MDI-QSDC system and method based on orthogonal state coding

Abstract

The present application relates to quantum secure direct communication, in particular to a MDI-QSDC system and method based on orthogonal state encoding, a sending end Alice generates a first initial Bell state, performs a unitary encoding operation on the held quantum bits to realize classical information encoding, simultaneously generates and inserts a first decoy state, records the position and state of the first decoy state, and sends the quantum bit sequence to a measurement node Charlie; a receiving end Bob randomly selects one from two Bell states orthogonal to the first initial Bell state to prepare a second initial Bell state, simultaneously generates and inserts a second decoy state, records the position and state of the second decoy state, and sends the quantum bit sequence to the measurement node Charlie; the measurement node Charlie performs joint Bell base measurement on the quantum states from the sending end Alice and the receiving end Bob, and publicly announces the measurement results to both parties; the present application can effectively overcome the defects of high system complexity and high implementation difficulty, serious performance decline in a collective noise environment, and inherent information leakage in quantum dialogue.

Description

Technical Field

[0001] This invention relates to quantum-secure direct communication, specifically to an MDI-QSDC system and method based on orthogonal state coding. Background Technology

[0002] Quantum-secure direct communication (MDI-QSDC) is a cutting-edge technology that allows the direct transmission of secret messages without the need for pre-generated keys. To defend against defects in measurement devices and side-channel attacks, measurement-device-independent quantum secure direct communication (MDI-QSDC) has been proposed. Currently, almost all MDI-QSDC protocols and their derivatives rely on the BB84 subroutine for security. This subroutine requires both communicating parties to randomly prepare decoy states using two or more non-orthogonal basis vectors (such as computational basis {|0>,|1>} and superposition basis {|+>,|->}). The theoretical basis for its security is the Heisenberg uncertainty principle, which states that measuring a non-orthogonal quantum state inevitably introduces a detectable perturbation.

[0003] The main disadvantages of existing technical solutions include:

[0004] 1) The system is complex and difficult to implement: it is necessary to randomly switch and use multiple different measurement bases, which places extremely high demands on the stability and precise control of the quantum light source, modulator and detector;

[0005] 2) Severe performance degradation in collective noise environment: Traditional non-orthogonal decoy states (such as |+> and |->) are very sensitive to collective dephasing noise and collective rotation noise, which leads to a sharp decrease in channel fidelity and transmission efficiency. In strong noise environment, in order to maintain security, it is usually necessary to significantly increase the proportion of decoy states, further sacrificing communication efficiency.

[0006] 3) Inherent information leakage exists in quantum dialogue: In the standard quantum dialogue framework, the public disclosure of measurement results will leak some information about the product of the encoded operations of the two communicating parties (usually 2 bits of classical information), which constitutes an inherent security limitation.

[0007] This invention aims to break through the paradigm that requires the use of conjugate coding and provide an MDI-QSDC scheme that uses only a single basis vector (orthogonal state) for coding, fundamentally reducing system complexity and improving the practicality and robustness of the system by utilizing the decoherent free subspace characteristics of orthogonal states under specific noise conditions. Summary of the Invention

[0008] (a) Technical problems to be solved

[0009] In view of the above-mentioned shortcomings of the existing technology, the present invention provides an MDI-QSDC system and method based on orthogonal state coding, which can effectively overcome the defects of the existing technology, such as system complexity and high implementation difficulty, severe performance degradation in collective noise environment, and inherent information leakage in quantum dialogue.

[0010] (II) Technical Solution

[0011] To achieve the above objectives, the present invention provides the following technical solution:

[0012] An MDI-QSDC system based on orthogonal state coding includes Alice as the transmitter, Bob as the receiver, and Charlie as the measurement node;

[0013] Alice, the transmitter, generates the first initial Bell state, performs unitary encoding on the qubits it holds to encode classical information, generates and inserts the first decoy state, records the position and state of the first decoy state, and sends the qubit sequence carrying the classical information encoding and the first decoy state to the measurement node Charlie through the quantum channel.

[0014] The receiver Bob randomly selects one of two Bell states orthogonal to the first initial Bell state to prepare the second initial Bell state. At the same time, it generates and inserts the second decoy state, records the position and state of the second decoy state, and sends the qubit sequence carrying the second decoy state to the measurement node Charlie through the quantum channel.

[0015] The measurement node Charlie, considered untrusted, performs joint Belki measurements on the quantum states from the sender Alice and the receiver Bob, and then publicly announces the measurement results to both parties through a classical authentication channel, providing classical information support for the sender Alice and the receiver Bob to complete message decoding, key screening and security assessment.

[0016] Preferably, the transmitting end Alice includes a first Bell state preparation unit, a unitary coding operation unit, and a first decoy management unit;

[0017] The first Bell state preparation unit generates the first initial Bell state;

[0018] The unitary encoding operation unit performs four Pauli operations (I, X, iY, Z) on the held qubits to encode 2 bits of classical information;

[0019] The first decoy management unit generates and inserts the first decoy state, and records the position and state of the first decoy state.

[0020] Preferably, the receiving end Bob includes a second Bell state preparation unit and a second decoy management unit;

[0021] The second Bell state preparation unit randomly selects one of two Bell states orthogonal to the first initial Bell state to prepare the second initial Bell state;

[0022] The second decoy management unit generates and inserts the second decoy state, and records the position and state of the second decoy state.

[0023] Preferably, the measurement node Charlie includes a Bell state measurement device and a classical communication interface;

[0024] The Bell state measurement device uses linear optical elements and a single-photon detector to perform joint Bell basis measurements on quantum states from the transmitter Alice and the receiver Bob;

[0025] The classic communication interface publicly announces the measurement results to the sender Alice and the receiver Bob through the classic authentication channel.

[0026] An MDI-QSDC method based on orthogonal state coding includes the following steps:

[0027] S1. Quantum bit sequence preparation and decoy state insertion:

[0028] Alice, the transmitter, prepares multiple pairs of first initial Bell states |ψ⁺> 12 and the quantum bit sequence A M This will be used for subsequent secret message encoding, and the quantum bit sequence A will be stored in the quantum bit sequence. E Used for entanglement swapping, multiple first decoy states The sent particle d2 is randomly inserted into the quantum bit sequence A. E This forms an extended qubit sequence A' E ;

[0029] At the receiving end, Bob starts from two initial Bell states |ψ⁺> 12 Orthogonal Bell states |ψ⁺> 34 、|ψ⁻> 34 In the process, multiple pairs of second initial Bell states are prepared by randomly selecting one method, and the quantum bit sequence B is then used. M Reserved for subsequent secret message encoding, the quantum bit sequence B E Used for entanglement swapping, multiple second decoy states / The sent particle d4 is randomly inserted into the quantum bit sequence B. E This forms an extended qubit sequence B' E ;

[0030] S2, Initial Transmission and Entanglement Swap:

[0031] The transmitting end Alice will extend the qubit sequence A' EThe data is sent to the measurement node Charlie, and the receiving end Bob will extend the qubit sequence B'. E Send to the measurement node Charlie;

[0032] Measurement node Charlie pairs the data from the extended qubit sequence A' E Extended qubit sequence B' E A joint bel basis measurement is performed on each pair of quantum states in the sequence A, and the measurement results are published, thereby making the sequence A a record of the quantum bits. M With the quantum bit sequence B M Establish entanglement and exchange between them;

[0033] S3, Initial eavesdropping detection:

[0034] Alice, the transmitter, and Bob, the receiver, announce the positions and initial states of the transmitted particles d2 and d4.

[0035] When the measurement node Charlie measures the decoy pair (d2,d4), the transmitter Alice and the receiver Bob measure the local partner particle pair (d1,d3) to verify whether their correlation is consistent with the measurement results published by the measurement node Charlie and the predictions of quantum mechanics. Any deviation indicates the presence of eavesdropping.

[0036] S4. Message Encoding and Secondary Transmission:

[0037] After eavesdropping detection, the sending end Alice detected the qubit sequence A. M Perform unitary encoding to encode its secret message, resulting in the message encoding sequence A'. M The remaining sending particles d2 are randomly inserted into the message encoding sequence A'. M This forms an extended qubit sequence A'' M Send to the measurement node Charlie;

[0038] At the receiving end, Bob randomly inserts the remaining transmitting particle d4 into the qubit sequence B. M This forms an extended qubit sequence B' M Send to the measurement node Charlie;

[0039] S5. Secondary eavesdropping detection:

[0040] Measurement node Charlie pairs the data from the extended qubit sequence A'' M Extended qubit sequence B' M Each pair of quantum states in the process undergoes a joint Belli measurement, and the measurement results are published. In the absence of eavesdropping, the measurement results should perfectly match the statistical correspondence of the initial decoy states in accordance with the predictions of quantum mechanics. Any deviation indicates the presence of eavesdropping.

[0041] S6, Message Decoding:

[0042] Measurement node Charlie measures the data from message-encoded sequence A' M Quantum bit sequence B M Perform a joint Belli measurement on each pair of quantum states and publish the results;

[0043] Since only the receiver Bob knows the second initial Bell state it has chosen, and combined with the measurement results published by the measurement node Charlie, the Bell state shared with the sender Alice can be uniquely derived. Therefore, the receiver Bob can uniquely decode the unitary coding operation applied by the sender Alice based on the measurement results, thereby obtaining the secret message.

[0044] Preferably, for quantum dialogue, this method supports bidirectional communication:

[0045] The receiver Bob needs to first go through an MDI-QSDC process based on orthogonal state coding to securely inform the sender Alice of the selection of its second initial Bell state;

[0046] After this, both parties can simultaneously access the qubit sequence A. M Quantum bit sequence B M Each node encodes its own secret message. The final measurement result of the measurement node Charlie contains the secret messages encoded by both parties. The sending end Alice and the receiving end Bob can decode each other's secret messages based on their understanding of the shared Bell state.

[0047] (III) Beneficial Effects

[0048] Compared with the prior art, the MDI-QSDC system and method based on orthogonal state coding provided by the present invention has the following beneficial effects:

[0049] 1) A fundamental change in security nature: from being based on the Heisenberg uncertainty principle to being based on entanglement monopair, completely immune to all side-channel attacks on the measurement equipment;

[0050] 2) Significantly reduced system complexity and cost: Only a single bel base is needed, avoiding the introduction of complex and unstable multi-basis-switching devices, simplifying the system structure and improving system stability;

[0051] 3) Excellent performance in noisy environments: By selecting specific Bell states as decoy states, a decoherent free subspace can be constructed. Under collective noise channels, its fidelity and communication efficiency are significantly higher than those of the traditional BB84 scheme.

[0052] 4) Effectively solves the information leakage problem: In quantum dialogue applications, Bob at the receiving end randomly selects a second initial Bell state. Since Bob's selection of the second initial Bell state is secret, the eavesdropper cannot know the final shared Bell state. Therefore, the 2-bit information leakage inherent in the traditional quantum dialogue (QD) protocol can be reduced to 1 bit.

[0053] 5) Doubling of communication distance: Based on the entanglement switching characteristics, the effective secure communication distance can be doubled compared to point-to-point solutions without increasing the complexity of repeaters. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the accompanying drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without any creative effort.

[0055] Figure 1 This is a schematic diagram of the system of the present invention;

[0056] Figure 2 This is a schematic diagram of the process of the present invention. Detailed Implementation

[0057] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0058] The core of this invention lies in abandoning the traditional conjugate coding paradigm and using only a set of orthogonal states under a single Bell basis to simultaneously complete message encoding and eavesdropping detection. Its security foundation shifts from the Heisenberg uncertainty principle to the single-match property of quantum entanglement, and by carefully selecting Bell states with decoherent free subspace characteristics under specific collective noise as decoy states, it achieves excellent noise robustness.

[0059] The following describes the specific functional modules of the MDI-QSDC system based on orthogonal state coding provided by this invention, using concrete examples (such as...). Figure 1 (As shown) and its technical effects. The system functional modules include: Alice (sender), Bob (receiver), and Charlie (measurement node);

[0060] Alice, the transmitter, generates the first initial Bell state, performs unitary encoding on the qubits it holds to encode classical information, generates and inserts the first decoy state, records the position and state of the first decoy state, and sends the qubit sequence carrying the classical information encoding and the first decoy state to the measurement node Charlie through a quantum channel (such as optical fiber).

[0061] The receiver Bob randomly selects one of two Bell states orthogonal to the first initial Bell state (this randomness is key to ensuring that the measurement node Charlie cannot know the final shared Bell state) to prepare the second initial Bell state. At the same time, it generates and inserts the second decoy state, records the position and state of the second decoy state, and sends the qubit sequence carrying the second decoy state to the measurement node Charlie through the quantum channel.

[0062] The measurement node Charlie, considered untrusted, performs joint Belki measurements on the quantum states from the sender Alice and the receiver Bob, and then publicly announces the measurement results to both parties through a classical authentication channel, providing classical information support for the sender Alice and the receiver Bob to complete message decoding, key screening and security assessment.

[0063] I. Sending end Alice

[0064] The transmitting end Alice includes a first Bell state preparation unit, a unitary coding operation unit, and a first decoy management unit;

[0065] The first Bell state preparation unit generates the first initial Bell state;

[0066] The unitary encoding operation unit performs four Pauli operations (I, X, iY, Z) on the held qubits to encode 2 bits of classical information;

[0067] The first decoy management unit generates and inserts the first decoy state, and records the position and state of the first decoy state.

[0068] II. Receiver Bob

[0069] The receiver Bob includes a second Bell state preparation unit and a second decoy management unit;

[0070] The second Bell state preparation unit randomly selects one of two Bell states orthogonal to the first initial Bell state to prepare the second initial Bell state;

[0071] The second decoy management unit generates and inserts the second decoy state, and records the position and state of the second decoy state.

[0072] III. Measurement Node Charlie

[0073] The measurement node Charlie includes a Bell state measurement device and a classical communication interface;

[0074] The Bell state measurement device uses linear optical elements (such as beam splitters BS, polarization beam splitters PBS1, PBS2, etc.) and single-photon detectors (D1, D2, D3, D4) to perform joint Bell basis measurements on quantum states from the transmitter Alice and the receiver Bob.

[0075] The classic communication interface publicly announces the measurement results to the sender Alice and the receiver Bob through the classic authentication channel.

[0076] Based on the aforementioned MDI-QSDC system based on orthogonal state coding, this invention also discloses an MDI-QSDC method based on orthogonal state coding, such as... Figure 2 As shown, it includes the following steps: S1. Quantum bit sequence preparation and decoy state insertion: Alice, the transmitter, prepares multiple pairs of first initial Bell states |ψ⁺> 12 And for each pair of first initial Bell states |ψ⁺> 12 The first qubit forms the qubit sequence A M This is reserved for subsequent secret message encoding, and the second qubit is used to form a qubit sequence A. E Used for entanglement swapping, combining multiple first decoy states The sent particle d2 is randomly inserted into the quantum bit sequence A. E This forms an extended qubit sequence A' E ; At the receiving end, Bob starts from two initial Bell states |ψ⁺> 12 Orthogonal Bell states |ψ⁺> 34 、|ψ⁻> 34 In the process, multiple pairs of second initial Bell states are prepared by randomly selecting one method, and the quantum bit sequence B is then used. M Reserved for subsequent secret message encoding, the quantum bit sequence B E Used for entanglement swapping, multiple second decoy states / The sent particle d4 is randomly inserted into the quantum bit sequence B. E This forms an extended qubit sequence B' E ; S2, Initial Transmission and Entanglement Swap: The transmitting end Alice will extend the qubit sequence A' E The data is sent to the measurement node Charlie, and the receiving end Bob will extend the qubit sequence B'. E Send to the measurement node Charlie; Measurement node Charlie pairs the data from the extended qubit sequence A' E Extended qubit sequence B' E A joint bel basis measurement is performed on each pair of quantum states in the sequence A, and the measurement results are published, thereby making the sequence A a record of the quantum bits. M With the quantum bit sequence B M Establish entanglement and exchange between them; S3, Initial eavesdropping detection: Alice, the transmitter, and Bob, the receiver, announce the positions and initial states of the transmitted particles d2 and d4. When the measurement node Charlie measures the decoy pair (d2,d4), the transmitter Alice and the receiver Bob measure the local partner particle pair (d1,d3) to verify whether their correlation is consistent with the measurement results published by the measurement node Charlie and the predictions of quantum mechanics. Any deviation indicates the presence of eavesdropping. S4. Message Encoding and Secondary Transmission: After eavesdropping detection, the sending end Alice detected the qubit sequence A. M Perform unitary encoding to encode its secret message, resulting in the message encoding sequence A'. M The remaining sending particles d2 are randomly inserted into the message encoding sequence A'. M This forms an extended qubit sequence A'' M Send to the measurement node Charlie; At the receiving end, Bob randomly inserts the remaining transmitting particle d4 into the qubit sequence B. M This forms an extended qubit sequence B' M Send to the measurement node Charlie; S5. Secondary eavesdropping detection: Measurement node Charlie pairs the data from the extended qubit sequence A'' M Extended qubit sequence B' M Each pair of quantum states in the process undergoes a joint Belli measurement, and the measurement results are published. In the absence of eavesdropping, the measurement results should perfectly match the statistical correspondence of the initial decoy states in accordance with the predictions of quantum mechanics. Any deviation indicates the presence of eavesdropping. S6, Message Decoding: Measurement node Charlie measures the data from message-encoded sequence A' M Quantum bit sequence B M Perform a joint Belli measurement on each pair of quantum states and publish the results; Since only the receiver Bob knows the second initial Bell state it has chosen, and combined with the measurement results published by the measurement node Charlie, the Bell state shared with the sender Alice can be uniquely derived. Therefore, the receiver Bob can uniquely decode the unitary coding operation applied by the sender Alice based on the measurement results, thereby obtaining the secret message.

[0077] For quantum dialogue, the technical solution in this application supports two-way communication: The receiver Bob needs to first go through an MDI-QSDC process based on orthogonal state coding to securely inform the sender Alice of the selection of its second initial Bell state; After this, both parties can simultaneously access the qubit sequence A. M Quantum bit sequence B M Each node encodes its own secret message. The final measurement result of the measurement node Charlie contains the secret messages encoded by both parties. The sending end Alice and the receiving end Bob can decode each other's secret messages based on their understanding of the shared Bell state.

[0078] To better illustrate the technical solution of this application, the following detailed explanation is provided in conjunction with two experiments.

[0079] Experiment 1: Performance Comparison of Orthogonal State Encoded Measurement Device Independent Quantum Secure Direct Communication (OSB MDI-QSDC, i.e., the technical solution of this invention) in Standard Telecommunication Optical Fiber • Experimental conditions: Quantum channel: standard single-mode fiber with an attenuation coefficient of 0.2 dB / km; Light source: weak coherent pulsed light source, with a center wavelength of 1550nm; Detectors: The measurement node Charlie uses four superconducting nanowire single-photon detectors (SNSPDs) with a detection efficiency of approximately 90%. Protocol parameters: Total number of pulses is 1×10 9 The proportion of decoys is 30%. Comparison object: Traditional BB84-based measurement device-independent quantum secure direct communication (MDI-QSDC) protocol.

[0080] •Experimental Results:

[0081] As shown in Table 1 below:

[0082] Table 1 Comparison of Experimental Results

[0083]

[0084] • Experimental conclusion: This invention significantly improves the practical performance in long-distance and collective noise environments.

[0085] Experiment 2: Verification of Information Leakage Resistance in Quantum Dialogue Using Orthogonal State Encoded Measurement Device Independent Quantum Secure Direct Communication (OSB MDI-QSDC, i.e., the technical solution of this invention)

[0086] • Experimental conditions: OSB MDI-QSDC and standard QD protocols were run under simulated collective dephasing noise conditions.

[0087] • Measurement Results: Information leakage is quantified by calculating the amount of information (mutual information I(AB:E)) that Eve obtains from the publicly available measurement results.

[0088] Standard QD protocol: I(AB:E) = 2.0 bits;

[0089] OSB MDI-QSDC: I(AB:E)=1.0bit.

[0090] • Experimental conclusion: This invention successfully reduced information leakage by 50% and enhanced the confidentiality of two-way communication.

[0091] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions will not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. An MDI-QSDC system based on orthogonal state coding, characterized in that: This includes the sending end Alice, the receiving end Bob, and the measurement node Charlie; Alice, the transmitter, generates the first initial Bell state, performs unitary encoding on the qubits it holds to encode classical information, generates and inserts the first decoy state, records the position and state of the first decoy state, and sends the qubit sequence carrying the classical information encoding and the first decoy state to the measurement node Charlie through the quantum channel. The receiver Bob randomly selects one of two Bell states orthogonal to the first initial Bell state to prepare the second initial Bell state. At the same time, it generates and inserts the second decoy state, records the position and state of the second decoy state, and sends the qubit sequence carrying the second decoy state to the measurement node Charlie through the quantum channel. The measurement node Charlie, considered untrusted, performs joint Belki measurements on the quantum states from the sender Alice and the receiver Bob, and then publicly announces the measurement results to both parties through a classical authentication channel, providing classical information support for the sender Alice and the receiver Bob to complete message decoding, key screening and security assessment.

2. The MDI-QSDC system based on orthogonal state coding according to claim 1, characterized in that: The transmitting end Alice includes a first Bell state preparation unit, a unitary coding operation unit, and a first decoy management unit; The first Bell state preparation unit generates the first initial Bell state; The unitary encoding operation unit performs four Pauli operations (I, X, iY, Z) on the held qubits to encode 2 bits of classical information; The first decoy management unit generates and inserts the first decoy state, and records the position and state of the first decoy state.

3. The MDI-QSDC system based on orthogonal state coding according to claim 2, characterized in that: The receiving end Bob includes a second Bell state preparation unit and a second decoy management unit; The second Bell state preparation unit randomly selects one of two Bell states orthogonal to the first initial Bell state to prepare the second initial Bell state; The second decoy management unit generates and inserts the second decoy state, and records the position and state of the second decoy state.

4. The MDI-QSDC system based on orthogonal state coding according to claim 3, characterized in that: The measurement node Charlie includes a Bell state measurement device and a classical communication interface; The Bell state measurement device uses linear optical elements and a single-photon detector to perform joint Bell basis measurements on quantum states from the transmitter Alice and the receiver Bob; The classic communication interface publicly announces the measurement results to the sender Alice and the receiver Bob through the classic authentication channel.

5. An MDI-QSDC method based on orthogonal state coding, applicable to the MDI-QSDC system based on orthogonal state coding as described in claim 1, characterized in that: Includes the following steps: S1. Quantum bit sequence preparation and decoy state insertion: Alice, the transmitter, prepares multiple pairs of first initial Bell states |ψ⁺> 12 and the quantum bit sequence A M This will be used for subsequent secret message encoding, and the quantum bit sequence A will be stored in the quantum bit sequence. E Used for entanglement swapping, multiple first decoy states The sent particle d2 is randomly inserted into the quantum bit sequence A. E This forms an extended qubit sequence A' E ; At the receiving end, Bob starts from two initial Bell states |ψ⁺> 12 Orthogonal Bell states |ψ⁺> 34 、|ψ⁻> 34 In the process, multiple pairs of second initial Bell states are prepared by randomly selecting one method, and the quantum bit sequence B is then used. M Reserved for subsequent secret message encoding, the quantum bit sequence B E Used for entanglement swapping, multiple second decoy states / The sent particle d4 is randomly inserted into the quantum bit sequence B. E This forms an extended qubit sequence B' E ; S2, Initial Transmission and Entanglement Swap: The transmitting end Alice will extend the qubit sequence A' E The data is sent to the measurement node Charlie, and the receiving end Bob will extend the qubit sequence B'. E Send to the measurement node Charlie; Measurement node Charlie pairs the data from the extended qubit sequence A' E Extended qubit sequence B' E A joint bel basis measurement is performed on each pair of quantum states in the sequence A, and the measurement results are published, thereby making the sequence A a record of the quantum bits. M With the quantum bit sequence B M Establish entanglement and exchange between them; S3, Initial eavesdropping detection: Alice, the transmitter, and Bob, the receiver, announce the positions and initial states of the transmitted particles d2 and d4. When the measurement node Charlie measures the decoy pair (d2,d4), the transmitter Alice and the receiver Bob measure the local partner particle pair (d1,d3) to verify whether their correlation is consistent with the measurement results published by the measurement node Charlie and the predictions of quantum mechanics. Any deviation indicates the presence of eavesdropping. S4. Message Encoding and Secondary Transmission: After eavesdropping detection, the sending end Alice detected the qubit sequence A. M Perform unitary encoding to encode its secret message, resulting in the message encoding sequence A'. M The remaining sending particles d2 are randomly inserted into the message encoding sequence A'. M This forms an extended qubit sequence A'' M Send to the measurement node Charlie; At the receiving end, Bob randomly inserts the remaining transmitting particle d4 into the qubit sequence B. M This forms an extended qubit sequence B' M Send to the measurement node Charlie; S5. Secondary eavesdropping detection: Measurement node Charlie pairs the data from the extended qubit sequence A'' M Extended qubit sequence B' M Each pair of quantum states in the process undergoes a joint Belli measurement, and the measurement results are published. In the absence of eavesdropping, the measurement results should perfectly match the statistical correspondence of the initial decoy states in accordance with the predictions of quantum mechanics. Any deviation indicates the presence of eavesdropping. S6, Message Decoding: Measurement node Charlie measures the data from message-encoded sequence A' M Quantum bit sequence B M Perform a joint Belli measurement on each pair of quantum states and publish the results; Since only the receiver Bob knows the second initial Bell state it has chosen, and combined with the measurement results published by the measurement node Charlie, the Bell state shared with the sender Alice can be uniquely derived. Therefore, the receiver Bob can uniquely decode the unitary coding operation applied by the sender Alice based on the measurement results, thereby obtaining the secret message.

6. The MDI-QSDC method based on orthogonal state coding according to claim 5, characterized in that: For quantum dialogue, this method supports bidirectional communication: The receiver Bob needs to first go through an MDI-QSDC process based on orthogonal state coding to securely inform the sender Alice of the selection of its second initial Bell state; After this, both parties can simultaneously access the qubit sequence A. M Quantum bit sequence B M Each node encodes its own secret message. The final measurement result of the measurement node Charlie contains the secret messages encoded by both parties. The sending end Alice and the receiving end Bob can decode each other's secret messages based on their understanding of the shared Bell state.

Images