A quantum key distribution device, method, and key rate estimation method based on marker source combined with light source monitoring.

Abstract

This invention discloses a quantum key distribution device, method, and key rate estimation method based on a labeled source combined with light source monitoring. In the transmitting end of the device, a first optical switch and a second optical switch simultaneously and randomly select a period of time to send a second signal light to the light source monitoring module and a first idle light to the same module, respectively. The idle light passes through a polarization rotator to obtain a second idle light with the same polarization state as the second signal light. The second signal light and the second idle light pass through a beam splitter and then enter a single-photon detector to measure the coincidence count and calculate the HOM interference visibility, thus achieving light source monitoring. This invention improves the security and confidentiality of quantum key transmission by using a labeled single-photon source combined with a three-intensity decoy state scheme and a light source monitoring scheme. By measuring the HOM interference visibility, the amount of information that may be leaked at the source end can be characterized, thereby more accurately estimating the key rate that can be extracted at the measurement end.

Description

Technical Field

[0001] This invention relates to a quantum key distribution device and method, and more particularly to a quantum key distribution device and method based on a labeled single-photon source for monitoring light sources. Background Technology

[0002] Quantum key distribution (QKD), a quantum-secure communication technology, originated in the early 1980s, first proposed by American scientists Charles H. Bennett and Gilles Brassard. In 1984, Bennett and Brassard proposed the quantum key distribution protocol (BB84 protocol), which first elucidated the theoretical framework for achieving secure key distribution through quantum mechanics principles. In 1989, Bennett et al. experimentally verified the basic principles of the BB84 protocol for the first time, realizing quantum key distribution using photons. This experiment laid the experimental foundation for quantum key distribution technology. In the following decades, scientists continuously improved and optimized quantum key distribution technology, enhancing its speed, security, and practicality.

[0003] Tagned single-photon sources are a key component in quantum communication, used to generate single photons with specific properties, and are one of the foundations for applications such as quantum key distribution. In the early 1990s, scientists first experimentally generated single photons in nonlinear optical materials. Most of the sources used in this research are weakly coherent sources (WCS), which follow a Poisson distribution and contain a significant proportion of vacuum state pulses. Since vacuum state pulses have a significant impact on the system's bit error rate over long distances, schemes based on tagged single-photon sources have a longer secure transmission distance compared to WCS-based protocols.

[0004] Based on the fundamental principles of quantum mechanics, QKD can securely distribute keys between Alice and Bob in legitimate communication. However, practical QKD systems suffer from unavoidable errors in quantum state preparation and potential side-channel information leakage. Passive side-channel attacks aim to obtain information from the quantum signal without interfering with it, thereby compromising the security of QKD. Exploiting these security vulnerabilities, eavesdroppers can launch attacks that threaten the actual security of the QKD system. Summary of the Invention

[0005] Purpose of the invention: The purpose of this invention is to provide a quantum key distribution device and method based on a labeled single-photon source for monitoring light sources, which can resist attacks and improve the reliability and security of the quantum key distribution process, as well as a key rate estimation method for the device.

[0006] Technical solution: The quantum key distribution device based on labeled single-photon source monitoring of the present invention includes a single-photon source module, a light source monitoring module, a first optical switch and a second optical switch at the transmitting end;

[0007] The single-photon source module sends a laser beam to a type II nonlinear crystal through a laser source to generate two photons with mutually perpendicular polarization states, namely the first signal light and the first idle light;

[0008] After the first signal light passes through the intensity modulator, it is randomly modulated into a certain number of light pulses with three different intensities, including signal state, decoy state and vacuum state. After the light pulses are randomly modulated by the encoder, a second signal light with four different quantum states is obtained. These four quantum states are |0>, |1>, |+1>, and |-1>, where |0> and |1> form the Z basis, and |+1> and |-1> form the X basis.

[0009] The second signal light is sent to the receiving end through the first optical switch, and the receiving end decodes the second signal light.

[0010] The first optical switch and the second optical switch simultaneously and randomly select a period of time. The first optical switch sends the second signal light to the light source monitoring module, and the second optical switch sends the first idle light to the light source monitoring module. In the light source monitoring module, the idle light passes through a polarization rotator to obtain a second idle light with the same polarization state as the second signal light. After passing through a beam splitter, the second signal light and the second idle light enter a single-photon detector to measure the coincidence count and calculate the HOM interference visibility, thereby realizing the monitoring of the light source.

[0011] Furthermore, the light source monitoring module includes a timer for delaying the time of the first idle light to synchronize it with the second signal light.

[0012] Furthermore, the reflected light from the beamsplitter is sent to the third single-photon detector, and the transmitted light from the beamsplitter is sent to the second single-photon detector; the reflected light from the beamsplitter is sent to the second single-photon detector, and the transmitted light from the beamsplitter is sent to the third single-photon detector; the coincidence count is measured in the second and third single-photon detectors, and the HOM interference visibility is calculated sequentially; the beam splitting ratio of the beamsplitter is 50 / 50. Furthermore, the first idle light is sent to the first single-photon detector via a second optical switch to predict the arrival time of the second signal light.

[0013] Furthermore, the receiving end includes a decoder and a fourth single-photon detector. The decoder performs a projection measurement operation on the second signal light by randomly selecting a measurement basis from the Z-based and X-based bases. The photons passing through the decoder enter the fourth single-photon detector for measurement.

[0014] The quantum key distribution method based on labeled single-photon source monitoring according to the present invention includes the following steps:

[0015] The single-photon source module at the transmitting end sends a laser beam to a type II nonlinear crystal through a laser source to generate two photons with mutually perpendicular polarization states, namely the first signal light and the first idle light;

[0016] The first signal light is randomly modulated into three light pulses with different intensities by an intensity modulator, including a signal state, a decoy state, and a vacuum state;

[0017] The optical pulse is randomly modulated into a second signal light with four different quantum states by an encoder; these four quantum states are |0>, |1>, |+1>, and |-1>, where |0> and |1> form the Z basis, and |+1> and |-1> form the X basis.

[0018] The second signal light is sent to the receiving end through the first optical switch. The receiving end decodes the second signal light to complete the quantum key distribution.

[0019] The first optical switch and the second optical switch simultaneously and randomly select a period of time. The first optical switch sends the second signal light to the light source monitoring module, and the second optical switch sends the first idle light to the light source monitoring module. In the light source monitoring module, the idle light passes through a polarization rotator to obtain a second idle light with the same polarization state as the second signal light. After passing through a beam splitter, the second signal light and the second idle light enter a single-photon detector to measure the coincidence count and calculate the HOM interference visibility, thereby realizing the monitoring of the light source.

[0020] Furthermore, the light source monitoring module includes a timer to delay the time of the first idle light, synchronizing it with the second signal light; the light source monitoring module also includes a beam splitter to reflect the second signal light with a 50% probability and send it to a third single-photon detector, and to project the second idle light with a 50% probability and send it to a second single-photon detector, measuring the coincidence count and calculating the HOM interferometry visibility accordingly.

[0021] The first idle light is sent to the first single-photon detector via the second optical switch to predict the arrival time of the second signal light.

[0022] The receiver includes a decoder and a fourth single-photon detector. The decoder performs a projection measurement operation on the second signal light by randomly selecting a measurement basis from the Z-based and X-based bases. The photons passing through the decoder enter the fourth single-photon detector for measurement.

[0023] The key rate estimation method for a quantum key distribution device based on a labeled single-photon source for monitoring light sources, as described in this invention, includes the following steps:

[0024] In the light source monitoring module, the relationship between the interference visibility V and the coincidence count N is calculated:

[0025] V=(N max -N min ) / N max ;

[0026] Where N max and N min These represent the maximum and minimum values ​​of the coincidence count in the light source monitoring module, respectively.

[0027] In the light source monitoring module, transmittance is calculated. Bit error rate With distinguishability D ωω The relationship between ′:

[0028]

[0029] Where, ω, ω ′ ∈{μ,ν,0}, representing the signal state μ, the decoy state ν, and the vacuum state 0, respectively;

[0030] In the light source monitoring module, the single-photon bit error rate is calculated:

[0031]

[0032] Calculate the security key rate based on the single-photon bit error rate;

[0033] in in

[0034] This indicates the basis mismatch error. This represents the original basis mismatch error;

[0035] The relationship between the original basis mismatch error Δ and the interferometric visibility V is as follows:

[0036]

[0037] n represents the number of photons, d represents the probability distribution of photon number. A η represents the dark count rate of a single-photon detector. A e represents the detection efficiency of a single-photon detector. i Y represents the bit error rate of the i-photon state. i This represents the transmittance of the i-photon state. This represents the fidelity between the density matrices of the X-basis and the Z-basis. This represents the single-photon transmittance.

[0038] Furthermore, the security key rate R:

[0039]

[0040] q represents the success factor against the basis, f(E) μ H1(x) represents the error correction efficiency; H2(x) represents the binary entropy function.

[0041] Gain Q λ and the bit error rate E λ expression

[0042]

[0043] Among them For photon number distribution, Y n Let n be the transmittance of photons, and e be the transmittance of photons. n Let n be the bit error rate of the photon;

[0044] Channel transmission rate:

[0045] t AB =10 -αl / 10 ;

[0046] Where l is the transmission distance between Alice and Bob, and α is the channel loss coefficient;

[0047] Total transmission and detection rates between the sender and receiver:

[0048] η = t AB η Bob ;

[0049] η Bob It is the detection efficiency of the single-photon detector at the receiving end;

[0050] Transmission rate of i-photon state:

[0051] η i =1-(1-η) i ;

[0052] Y i Let Y be the transmittance of photon i, and Y0 be the dark count rate.

[0053]

[0054] The bit error rate of the i-photon state e i :

[0055]

[0056] e d It is the probability of a photon triggering an error in a single-photon detector, and the bit error rate of the background light is e0 = 1 / 2;

[0057] The single-photon transmittance, considering light source safety, was obtained using the three-intensity decoy state method.

[0058]

[0059] Furthermore, the photon number distribution It conforms to the sub-Poisson distribution;

[0060]

[0061] Beneficial effects: Compared with the prior art, the advantages of the present invention are: (1) The present invention uses an optical switch to obtain idle light and signal light, and monitors the interference of quantum states through a light source monitoring module. On the one hand, it can detect potential eavesdroppers, and on the other hand, by measuring the size of the visibility of the Hong-Ou-Mandel interference, it can characterize the amount of information that may be leaked at the source end, thereby more accurately estimating the key extraction rate at the measurement end; (2) The present invention combines the labeling single photon source technology with the BB84 protocol and the Hong-Ou-Mandel interference experiment. This device effectively resists side-channel attacks introduced by active modulation, and can also provide high confidentiality and reliability, and is suitable for various quantum communication application scenarios. (3) Labeling single photon sources and combining the three-intensity decoy state scheme and the light source monitoring scheme greatly improves the security and confidentiality of quantum key transmission. Attached Figure Description

[0062] Figure 1 This is a structural diagram of the quantum key distribution device of the present invention;

[0063] Figure 2 The figure shows the simulation results of the key rate R varying with transmission distance according to an embodiment of the present invention.

[0064] Figure 3 The average bit error rate E of the signal optical signal in this embodiment of the invention. μ Simulation results showing how the transmission distance changes;

[0065] Figure 4 The total signal optical gain Q in this embodiment of the invention μ Simulation results showing how the transmission distance changes. Detailed Implementation

[0066] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0067] like Figure 1As shown, the quantum key distribution device based on a tag source combined with light source monitoring includes a transmitter and a receiver; wherein the transmitter includes a tag single-photon source module, a light source monitoring module, and optical switches OS1 and OS2.

[0068] The labeled single-photon source module includes a laser source (Laser), a type 2 nonlinear crystal (PPLN, periodically polarized lithium niobate crystal, type IIPPLN), a polarization beam splitter (PBS), an intensity modulator (IM), an encoder (Encoder), and a first single-photon detector (APD1).

[0069] A laser source emits a laser beam, which, upon passing through a type II nonlinear crystal PPLN, undergoes a spontaneous parametric down-conversion (SPDC) process with a certain probability, generating a pair of correlated photons. One photon is horizontally polarized, and the other is vertically polarized. This correlated photon pair then reaches the polarization beam splitter PBS. The horizontally polarized photon is directly transmitted into the upper path, while the vertically polarized photon is reflected into the lower path. The upper path is called the first signal light S1, and the lower path is called the first idle light I1. In practical applications, a polarization rotator PR is placed before the polarization beam splitter PBS to exchange the polarization states. This allows the vertically polarized photon to be directly projected into the upper path (called the first signal light S1), while the horizontally polarized photon is reflected into the lower path (called the first idle light I1).

[0070] The first signal light S1 is randomly modulated by the intensity modulator IM into three quantum state light pulses, with average intensities of signal state (μ), decoy state (ν), and vacuum state (0), respectively. The light pulses then pass through the encoder for encoding and modulation, resulting in the second signal light S2. This signal light then reaches the first optical switch OS1, which can control whether the signal light is sent to the receiver or enters the light source monitoring module. During quantum key distribution, the second signal light S2 is sent to the receiver via the first optical switch OS1. When light source monitoring is required, the first optical switch OS1 and the second optical switch OS2 simultaneously randomly select a period of time to send the second signal light S2 to the light source monitoring module and the first idle light I1 to the light source monitoring module, respectively. In this embodiment, a few minutes are randomly selected for the transmission to the light source monitoring module. The three-intensity decoy state scheme can generate decoy state signals, taking advantage of the fact that eavesdroppers cannot distinguish whether the photons entering the channel belong to the signal state or the decoy state, thereby reducing the risk of photon number splitting attacks.

[0071] After the first idle light I1 passes through the second optical switch OS2, it either enters the single-photon detector or, at random intervals, enters the light source monitoring module. When the first idle light I1 enters the first single-photon detector APD1, since the photon counts of the first signal light S1 and the first idle light I1 follow the same probability distribution and are simultaneous, the arrival time of the first signal light S1 can be predicted using the response of the first single-photon detector APD1. This achieves precise marking of the signal light using the idle light and the triggering of the single-photon detector, effectively reducing the proportion of vacuum-state photons in the signal light, thereby significantly reducing the system's bit error rate and improving the overall system's communication efficiency and security.

[0072] The light source monitoring module includes a delay unit (OD), a polarization rotator (PR), a beam splitter (BS), a second single-photon detector (APD2), and a third single-photon detector (APD3).

[0073] When the first optical switch OS1 and the second optical switch OS2 transmit the second signal light S2 and the first idle light I1 to the light source monitoring module respectively, the first idle light I1 passes through the delay unit OD and then through the polarization rotator PR, changing from vertically polarized light to horizontally polarized light, thus obtaining the second idle light I2. Subsequently, the second idle light I2 and the second signal light S2 pass through the beam splitter BS and the second single-photon detector APD2 and the third single-photon detector APD3 on the two arms to measure the coincidence count.

[0074] The delay unit OD here delays the arrival time of the first idle light I1, allowing it to arrive at the beam splitter BS simultaneously with the second signal light S2. Subsequently, the HOM interference visibility can be calculated using coincidence counting. The overall signal distinguishability and passive side-channel information leakage can be revealed based on the HOM interference visibility between different transmitted signals, thus enabling the monitoring of the light source. Without this module, the inherent errors of actual modulation devices (IM, PM, etc.) should not be ignored. Ignoring the light source device errors and assuming a perfect light source would result in an excessively high calculated key rate, posing a security risk.

[0075] The receiver includes a decoder and a single-photon detector (APD4). Its main function is to receive the second signal light S2 from the transmitter, randomly select a measurement basis from the Z-base and X-base to perform projection measurement on the second signal light, and then demodulate it through the decoder to obtain the third signal light S3, which enters the fourth single-photon detector (APD4) for measurement.

[0076] The quantum key distribution based on marker source combined with light source monitoring described in this invention stipulates that Alice is the sender and Bob is the receiver. According to the BB84 protocol, the specific process of quantum key distribution (QKD) is as follows.

[0077] The laser source at the Alice end emits a laser beam. After the laser is pumped onto a type II nonlinear crystal PPLN, a parametric conversion process occurs, generating a pair of correlated photons, one of which is horizontally polarized and the other is vertically polarized. Subsequently, the correlated photon pair reaches the polarization beam splitter PBS. In this embodiment, the horizontally polarized state of the correlated photon pair is directly transmitted into the upper path and is called the first signal light S1, while the other vertically polarized beam is reflected into the lower path and is called the first idle light I1. Alternatively, the polarization states can be exchanged by adding a polarization converter.

[0078] By inputting three electrical signals of different amplitudes into the intensity modulator IM, the first signal light S1 can be randomly modulated into a certain number of three quantum state light pulses with average intensities of signal state (μ), decoy state (ν), and vacuum state (0), respectively. Then, it is encoded and modulated by the encoder at the Alice end. By inputting four electrical signals of different amplitudes into the encoder, the light pulses are adjusted into different quantum states: |0>, |1>, |+1>, and |-1>. The second signal light S2 obtained after modulation then reaches the first optical switch OS1 and is then transmitted to the receiver Bob through the fiber.

[0079] After the first idle light I1 passes through the second optical switch OS2, the second optical switch OS2 will control the first idle light I1 to enter the first single-photon detector APD1. The first single-photon detector APD1 will detect the first idle light I1. The response of the first single-photon detector APD1 will determine whether the first signal light S1 is in a vacuum state. If the detector does not respond, it means that there is a vacuum state in the first signal light S1. Then Alice will notify Bob that the photon is in a vacuum state, and Bob's fourth single-photon detector APD4 will not detect the photon.

[0080] The Bob end receives the second signal light S2 from the transmitting end and inputs two types of electrical signals of different amplitudes into the decoder, which correspond to the two bases of the receiver decoder, namely the Z base and the X base. The Z base consists of two intrinsic quantum states, |0> and |1>, and the X base consists of two intrinsic quantum states, |+1> and |-1>. After demodulation, the third signal light S3 is obtained and then reaches the fourth single-photon detector APD4 to complete the detection of the signal light.

[0081] During quantum key transmission, the first optical switch OS1 and the second optical switch OS2 simultaneously and randomly select a period of time to transmit the second signal light S2 and the first idle light I to the light source monitoring module. The first idle light I is delayed by the delay unit OD to ensure that it arrives at the beam splitter BS at the same time as the second signal light S2. The first idle light I is converted from vertically polarized light to horizontally polarized light by the polarization rotator PR to obtain the second idle light I2. Subsequently, the second signal light S2 and the second idle light I2 enter the beam splitter BS and the second single-photon detector APD2 and the third single-photon detector APD3 on the two arms. The coincidence count is measured by the single-photon detectors, thereby calculating the interference visibility V between the signal light and the idle light, which plays the role of light source detection.

[0082] In practical QKD transmission, Alice can only send a limited number of signal pulses, so statistical fluctuations are inevitable during parameter estimation. These fluctuations primarily affect the number of pulses under different substrates and intensities. The key rate estimation method for a quantum key distribution device based on a marker source combined with light source monitoring, as described in this invention, includes the following steps.

[0083] Assume Alice sends a total of N pulses; Alice sends pulses with probability P. μ P ν 1-P μ -P ν Send pulses of signal, decoy, and vacuum intensities; Alice's probabilities of generating pulses in Z-based and X-based systems are P0 and P1, respectively. za and 1-P za Bob uses Z-basis and X-basis to measure the probability of pulses, respectively, P. zb and 1-P zb .

[0084] Alice sends N signal state pulses under Z-base. zμ =NP μ P za P zb Alice sends N signal state pulses under the X-base. xμ =NP μ (1-P za (1-P) zb );

[0085] Alice sends N decoy state pulses under Z-base. zν =NP ν P za P zb Alice sends N signal state pulses under the X-base. xν =NP ν (1-P za (1-P) za );

[0086] The number of vacuum pulses sent by Alice is N0 = N(1-P). μ -P ν ).

[0087] Considering that X-based and Z-based data are processed independently and do not affect each other, the subscripts with X-based and Z-based subscripts will be omitted in the following expressions in this embodiment to avoid misunderstanding.

[0088] After accounting for statistical fluctuations, the upper and lower bounds of the system gain and qubit error rate under Z-based and X-based systems can be uniformly written as:

[0089]

[0090] Specifically, for vacuum state gain:

[0091]

[0092] Where λ∈{μ,ν,0},ξ∈{X,Z}, L and U represent the lower and upper bounds, respectively, and γ represents the standard deviation.

[0093] Based on the quantum key distribution (QKD) process, the expression for the secure key rate R is:

[0094]

[0095] Where q is the base pair success factor (for the BB84 protocol, Alice and Bob have a 50% probability of successfully pairing bases, so the value is 1 / 2), and f(E) is the base pair success factor. μ H1(x) represents the error correction efficiency; H2(x) is the binary entropy function, and its expression is:

[0096] H2(x)=-xlog2 x-(1-x)log2(1-x)

[0097] Gain Q λ and the bit error rate E λ The expression is:

[0098]

[0099]

[0100] The number of photons in a labeled single-photon source follows a distribution:

[0101]

[0102] Where n represents the number of photons. The photon number distribution probability of the parametric downconversion source can be obtained according to different experimental conditions. In this embodiment, it is a sub-Poisson distribution, where λ represents the average light intensity and d A and η A These represent the dark count rate and detection efficiency of the single-photon detector, respectively.

[0103] Channel transmission rate:

[0104] t AB =10 -αl / 10

[0105] Where l is the transmission distance between Alice and Bob, and α is the channel loss coefficient.

[0106] Total transmission and detection rate between Alice and Bob:

[0107] η = t AB η Bob

[0108] Where, η Bob It is the detection efficiency of the Bob single-photon detector at the receiving end.

[0109] Transmission rate of i-photon state:

[0110] η i =1-(1-η) i

[0111] Y i Yi is the transmittance of the i-photon state, and Y0 is the dark count rate.

[0112]

[0113] The bit error rate of the i-photon state e i :

[0114]

[0115] Among them, e d It is the probability of a photon triggering an error in a single-photon detector, and the bit error rate of the background light is e0 = 1 / 2.

[0116] In practical QKD transmission, due to device imperfections during Alice's transmission, side-channel information can leak to Eve to distinguish between the signal state and the decoy state. Therefore, a universal security model that can tolerate this side-channel leakage is needed. This invention introduces a distinguishability D. ωω ′(ω,ω ′ ∈{μ,ν,0}), the following is the penetration rate. and bit error rate With distinguishability D ωω The relationship between ′:

[0117]

[0118] Furthermore, establish the distinguishability D. μν With fidelity The relationship between them is as follows:

[0119]

[0120] This leads to the derivation of the single-photon transmittance when introducing distinguishability with a labeled source. The expression for the estimated value is shown below:

[0121]

[0122] Furthermore, the original single-photon bit error rate without light source monitoring was derived when introducing distinguishability under a labeled source. The expression for the estimated value is shown below:

[0123]

[0124] in:

[0125]

[0126] In the light source monitoring module, the HOM interferometry visibility between different emitted signals reveals the overall signal distinguishability and the extent of passive side-channel information leakage. This feature can be used to assess defects caused by the passive side-channel. The coincidence count can be measured using a single-photon detector in the module. To characterize the indistinguishability of photons, the HOM interferometry visibility is defined as the difference between the maximum and minimum coincidence counts divided by the maximum coincidence count:

[0127] V=(N max -N min ) / N max

[0128] The above V is the calculated value after measuring the coincidence count by the experimental setup. It can be seen that when the interference is completely orthogonal (distinguished), the visibility is 0, while when it is completely indistinguishable, the visibility is 1.

[0129] Ideally, attacker Eve would be unable to distinguish any of the bases because their density matrices should be identical. Imperfect pattern matching leads to differences in the density matrices of the bases between different bits, creating a vulnerability that Eve can exploit to attack the device. The value used to quantify this effect is called the basis mismatch error, the original basis mismatch error being:

[0130]

[0131] in The fidelity between the X-basis and Z-basis density matrices, and the relationship between interferometric visibility and fidelity are as follows:

[0132]

[0133] From the above two equations, the relationship between interference visibility and basis mismatch error can be derived as follows:

[0134]

[0135] To simulate the impact of basis mismatch error, and considering Eve's ability to use a lossless channel, the calculated imbalance was corrected. The corrected basis mismatch error is:

[0136]

[0137] Combining the above process, the corrected single-photon bit error rate can be obtained.

[0138]

[0139] The corrected single-photon bit error rate Substitute it into the formula for the secure key rate R instead of the original single-photon bit error rate. The corrected security key rate R is obtained.

[0140] To test the security performance of the system, the device described in this invention was compared with a traditional WCS light source, including key rate R and total bit error rate E of the signal light. μ and the total gain Q of the signal light μ The parameters of the device described in this invention are calculated using the key rate estimation method described in this invention. During the simulation process, the interference visibility is set to a value of V to facilitate the observation of the system's security performance.

[0141] Simulation results and parameter tables are shown below. Figures 2-4 And Table 1.

[0142] Table 1 Simulation Parameters

[0143] N γ A ]]> ​ d A ]]> [Y0] e d ]]> f α(dB / km) Bob ]]> ​ <![CDATA[10 12 ]]> 5.3 0.75 <![CDATA[10 -7 ]]> <![CDATA[10 -7 ]]> 0.015 1.22 0.20 0.7

[0144] Analysis of simulation experiment results: Figure 2This paper compares the key generation rate R of WCS (weakly coherent source) and HSPS (labeled single-photon source) as a function of transmission distance under different interferometric visibility conditions. The figure shows that at an interferometric visibility of 0.5, WCS has a slight advantage at the near end (slightly higher key generation rate), while HSPS has a longer transmission distance at the far end. As the interferometric visibility V decreases, the transmission distance of both WCS and HSPS decreases, but WCS is more significantly affected by the interferometric visibility, and its advantage at the near end gradually diminishes until it becomes inferior to HSPS.

[0145] Figure 3 The average bit error rate E of the signal light from WCS and HSPS light sources under different interference visibility conditions. μ Comparison of changes with transmission distance. Under the same interference visibility V, the average bit error rate of the signal light from the WCS source increases significantly at the end of the coding distance, while the average bit error rate of the signal light from the HSPS source remains relatively small.

[0146] Figure 4 The total signal light gain Q of WCS and HSPS light sources under different interference visibility conditions. μ A comparison of how the signal gain changes with transmission distance. As the interference visibility V decreases, the total signal gain of the HSPS light source gradually exceeds that of the WCS light source at the near end, while maintaining its advantage at the far end.

[0147] The results show that the device has higher security and longer transmission distance than the traditional WCS light source. At the same time, it solves the problem that the HSPS light source has a lower key rate than WCS at the near end under non-ideal conditions.

Claims

1. A quantum key distribution apparatus based on monitoring of a light source of a tagged single-photon source, characterized by The sending end comprises a single photon source module, a light source monitoring module, a first optical switch and a second optical switch; The single photon source module sends a laser beam to a type II nonlinear crystal through a laser source to generate two photons with perpendicular polarization states, which are a first signal light and a first idle light respectively; The first signal light is randomly modulated by an intensity modulator to generate a certain number of optical pulses with three different intensities, including a signal state, a decoy state and a vacuum state, and the optical pulses are randomly modulated by an encoder to obtain a second signal light with four different quantum states, which are ∣0>, ∣1>, ∣+1> and ∣-1> respectively, wherein ∣0> and ∣1> form a Z basis, and ∣+1> and ∣-1> form an X basis; The second signal light is sent to the receiving end through the first optical switch, and the receiving end decodes the second signal light; The first optical switch and the second optical switch randomly extract a time period at the same time, the first optical switch sends the second signal light to the light source monitoring module, and the second optical switch sends the first idle light to the light source monitoring module; in the light source monitoring module, the idle light passes through a polarization rotator to obtain a second idle light with the same polarization state as the second signal light; the second signal light and the second idle light pass through a beam splitter and then enter single photon detectors to measure coincidence counts, and HOM interference visibility is calculated to realize monitoring of the light source.

2. The tagged single-photon source based light source monitoring quantum key distribution apparatus according to claim 1, wherein, The light source monitoring module comprises a time delay device for delaying the first idle light to synchronize it with the second signal light.

3. The tagged single-photon source based light source monitoring quantum key distribution apparatus according to claim 1, wherein, The reflected light of the second signal light passing through the beam splitter is sent to a third single photon detector, and the transmitted light of the second signal light passing through the beam splitter is sent to a second single photon detector; the reflected light of the second idle light passing through the beam splitter is sent to the second single photon detector, and the transmitted light of the second idle light passing through the beam splitter is sent to the third single photon detector; the coincidence counts in the second single photon detector and the third single photon detector are measured, and HOM interference visibility is calculated in turn; the splitting ratio of the beam splitter is 50 / 50.

4. The tagged single-photon source based light source monitoring quantum key distribution apparatus according to claim 1, wherein, The first idle light passes through the second optical switch and is sent to a first single photon detector to predict the arrival time of the second signal light.

5. The tagged single-photon source based light source monitoring quantum key distribution apparatus according to claim 1, wherein, The receiving end comprises a decoder and a fourth single photon detector, the decoder performs projection measurement operation on the second signal light by randomly selecting a measurement basis from the Z basis and the X basis, and the photons passing through the decoder enter the fourth single photon detector for measurement.

6. A method of quantum key distribution based on monitoring of a light source of a tagged single-photon source, characterized in that The method comprises the following steps: The single photon source module of the sending end sends a laser beam to a type II nonlinear crystal through a laser source to generate two photons with perpendicular polarization states, which are a first signal light and a first idle light respectively; The first signal light is randomly modulated by an intensity modulator to generate optical pulses with three different intensities, including a signal state, a decoy state and a vacuum state; The optical pulses are randomly modulated by an encoder to obtain a second signal light with four different quantum states; the four quantum states are ∣0>, ∣1>, ∣+1> and ∣-1> respectively, wherein ∣0> and ∣1> form a Z basis, and ∣+1> and ∣-1> form an X basis; The second signal light is sent to the receiving end through the first optical switch, and the receiving end decodes the second signal light to complete quantum key distribution; The first optical switch and the second optical switch simultaneously extract a period of time, the first optical switch sends the second signal light to the light source monitoring module, and the second optical switch sends the first idle light to the light source monitoring module; in the light source monitoring module, the idle light passes through the polarization rotator to obtain the second idle light with the same polarization state as the second signal light; the second signal light and the second idle light pass through the beam splitter and then enter the single-photon detector to measure the coincidence count, and the HOM interference visibility is calculated to realize monitoring of the light source.

7. The tagged single-photon source based light source monitoring quantum key distribution method of claim 6, wherein, The light source monitoring module includes a time delay device that delays the first idle light to synchronize it with the second signal light; the reflected light of the second signal light passing through the beam splitter is sent to the third single-photon detector, and the transmitted light of the second signal light passing through the beam splitter is sent to the second single-photon detector; The reflected light of the second idle light passing through the beam splitter is sent to the second single-photon detector, and the transmitted light of the second idle light passing through the beam splitter is sent to the third single-photon detector; the coincidence count is measured in the second single-photon detector and the third single-photon detector, and the HOM interference visibility is calculated in turn; the beam splitting ratio of the beam splitter is 50 / 50; The first idle light is sent to the first single-photon detector through the second optical switch to predict the arrival time of the second signal light; The receiving end includes a decoder and a fourth single-photon detector, the decoder performs a projection measurement operation on the second signal light by randomly selecting a measurement basis from a Z basis and an X basis, and the photons passing through the decoder enter the fourth single-photon detector for measurement.

8. A method of key rate estimation applied to the apparatus of any of claims 1-5, wherein, The method comprises the following steps: In the light source monitoring module, the relationship between the interference visibility V and the coincidence count N is calculated: V = (N max -N min ) / N max ; where N max and N min represent the maximum and minimum values of coincidence counts in the light source monitoring module, respectively; In the light source monitoring module, the transmittance is calculated bit error rate and the distinguishability D ωω between the relationship: where ω, ω ′ ∈ {μ,ν,0} are the signal state μ, the decoy state ν and the vacuum state 0, respectively; In the light source monitoring module, the single-photon error rate is calculated: According to the single-photon error rate, the security key rate is calculated; wherein wherein denotes the basis vector mismatch error, denotes the original basis vector mismatch error; The relationship between the original basis vector mismatch error Δ and the interference visibility V is: n denotes the number of photons, λ ∈ {μ, v, 0}, denotes the photon number distribution probability, denotes the fidelity between the density matrices of the X and Z bases, denotes the single photon transmission; Q λ is the gain, E λ is the quantum bit error rate, L represents the lower bound, e0 denotes the error rate of the background light.

9. The key rate estimation method of claim 8, wherein, The security key rate R is: q denotes the base success factor, f(E μ ) denotes the error correction efficiency; H2(x) denotes the binary entropy function; Gain Q λ And quantum bit error rate E λ Expression of wherein is is the photon number distribution, Y n is the n-photon transmittance, e n is the n-photon error rate; The transmission rate of the channel is: t AB ＝10 -αl / 10 ； Wherein, l is the transmission distance between Alice and Bob, and α is the loss coefficient of the channel; The total transmission and detection rate between the sending end and the receiving end is: η = t AB η Bob ; η Bob is the detection efficiency of the receiving end single-photon detector; The transmission rate of the i-photon state is: η i = 1 - (1 - η) i ; Y i Y is the transmittance for i-photons, Y0 is the dark count rate: Error rate e of i-photon state i : e d is the probability of a photon-triggered error single-photon detector, the bit error rate of the background light e0= 1 / 2; Single photon transmittance in consideration of light source safety by three intensity decoy state method 10. The key rate estimation method of claim 8, wherein, The photon number distribution Sub-Poissonian distribution; where d A represents the dark count rate of the single photon detector, η A represents the detection efficiency of the single photon detector.

Images