One-step quantum dialogue method

Abstract

This invention belongs to the field of quantum dialogue and discloses a one-step quantum dialogue method. In this method, communicator A prepares a large number of identical polarization-spatial hyperentangled states and sends one photon from each hyperentangled state to communicator B through a quantum channel, establishing a hyperentangled quantum channel between the two parties. After confirming the security of the photon transmission process, both parties encode the photon pairs according to the information to be transmitted. Then, by running nonlocal Bell state measurements and publishing the detector responses, both parties can read the information transmitted by the other, thus achieving bidirectional quantum communication, i.e., quantum dialogue. Compared with existing quantum dialogue protocols, this invention reduces the number of photon transmissions in the channel from two to one, simplifying experimental operations and effectively reducing the photon loss rate, which can effectively promote the practical application of quantum dialogue.

Description

Technical Field

[0001] This invention belongs to the field of quantum dialogue, specifically relating to a one-step quantum dialogue method. Background Technology

[0002] Quantum secure communication is a secure communication technology with great development potential. It protects information security based on the fundamental principles of quantum mechanics. Two important research directions in quantum secure communication are quantum key distribution (QKD) and quantum secure direct communication (QSDC). The main purpose of the QKD protocol is to distribute a series of secure keys between the sender and receiver. Combining one-time pad and classical communication (transmitting ciphertext) enables secure information transmission. The QSDC protocol uses quantum states as information carriers and directly transmits secret information using quantum channels without the need for pre-generated keys, greatly simplifying the quantum secure communication process.

[0003] Traditional QSDC protocols require photons to travel through a quantum channel for two rounds. During each round of photon transmission, photons may experience transmission loss or quantum state decoherence due to channel noise. In 2022, Sheng et al. proposed a one-step quantum secure direct communication (QSDC) protocol, which achieves secure communication with only one round of photon transmission in the channel. The one-step QSDC protocol is of great significance for reducing the loss of quantum states in quantum channels and extending the secure communication distance.

[0004] The QSDC protocol only enables one-way information transmission, meaning information can only be transmitted from sender to receiver. Due to the complexity of systems in practical applications, bidirectional information transmission is sometimes required. Therefore, the idea of ​​bidirectional quantum secure direct communication (quantum dialogue, QD) was proposed. Quantum dialogue (QD), or bidirectional QSDC, allows two communicating parties to simultaneously exchange messages while guaranteeing absolute information security.

[0005] In 2004, Nguyen first proposed the concept of Quantum Direct Communication (QD), where two communicating parties can simultaneously and directly transmit each other's secret information. He also proposed the first QD protocol based on entangled states, known as the NBA protocol. In 2005, Man Zhongxiao et al. pointed out that the NBA protocol had security threats, as attackers could steal all secret messages without being detected using intercept-retransmission attacks. They also proposed an improved version of the NBA protocol, known as the MAN protocol. In 2006, Man Zhongxiao et al. proposed a controllable QD scheme based on GHz entangled states. In 2008, Ji Xin et al. proposed a QD scheme based on single photons and unitary transformations. In 2010, Shi Guofang et al. combined the ideas of quantum secure direct communication and the BB84 protocol to propose a secure QD protocol based on single photons. In 2014, Ye Tianyu et al. designed a quantum-encrypted, information leakage-resistant QD protocol. Since then, with the continuous deepening of research, researchers have continuously proposed QD schemes that can overcome information leakage.

[0006] Most existing quantum dot-mapping (QD) schemes are two-step schemes, requiring photons to be transmitted twice in the quantum channel. As the communication distance increases, photons may experience transmission loss or quantum state decoherence due to channel noise during each transmission, significantly limiting the communication distance and threatening the efficiency and security of bidirectional communication. A few existing one-step QD schemes exist, such as patent application CN105933114A. To achieve bidirectional communication, the communicating party 1 needs to prepare a large number of different two-photon Bell states and three-photon GHZ states, and perform complete Bell state and complete GHZ state measurements. However, the initial state preparation and measurement processes are very complex, and complete Bell state and complete GHZ state measurements are not achievable under current experimental conditions. Therefore, the method proposed in patent application CN105933114A cannot be implemented under current experimental conditions. Summary of the Invention

[0007] To address the aforementioned issues, this invention introduces the concept of one-step QSDC into QD, providing an efficient one-step quantum dialogue method that requires only one transmission of photons in the quantum channel and is achievable under current experimental conditions. This is of great significance for improving the communication efficiency of QD, reducing information loss, and extending communication distance, and can strongly promote the practical application of QD.

[0008] The efficient one-step quantum dialogue method described in this invention includes the following steps:

[0009] Step 1: Alice prepares a large number of identical initial polarization-space hyperentangled photon pairs to form the S1 and S2 sequences, and randomly prepares a large number of polarization-space encoded single photons as security detection photons, which are randomly inserted into the S2 sequence to form the S2' sequence;

[0010] Step 2: Alice sends the S2' sequence to Bob via the quantum channel. Bob stores all received photons. Alice announces the position of the security detection photon and the preparation basis for the two degrees of freedom. Bob extracts the security detection photon, measures the photon in his hand according to the measurement basis for the two degrees of freedom announced by Alice, and announces the measurement results. Alice performs a security check to confirm whether the photon transmission process is secure. If secure, proceed to the next step; if insecure, terminate the communication.

[0011] Step 3: Alice extracts all photons from the S1 sequence and uses I and σ to represent the information to be transmitted, 0 and 1 respectively. z The operation encodes the photon in its polarization degrees of freedom, and simultaneously, randomly selects I and σ for each photon. X Operation: Bob extracts all remaining photons in the S2' sequence and, based on the information he wants to transmit (0 and 1), uses I and σ respectively. X The operation encodes photons in the polarization degrees of freedom, and simultaneously, randomly selects I and σ for each photon. Z operate;

[0012] Step 4: After encoding is completed, both communicating parties run a nonlocal Bell state measurement (BSM), which uses spatial degree-of-freedom entanglement to assist in the complete Bell state measurement (BSM) of polarization degree-of-freedom. After the measurement is completed, both parties publish the detector response at their respective locations. Based on the detector response and their own random operations, both parties can read the information transmitted by the other party, thereby realizing two-way real-time quantum communication, i.e., quantum dialogue.

[0013] As a further improvement to the present invention, step 1 specifically involves Alice preparing a polarization-spatial hyperentangled photon pair in a quantum state of... Where, |φ + > p It belongs to one of the four Bell states under polarization degrees of freedom. The expressions for the four polarization Bell states are as follows:

[0014]

[0015] |φ + > s It belongs to one of the four Bell states under spatial degrees of freedom. The expressions for the four spatial Bell states are as follows:

[0016]

[0017] Where |> is the Dirac symbol, representing the right vector; |H> represents the horizontal polarization of the photon, and |V> represents the vertical polarization of the photon; a1, a2, a′1, and a′2 represent the different spatial modes at the four Alice locations;

[0018] Alice prepares a large number of polarization-spatial encoded single photons As security detection photons, they are randomly inserted into the S2 sequence; where, |χ> P ∈{Z p , X P}, |λ> S ∈{Z s , X s}, Z p (Z s ) and X p (X s ) respectively represent the direct product and diagonal basis of the polarization / spatial degrees of freedom; specifically, Z p (Z s ) and X p (X s ) are described as:

[0019]

[0020]

[0021] As a further improvement of the present invention, step 2 is specifically that the security detection includes: in the ideal case without eavesdropping, Bob's measurement result in any degree of freedom should be consistent with the initial state prepared by Alice; if Bob's measurement result is inconsistent with the initial state prepared by Alice, it means that an error has occurred; after all the security detection photons have been measured, if the error rate in any one of the DOFs exceeds the set threshold, Alice and Bob determine that the photon transmission process is insecure and abandon the communication.

[0022] As a further improvement of the present invention, in step 3, Alice extracts the photons in the S1 sequence and, according to the information 0 and 1 to be transmitted, uses I and σ z respectively represent the invariant operation and phase flip operation of the polarization degree of freedom; I = |H><H| + |V><V| represents the classical information 0, σ z = |H><H| - |V><V| represents the classical information 1, and at the same time randomly performs the operations of I and σ X = |H><V| + |V><H| on each photon; Bob extracts the remaining photons in the S2' sequence and, according to the information 0 and 1 he wants to transmit, uses I and σ X operations to encode the photons, where, σ X is the bit flip operation of the polarization degree of freedom; I represents the classical information 0, σ X represents the classical information 1, and at the same time randomly performs the operations of I and σ Z on each photon.

[0023] As a further improvement of the present invention, in step 4, both parties run a nonlocally polarized complete BSM, using spatial degree-of-freedom entanglement to assist in achieving a complete BSM for the polarization degrees of freedom; after the measurement is completed, both parties publish their detector response status, with a total of 16 detector response statuses; among them, D1-D8 represent 8 photon detectors, and the detector response statuses of both parties corresponding to the 4 polarization Bell states are |φ + > P :D1D5, D2D6, D3D7, D4D8, |φ - > P : D1D7, D3D5, D4D6, D2D8, |ψ + > P :D1D6, D2D5, D3D8, D4D7, |ψ - > P D1D8, D2D7, D3D6, D4D5; based on the detector response and their own random operations, both parties read the information transmitted by the other, thereby realizing two-way real-time quantum communication, i.e., quantum dialogue.

[0024] The beneficial effects of this invention are as follows: The method described in this invention only requires photons to be transmitted once in the quantum channel, which can effectively reduce the photon transmission loss rate, reduce information loss, and extend the communication distance. After both parties run the nonlocal BSM, although both parties need to publish the encoded detector response results, i.e., the polarization BSM results are made public, since the random operations of both parties are not made public, a third party cannot infer the information transmitted by Alice and Bob based on the polarization BSM results. At the same time, the security of the photon transmission process is guaranteed by security detection. This scheme has absolute security in theory and can effectively protect the security of the information transmitted by both parties. The initial state preparation process and measurement process of this invention are simple, requiring only the preparation of the same polarization-space hyperentangled state and the implementation of spatial entanglement-assisted fully polarized Bell state measurement, which can be achieved under current experimental conditions. This invention can effectively promote the practical application of quantum dialogue. Attached Figure Description

[0025] Figure 1 This is a schematic diagram of the communication process of the one-step quantum dialogue scheme of the present invention;

[0026] Figure 2 This is a schematic diagram illustrating the principle of the one-step quantum dialogue scheme of the present invention.

[0027] Figure 3 This is an experimental schematic diagram of the one-step quantum dialogue scheme of the present invention. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0029] like Figure 1 and Figure 2 As shown, this invention is a one-step quantum dialogue method, comprising the following steps:

[0030] Step 1: Alice prepares a large number of identical initial polarization-spatial hyperentangled photon pairs, forming the S1 and S2 sequences. She then randomly prepares a large number of polarization-spatial encoded single photons as security detection photons, randomly inserting them into the S2 sequence to form the S2' sequence. Step 2: Alice sends the S2' sequence to Bob via a quantum channel. Bob stores all received photons. Alice announces the position of the security detection photon and the preparation basis for the two degrees of freedom. Bob extracts the security detection photon, measures the photon in his hand according to the measurement basis for the two degrees of freedom announced by Alice, and announces the measurement results. Alice performs security detection and estimates the error rate of the security detection photon in the two degrees of freedom. If the error rate of both degrees of freedom is lower than a pre-set threshold, the next step is performed. If the error rate of any degree of freedom is higher than the set threshold, communication is terminated.

[0031] Step 3: Alice extracts the photons from the S1 sequence and uses I and σ respectively according to the information to be transmitted, 0 and 1. z The operation encodes photons in their polarization degrees of freedom. Bob extracts photons from the S2' sequence and, based on the information he wants to transmit (0 and 1), uses I and σ respectively. X The operation encodes photons in the polarization degrees of freedom; furthermore, to prevent information leakage, Alice randomly applies I and σ to the photons in the S1 sequence in the polarization degrees of freedom. X In this operation, Bob randomly applies I and σ to the photons in the S2' sequence in the polarization degrees of freedom. z operate;

[0032] Step 4: After encoding, both communicating parties run nonlocal Bell state analysis, that is, use spatial degree of freedom entanglement to achieve complete Bell state measurement of polarization degree of freedom. After the measurement is completed, both parties announce the detector response at their respective locations. There are 16 possible responses as shown in the table below. Both parties can read the information transmitted by the other party based on the detector response and their own random operations, thereby realizing two-way real-time quantum communication, i.e., quantum dialogue.

[0033]

[0034] like Figure 3 As shown, the process of this invention will be analyzed below with specific examples:

[0035] Alice and Bob share the initial polarization Bell state |φ + > pAlice transmits information 1, and Bob transmits information 0. Therefore, Alice's encoding operation is σ. Z Bob's encoding operation is I. Furthermore, to prevent information leakage, Alice also performs σ operations on the photons of the S1 sequence. X The operation involves flipping bits, and Bob also runs σ on the photon of S2'. Z The operation involves flipping the phase. Initial state |φ + After encoding, it is converted to |φ + > The specific process is as follows:

[0036]

[0037] To read the message, Alice and Bob, with the aid of spatial modular entanglement, performed the following... Figure 3 The nonlocally fully polarized BSM is shown.

[0038] When photons pass through the beam splitter PBS, they can transmit |H> photons and reflect |V> photons. After passing through the HWP, they can... and Furthermore, Alice's prepared state in terms of spatial degrees of freedom a′1 and a′2 is transformed into b1 and b2 respectively after the Bob operation.

[0039]

[0040] This corresponds to the responses of detectors D3D5, D4D6, D1D7, and D2D8.

[0041] Alice and Bob obtained the measurement results |ψ + >, Alice knows herself |φ + >→|ψ - The results show that a phase flip was performed on this basis, but Bob did not perform a bit flip. Therefore, Alice knows that Bob transmitted the secret message 0; Bob knows that he himself has... + >→|φ - The results showed that a double bit and phase flip was performed on this basis, while Bob did not perform a bit flip. Bob knew that Alice transmitted a secret message of 1. Both parties read the secret information transmitted by each other, realizing two-way real-time quantum communication, i.e., quantum dialogue.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to further limit the present invention. All equivalent changes made based on the description and drawings of the present invention are within the protection scope of the present invention.

Claims

1. A one-step quantum dialogue method, characterized in that, Includes the following steps: Step 1: Alice prepares a large number of identical initial polarization-space hyperentangled photon pairs to form the S1 and S2 sequences, and randomly prepares a large number of polarization-space encoded single photons as security detection photons, which are randomly inserted into the S2 sequence to form the S2' sequence; Step 2: Alice sends the S2' sequence to Bob via the quantum channel. Bob stores all received photons. Alice announces the position of the security detection photon and the preparation basis for the two degrees of freedom. Bob extracts the security detection photon, measures the photon in his hand according to the measurement basis for the two degrees of freedom announced by Alice, and announces the measurement results. Alice performs a security check to confirm whether the photon transmission process is secure. If secure, proceed to the next step; if insecure, terminate the communication. Step 3: Alice extracts all photons from the S1 sequence and uses I and σ to represent the information to be transmitted, 0 and 1 respectively. z The operation encodes the photon in its polarization degrees of freedom, and simultaneously, randomly selects I and σ for each photon. X Operation: Bob extracts all remaining photons from the S2' sequence and, based on the information he wants to transmit (0 and 1), uses I and σ respectively. X The operation encodes photons in the polarization degrees of freedom, and simultaneously, randomly selects I and σ for each photon. Z operate; Step 4: After encoding is completed, both communicating parties perform nonlocal Bell state measurement, that is, use spatial degree of freedom entanglement to achieve complete Bell state measurement of polarization degree of freedom; after the measurement is completed, both parties announce the detector response at their respective locations; based on the detector response and their own random operations, both parties read the information transmitted by the other party, thereby realizing two-way real-time quantum communication, that is, quantum dialogue.

2. The one-step quantum dialogue method according to claim 1, characterized in that, Step 1 specifically involves Alice preparing a polarization-spatial hyperentangled photon pair in a quantum state of... Where, |φ + > p It belongs to one of the four Bell states under polarization degrees of freedom. The expressions for the four polarization Bell states are as follows: |φ + > s It belongs to one of the four Bell states under spatial degrees of freedom. The expressions for the four spatial Bell states are as follows: Where |> is the Dirac symbol, representing the right vector; |H> represents the horizontal polarization of the photon, and |V> represents the vertical polarization of the photon; a1, a2, a′1, and a′2 represent the different spatial modes at the four Alice locations; Alice prepares a large number of polarization-space encoded single photons. As a security detection photon, it is randomly inserted into the S2 sequence; where, |χ> P ∈{Z p ,X P },|λ> S ∈{Z s ,X s }, Z p (Z s ) and X p (X s ) represent the rectangular product and diagonal basis of polarization / spatial degrees of freedom, respectively; specifically, Z p (Z s ) and X p (X s The description is as follows:

3. The one-step quantum dialogue method according to claim 1, characterized in that, Step 2 specifically involves security checks, including: in an ideal scenario where there is no eavesdropping, Bob's measurement results in any degree of freedom should be consistent with the initial state prepared by Alice; if Bob's measurement results are inconsistent with the initial state prepared by Alice, it indicates that an error has occurred; after all security check photon measurements are completed, if the error rate in any DOF exceeds the set threshold, Alice and Bob determine that the photon transmission process is insecure and abandon communication.

4. The one-step quantum dialogue method according to claim 1, characterized in that, In step 3, Alice extracts the photons in the S1 sequence. According to the information 0 and 1 to be transmitted, she uses I and σ respectively z which represent the invariant operation and the phase flip operation of the polarization degree of freedom respectively; I = |H><H| + |V><V| represents the classical information 0, and σ z = |H><H| - |V><V| represents the classical information 1. At the same time, the operations I and σ are randomly performed on each photon X = |H><V| + |V><H|; Bob extracts the remaining photons in the S2' sequence. According to the information 0 and 1 he wants to transmit, he uses I and σ X operations to encode the photons. Among them, σ X is the bit flip operation of the polarization degree of freedom; I represents the classical information 0, and σ X represents the classical information 1. At the same time, the operations I and σ are randomly performed on each photon Z operation.

5. The one-step quantum dialogue method according to claim 1, characterized in that, In step 4, both parties run a nonlocally polarized complete BSM, using spatial degree-of-freedom entanglement to assist in achieving a complete BSM for the polarization degrees of freedom. After the measurement is completed, both parties publish their detector responses, which are 16 possible. Among them, D1-D8 represent 8 photon detectors, and the detector responses of both parties corresponding to the 4 polarization Bell states are |φ + > P :D1D5, D2D6, D3D7, D4D8, |φ - > P :D1D7, D3D5, D4D6, D2D8, |ψ + > P :D1D6, D2D5, D3D8, D4D7, |ψ - > P D1D8, D2D7, D3D6, D4D5; based on the detector response and their own random operations, both parties read the information transmitted by the other, thereby realizing two-way real-time quantum communication, i.e., quantum dialogue.

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