A quantum secure direct communication method based on symmetric full-passive light source

Abstract

The application discloses a quantum secure direct communication method based on a symmetric passive light source, wherein information receivers use four phase random coherent pulses to generate weak coherent pulse beams with random intensity and quantum state through beam splitters and polarization beam splitters interference, beam combination and attenuation, and send the beams to information senders. The information senders send the photon pulses back to the information receivers after encoding. The information receivers decode the information sent by the information senders according to the initial pulse information sent by the information receivers. The method does not need to actively modulate the intensity and quantum state of the light source, can simultaneously realize passive decoy states and passive encoding, can simplify experimental operation, can resist side channel attacks of a light source modulator by a third-party eavesdropper, and can enhance the security of quantum secure direct communication.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of quantum communication, and particularly relates to a quantum secure direct communication method based on a symmetric passive light source. BACKGROUND

[0002] Quantum secure direct communication (QSDC) is an important branch of quantum communication. It can securely transmit information directly between the communicating parties. In 2000, Long Guilu et al. proposed the first quantum secure direct communication protocol. In 2003, Deng Fuguo et al. proposed a two-step QSDC scheme based on EPR entangled pairs using the idea of dense coding; in 2004, the research group proposed a one-time pad QSDC scheme based on single photons; the one-time pad QSDC scheme based on single photons and the two-step QSDC scheme based on entanglement were experimentally verified in 2016 and 2017, respectively. However, in practical applications, devices are not perfect. These imperfect devices may provide opportunities for third-party eavesdroppers, threatening the security of the protocol. In 2020, Zhou Zengrong et al. proposed a measurement-device-independent (MDI) quantum secure direct communication protocol, which can resist all attacks on the measurement device side. However, imperfections in the light source device can also introduce some security vulnerabilities, especially when we actively modulate the light intensity and quantum state, a third-party eavesdropper can conduct a Trojan horse attack to steal information. In 2023, Wang et al. proposed the idea of a passive light source. In the same year, their group proposed an improved symmetric passive light source. Passive encoding and passive entangled state selection are achieved through phase-random coherent pulses. Using this symmetric passive light source, there is no need to actively modulate the entangled state light intensity, and there is no need to perform active encoding operations, which can simplify the experimental setup and eliminate side-channel information leakage caused by active operations. Moreover, this method also does not require screening of the encoded particles, which can greatly reduce the loss. Currently, the symmetric passive light source technology has not been applied to QSDC protocols. SUMMARY

[0003] The purpose of the present application is to overcome the deficiencies in the prior art, and to provide a quantum secure direct communication method and system based on a symmetric passive light source, which can simplify experimental operations, resist side-channel attacks on the light source modulator, and improve communication security.

[0004] To achieve the above purpose, the present application adopts the following technical solutions:

[0005] A quantum secure direct communication method based on a symmetric passive light source, comprising the following steps:

[0006] Step 1: The information receiver prepares four intensity μ, phase-random coherent pulses, pulses μ1 and μ2 generate pulse μ through BS interference 1+2 、μ 1-2Pulses μ3 and μ4 are generated by BS interference to generate pulse μ. 3+4 μ 3-4 , measuring μ 1+2 and μ 3+4 Obtain μ 1-2 and μ 3-4 The intensity and phase information, and then the pulse μ 1-2 With pulse μ 3-4 A bundle of μ was synthesized using PBS. 1-2+3-4 It is then attenuated into a weakly coherent pulse μ by an intensity attenuator. out The information recipient determines the amount based on μ. 1+2 and μ 3+4 The measurement results are used to filter out the states that want to be sent and then send them to the information sender.

[0007] Step 2: The sender stores the received photon pulses. Then, the receiver and sender agree to select a subset of photons for the first round of security checks. The receiver publishes information about the photons at the corresponding locations, and the sender estimates the bit error rate based on this information. If the bit error rate is below a threshold, communication continues.

[0008] Step 3: The information sender randomly selects a portion of the remaining signal-state photons for random encoding, and encodes the remaining signal-state photons for information encoding. After encoding, the information is sent to the information receiver.

[0009] Step 4: The information receiver performs X-basis or Z-basis measurements on the received photons.

[0010] Step 5: The information sender publishes the location and random coding information of the randomly coded photon. The information receiver compares the measurement results of the corresponding location, estimates the bit error rate, and continues communication when the bit error rate is lower than the threshold.

[0011] Step 6: The information receiver reconstructs the information sender's information through classical post-processing based on the measurement information of photons at other locations.

[0012] Furthermore, the four coherent pulses with intensity μ and random phase mentioned in step 1 are described as follows:

[0013]

[0014]

[0015] Where μ represents the intensity of the four coherent pulses; α, β, γ, δ represent the random phases of the four coherent pulses; j is an imaginary number, j 2 = -1. Furthermore, the photons in μ1 and μ2 are in a quantum state. Photons in μ3 and μ4 are in a quantum state. where |H> and |V> are the horizontal and vertical polarization of the photon respectively.

[0016] Further, the pulse μ 1+2 , μ 1-2 , μ 3+4 , μ 3-4 , μ 1-2+3-4 and μ out in step 1 are expressed as:

[0017]

[0018]

[0019] where the subscripts R, L represent the quantum state of the photon in the pulse.

[0020]

[0021] where

[0022]

[0023]

[0024]

[0025]

[0026] is the quantum state of the photon in the pulse.

[0027] Further, the information receiver in step 1 screens the state to be sent according to the measurement results of μ 1+2 and μ 3+4 , specifically, the information receiver calculates I, θ, φ of μ out according to the measurement results of μ 1+2 and μ 3+4 , when the following intervals are satisfied, the photon pulse is sent to the information sender.

[0028] φ∈(φ x -Δφ,φ x +Δφ)

[0029]

[0030] where Δθ, Δφ are selected according to the actual system, when φ x respectively take 0, π, The states of the transmitted photons are denoted as |H>, |V>, |+> and |->. In addition, the information receiver will also denote the states as vacuum state (vac), decoy state (d) and signal state (s) according to the size of I. That is, the total number of states sent by the information receiver is 4*3=12.

[0031] Further, the selection of a part of the photons for the first round of security detection in step 2 specifically includes all vacuum state photons, all decoy state photons and a part of the signal state photons selected at random.

[0032] Further, the information encoding and random encoding of the photons in the hand of the information sender in step 3 are performed. The encoding operation is

[0033] U0=|H><H|+|V><V|, U1=|V><H|-|H><V|.

[0034] The random encoding is randomly encoded using U0 and U1, and the information encoding is selected according to the information to be sent, U0 represents information 0, and U1 represents information 1.

[0035] Further, the X basis or Z basis measurement of the received photons by the information receiver in step 4 is specifically that when the initial state sent by the information receiver is |H> and |V>, the Z basis measurement is performed, and when the initial state sent by the information receiver is |+> and |->, the X basis measurement is performed.

[0036] The present application has the following beneficial effects:

[0037] 1. The quantum secure direct communication method based on the symmetric full passive light source provided by the present application uses the decoy state method, can resist photon number splitting attack and coherent attack, improves the security capacity of quantum secure direct communication and improves the communication distance.

[0038] 2. The quantum secure direct communication method based on the symmetric full passive light source provided by the present application can passively modulate the intensity of the decoy state and the quantum state, can resist side channel attacks on the light source modulator and improves the security of quantum secure direct communication.

[0039] 3. The quantum secure direct communication method based on the symmetric full passive light source provided by the present application uses a symmetric structure light source, so that the generated Z basis and X basis quantum states are mutually symmetric, which can greatly reduce the complexity of experimental data processing. And there is no need to discard the data, which can effectively improve the resource utilization rate. BRIEF DESCRIPTION OF DRAWINGS

[0040] Figure 1 is a flowchart of the quantum secure direct communication method provided by the embodiment of the present application;

[0041] Figure 2This is a structural principle block diagram of a quantum-secure direct communication system provided in an embodiment of the present invention;

[0042] Figure 3 This is a structural diagram of a symmetrical fully passive light source provided in an embodiment of the present invention;

[0043] Figure 4 This is a comparison chart of the optimal performance of the quantum-secure direct communication method provided in this embodiment of the invention and the existing active modulation light source scheme. Detailed Implementation

[0044] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and should not be used to limit the scope of protection of the present invention.

[0045] Example 1:

[0046] As attached Figure 1 As shown, the quantum-secure direct communication implementation scheme in this embodiment includes the following steps:

[0047] Step 1: As Figure 3 As shown, Bob, the information receiver, prepares four coherent pulses with intensity μ and random phase. Pulses μ1 and μ2 are used to generate pulse μ through BS interference. 1+2 μ 1-2 Pulses μ3 and μ4 are generated by BS interference to generate pulse μ. 3+4 μ 3-4 , measuring μ 1+2 and μ 3+4 Obtain μ 1-2 and μ 3-4 The intensity and phase information, and then the pulse μ 1-2 With pulse μ 3-4 A bundle of μ was synthesized using PBS. 1-2+3-4 It is then attenuated into a weakly coherent pulse μ by an intensity attenuator. out The information recipient determines the amount based on μ. 1+2 and μ 3+4 The measurement results are used to filter out the states that want to be sent and send them to the information sender, Alice.

[0048] Four of these coherent pulses have an intensity of μ and a random phase:

[0049]

[0050]

[0051] Where μ represents the intensity of the four coherent pulses; α, β, γ, δ represent the random phases of the four coherent pulses; j is an imaginary number, j 2= -1. Furthermore, the photons in μ1 and μ2 are in a quantum state. Photons in μ3 and μ4 are in a quantum state. Where |H> and |V> represent the horizontal and vertical polarization of the photon, respectively.

[0052] Pulse μ after BS interference 1+2 μ 1-2 and μ 3+4 μ 3-4 for

[0053]

[0054]

[0055] After beam combining by PBS, the pulse μ 1+2+3+4 for:

[0056]

[0057] Finally, it decays to μ via BS. out :

[0058]

[0059] in

[0060]

[0061]

[0062]

[0063]

[0064] This represents the quantum state of the photon in the pulse.

[0065] The information recipient, based on μ 1+2 and μ 3+4 The measurement results were used to calculate μ out When I, θ, and φ satisfy the following intervals, the photon pulse is sent to the information sender.

[0066] φ∈(φ x -Δφ,φ x +Δφ)

[0067]

[0068] Where Δθ and Δφ are selected according to the actual system, when φ x Take values ​​of 0 and π respectively. When the state is sent, it is denoted as |H>, |V>, |+>, |->. Wherein, In addition, the information receiver will also record the state as vacuum state (vac), decoy state (d), and signal state (s) according to the magnitude of I.

[0069] Step 2: The sender stores the received photon pulses. Then, it randomly selects a subset of photons for the first round of security checks. The receiver publishes information about the photons at the corresponding locations, and the sender estimates the bit error rate based on this information. Communication continues only if the bit error rate is below a threshold.

[0070] A subset of photons is selected for the first round of security testing, including all vacuum-state photons, all decoy-state photons, and a randomly selected subset of signal-state photons.

[0071] Step 3: The information sender randomly selects a portion of the remaining signal-state photons for random encoding, and encodes the remaining signal-state photons for information encoding. After encoding, the information is sent to the information receiver.

[0072] The encoding operation is as follows:

[0073] U0=|H> <H|+|V><V|,U1=|V><H|-|H><V|。

[0074] The random encoding uses U0 and U1 codes randomly. The information encoding selects U0 and U1 codes according to the information to be sent. U0 represents information 0 and U1 represents information 1.

[0075] Step 4: The information receiver performs X-basis or Z-basis measurements on the received photons.

[0076] When the initial state sent by the information receiver is |H> and |V>, Z-basis measurement is performed; when the initial state sent by the information receiver is |+> and |->, X-basis measurement is performed.

[0077] Step 5: The information sender publishes the location and random coding information of the randomly coded photon. The information receiver compares the measurement results of the corresponding location, estimates the bit error rate, and continues communication when the bit error rate is lower than the threshold.

[0078] Step 6: The information receiver reconstructs the information sender's information through classical post-processing based on the measurement information of photons at other locations.

[0079] Figure 4 This is a comparison chart showing the optimal performance of the quantum-safe direct communication method provided in this invention with existing active modulation light source schemes. The quantum-safe direct communication method based on a symmetric fully passive light source proposed in this invention uses a symmetric light source structure, ensuring that the generated Z-based and X-based quantum states are mutually symmetrical, which can significantly reduce the complexity of experimental data processing. Furthermore, it eliminates the need for data filtering and discarding, effectively improving resource utilization.

[0080] Example 2:

[0081] like Figure 2 As shown, this embodiment of the invention also provides a quantum-secure direct communication system, including an information receiver and an information sender. The communication method is described in [reference needed]. Figure 1 The information receiver generates random photon pulses of random intensity quantum states using a fully passive light source and sends them to the information sender. The information sender receives and stores the pulses, then selects a subset of photons for the first round of security checks. After passing the security checks, the information sender encodes the information and performs random encoding, then sends the encoded photons back to the information receiver, who performs decoding and the second round of security checks. The specific methods and steps involved are detailed in Example 1 and will not be repeated here for brevity.

[0082] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied on one or more computer-usable storage media (including but not limited to disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0083] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of this application. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0084] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0085] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes ​ The steps of the function specified in one or more boxes.

[0086] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the technical principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A quantum-secure direct communication method based on a symmetric fully passive light source, characterized in that: The method includes the following steps: Step 1: The information receiver prepares four coherent pulses with intensity μ and random phase. Pulses μ1 and μ2 are used to generate pulse μ through BS interference. 1+2 μ 1-2 Pulses μ3 and μ4 are generated by BS interference to generate pulse μ. 3+4 μ 3-4 , measuring μ 1+2 and μ 3+4 Obtain μ 1-2 and μ 3-4 The intensity and phase information, and then the pulse μ 1-2 With pulse μ 3-4 Synthesize a μ beam using PBS 1-2+3-4 It is then attenuated into a weakly coherent pulse μ by an intensity attenuator. out The information recipient, based on μ 1+2 and μ 3+4 The measurement results are used to filter out the states that want to be sent and then send them to the information sender. Step 2: The information sender stores the received photon pulses. Then, after consultation between the information receiver and the information sender, a portion of the photons are selected for the first round of security testing. The information receiver publishes the information of the photons at the corresponding positions. The information sender estimates the bit error rate based on the information of the information receiver. When the bit error rate is lower than the threshold, communication continues. Step 3: The information sender randomly selects a portion of the remaining signal state photons for random encoding, and encodes the remaining signal state photons for information encoding. After encoding, the information is sent to the information receiver. Step 4: The information receiver performs X-basis or Z-basis measurements on the received photons; Step 5: The information sender publishes the location and random coding information of the randomly coded photons. The information receiver compares the measurement results of the corresponding locations, estimates the bit error rate, and continues communication when the bit error rate is lower than the threshold. Step 6: The information receiver reconstructs the information sender's information through classical post-processing based on the measurement information of photons at other locations.

2. The quantum-secure direct communication method based on a symmetric fully passive light source according to claim 1, characterized in that: The four coherent pulses with intensity μ and random phase mentioned in step 1 are described as follows: Where μ represents the intensity of the four coherent pulses; α, β, γ, δ represent the random phases of the four coherent pulses; j is an imaginary number, j 2 =-1; the subscripts R and L represent the quantum states of photons in coherent light, where R indicates that the photon is in a quantum state. L indicates that the photon is in a quantum state. Where |H> and |V> represent the horizontal and vertical polarization of the photon, respectively.

3. The quantum-secure direct communication method based on a symmetric fully passive light source according to claim 2, characterized in that: The pulse μ mentioned in step 1 1+2 μ 1-2 μ 3+4 μ 3-4 μ 1-2+3-4 and μ out The expression is as follows: In this context, the subscripts R and L represent the quantum state of the photon in the pulse; in in This indicates that the quantum state of the photon in the pulse is 4. A quantum-secure direct communication method based on a symmetric fully passive light source according to claim 3, characterized in that: The information receiver mentioned in step 1, according to μ 1+2 and μ 3+4 The measurement results are used to filter out the states to be sent. Specifically, the information receiver selects the states to be sent based on μ. 1+2 and μ 3+4 The measurement results were used to calculate μ out When I, θ, and φ satisfy the following intervals, the photon pulse is sent to the information sender; φ∈(φ x -Df,f x +Df) Where Δθ and Δφ are selected according to the actual system requirements, and φ x The value of is 0, π. The corresponding states sent are denoted as |H>, |V>, |+>, and |->. The information receiver will denot the states as vacuum state (vac), decoy state (d), and signal state (s) according to the magnitude of I. That is, there are a total of 4*3=12 states sent by the information receiver.

5. A quantum-secure direct communication method based on a symmetric fully passive light source according to claim 4, characterized in that: The selection of a subset of photons for the first round of security testing, as described in step 2, specifically includes all vacuum-state photons, all decoy-state photons, and a randomly selected subset of signal-state photons.

6. A quantum-secure direct communication method based on a symmetric fully passive light source according to claim 5, characterized in that: In step 3, the information sender performs information encoding and random encoding on the signal-state photons in its hand, wherein the encoding operation is as follows: U0=|H> <H|+|V><V|,U1=|V><H|-|H><V|; The random encoding uses U0 and U1 codes randomly. The information encoding selects U0 and U1 codes according to the information to be sent. U0 represents information 0 and U1 represents information 1.

7. A quantum-secure direct communication method based on a symmetric fully passive light source according to claim 1, characterized in that: In step 4, the information receiver performs X-basis or Z-basis measurements on the received photons. Specifically, when the initial state sent by the information receiver is |H> and |V>, Z-basis measurement is performed; when the initial state sent by the information receiver is |+> and |->, X-basis measurement is performed.

8. A quantum-safe direct communication system, characterized in that, It includes an information sender and an information receiver for performing the communication method according to any one of claims 1 to 7.

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