Coding conjugacy evaluation method for QKD light source
Through specific phase modulation steps and interference measurement methods, the accuracy problem of the coding basis/measurement basis conjugation evaluation in the QKD device is solved, ensuring the reliability and accuracy of the security verification results of the QKD device.
Patent Information
- Application Number
- CN202410381611.9
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2024-03-29
- Publication Date
- 2025-09-30
AI Technical Summary
In the existing technology, the coding basis/measurement basis conjugation evaluation method of QKD equipment cannot accurately determine the true solution of the phase angle, resulting in insufficient security verification and security threats.
Through a specific combination of phase modulation amounts, a first modulation step, a return step, a second modulation step, an interference measurement step and an evaluation step are adopted, the counting rate of the interference signal is measured using a light detector, and the maximum conjugate error is calculated to determine whether the conjugation meets the preset threshold.
The phase angle is accurately solved in the range of (0, π), which avoids the misunderstanding of the function near the boundary extreme points and ensures the reliability and accuracy of the security verification results of the QKD equipment.
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Figure CN120729434A_ABST
Abstract
Description
Technical Field
[0001] The present invention relates to the field of quantum key distribution (QKD), and in particular to a method for evaluating the coding conjugation of a QKD light source. Background Art
[0002] The security of a real-world decoyed BB84 protocol system relies on the implementation and verification of the device models used in its security proof. If these device models are not implemented correctly, the system could be vulnerable to security threats. To mitigate these threats, real-world QKD devices must meet security requirements through practical safety measures such as solution design, parameter calibration, safety isolation, and monitoring and alarm monitoring. To verify that the quantum optoelectronic modules in QKD devices meet the security requirements of the security proof, a security assessment environment based on security assessment tools is required, following appropriate test procedures and judgment criteria.
[0003] For the evaluation of the conjugation of the coding basis / measurement basis, it is necessary to test the phase angle of each quantum state corresponding to the coding basis / measurement basis. For different coding and decoding implementation schemes, the current test schemes are also different. Among them, for the phase (in a broad sense, also for the time phase) coding and decoding scheme, in the "GM / T 0114-2021 Specification for Testing of Decoy State BB84 Quantum Key Distribution Products" (hereinafter referred to as the "Specification", the full text of which will be introduced into this article), the test light enters the coding / decoding module under test twice in the forward and reverse directions, thereby avoiding the phase drift in the coding / decoding module and ensuring the stability of the test. On the basis of the stable test, the phase angle is calculated by proportional analysis of the detector count rate.
[0004] However, the phase angle calculated by the formula is not a unique solution. For example, there are two solutions for φ2 and φ3 given in the specification. The test steps provided by the specification cannot determine which of the two solutions is the true solution. Therefore, it is necessary to further improve its test steps and update the calculation formula. Summary of the Invention
[0005] In view of the above-mentioned defects of the prior art, the present invention proposes a method for evaluating the coding conjugation of a QKD light source, which makes the function The solution will be performed at the middle point of the (0, π) range, thus avoiding the function Solving at the boundary of the range (where the function value is near the extreme point 1 or 0) leads to the problem that another solution very close to the one outside the range cannot be distinguished.
[0006] Specifically, the present invention relates to a method for evaluating the coding conjugation property of a QKD light source, which comprises a first modulation step, a folding step, a second modulation step, an interference measurement step, and an evaluation step;
[0007] The first modulation step is used to cause the quantum light entering the ground / state preparation module for the first time to be split by its unequal-arm interferometer and output a first component and a second component, wherein a first modulation phase is applied to the first component;
[0008] The return step is used to return the first component and the second component output by the base / state preparation module in the first modulation step to the base / state preparation module;
[0009] The second modulation step is used to load a second modulation phase on the second component returned to the ground / state preparation module;
[0010] The interferometric measurement step is used to generate an interference signal by interfering the first component loaded with the first modulation phase and the second component loaded with the second modulation phase, and measure the interference signal using a light detector to obtain a count rate;
[0011] The evaluation step is used to calculate the maximum conjugate error ∑ based on the count rate and determine whether it meets the preset threshold requirement;
[0012] in:
[0013] A first modulation step is performed at a first modulation phase φ0, a second modulation step is performed at a second modulation phase φ0, and a count rate S is acquired in an interferometric measurement step. 00 ;
[0014] A first modulation step is performed at a first modulation phase φ0, a second modulation step is performed at a second modulation phase φ1, and a count rate S is acquired in an interferometric measurement step. 01 ;
[0015] A first modulation step is performed at a first modulation phase φ0, a second modulation step is performed at a second modulation phase φ2, and a count rate S is acquired in an interferometric measurement step. 02 ;
[0016] A first modulation step is performed at a first modulation phase φ0, a second modulation step is performed at a second modulation phase φ3, and a count rate S is acquired in an interferometric measurement step. 03 ;
[0017] In the evaluation step, the maximum conjugate error ∑=Max(|AE|,|BE|,|CE|,|DE|) is calculated, where φ′0=0, d is the detector dark count rate, and η is the total channel efficiency.
[0018] Furthermore, in the first modulation step, the first component and the second component are transmitted along the first arm and the second arm respectively in the unequal-arm interferometer, and the first component is loaded with a first modulation phase on the first arm; in the second modulation step, the first component and the second component are transmitted along the second arm and the first arm respectively in the unequal-arm interferometer, and the second component is loaded with a second modulation phase on the first arm.
[0019] Preferably, the phase modulation frequency used in the first and second modulation steps is twice the repetition frequency of the quantum light; and / or, in the interference measurement step, the first component of one of two adjacent quantum lights interferes with the second component of the other.
[0020] Furthermore, in the evaluation step, the relative error of conjugation is also calculated And determine whether it meets the preset threshold requirements.
[0021] Furthermore, the count rate is the detection counts per second / the operating frequency of the light detector.
[0022] Preferably, the quantum light first enters the ground / state preparation module through the circulator, and the interference signal enters the light detector through the circulator. In the return step, the first component and the second component are reflected back to the ground / state preparation module by a reflector.
[0023] Preferably, the modulation phases φ0, φ1, φ2, and φ3 are 0, π / 2, π, and 3π / 2, respectively.
[0024] Preferably, in the interferometric measurement step, the interference signal is measured using a single photon detector.
[0025] Further preferably, the average photon number level of the interference signal reaching the single-photon detector is consistent with the average photon number level of the signal state light pulse, and the detection count of the interference signal by the single-photon detector is more than twice the dark count of the single-photon detector. BRIEF DESCRIPTION OF THE DRAWINGS
[0026] Figure 1 The hardware environment of the coding conjugation evaluation method for a QKD light source according to the present invention is schematically shown. DETAILED DESCRIPTION
[0027] Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided by way of example so as to fully convey the spirit of the present invention to those skilled in the art to which the present invention belongs. Therefore, the present invention is not limited to the embodiments disclosed herein.
[0028] Figure 1 The hardware environment of the coding conjugation evaluation method for a QKD light source according to the present invention is schematically shown.
[0029] like Figure 1 As shown, the hardware device (i.e., companion test device) used for the QKD transmitting end of the device to be tested (i.e., QKD light source) may include a light detector, an optical transmission unit, and a reflection unit, wherein the QKD transmitting end is provided with a light source and a ground / state preparation module.
[0030] The optical transmission unit may have a first port 1, a second port 2, and a third port 3, wherein light input through the first port 1 is output through the second port 2, and light input through the second port 2 is output through the third port 3. As a preferred example, the optical transmission unit may be a circulator.
[0031] Before starting the evaluation, the light source in the device under test can be connected to the first port 1 of the optical transmission unit, the second port 2 of the optical transmission unit can be connected to the input port of the ground / state preparation module in the device under test, the third port 3 of the optical transmission unit can be connected to the photodetector, and the output port of the ground / state preparation module can be connected to the reflection unit. Therefore, the quantum light output by the light source can be forwardly input into the ground / state preparation module via the optical transmission unit. The quantum light (for example, including signal state light pulses and decoy state light pulses) that is forwardly input into the ground / state preparation module is output through the output port of the ground / state preparation module, reaches the reflection unit, and returns to the output port of the ground / state preparation module after being reflected by the reflection unit, thereby reversely inputting into the ground / state preparation module. The quantum light that is reversely input into the ground / state preparation module is output through the input port of the ground / state preparation module and reaches the second port of the optical transmission unit. Finally, it reaches the photodetector via the third port of the optical transmission unit, and is counted and measured by the photodetector.
[0032] As a preferred example, the light detector may be a single-photon detector.
[0033] As a preferred example, the reflecting unit may be a reflector. When the unequal-arm interferometer in the ground / state preparation module is a single-mode Faraday-Michelson interferometer, the reflector may be a Faraday reflector. When the unequal-arm interferometer in the ground / state preparation module is a Mach-Zehnder interferometer using a polarization-maintaining fiber, the reflector may be a polarization-maintaining reflector.
[0034] In e.g. Figure 1 Under the hardware environment shown, the coding conjugation evaluation method for a QKD light source of the present invention can achieve the evaluation of coding conjugation with the help of a first modulation step, a return step, a second modulation step, an interference measurement step and an evaluation step.
[0035] According to the present invention, the first modulation step is used to cause the quantum light entering the ground / state preparation module for the first time to be split by its unequal-arm interferometer and output a first component and a second component, wherein the first component is loaded with a first modulation phase.
[0036] For example, Figure 1As shown, when quantum light from a light source first enters the ground / state preparation module from its input port via a circulator, it is split into a first component and a second component at the input end of an unequal-arm interferometer within the ground / state preparation module. The first component and the second component are transmitted along the first and second arms of the unequal-arm interferometer, respectively. A first modulation phase can be applied to the first component by controlling the phase modulation voltage of a phase modulator provided on the first arm. Therefore, the phase-modulated first component and the unmodulated second component are output from the output end of the unequal-arm interferometer at different time positions and, in turn, leave the ground / state preparation module from its output port at different times.
[0037] In the present invention, the return step is used to return the first component and the second component output by the base / state preparation module in the first modulation step to the base / state preparation module and input them into the base / state preparation module in reverse.
[0038] For example, Figure 1 As shown, the first component (which is loaded with the first modulation phase) and the second component leaving the output port of the ground / state preparation module will return to the output port of the ground / state preparation module along the original path under the reflection of the reflector, and be input into the ground / state preparation module in reverse.
[0039] At this time, the second phase modulation can be performed on the second component returned to the ground / state preparation module with the help of the second modulation step.
[0040] For example, when the first component and the second component are reversely input into the ground / state preparation module via the output port, the returned first component and the second component are transmitted along the second arm and the first arm of the unequal-arm interferometer, respectively, within the ground / state preparation module, thanks to the action of the reflector. The second component can then be imbued with a second modulation phase by controlling the phase modulation voltage of the phase modulator on the first arm.
[0041] Furthermore, in the interferometry step, the returned first component (which is loaded with the first modulation phase) and the second component loaded with the second modulation phase interfere to generate an interference signal, and the interference signal is measured using a photodetector to obtain a corresponding count rate (for example, detection counts per second / photodetector operating frequency). At this point, those skilled in the art will understand that appropriate optical and electronic delay technologies can be used to cause the returned first component (which is loaded with the phase for the first time through the first phase modulation) and the returned second component (which is loaded with the phase for the second time through the second phase modulation) to interfere before reaching the circulator to generate an interference signal, thereby allowing the interference signal to reach the photodetector through the circulator and be measured.
[0042] For example, the phase modulation frequency (2nMHz) of the phase modulator in the first arm of the unequal-arm interferometer can be designed to be twice the repetition frequency (nMHz) of the quantum light, and optical and electronic delay technology can be used to make the (returned) first component of one of the two adjacent quantum lights interfere with the (returned) second component of the other before reaching the circulator.
[0043] Different from the prior art, in the evaluation method of the present invention, the first and second modulation steps are performed under the following four specific combinations of the first modulation phase and the second modulation phase, and four sets of counting rates are obtained accordingly with the aid of the interference measurement step, thereby allowing the conjugation evaluation results to be obtained reliably and accurately.
[0044] Specifically, the first modulation step can be performed at a first modulation phase φ0, and the second modulation step can be performed at a second modulation phase φ0, so as to obtain the count rate S by means of the interferometric measurement step. 00 .
[0045] A first modulation step is performed at a first modulation phase φ0, and a second modulation step is performed at a second modulation phase φ1, so that the count rate S is obtained by means of an interferometric measurement step. 01 .
[0046] A first modulation step is performed at a first modulation phase φ0, and a second modulation step is performed at a second modulation phase φ2, so that the count rate S is obtained by means of an interferometric measurement step. 02 .
[0047] A first modulation step is performed at a first modulation phase φ0, and a second modulation step is performed at a second modulation phase φ3, so that the count rate S is obtained by means of an interferometric measurement step. 03 .
[0048] As a preferred example, the modulation phases φ0, φ1, φ2, and φ3 may be 0, π / 2, π, and 3π / 2.
[0049] At least the above counting rate S is obtained 00 、S 01 、S 02 、S 03 Afterwards, the maximum conjugate error ∑ or the relative conjugate error can be calculated with the help of the evaluation step And determine whether it meets the preset threshold requirements.
[0050] According to the present invention, and Using the obtained count rate S 00 、S 01 、S 02 and S 03, the interference light intensity μ′ is calculated 00 , μ′ 0$ , μ′ 0％ and μ′ 02 , where d is the dark count rate of the photodetector (e.g., single photon), and η is the total channel efficiency, which is determined by factors such as the photodetector quantum efficiency.
[0051] Then, we can set φ′0=0, according to the relationship Calculate the phase difference φ′ " ,φ′ ％ and φ′ & .
[0052] Furthermore, according to the relationship Using the phase difference φ′0, φ′ " ,φ′ ％ and φ′ & The maximum conjugate error ∑=Max(|AE|,|BE|,|CE|,|DE|) or the relative conjugate error is calculated.
[0053] In the coding conjugation evaluation method for QKD light source proposed in the present invention, the function The solution of will be able to be performed at the middle point of the (0, π) range, thus avoiding the function Solving at the boundary of the range (where the function value is near the extreme point 1 or 0) leads to the problem that another solution very close to the one outside the range cannot be distinguished.
[0054] Furthermore, in a preferred example, the optical power of the light source can be adjusted, for example, so that the average photon number level of the interference signal that ultimately reaches the single-photon detector is consistent with the average photon number level of the signal-state light pulse, and at least the detection count of the interference signal by the single-photon detector is ensured to be more than twice the dark count of the single-photon detector.
[0055] Furthermore, optical and electronic delay technologies can be used to ensure that the peak position of the interference signal required for measurement is within the wide range of the detection gate of the single-photon detector.
[0056] Although the present invention has been described above through specific embodiments in conjunction with the accompanying drawings, it is easy for those skilled in the art to recognize that the above embodiments are merely exemplary and are used to illustrate the principles of the present invention. They do not limit the scope of the present invention. Those skilled in the art can make various combinations, modifications and equivalent substitutions to the above embodiments without departing from the spirit and scope of the present invention.
Claims
1. A method for evaluating the coding conjugation of a QKD light source, comprising a first modulation step, a foldback step, a second modulation step, an interferometric measurement step, and an evaluation step; The first modulation step is used to make the quantum light entering the ground / state preparation module for the first time be split by its unequal-arm interferometer and output a first component and a second component, wherein, The first component is loaded with a first modulation phase; The return step is used to return the first component and the second component output by the base / state preparation module in the first modulation step to the base / state preparation module; The second modulation step is used to load a second modulation phase on the second component returned to the ground / state preparation module; The interferometric measurement step is used to generate an interference signal by interfering the first component loaded with the first modulation phase and the second component loaded with the second modulation phase, and measure the interference signal using a light detector to obtain a count rate; The evaluation step is used to calculate the maximum conjugate error ∑ based on the count rate and determine whether it meets the preset threshold requirement; in: A first modulation step is performed at a first modulation phase φ0, a second modulation step is performed at a second modulation phase φ0, and a count rate S is acquired in an interferometric measurement step. 00 ; A first modulation step is performed at a first modulation phase φ0, a second modulation step is performed at a second modulation phase φ1, and a count rate S is acquired in an interferometric measurement step. 01 ; A first modulation step is performed at a first modulation phase φ0, a second modulation step is performed at a second modulation phase φ2, and a count rate S is acquired in an interferometric measurement step. 02 ; A first modulation step is performed at a first modulation phase φ0, a second modulation step is performed at a second modulation phase φ3, and a count rate S is acquired in an interferometric measurement step. 03 ; In the evaluation step, the maximum conjugate error ∑ = Max(|AE|,|BE|,|CE|,|DE|) is calculated, where d is the dark count rate of the photodetector, and η is the total channel efficiency.
2. The coding conjugation evaluation method according to claim 1, wherein: In the first modulation step, the first component and the second component are transmitted along the first arm and the second arm respectively in the unequal-arm interferometer, and the first component is loaded with the first modulation phase on the first arm; in the second modulation step, the first component and the second component are transmitted along the second arm and the first arm respectively in the unequal-arm interferometer, and the second component is loaded with the second modulation phase on the first arm.
3. The coding conjugation evaluation method according to claim 1, wherein: The phase modulation frequency used in the first and second modulation steps is twice the repetition frequency of the quantum light; and / or, in the interference measurement step, the first component of one of two adjacent quantum lights interferes with the second component of the other.
4. The method for evaluating coding conjugation according to any one of claims 1 to 3, wherein: In the evaluation step, the relative error of conjugativity is also calculated And determine whether it meets the preset threshold requirements.
5. The method for evaluating coding conjugation according to any one of claims 1 to 3, wherein: The count rate is the number of detections per second / the operating frequency of the light detector.
6. The method for evaluating coding conjugation according to any one of claims 1 to 3, wherein: The quantum light enters the ground / state preparation module for the first time through the circulator, and the interference signal enters the light detector through the circulator.
7. The coding conjugation evaluation method according to claim 6, wherein: In the return step, the first component and the second component are reflected back to the ground / state preparation module by means of a reflection mirror.
8. The method for evaluating coding conjugation according to any one of claims 1 to 3, wherein: The modulation phases φ0, φ1, φ2, and φ3 are 0, π / 2, π, and 3π / 2, respectively.
9. The method for evaluating coding conjugation according to any one of claims 1 to 3, wherein: In the interferometry step, the interference signal is measured using a single-photon detector.
10. The coding conjugation evaluation method according to claim 9, wherein: The average photon number level of the interference signal reaching the single-photon detector is consistent with the average photon number level of the signal state light pulse, and the detection count of the interference signal by the single-photon detector is more than twice the dark count of the single-photon detector.