantum state of user B, and the unitary operation applied by user A is U T =σ Z .

9. The measurement device-independent quantum dialogue method based on entanglement exchange according to claim 1, characterized in that: In step 11, after the detection party C announces the Bell state measurement result of the entangled photon pair, user A knows the encoding operation U that he has performed. MA , inversely deduce the state of user B after encoding, and decode the encoding operation U performed by user B MB , thus knowing the information that user B wants to transmit; for user B, it knows the quantum state of user A before and after encoding, and can infer the encoding operation U of user A. MA , we know the information that user A wants to transmit, specifically: User B transmits information 0, and user A transmits information 1: User B first executes U MB =I, after encoding we get |ψ + > bb' ; Assume that the results of the first two BSMs performed by the detection party C are |ψ + >|ψ - >, then user A has S in his hand A ,S A 'Sequence of entangled photons to perform operation U T =σ Z get , and then by S A Sequence of photons applying operation U MA =σ z Encode to get User A sends the encoded photon pair to the detector C for the third BSM, and the detector C announces the BSM result as |ψ - > aa' ; User A according to U MA =σ z It can be determined that the state after Bob's encoding is |ψ + > bb' , combined with the encoding rules, we can know that the information transmitted by user B is 0. Similarly, user B knows the state of user A before encoding, and knowing the state after encoding, we can infer that user A used U MA =σ z Encode and then know that the information transmitted by user A is 1.

10. The measurement device-independent quantum dialogue method based on entanglement exchange according to claim 1, characterized in that: When the detecting party C is dishonest or even completely controlled by the eavesdropper E, in steps 4, 6 and 9, although the detecting party C or the eavesdropper E knows the results of the three rounds of BSM, since the detecting party C or the eavesdropper E does not know the encoding operation of user B, it cannot obtain the information transmitted to each other by user A and user B.

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