Quantum key distribution method and system based on mode matching and passive decoy state

Abstract

The present invention belongs to the field of quantum communication technology, and specifically relates to a quantum key distribution method and system based on mode pairing and passive decoy state. In view of the shortcomings of the existing quantum key distribution method based on mode pairing using the active decoy state method, which may have the problem of side channel information leakage, the present invention adopts the following technical solution: a quantum key distribution method based on mode pairing and passive decoy state, including: both parties generate a pair of entangled photons; both parties encode information on the signal photons through the signal path and the decoy path respectively to obtain a coherent quantum state, and randomly send the modulated signal state or decoy state to Charlie; Charlie performs single-photon interferometry on the coherent quantum states sent by both parties and publishes the measurement results; repeats mode pairing after N rounds; basis vector screening; key mapping; parameter estimation; key extraction. The beneficial effects of the present invention are: ensuring a high key generation rate while improving security.

Description

Technical Field

[0001] The present invention belongs to the field of quantum communication technology, and in particular relates to a quantum key distribution method and system based on mode pairing and passive decoy state. Background Art

[0002] The power communication network is an integral part of the power system, and its secure operation is crucial for its stable operation. Power system operations, control commands, and business operations involve a significant amount of private data, requiring high levels of real-time performance and security. Therefore, power systems ensure data communication security by building dedicated power networks. With the advancement of information technology, dedicated networks are also vulnerable to intrusion, and attacks on power systems are a common occurrence. Therefore, ensuring the operational security of power systems has become a crucial research topic.

[0003] Applying new quantum cryptography technologies to ensure the security of power communication networks is a key research area. Quantum Key Distribution (QKD) technology (also known as the QKD protocol) is currently one of the most heavily invested and researched areas in quantum cryptography. Unlike other cryptographic technologies, the QKD protocol leverages the properties of quantum states to ensure the security of the key distribution process. While using a one-time pad, it achieves absolute security as proven by information theory and is remarkably resistant to attacks using the ultra-high parallel computing power of quantum computing.

[0004] A common quantum key distribution method is measurement-device-independent quantum key distribution (MDI-QKD). In this method, two communicating parties, A and B, are both transmitters. They simultaneously send fixed-pair coherent optical pulses to an untrusted measurement device, C, in the channel. Each pair of coherent optical pulses corresponds to a single photon signal. C then publishes the interference result of the two single-photon signals sent by A and B to assist A and B in generating a key. However, if one coherent optical pulse is lost during the transmission process, that pair of coherent optical pulses cannot be used to generate the key, resulting in a decrease in the number of single-photon signals used for key generation. Consequently, the key encoding rate is low.

[0005] In 2022, Professor Ma Xiongfeng's team proposed a mode-pairing quantum key distribution (MP-QKD) protocol. By combining two successful detection events in the original dual-field protocol into a pair, this protocol achieves dual-mode interference, effectively reducing the technical complexity of the experiment. (See CN112491536A for details.) However, MP-QKD uses a weakly coherent light source as the signal source, which contains fewer single-photon components, significantly limiting the key rate.

[0006] Furthermore, existing mode-pairing quantum key distribution (MP-QKD) methods do not involve decoy states. When using traditional active decoy state methods, side-channel information leakage may occur. Although active modulation (active decoy states) can effectively implement MP-QKD protocols, passive decoy state methods are still necessary in some special scenarios. For example, if the intensity modulator design is flawed, some side information will be introduced during the decoy state preparation process. In this case, active modulation of the main pair pulse intensity may lead to serious security issues. Summary of the Invention

[0007] The present invention addresses the shortcomings of existing quantum key distribution methods based on pattern pairing, which use active decoy states and may have side channel information leakage issues. This invention provides a quantum key distribution method based on pattern pairing and passive decoy states. This method replaces weakly coherent light sources with labeled coherent light sources with higher single-photon content to achieve a higher key generation rate. Passive decoy state modules are placed on Alice and Bob's terminals to prevent side channel information leakage in the network. This allows Alice and Bob to passively select different decoy state modes based on the response results of their respective local detectors when randomly selecting decoy state pulses, thereby increasing security. The present invention also provides a quantum key distribution system based on pattern pairing and passive decoy states.

[0008] To achieve the above object, the present invention adopts the following technical solution: a quantum key distribution method based on mode pairing and passive decoy state, the quantum key distribution method based on mode pairing and passive decoy state comprising the following steps:

[0009] S1, Alice, and Bob each generate a pair of entangled photons, where the idle photon is received by the local first detector and the signal photon is sent to the passive decoy state module;

[0010] S2, Alice, and Bob encode information on the signal photon through the signal path and the decoy path respectively to obtain a coherent quantum state A i and B i and randomly sends the modulated signal state or decoy state to Charlie;

[0011] S3, the coherent quantum state sent by Charlie to Alice and Bob A i and B i Perform single-photon interferometry measurements and publish the results. A successful detection is when only one of Charlie's two detectors responds.

[0012] S4, repeat S1 to S3 for N rounds and then perform pattern matching;

[0013] S5. Basis screening: Determine and screen the basis type based on the strengths chosen by Alice and Bob in the two successful pairing rounds;

[0014] S6, key mapping: Alice and Bob determine the initial key based on the basis, strength and phase of each pair respectively;

[0015] S7, parameter estimation;

[0016] S8. Key extraction.

[0017] As an improvement, in S2, the signal passes through the first beam splitter of the passive decoy module and enters the signal path and the decoy path respectively, where it is modulated. After the modulated signal passes through the second beam splitter, one path is sent to Charlie, and the other path passes through the third beam splitter to reach the two local detectors of Alice or Bob.

[0018] For Alice’s i The coherent quantum state is expressed as A i , where the superscript Represents Alice's end, is the intensity of the coherent state, is the phase of the coherent state, , is an imaginary unit;

[0019] If the signal is sent, the strength Randomly select from {0, μ}, and the phase Randomly select from [0, 2π), modulate the intensity of the decoy path to zero;

[0020] If the decoy state is sent, the variable attenuator of the decoy path remains unmodulated, and both paths randomly select the intensity from {0, μ} , the pulse phases on the two paths are randomly selected from [0, 2π);

[0021] Alice obtains different decoy state modes based on the response results of the second and third local detectors, and obtains the decoy state pulse phase .

[0022] As an improvement, in S2, Alice divides the detection events into four categories based on the response results of the second and third local detectors: neither responds, the first responds and the second does not respond, the first does not respond and the second responds, and both respond.

[0023] The probabilities of the four types of response events are:

[0024]

[0025] The average number of photons is The photon number distribution, is the probability of one of the four types of detection events occurring, Indicates four types of detection events, , n is the number of photon states;

[0026] The photon state is projected onto Alice's local second and third detectors. Probability Expressed as:

[0027]

[0028] in, The third beam splitter The transmittance coefficient, and are the detection efficiencies of the second and third local detectors respectively.

[0029] As an improvement, in S2, when the dark counts of Alice's three detectors are the same, that is, , and the detection efficiency is also the same, that is , the probability of the photon number of the four types of events is:

[0030]

[0031] in, is the transmittance of the third beam splitter. When the transmittance of the third beam splitter is 0.5, then and same.

[0032] As an improvement, in S4, when both Alice and Bob send signal states, for all rounds of successful detection, Alice and Bob combine two rounds of successful detection whose interval does not exceed the maximum pairing interval into a pair, and use the coding phases or intensities in these two rounds to form a data pair.

[0033] As an improvement, in S5, if the strength selected by Alice in two successful pairing rounds is (0, μ) or (μ, 0), Alice marks the data pair as Z basis; if the strength is (μ, μ), it is marked as X basis; if the strength is (0, 0), it is marked as 0 basis; Bob uses the same method to set the basis of the data pair; after the basis is set, Alice and Bob announce the basis of each data pair. If both announce the X basis or the Z basis, it is retained; otherwise, it is discarded.

[0034] As an improvement, in S6, for the index value i and j For each Z-basis data pair, if Alice’s strength ( , )=(0, μ ), then Alice will give her key Set to 0, otherwise Set to 1; Bob's initial key bit setting is exactly opposite to Alice's, that is, Bob's strength = (0, μ ), his key Set to 1, otherwise Set to 0;

[0035] For X-basis data pairs, the initial key Obtained from the relative phase, the calculation formula is:

[0036]

[0037]

[0038] ;

[0039] Bob determines the initial key bits in a similar manner k b and alignment angle θ b , but Bob has an additional key flip operation: if in two rounds, the i Hedi j If the detector response is (L,L) or (R,R), Bob keeps his key bits; if the detector response is (L,R) or (R,L), Bob flips the key bits, and in the X basis, only when Alice and Bob’s alignment angles are equal, that is, θ a = θ b The data pair will be kept only when the value is set to 0, otherwise the data pair will be discarded.

[0040] As an improvement, in S7, Alice and Bob perform parameter estimation on the phase flip error rate and quantum bit error rate of the Z basis.

[0041] As an improvement, in S8, Alice and Bob use the Z basis pair in the sent signal state to generate the key, and according to 、 and Perform key negotiation and secret amplification to obtain secure keys;

[0042] The key generation rate is expressed as:

[0043]

[0044] in, , represents the logarithmic expected value generated in each round, l is the maximum pairing interval, p is the probability that a round is a successful detection event, r s is the probability that a successfully detected pulse pair is a signal pair, and are the proportion of expected single photon pairs in the signal pair and the phase error rate of single photon pairs, f is the error correction efficiency, is the bit error rate of the signal pair, is the binary Shannon entropy function.

[0045] A quantum key distribution system based on mode pairing and passive decoy state includes two communication devices and a measuring device for executing the aforementioned quantum key distribution method based on mode pairing and passive decoy state, wherein the measuring device is communicatively connected to the two communication devices respectively, and the two communication devices are communicatively connected to each other.

[0046] The quantum key distribution method based on mode pairing and passive decoy states of the present invention, based on the existing mode pairing quantum key distribution protocol, replaces the weak coherent light source with a label-paired coherent light source with a high single-photon component as the signal light source at Alice and Bob to achieve a higher key generation rate. At the same time, passive decoy state devices are placed at Alice and Bob to avoid information leakage in the side channel of the network. When Alice and Bob randomly select decoy state pulses, they can passively select decoy states of different modes according to the response results of their respective local detectors, thereby increasing security. The present invention has the following advantages: (1) It is an extension of the mode-pairing quantum key distribution method, and its key generation rate can break through the linear key rate limit; (2) Compared with the original mode-pairing quantum key distribution protocol under the same conditions, it has a higher key generation rate and a longer transmission distance; (3) The mode-pairing strategy is adopted, and no global phase lock is required during implementation, which reduces the difficulty of experimental technology; (4) The passive decoy state method is adopted to avoid the leakage of additional information through the side channel, thereby improving the security of the quantum key distribution protocol; (5) It can be implemented through existing optical equipment and has great application prospects in power communication scenarios. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 This is an architectural diagram of a quantum key distribution system based on pattern pairing and passive decoy states according to an embodiment of the present invention.

[0048] Figure 2 This is a flowchart of a quantum key distribution method based on pattern pairing and passive decoy state according to an embodiment of the present invention.

[0049] Figure 3 This is a simulation result diagram of the quantum key distribution method based on mode pairing and passive decoy state in an embodiment of the present invention. DETAILED DESCRIPTION

[0050] The technical solutions of the embodiments of the present invention are explained and described below, but the following embodiments are only preferred embodiments of the present invention and are not exhaustive. Based on the embodiments in the embodiments, other embodiments obtained by those skilled in the art without creative work are all within the scope of protection of the present invention.

[0051] See also Figure 1 The quantum key distribution system based on pattern pairing and passive decoy state in an embodiment of the present invention includes two communication devices Alice and Bob and a measuring device Charlie, wherein the measuring devices are respectively communicatively connected to the two communication devices, and the two communication devices are communicatively connected to each other.

[0052] Alice and Bob's channels to Charlie are symmetric and independent and identically distributed. For the same process for Alice and Bob, only Alice's is explained.

[0053] Alice end includes a heralded pair-coherent source (HPCS), a first detector D1 a , first beam splitter BS1 a , variable attenuator on path S (signal path) and first phase encoder PM1 a , variable attenuator on path D (decoy path) and second phase encoder PM2 a , the second beam splitter BS2 after the path S and path D merge a , the third beam splitter BS3 a , the second detector D2 a , the third detector D3 a . After passing through the second beam splitter BS2 a The signal goes all the way to Charlie, and the other goes through the third beam splitter BS3 a Then it reaches the second detector D2 a , the third detector D3 a。

[0054] Charlie has two detectors D L and D R , respectively detecting the beams from Alice and Bob passing through the second beam splitter BS2 a The signal after beam splitting.

[0055] See also Figure 2 The quantum key distribution method based on mode pairing and passive decoy state of an embodiment of the present invention includes:

[0056] S1, Alice, and Bob each generate a pair of entangled photons, where the idle photon is received by the local first detector and the signal photon is sent to the passive decoy state module;

[0057] S2, Alice, and Bob encode information on the signal photon through the signal path and the decoy path respectively to obtain a coherent quantum state A i and B i and randomly sends the modulated signal state or decoy state to Charlie;

[0058] S3, the coherent quantum state sent by Charlie to Alice and Bob A i and B iPerform single-photon interferometry measurements and publish the results. A successful detection is when only one of Charlie's two detectors responds.

[0059] S4, repeat S1 to S3 for N rounds and then perform pattern matching;

[0060] S5. Basis screening: Determine and screen the basis type based on the strengths chosen by Alice and Bob in the two successful pairing rounds;

[0061] S6, key mapping: Alice and Bob determine the initial key based on the basis, strength and phase of each pair respectively;

[0062] S7, parameter estimation;

[0063] S8. Key extraction.

[0064] In this embodiment, in S1, Alice and Bob generate a pair of entangled photons through the nonlinear crystal of HPCS and enter the idle optical path and signal optical path respectively. The photons in the idle optical path reach the first detector D1. a , used to predict the arrival time of photons in the signal light path, only when the first detector D1 a When responding, the pulse modulated by the photons in the signal light path is used for encoding. The photon distribution function expression in the signal pulse emitted by the tag pair coherent light source is:

[0065]

[0066] Where, The average number of photons is The photon number distribution (i.e. the photon number distribution in HPCS), represents the average intensity of the signal pulse, n represents the number of photons, and are the dark count rate and detection efficiency of the detector, represents the post-selection probability, is the modified Bessel function of the first kind.

[0067] Theoretically, the photon number distribution function of a weak coherent light source is: , with the same parameters ( , , η ) conditions, the ratio of the number of photon pulses of the two light sources is shown in Table 1.

[0068] Table 1 Ratios of vacuum pulses, single-photon pulses, and multi-photon pulses in different light sources

[0069]

[0070] As can be seen from Table 1, compared with the weak coherent light source, the pulses generated by the tag-paired coherent light source have a higher single-photon component and a reduced vacuum component, which is closer to the ideal single-photon source and is beneficial to improving the key generation rate of MP-QKD.

[0071] In this embodiment, in S2, Alice randomly sends a signal state or a deception state in each round of distribution, and for the first i wheel( i =1, 2, ..., N ) quantum state, its coherent quantum state is A i , where the superscript Represents Alice's end, is the intensity of the coherent state, is the phase of the coherent state, , is a virtual unit. The specific distribution process is as follows:

[0072] If the signal state is sent at this time, The intensity will be randomly selected from {0, μ}, while the phase The first phase modulator is randomly selected from [0, 2π), that is, the decoy path D is blocked (the variable attenuator of the decoy path is modulated to zero), The phase of the modulation signal state;

[0073] If the decoy state is sent at this time, the variable optical attenuator (VOA) of the decoy path D is not modulated, and the intensity of the signal path and the decoy path are randomly selected from {0, μ} , and the phase modulator and Randomly select the phase from [0, 2π) as the pulse phase on the two paths;

[0074] Different decoy state modes are obtained according to the response results of the local second and third detectors in the passive decoy state module, and the decoy state pulse phase is obtained. .

[0075] The specific decoy mode is as follows: Alice detects two local detectors ( ) response results, the detection events are divided into four categories, respectively Indicates that the event The two detectors do not respond. correspond Responsive and No response, Corresponding to Responsive and No response, event Both detectors respond. If the second detector is known The dark count is , the third detector The dark count is , and projected onto and The photon number state is , the probability of different response events of the local detector can be calculated as shown in Table 2.

[0076] Table 2 Probability of different events

[0077]

[0078] For any photon state, projected onto The probability can be expressed as:

[0079]

[0080] in, The third beam splitter The transmittance coefficient, and The second detector and the third detector On this basis, the probability of the response event can be obtained as:

[0081]

[0082] For simplicity and without loss of generality, it is assumed that the dark counts of each detector in the system are the same, that is, , and the detection efficiency is also the same, that is , so the probability of the photon number of the four events can be obtained as:

[0083]

[0084] If the beam splitter The transmittance is 0.5, then in the above formula and same.

[0085] Bob performs the same quantum state preparation process as Alice to prepare its coherent quantum state. .

[0086] In this embodiment, in S3, Charlie sends A i and B i Perform single photon interferometry and publish the measurement results, in which Charlie's two detectors (DL and D R A successful detection is when there is only one response in the detection. After N rounds of repetition, Alice and Bob perform subsequent processing on the acquired data.

[0087] In this embodiment, in S4, when both Alice and Bob are in the signal state, for all successful detection rounds, Alice and Bob combine two successful detection rounds separated by no more than the maximum pairing interval l into a pair, and use the encoding phases or intensities in these two rounds to form a data pair. Specifically, (i) first find the first successful detection round and record it as the preceding pulse; (ii) search backward for the next successful detection round. If the interval between the newly found successful detection round and the existing preceding pulse is within the maximum pairing interval l, then this round is determined to be the corresponding subsequent pulse, and pairing is successful; otherwise, pairing fails, the existing preceding pulse is discarded, and this round is set as the new preceding pulse; (iii) continue to search backward, repeating steps (i) to (ii) until all pairings are completed.

[0088] In this embodiment, in S5, a basis is set based on the strengths of the two rounds i and j that form a pair, including a Z basis, an X basis, or a 0 basis. If Alice selects a strength of (0, μ) or (μ, 0) for the two rounds that are successfully paired, Alice marks the data pair as a Z basis; if the strength is (μ, μ), it is marked as an X basis; if the strength is (0, 0), it is marked as a 0 basis. Bob uses the same method to set the basis for the data pair. After the basis is set, Alice and Bob announce the basis for each data pair. If both announce an X basis or a Z basis, it is retained; otherwise, it is discarded.

[0089] In this embodiment, in S6, Alice and Bob determine the initial key based on the basis, strength, and phase selected for each pair. For each Z-basis data pair with index values ​​i and j, if Alice selects strength = (0, μ), Alice sets her key to 0; otherwise, it is set to 1. Bob's initial key bit setting is exactly the opposite of Alice's, that is, if Bob selects strength = (0, μ), he sets his key to 1, otherwise, it is set to 0. For X-basis data pairs, the initial key is obtained from the relative phase. By Available ,and ; Bob determines the initial key bits in a similar manner k b and alignment angle θ b, but Bob has an additional key flip operation. If in both rounds, the detector responses of the i-th and j-th rounds are (L, L) or (R, R), then Bob keeps his key bits; if the detector response is (L, R) or (R, L), then Bob needs to flip his key bits, and in the X basis, only when Alice and Bob’s alignment angles are equal ( θ a = θ b ), the data pair will be kept, otherwise the data pair will be discarded.

[0090] In this embodiment, in S7, Alice and Bob perform parameter estimation on the phase flip error rate and quantum bit error rate of the Z-basis data.

[0091] In this embodiment, in S8, Alice and Bob use the Z basis pair in the signaling state to generate the key. 、 and Perform key negotiation and secret amplification to obtain a secure key.

[0092] Since only the light source distribution and the modulation method of the decoy state intensity are changed, the success events, pairing strategy, mode pairing, basis vector screening, parameter estimation, and key extraction remain unchanged. Therefore, the key generation rate formula should be the same as the original MP-QKD protocol, expressed as:

[0093]

[0094] in, , represents the logarithmic expected value generated in each round, l is the maximum pairing interval, p is the probability that a round is a successful detection event, r s is the probability that a successfully detected pulse pair is a signal pair, and are the proportion of expected single photon pairs in the signal pair and the phase error rate of single photon pairs, f is the error correction efficiency, is the bit error rate of the signal pair, is the binary Shannon entropy function.

[0095] In order to facilitate the subsequent key generation rate analysis, i Alice's sending state in the round is recorded as ,in Indicates that the transmitted light intensity is 0 or μ , is a random phase. Bob’s coherent state is recorded as , , is a random phase. Use array Indicates the i The strength of Alice and Bob in the round.

[0096] For the first ( i , j ) pulse pairs, let ,in is a modulo 2 addition operation, when hour,( i , j ) pair is set as Z basis pair. i In the round, two variables L are used i 、R i To express the i Round D L and D R The response variable of the detector is , detection probability Expressed as:

[0097]

[0098] in, is the dark count rate of the detector, is the photon number distribution function expression of HPCS, represents the total transmittance of the system, where represents the transmittance of the channel, is the fiber loss system, is the transmission distance, i.e. the distance between Alice and Bob, is the efficiency of the detector.

[0099] No. i The phase-random coherent state emitted by the wheel can also be regarded as a mixture of photon number states, Indicates that Alice and Bob emit photon numbers as and The detection probability when , the detection probability can be expressed as:

[0100]

[0101] According to formula (2), i The probability of a successful response to a signal is:

[0102]

[0103] The signal pairs are independent of each other. i Round and j After round pairing, the probability of successful response in the Z basis is:

[0104] .

[0105] In this embodiment, the passive decoy module includes a signal path S (including a variable attenuator and a first phase encoder PM1 a ), the deception path D includes a variable attenuator and a second phase encoder PM2 a ) and the second beam splitter BS2 a , the third beam splitter BS3 a and two local single photon detectors (the second detector D2 a , the third detector D3 a ), so in the passive deception mode, Alice detects the two local detectors (D2 a 、 D3 a ) response results, and obtain four types of response events. At the same time, Bob also has four types, so it causes the two detectors D on Charlie's side to L and D R There are many types of response conditions, and there are improvements in the way and number of passive decoy states.

[0106] In the passive decoy mode pairing scheme, when A successful response occurs when and There are four possible cases (generating a signal pair): ,in, In this case, an error code will occur.

[0107] In order to simplify the symbolic formulas involved, several events are introduced:

[0108] .

[0109] The probability of forming a signal pair for:

[0110] .

[0111] Alice and Bob estimate the qubit error rate of the original key data in the Z basis pair for:

[0112] .

[0113] In the trap state window, the single photon pair ratio in the effective signal pair is estimated according to formula (4): for:

[0114] .

[0115] In the passive decoy state mode pairing scheme, if the decoy state estimation is perfect, the phase error rate is the same as that of the phase-encoded MDI-QKD scheme, and the gain and error rate of the X basis can be directly estimated using the following formula:

[0116]

[0117]

[0118] in, , e 0 is the error rate caused by background light, e d is the optical error rate caused by imperfect optical calibration of the system.

[0119] Figure 3 The simulation results of this embodiment are shown in the figure. In the figure, the horizontal axis is the transmission distance (km), the vertical axis is the key generation rate (Key generation rate), the red dotted line is the linear security key rate generation bound (PLOB) when there is no relay, and the black dotted line indicates that the maximum pairing distance is 10 2 The key generation rate of the method of this embodiment is 10. The black solid line indicates that the maximum pairing distance is 10 3 The key generation rate of the method of this embodiment is 10. The black solid line with a circle indicates that the maximum pairing distance is 10 4 The key generation rate of the method of this embodiment is shown in the figure. The black solid line with * indicates that the maximum pairing distance is 10 6 The key generation rate of the method of this embodiment.

[0120] from Figure 3 It can be seen that under the same simulation parameters, as the maximum pairing distance increases, the key generation rate of the method of this embodiment continues to improve. 3 When the key rate is 10 -8 When the simulation parameters are the same, the maximum pairing distance is 10 3 The communication distance of the method of this embodiment can reach about 400km, and the maximum pairing distance is 10 6 The communication distance of the method in this embodiment has exceeded 500km.

[0121] The above analysis results show that the method of this embodiment has a maximum pairing distance greater than 10 3 At the same time, it can break through the linear limitation of the key rate of quantum key distribution, and its key rate and communication distance are greatly improved.

[0122] The passive decoy state method is used to avoid the leakage of additional information through the side channel, thus improving the security of the quantum key distribution protocol. At the same time, because the protocol adopts a pattern matching strategy, no global phase lock is required during implementation, which reduces the difficulty of experimental technology. This is of great significance for applying new quantum cryptography technologies to the operational safety of power systems. Alice obtains four types of response events based on the two local detectors, and Bob also obtains four types, which causes the two detectors D at Charlie's end to L and D R There are many types of response conditions, and there are improvements in the way and number of passive decoy states.

[0123] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Those skilled in the art will understand that the present invention includes, but is not limited to, the contents described in the above specific embodiments. Any modifications that do not deviate from the functional and structural principles of the present invention are intended to be included within the scope of the claims.

Claims

1. A quantum key distribution method based on mode pairing and passive decoy states, characterized by: The quantum key distribution method based on mode pairing and passive decoy state comprises the following steps: S1, Alice, and Bob each generate a pair of entangled photons, where the idle photon is received by the local first detector and the signal photon is sent to the passive decoy state module; S2, Alice, and Bob encode information on the signal photon through the signal path and the decoy path respectively to obtain a coherent quantum state A i and B i and randomly sends the modulated signal state or decoy state to Charlie; S3, the coherent quantum state sent by Charlie to Alice and Bob A i and B i Perform single-photon interferometry measurements and publish the results. A successful detection is when only one of Charlie's two detectors responds. S4, repeat S1 to S3 for N rounds and then perform pattern matching; S5. Basis screening: Determine and screen the basis type based on the strengths chosen by Alice and Bob in the two successful pairing rounds; S6, key mapping: Alice and Bob determine the initial key based on the basis, strength and phase of each pair respectively; S7, parameter estimation; S8, key extraction; In S2, the signal passes through the first beam splitter of the passive decoy module and enters the signal path and the decoy path respectively, where it is modulated. After the modulated signal passes through the second beam splitter, one path is sent to Charlie, and the other path passes through the third beam splitter to reach the two local detectors of Alice or Bob. For Alice’s i The coherent quantum state is expressed as , where the superscript Represents Alice's end, is the intensity of the coherent state, is the phase of the coherent state, , is an imaginary unit; If the signal is sent, the strength Randomly select from {0, μ}, and the phase Randomly select from [0, 2π), modulate the intensity of the decoy path to zero; If the decoy state is sent, the variable attenuator of the decoy path remains unmodulated, and both paths randomly select the intensity from {0, μ} , the pulse phases on the two paths are randomly selected from [0, 2π); Alice obtains different decoy state modes based on the response results of the second and third local detectors, and obtains the decoy state pulse phase ; In S4, when both Alice and Bob are sending signal states, for all successful detection rounds, Alice and Bob combine two successful detection rounds whose interval does not exceed the maximum pairing interval into a pair, and use the encoding phases or intensities in these two rounds to form a data pair; In S5, if the strength selected by Alice in two successful rounds is (0, μ) or (μ, 0), Alice marks the data pair as Z-basis; if the strength is (μ, μ), it is marked as X-basis; if the strength is (0, 0), it is marked as 0-basis. Bob uses the same method to set the basis of the data pair. After the basis is set, Alice and Bob announce the basis of each data pair. If both announce the X basis or the Z basis, it is retained; otherwise, it is discarded. In S6, for index value i and j For each Z-basis data pair, if Alice’s strength ( , )=(0, μ ), then Alice will give her key Set to 0, otherwise Set to 1; Bob's initial key bit setting is exactly opposite to Alice's, that is, Bob's strength = (0, μ ), his key Set to 1, otherwise Set to 0; For X-basis data pairs, the initial key Obtained from the relative phase, the calculation formula is: ； Bob determines the initial key bits in a similar manner k b and alignment angle θ b , but Bob has an additional key flip operation: if in two rounds, the i Hedi j If the detector response is (L,L) or (R,R), Bob keeps his key bits; if the detector response is (L,R) or (R,L), Bob flips the key bits, and in the X basis, only when Alice and Bob’s alignment angles are equal, that is, θ a = θ b The data pair will be kept only when , otherwise the data pair will be discarded; In S7, Alice and Bob perform parameter estimation on the phase flip error rate and qubit error rate of the Z basis; In S8, Alice and Bob use the Z basis pair in the sent signal state to generate the key, and according to 、 and Perform key negotiation and secret amplification to obtain secure keys; The key generation rate is expressed as: in, , represents the logarithmic expected value generated in each round, l is the maximum pairing interval, p is the probability that a round is a successful detection event, r s is the probability that a successfully detected pulse pair is a signal pair, and are the proportion of expected single photon pairs in the signal pair and the phase error rate of single photon pairs, f is the error correction efficiency, is the bit error rate of the signal pair, is the binary Shannon entropy function.

2. The quantum key distribution method based on mode pairing and passive decoy state according to claim 1, characterized in that: In S2, Alice classifies the detection events into four categories based on the response results of the second and third local detectors: neither responds, the first responds and the second does not respond, the first does not respond and the second responds, and both respond. The probabilities of the four types of response events are: The average number of photons is The photon number distribution, is the probability of one of the four types of detection events occurring, Indicates four types of detection events, , n is the number of photon states; The photon state is projected onto Alice's local second and third detectors. Probability Expressed as: in, The third beam splitter The transmittance coefficient, and are the detection efficiencies of the second and third local detectors respectively.

3. The quantum key distribution method based on pattern pairing and passive decoy state according to claim 2, characterized in that: In S2, when the dark counts of Alice's three detectors are the same, , and the detection efficiency is also the same, that is , the probability of the photon number of the four types of events is: in, is the transmittance of the third beam splitter. When the transmittance of the third beam splitter is 0.5, then and same.

4. A quantum key distribution system based on mode matching and passive decoy states, characterized by: It includes two communication devices and a measuring device for executing the quantum key distribution method based on pattern pairing and passive decoy state as described in any one of claims 1 to 3, wherein the measuring device is communicatively connected to the two communication devices respectively, and the two communication devices are communicatively connected to each other.

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