A continuous variable quantum secure direct communication method with four-state discrete modulation

Abstract

The present invention belongs to the technical field of quantum secure communication, and relates to a four-state discrete modulation continuous variable quantum secure direct communication method, which specifically comprises the following steps: S1, the information sender Alice divides the information into data blocks and adds detection bits to obtain secret information; S2, the information sender Alice prepares a dual-mode compressed entangled light S A Beam and S B The information sender Alice keeps S A The beam is used as the signal light, and S B The light beam is sent to the information receiver Bob as detection light; S3, after receiving the detection light, the information receiver Bob authenticates the identity with the information sender Alice and determines whether the channel is secure; in the present invention, in the information modulation stage, the method maps the secret information with the detection bit to four coherent states and performs four-state discrete modulation, which is not only more compatible with the current classical communication system, but also can achieve a longer communication distance than Gaussian modulation continuous variable quantum secure direct communication.

Description

Technical Field

[0001] The invention belongs to the technical field of quantum secure communication and relates to a continuous variable quantum secure direct communication method of four-state discrete modulation. Background Art

[0002] In the field of quantum secure communication technology, quantum secure direct communication (QSDC) is an important form of quantum communication. It is based on the basic principles of quantum mechanics and can directly transmit secret information through quantum channels to achieve unconditional secure and confidential communication. Existing theoretical studies have shown that QSDC can eliminate security vulnerabilities related to key distribution, key storage and management, and ciphertext transmission, and after directly transmitting information through quantum channels, the security and immediacy of communication have been significantly improved. After Long et al. proposed the first QSDC scheme using Einstein-Podolsky-Rosen (EPR) in 2000, QSDC based on discrete variables has developed rapidly. In recent years, many QSDC schemes based on discrete variables based on different types of quantum states or using various technologies have been proposed.

[0003] Compared with the need to meet the conditions of single photon detection in discrete variables, the continuous variable (CV) quantum communication system can be integrated with the existing optical communication system, which is more conducive to its experimental realization and practical promotion, and the state preparation and measurement of continuous variable QSDC are simpler. Therefore, a continuous variable quantum secure direct communication (CV-QSDC) scheme based on Gaussian modulation is proposed to systematically solve the problem of performance analysis. However, under the conditions of low signal-to-noise ratio and long-distance transmission, the negotiation efficiency under the Gaussian modulation protocol is very low. A. Leverrier and P. Grangier first considered the use of discrete modulation and proposed a four-state discrete modulation coherent state continuous variable quantum key distribution (CVQKD) protocol. They found that discrete modulation (such as four-state discrete modulation) can achieve higher negotiation efficiency under low signal-to-noise ratio and achieve long-distance transmission under low signal-to-noise ratio.

[0004] Drawing on the application of discrete modulation technology in the above-mentioned CVQKD system, a continuous variable quantum secure direct communication method with four-state discrete modulation is proposed to achieve long-distance quantum secure direct communication under low signal-to-noise ratio. Summary of the invention

[0005] The purpose of the present invention is to provide a continuous variable quantum secure direct communication method of four-state discrete modulation, which mainly solves the technical problems mentioned in the prior art.

[0006] To achieve the above object, the present invention provides the following technical solutions:

[0007] A four-state discrete modulation continuous variable quantum secure direct communication method, which uses four-state discrete modulation to achieve long-distance transmission, specifically includes the following steps:

[0008] S1, the information sender Alice divides the information into data blocks and adds detection bits to obtain the secret information;

[0009] S2. The information sender Alice prepares dual-mode compressed entangled light, and the dual-mode compressed entangled light includes S A Beam and S B beam;

[0010] The information sender Alice retains S A The beam is used as the signal light, and S B The light beam is sent as detection light to the information receiver Bob;

[0011] S3, after receiving the detection light, the information receiver Bob performs identity authentication with the information sender Alice and determines whether the channel is secure;

[0012] If the identity authentication is correct and the channel is secure, the information sender Alice loads the secret information onto the signal light through four-state discrete modulation to generate a modulated signal light S′ A , the information sender Alice transmits the modulated signal light S′ A Sending to the information receiver Bob via the channel;

[0013] If the identity authentication fails or the channel is not secure, the transmission is terminated and the process returns to S2 to retransmit the transmission.

[0014] S4, the information receiver Bob receives the modulated signal light S' A After that, the modulated signal light S′ A and the S B The beams are measured jointly and the measurement result X is obtained. m and P m ;

[0015] S5, the information sender Alice sends the detection bit information to the information receiver Bob through the classic authentication channel, and the information receiver Bob selects the detection bit information corresponding to the detection bit information transmitted by the information sender Alice from the measurement results, compares the two, and then analyzes the overall error rate to detect whether the channel is secure;

[0016] If the channel is not secure, the transmission is terminated and the process returns to S2 to perform the transmission again.

[0017] If the channel is secure, the information receiver Bob de-maps the secret information and determines whether to continue the communication;

[0018] If communication continues, the process returns to S1; if communication does not continue, the process ends.

[0019] Preferably, in S2, the method for preparing the dual-mode compressed entangled light specifically includes:

[0020] The information sender Alice uses the dual-mode compression operator S(r) to convert the coherent light s1 and s2 emitted by the laser into dual-mode compressed entangled light S A and S B , expressed as:

[0021]

[0022] Where r is the compression coefficient, cosh(r) is the hyperbolic cosine function, sinh(r) is the hyperbolic sine function, is the conjugate operator of the two-mode compression operator S(r).

[0023] Preferably, in S3, the identity authentication method specifically includes:

[0024] The information receiver Bob selects a set of random positions on the detection light, measures two orthogonal components of the detection light at the random positions, obtains a first measurement result, and publishes the selected positions;

[0025] The information sender Alice selects a measurement position of the detection light, measures two orthogonal components of the signal light, and obtains a second measurement result, wherein the measurement position is the same as the measurement position of the detection light selected by the information receiver Bob;

[0026] Comparing the second measurement result with the first measurement result, and performing statistical analysis based on the measurement position to determine whether the identity authentication is successful;

[0027] If the error rate of the statistical result is lower than the set threshold, the identity authentication is considered to have failed; otherwise, the identity authentication is considered to have succeeded.

[0028] Preferably, in S3, the method for determining the channel security specifically includes:

[0029] The information sender Alice selects a set of random positions on the signal light, measures two orthogonal components of the signal light at the random positions, obtains a third measurement result, and publishes the selected positions;

[0030] The information receiver Bob selects a measurement position of the signal light, measures two orthogonal components of the detection light, and obtains a fourth measurement result, wherein the measurement position is the same as the measurement position of the signal light selected by the information sender Alice;

[0031] Perform entanglement judgment on the fourth measurement result and the third measurement result, and the judgment condition is:

[0032] 〈[△(X A +X B )] 2 〉+〈[△(P A -P B )] 2 〉<2

[0033] Where, X A and P A are the two orthogonal components of the signal light, namely the canonical position X A and the canonical momentum P A ;X B and P B are the two orthogonal components of the detection light, namely the canonical position X B and the canonical momentum P B ;

[0034] If the measurement result satisfies the entanglement judgment condition, the channel is considered to be safe;

[0035] If the measurement result does not meet the entanglement judgment condition, the channel is considered to be unsafe.

[0036] Preferably, in S4, the measurement result X obtained by the information receiver Bob m and P m Respectively expressed as:

[0037] X m =(X′ A -X B )

[0038] P m =(P′ A -P B )

[0039] Where XB and PB are the canonical position and canonical momentum of the detection light, respectively, and X′ B and P′ B are the modulated signal light S′ A The canonical position and canonical momentum of m and P m They are respectively the measurement results of the canonical position and canonical momentum of the information receiver Bob.

[0040] Preferably, in S5, the method for detecting whether the channel is secure specifically includes:

[0041] If the error rate is lower than a preset safety threshold, the channel is considered safe; otherwise, the channel is considered unsafe and the transmission is terminated.

[0042] Compared with the prior art, the present invention has the following beneficial effects:

[0043] 1. In the present invention, in the information modulation stage, the method maps the secret information with the detection bit to four coherent states and performs four-state discrete modulation, which is not only more compatible with the current classical communication system, but also can achieve a longer communication distance than Gaussian modulation continuous variable quantum secure direct communication.

[0044] 2. In the present invention, the modulation variances of the Gaussian modulation protocol and the four-state discrete modulation protocol are set to 0.3 and 18.8 respectively. Compared with the Gaussian modulation CVQSDC protocol, the four-state discrete modulation CVQSDC protocol can significantly extend the maximum transmission distance. BRIEF DESCRIPTION OF THE DRAWINGS

[0045] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0046] Figure 1 It is a flow chart of the quantum secure direct communication method of the four-state discrete modulation of the present invention;

[0047] Figure 2 It is the distribution diagram of the four-state discrete modulation in the phase space of the present invention;

[0048] Figure 3 It is a performance analysis diagram of the effective information volume and transmission distance of the present invention. DETAILED DESCRIPTION

[0049] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0050] like Figure 1-Figure 3As shown, the present invention provides a four-state discrete modulation continuous variable quantum secure direct communication method, which uses four-state discrete modulation to achieve long-distance transmission, and specifically includes the following steps:

[0051] Step 1: Alice, the sender of the information, first divides the information into data blocks and randomly inserts the detection bit into each data block to obtain the secret information.

[0052] Step 2: The information sender Alice uses the dual-mode compression operator S(r) to convert the coherent light emitted by the laser into dual-mode compressed entangled light according to the random bit string. The dual-mode compressed entangled light includes S A Beam and S B The beam can be expressed as:

[0053]

[0054] Where r is the compression coefficient, cosh(r) is the hyperbolic cosine function, sinh(r) is the hyperbolic sine function, is the conjugate operator of the two-mode compression operator S(r); the two-mode compression state can be generated by a non-degenerate optical parametric amplifier; at the same time, the information sender Alice retains S A The beam is used as the signal light, and S B The light beam is sent as detection light to the information receiver Bob.

[0055] Step 3: After receiving the detection light, the information receiver Bob authenticates himself with the information sender Alice to determine whether the channel is secure.

[0056] The identity verification methods include:

[0057] The information receiver Bob selects a set of random positions on the detection light, measures two orthogonal components of the detection light at the random positions, obtains a first measurement result, and publishes the selected position; the information sender Alice selects a measurement position of the detection light, measures two orthogonal components of the signal light, obtains a second measurement result, and the measurement position is the same as the measurement position of the detection light selected by the information receiver Bob; then the second measurement result is compared with the first measurement result, and the statistical results are combined with the measurement positions to determine whether the identity authentication is successful; if the error rate of the statistical results is lower than the set threshold, the identity authentication is considered to have failed, otherwise the identity authentication is considered to have succeeded.

[0058] The method for determining channel security specifically includes:

[0059] The information sender Alice selects a set of random positions on the signal light, and measures the two orthogonal components of the signal light at the random positions to obtain the third measurement result, and publishes the selected position; the information receiver Bob selects the measurement position of the signal light, measures the two orthogonal components of the detection light, and obtains the fourth measurement result, and the measurement position is the same as the measurement position of the signal light selected by the information sender Alice; then the fourth measurement result and the third measurement result are entangled, and the judgment condition is:

[0060] 〈[△(X A +X B )] 2 〉+〈[△(P A -P B )] 2 〉<2

[0061] Where, X A and P A are the two orthogonal components of the signal light, namely the regular position X A and the canonical momentum P A ;X B and P B are the two orthogonal components of the detected light, i.e. the canonical position X B and the canonical momentum P B ;

[0062] If the measurement result meets the entanglement judgment condition, the channel is considered safe;

[0063] If the measurement result does not meet the entanglement judgment condition, the channel is considered to be unsafe, indicating that there is an eavesdropper in the channel.

[0064] In this embodiment, if the identity authentication is successful and the channel is secure, the information sender Alice saves the S A The secret information is encoded on the orthogonal components of the light beam, resulting in four coherent states │α k 〉; then generate modulated signal light S′ A And send it to the information receiver Bob;

[0065] Among them, │α k 〉=│αe^i(2k+1)π / 4〉,k=0,1,2,3;

[0066] Where α is the whole amplitude (a positive real number used to maximize the effective information amount, and the modulation variance is V A =2α 2 ), where the encoding is the canonical position X′ of the coherent state through the ± random sequence A and the canonical momentum P′ A Modulation is performed to complete the task. The specific modulation relationship is shown in the following table:

[0067]

[0068] If the identity authentication fails or the channel is not secure, the transmission is terminated and then returns to step 2 to perform the transmission again.

[0069] Step 4: Information sender Alice modulates the signal light S′ A The information is transmitted to the information receiver Bob through the channel (quantum channel), and the information receiver Bob modulates the signal light S' A The detection light is jointly measured and the measurement result is obtained, which can be expressed as:

[0070] X m =(X′ A -X B )

[0071] P m =(P′ A -P B )

[0072] Where, X B and P B are the canonical position and canonical momentum of the detected light, X′ B and P′ B The modulated signal light S′ is A The canonical position and canonical momentum of m and P m They are the measurement results of the canonical position and canonical momentum of the information receiver Bob, which can be further expressed as α′eiθ; the measurement results are then mapped to obtain the original information.

[0073] The information mapping process is shown in the following table:

[0074]

[0075]

[0076] Among them, X m = |α′|cosθ, P m =│α′│sinθ, get information

[0077] Step 5: Information sender Alice sends the detection bit information to information receiver Bob through the classic authentication channel. Information receiver Bob selects the detection bit information corresponding to the information sent by information sender Alice from the measurement results, compares the two, and then analyzes the overall error rate to detect whether the channel is secure.

[0078] The method for detecting whether a channel is secure specifically includes:

[0079] If the error rate is lower than the preset safety threshold (the safety threshold is determined by comparing the measurement results selected by the information receiver Bob with the measurement results published by the information sender Alice, and the percentage of the correct results in the total amount of redundant information; ideally, the safety threshold is generally considered to be quite low; in actual channel transmission, the impact of channel environment noise on the system can be determined through experiments, thereby determining the safety threshold), then the channel is considered safe, S A The transmission of the light beam is safe, assuming that there is no eavesdropper monitoring the quantum channel. Then the information receiver Bob de-maps the secret information and determines whether to continue communication. If communication continues, it returns to step one to continue execution. If communication does not continue, it indicates that the communication is over. Otherwise, it is considered that the channel is not safe and the communication is eavesdropped. The transmission is terminated and then returns to step two to retransmit the communication.

[0080] It should be noted that in this embodiment, the actual quantum channel and communication equipment will inevitably have a certain impact on the transmission and measurement of the quantum state, thereby affecting the performance of the entire system; therefore, after obtaining the initial data, the data needs to be post-processed.

[0081] In the present invention, during the information modulation stage, the method divides the information into data blocks, inserts detection bits to obtain secret information, and then maps the secret information to four coherent states, performing four-state discrete modulation. This is not only more compatible with current classical communication systems, but also can achieve a longer communication distance than Gaussian modulation continuous variable quantum secure direct communication.

[0082] In this embodiment, in order to verify the feasibility and effectiveness of the method of the present invention, the following experiments were performed:

[0083] The functional relationship between the effective amount of information and the transmission distance between the information sender Alice and the information receiver Bob of the four-state discrete modulation CV-QSDC protocol and the Gaussian modulation protocol. The modulation variances of the two protocols are set to 0.3 and 18.8 respectively. Under this variance, each protocol obtains the best performance under practical conditions.

[0084] Simulation results reference Figure 3 As shown, Figure 3 The solid line in the middle represents the CVQSDC protocol with four-state discrete modulation, and the dotted line represents the CVQSDC protocol with Gaussian modulation. The modulation variances of the Gaussian modulation protocol and the four-state discrete modulation protocol are set to the optimal values ​​of 0.3 and 18.8, respectively. Compared with the Gaussian modulation CVQSDC protocol, the four-state discrete modulation CVQSDC protocol can significantly extend the maximum transmission distance.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the aforementioned embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A four-state discrete modulation continuous variable quantum secure direct communication method, characterized in that: Four-state discrete modulation is used to achieve long-distance transmission, which specifically includes the following steps: S1, the information sender Alice divides the information into data blocks and adds detection bits to obtain the secret information; S2. The information sender Alice prepares dual-mode compressed entangled light, and the dual-mode compressed entangled light includes S A Beam and S B beam; The information sender Alice retains S A The beam is used as the signal light, and S B The light beam is sent as detection light to the information receiver Bob; S3, after receiving the detection light, the information receiver Bob performs identity authentication with the information sender Alice and determines whether the channel is secure; If the identity authentication is correct and the channel is secure, the information sender Alice loads the secret information onto the signal light through four-state discrete modulation to generate a modulated signal light S′ A , the information sender Alice transmits the modulated signal light S′ A Sending to the information receiver Bob via the channel; If the identity authentication fails or the channel is not secure, the transmission is terminated and the process returns to S2 to retransmit the transmission. S4, the information receiver Bob receives the modulated signal light S' A After that, the modulated signal light S′ A and the S B The beams are measured jointly and the measurement result X is obtained. m and P m ; S5, the information sender Alice sends the detection bit information to the information receiver Bob through the classic authentication channel, and the information receiver Bob selects the detection bit information corresponding to the detection bit information transmitted by the information sender Alice from the measurement results, compares the two, and then analyzes the overall error rate to detect whether the channel is secure; If the channel is not secure, the transmission is terminated and the process returns to S2 to perform the transmission again. If the channel is secure, the information receiver Bob de-maps the secret information and determines whether to continue the communication; If communication continues, the process returns to S1; if communication does not continue, the process ends.

2. The method of continuous variable quantum secure direct communication with four-state discrete modulation according to claim 1, characterized in that: In S2, the method for preparing the dual-mode compressed entangled light specifically includes: The information sender Alice uses the dual-mode compression operator S(r) to convert the coherent light s1 and s2 emitted by the laser into dual-mode compressed entangled light S A and S B , expressed as: Where r is the compression coefficient, cosh(r) is the hyperbolic cosine function, sinh(r) is the hyperbolic sine function, is the conjugate operator of the two-mode compression operator S(r).

3. The method of continuous variable quantum secure direct communication with four-state discrete modulation according to claim 1, characterized in that In S3, the identity authentication method specifically includes: The information receiver Bob selects a set of random positions on the detection light, measures two orthogonal components of the detection light at the random positions, obtains a first measurement result, and publishes the selected positions; The information sender Alice selects a measurement position of the detection light, measures two orthogonal components of the signal light, and obtains a second measurement result, wherein the measurement position is the same as the measurement position of the detection light selected by the information receiver Bob; Comparing the second measurement result with the first measurement result, and performing statistical analysis based on the measurement position to determine whether the identity authentication is successful; If the error rate of the statistical result is lower than the set threshold, the identity authentication is considered to have failed; otherwise, the identity authentication is considered to have succeeded.

4. The method of continuous variable quantum secure direct communication with four-state discrete modulation according to claim 1, characterized in that: In S3, the method for determining the channel security specifically includes: The information sender Alice selects a set of random positions on the signal light, measures two orthogonal components of the signal light at the random positions, obtains a third measurement result, and publishes the selected positions; The information receiver Bob selects a measurement position of the signal light, measures two orthogonal components of the detection light, and obtains a fourth measurement result, wherein the measurement position is the same as the measurement position of the signal light selected by the information sender Alice; Perform entanglement judgment on the fourth measurement result and the third measurement result, and the judgment condition is: 〈[△(X A +X B )] 2 〉+〈[△(P A -P B )] 2 〉<2 Where, X A and P A are the two orthogonal components of the signal light, namely the canonical position X A and the canonical momentum P A ;X B and P B are the two orthogonal components of the detection light, namely the canonical position X B and the canonical momentum P B ; If the measurement result satisfies the entanglement judgment condition, the channel is considered to be safe; If the measurement result does not meet the entanglement judgment condition, the channel is considered to be unsafe.

5. The method of continuous variable quantum secure direct communication with four-state discrete modulation according to claim 1, characterized in that: In S4, the information receiver Bob obtains the measurement result X m and P m Respectively expressed as: X m =(X′ A -X B ) P m =(P′ A -P B ) Where XB and PB are the canonical position and canonical momentum of the detection light, respectively, and X′ B and P′ B are the modulated signal light S′ A The canonical position and canonical momentum of m and P m They are respectively the measurement results of the canonical position and canonical momentum of the information receiver Bob.

6. The method of continuous variable quantum secure direct communication with four-state discrete modulation according to claim 1, characterized in that: In S5, the method for detecting whether the channel is secure specifically includes: If the error rate is lower than a preset safety threshold, the channel is considered safe; otherwise, the channel is considered unsafe and the transmission is terminated.

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