QKD light source coding conjugacy evaluation method
By calculating the phase difference in the QKD device and determining the coding conjugation using a monotonically increasing and decreasing trend, the problem in the existing technology of being unable to uniquely determine the correct solution of the phase angle is solved, and the accuracy of security verification is improved.
Patent Information
- Application Number
- CN202410381553.X
- 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 the QKD device cannot uniquely determine the correct solution of the phase angle, resulting in insufficient security verification.
During the initial test and calibration test, the phase differences φ′0, φ′1, φ′2, φ′3 are calculated using the counting rates S00, S01, S13, and S02, and the correct solution is determined through the monotonically increasing and decreasing trends. The interference signal is generated by combining optical and electronic delay technology for measurement.
The coding conjugation of the QKD device is accurately determined, which improves the accuracy and reliability of security verification and makes up for the limitations of existing specifications.
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Figure CN120729433A_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 conjugation property of QKD light source coding. 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 QKD light source coding conjugation evaluation method, which uses The different trends of monotonically decreasing and monotonically increasing of the function on the left side (<π) and the right side (>π) are used to determine which solution the actual value is, thereby accurately giving the numerical value of the actual measured object, making up for the limitations of the existing "Specifications".
[0006] Specifically, the QKD light source coding conjugation evaluation method of the present invention may include an initial test process, a correction test process, a phase difference correction process, and an evaluation process;
[0007] During the initial test, a measurement step is performed at the first modulation phase φ0 and the second modulation phase φ0 to obtain the count rate S 00 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ1 to obtain the count rate S 01 , the measurement step is performed under the first modulation phase φ1 and the second modulation phase φ3 to obtain the count rate S 13 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ2 to obtain the count rate S 02 ; and by means of a phase difference evaluation step, using the counting rate S 00 、S 01 、S 13 and S 02 , calculate the phase differences φ′0, φ′1, φ′2 and φ′3; where,
[0008] The measurement step is configured to cause quantum light that first enters the ground / state preparation module 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; return the output first and second components to the ground / state preparation module, wherein a second modulation phase is applied to the second component; cause the first component loaded with the first modulation phase and the second component loaded with the second modulation phase to interfere with each other to generate an interference signal, and measure the interference signal using a light detector to obtain a count rate;
[0009] The phase difference evaluation step is used to calculate the phase differences φ′0, φ′1, φ′2, and φ′3, where φ′0=0, d is the dark count rate of the photodetector, η is the total channel efficiency;
[0010] During the calibration test, the values of φ2 and φ3 are changed, and the measurement steps are performed at the first modulation phase φ0 and the second modulation phase φ0 to obtain the count rate S 00 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ1 to obtain the count rate S 01 , the measurement step is performed under the first modulation phase φ1 and the second modulation phase φ3 to obtain the count rate S 13 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ2 to obtain the count rate S 02 ; and by means of a phase difference evaluation step, using the counting rate S 00 、S 01 、S 13 and S 02 , calculate the phase differences φ′0, φ′1, φ′2 and φ′3;
[0011] In the phase difference correction process, by comparing the values of φ′2 and φ′3 obtained in two different correction test processes, or comparing the values of φ′2 and φ′3 obtained in the correction test process with the values obtained in the initial test process, the monotonic change relationship of φ′2 with respect to φ2 and the monotonic change relationship of φ′3 with respect to φ3 are judged, and the monotonic change relationship of φ′2 with respect to φ2 and the monotonic change relationship of φ′3 with respect to φ3 are determined accordingly. or or Among them, φ′0=0,
[0012] During the evaluation process, the phase differences φ′0, φ′1, φ′2, and φ′3 determined during the phase difference correction process are used to calculate the maximum conjugate error ∑=Max(|AE|,|BE|,|CE|,|DE|), and determine whether it meets the preset threshold requirements, where:
[0013] Furthermore, during the calibration test, φ2 is increased or decreased by δφ2, and φ3 is increased or decreased by δφ3, δφ2≤2(π-φ′2), δφ3≤2(π-φ′3);
[0014] During the phase difference correction process, if the phase difference φ′2 obtained by increasing δφ2 corresponding to φ2 is smaller than the phase difference φ′2 obtained by corresponding to φ2, or the phase difference φ′2 obtained by decreasing δφ2 corresponding to φ2 is larger than the phase difference φ′2 obtained by corresponding to φ2, If the phase difference φ′3 obtained by increasing δφ3 corresponding to φ3 is smaller than φ′3 obtained by corresponding to φ3, or the phase difference φ′3 obtained by decreasing δφ3 corresponding to φ3 is larger than φ′3 obtained by corresponding to φ3,
[0015] Furthermore, during the calibration test, φ2 is increased and decreased by δφ2, and φ3 is increased and decreased by δφ3;
[0016] During the phase difference correction process, if the phase difference φ′2 obtained by increasing δφ2 by φ2 is smaller than the phase difference δφ′2 obtained by decreasing δφ2 by φ2, If the phase difference φ′3 obtained by increasing φ3 by δφ3 is smaller than the phase difference φ′3 obtained by decreasing φ3 by δφ3,
[0017] Furthermore, in the measurement step, for the quantum light that first enters the ground / state preparation module, the first component and the second component are respectively transmitted along the first arm and the second arm in the unequal-arm interferometer, and the first component is loaded with the first modulation phase on the first arm; the returning first component and the second component are respectively transmitted along the second arm and the first arm in the unequal-arm interferometer, and the second component is loaded with the second modulation phase on the first arm.
[0018] Furthermore, in the measuring step, the phase modulation frequency is twice the repetition frequency of the quantum light, and / or a first component of one of two adjacent quantum lights interferes with a second component of the other.
[0019] Furthermore, during the evaluation process, the relative error of conjugation is also calculated. And determine whether it meets the preset threshold requirement; and / or, the counting rate is the detection counts per second / the operating frequency of the light detector.
[0020] Furthermore, the quantum light first enters the ground / state preparation module through the circulator, and the interference signal enters the light detector through the circulator; and / or, the first component and the second component are reflected back to the ground / state preparation module by means of a reflector.
[0021] Furthermore, the modulation phase φ , , φ1, φ2, and φ3 are 0, π / 2, π, and 3π / 2 respectively.
[0022] Preferably, the light detector is a single-photon detector, wherein the average number of photons of the interference signal reaching the single-photon detector is consistent with the average number of photons 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
[0023] Figure 1 The hardware environment of the QKD light source coding conjugation evaluation method according to the present invention is schematically shown. DETAILED DESCRIPTION
[0024] 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.
[0025] Figure 1 The hardware environment of the QKD light source coding conjugation evaluation method according to the present invention is schematically shown.
[0026] like Figure 1As 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.
[0027] 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.
[0028] 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.
[0029] As a preferred example, the light detector may be a single-photon detector.
[0030] 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.
[0031] In e.g. Figure 1 Under the hardware environment shown, the QKD light source coding conjugation evaluation method of the present invention can achieve the evaluation of coding conjugation with the help of measurement steps and phase difference evaluation steps through the initial test process, correction test process, phase difference correction process and evaluation process, thereby solving the problem that the correct solution cannot be uniquely determined in the prior art.
[0032] According to the present invention, the measurement step is used to cause the quantum light that first enters the ground / state preparation module to be split by its unequal-arm interferometer and output a first component and a second component, wherein a first modulation phase is loaded on the first component; the output first component and second component are returned to the ground / state preparation module, wherein a second modulation phase is loaded on the second component; the first component loaded with the first modulation phase and the second component loaded with the second modulation phase are interfered to generate an interference signal, and the interference signal is measured using a light detector to obtain a corresponding counting rate.
[0033] For example Figure 1 As 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.
[0034] 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.
[0035] When the first and second components are reversely input into the ground / state preparation module via the output port, the returned first and second components are transmitted along the second and first arms of the unequal-arm interferometer, respectively, within the ground / state preparation module, thanks to the action of the reflector. The second component can be imbued with a second modulation phase by controlling the phase modulation voltage of the phase modulator on the first arm.
[0036] Furthermore, the returned first component (which is loaded with the first modulation phase) and the second component loaded with the second modulation phase can interfere with each other to generate an interference signal, and the interference signal can be measured using a light detector to obtain the corresponding counting rate (i.e., detection counts per second / light detector operating frequency).
[0037] Those skilled in the art will appreciate that, through appropriate optical and electronic delay techniques, the returned first component (which is first phase-loaded via the first phase modulation) and the returned second component (which is second phase-loaded via the second phase modulation) can interfere with each other before reaching the circulator to generate an interference signal, thereby allowing the interference signal to pass through the circulator and reach the photodetector for measurement. For example, the phase modulation frequency (2 nmhz) 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 techniques can be used to cause the (returned) first component of one of two adjacent quantum lights to interfere with the (returned) second component of the other before reaching the circulator.
[0038] In the initial test process of the present invention, the measurement steps are respectively performed under four sets of first modulation phases and second modulation phases, and a corresponding set of phase differences φ′0, φ′1, φ′2 and φ′3 are obtained by means of the phase difference evaluation step.
[0039] Specifically, the measurement step can be performed under the first modulation phase φ0 and the second modulation phase φ0 to obtain the corresponding count rate S 00 .
[0040] The measurement steps are performed under the first modulation phase φ0 and the second modulation phase φ1 to obtain the corresponding count rate S 01 .
[0041] The measurement steps are performed under the first modulation phase φ1 and the second modulation phase φ3 to obtain the corresponding count rate S 13 .
[0042] The measurement steps are performed under the first modulation phase φ0 and the second modulation phase φ2 to obtain the corresponding count rate S 02 .
[0043] As a preferred example, the modulation phase φ , , φ1, φ2, and φ3 can take the values of 0, π / 2, π, and 3π / 2, respectively.
[0044] The count rate S can then be used with the aid of a phase difference evaluation step. 00 、S 01 、S 13 and S 02 , calculate the corresponding phase differences φ′0, φ′1, φ′2 and φ′3.
[0045] Specifically, in the phase difference evaluation step, the counting rate S obtained by the above measurement step can be used. 00 、S 01 、S 13 and S 02 , first according to the relationship The corresponding interference light intensity μ′ is calculated 00 , μ′ 01 , μ′ 13 and μ′ 02 , where d is the dark count rate of the photodetector, η is the total channel efficiency, and factors such as the (single-photon) photodetector quantum efficiency determine the total channel efficiency.
[0046] Therefore, when the phase difference φ′0=0 is set, according to the relationship Using the interference light intensity μ′ 00 , μ′ 01 , μ′ 13 and μ′ 02 , the phase differences φ′1, φ′2 and φ′3 are calculated.
[0047] In the present invention, in order to obtain a unique correct solution, it is also necessary to calculate at least another set of phase differences φ′0, φ′1, φ′2 and φ′3 with the help of a correction test process, so as to determine the correct values of phase differences φ′2 and φ′3 with the help of a phase difference correction process.
[0048] In the calibration test process of the present invention, the count rate S can be obtained by changing the values of φ2 and φ3 and performing a measurement step at the first modulation phase φ0 and the second modulation phase φ1 based on the changed φ2 and φ3 (φ0 and φ1 remain unchanged). 00 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ1 to obtain the count rate S 01 , the measurement step is performed under the first modulation phase φ1 and the second modulation phase φ3 to obtain the count rate S 13 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ2 to obtain the count rate S 02 , and based on the currently acquired count rate S 00 、S 01 、S 13 and S 02 , the corresponding phase differences φ′0, φ′1, φ′2 and φ′3 are calculated with the help of the phase difference evaluation step.
[0049] In the present invention, one or more correction test processes may be performed according to different phase difference correction methods, thereby obtaining another group or multiple groups of phase differences φ′0, φ′1, φ′2 and φ′3.
[0050] In the phase difference correction process of the present invention, the values of φ′2 and φ′3 obtained in two different correction test processes can be compared, or the values of φ′2 and φ′3 obtained in the correction test process can be compared with the values obtained in the initial test process to determine the monotonic change relationship of φ′2 with respect to φ2 and the monotonic change relationship of φ′3 with respect to φ3, so as to determine the monotonic change relationship of φ′2 with respect to φ2 and the monotonic change relationship of φ′3 with respect to φ3. or Choose the correct value of φ′2 in or The correct value of φ′3 is selected. Those skilled in the art will understand that the values of φ′0 and φ′1 are always φ′0=0.
[0051] Among them, when the phase difference φ′2 has a unidirectional decreasing trend with respect to φ2, on the contrary
[0052] When the phase difference φ′3 has a unidirectional decreasing trend with respect to φ3, on the contrary
[0053] As an example, during the calibration test, φ2 may be fine-tuned, for example, by reducing (or increasing) it by δφ2, where δφ2≤2(π-φ′2).
[0054] Then, based on the finely adjusted φ2, a measurement step is performed at the first modulation phase φ0 and the second modulation phase φ0 to obtain the count rate S 00 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ1 to obtain the count rate S 01 , the measurement step is performed under the first modulation phase φ1 and the second modulation phase φ3 to obtain the count rate S 13 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ2 to obtain the count rate S 02 , and based on the currently acquired count rate S 00 、S 01 、S 13 and S 02 , the corresponding phase differences φ′0, φ′1, φ′2, and φ′3 are calculated with the help of the phase difference evaluation step. Among them, the calculated phase difference φ′2 can be recorded as φ′, which corresponds to the fine-tuning of φ2 by reducing (or increasing) δφ2. 2- (or φ′ 2+ ).
[0055] Therefore, the phase difference φ′ obtained by the calibration test process can be used in the phase difference calibration process. 2- (or φ′2+ ) is compared with the phase difference φ′2 obtained by the initial test process, and 2- Greater than (or φ′ 2+ When the phase difference φ′2 is less than φ′2, the value of the phase difference φ′2 is corrected to
[0056] Similarly, φ3 can be fine-tuned during the calibration test, for example, by reducing (or increasing) δφ3, where δφ3≤2(π-φ′3).
[0057] Then, based on the finely adjusted φ3, a measurement step is performed at the first modulation phase φ0 and the second modulation phase φ0 to obtain the count rate S 00 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ1 to obtain the count rate S 01 , the measurement step is performed under the first modulation phase φ1 and the second modulation phase φ3 to obtain the count rate S 13 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ2 to obtain the count rate S 02 , and based on the currently acquired count rate S 00 、S 01 、S 13 and S 02 , the corresponding phase differences φ′0, φ′1, φ′2, and φ′3 are calculated with the help of the phase difference evaluation step. Among them, the calculated phase difference φ′3 can be recorded as φ′, which corresponds to the fine-tuning of φ3 by reducing (or increasing) δφ3. 3- (or φ′ 3+ ).
[0058] Therefore, the phase difference φ′ obtained by the calibration test process can be used in the phase difference calibration process. 3- (or φ′ 3+ ) is compared with the phase difference φ′3 obtained by the initial test process, and 3- Greater than (or φ′ 3+ When the phase difference φ′3 is less than φ′3, the value of the phase difference φ′3 is corrected to
[0059] As another example, during the calibration test, φ2 may be fine-tuned by decreasing and increasing δφ2, respectively.
[0060] Then, based on the two finely adjusted φ2, a measurement step is performed at the first modulation phase φ0 and the second modulation phase φ0 to obtain the count rate S 00 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ1 to obtain the count rate S 01 , the measurement step is performed under the first modulation phase φ1 and the second modulation phase φ3 to obtain the count rate S13 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ2 to obtain the count rate S 02 , and based on the currently acquired count rate S 00 、S 01 、S 13 and S 02 , the corresponding phase differences φ′0, φ′1, φ′2, and φ′3 are calculated by means of the phase difference evaluation step. Those skilled in the art will appreciate that, in this example, there are at least two sets of phase differences φ′0, φ′1, φ′2, and φ′3 corresponding to the two fine-tuning methods of reducing and increasing δφ2, respectively. The calculated phase difference φ′2 corresponding to the fine-tuning of φ2 by reducing (increasing) δφ2 can be denoted as φ′ 2- (φ′ 2+ ).
[0061] Compared with the previous example, in this example, with this different fine-tuning method, there is no need to limit the value range of δφ2.
[0062] Therefore, the phase difference φ′ obtained in two different calibration test processes can be used in the phase difference correction process. 2- and φ′ 2+ Compare, and in φ′ 2- Greater than φ′ 2+ When the phase difference φ′2 is corrected to
[0063] Similarly, φ3 can be fine-tuned by reducing and increasing δφ3 during the calibration test.
[0064] Then, based on the two finely adjusted φ3, a measurement step is performed at the first modulation phase φ0 and the second modulation phase φ0 to obtain the count rate S 00 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ1 to obtain the count rate S 01 , the measurement step is performed under the first modulation phase φ1 and the second modulation phase φ3 to obtain the count rate S 13 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ2 to obtain the count rate S 02 , and based on the currently acquired count rate S 00 、S 01 、S 13 and S 02, the corresponding phase differences φ′0, φ′1, φ′2, and φ′3 are calculated by means of the phase difference evaluation step. Similarly, in this example, there are at least two sets of phase differences φ′0, φ′1, φ′2, and φ′3 corresponding to the two fine-tuning methods of reducing and increasing δφ3, respectively. Among them, the calculated phase difference φ′3 corresponding to the fine-tuning of φ3 by reducing (increasing) δφ3 can be recorded as φ′ 3- (φ′ 3+ ), and there is no need to limit the value range of δφ3.
[0065] Therefore, the phase difference φ′ obtained in two different calibration test processes can be used in the phase difference correction process. 3- and φ′ 3+ Compare, and in φ′ 3- Greater than φ′ 3+ When the phase difference φ′3 is corrected to
[0066] Furthermore, after the appropriate phase differences φ′0, φ′1, φ′2, and φ′3 are determined through calibration, the maximum conjugate error ∑=Max(|SE|,|BE|,|CE|,|DE|) or the relative conjugate error can be calculated using the determined phase differences φ′0, φ′1, φ′2, and φ′3 during the evaluation process. And judge whether it meets the preset threshold requirements, where:
[0067] Based on the above content, it can be seen that in the QKD light source coding conjugation evaluation method proposed in the present invention, The different trends of monotonically decreasing and monotonically increasing of the function on the left side (<π) and the right side (>π) are used to determine which solution the actual value is, thereby accurately giving the numerical value of the actual measured object, making up for the limitations of the existing "Specifications".
[0068] 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.
[0069] 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.
[0070] 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 QKD light source coding conjugation evaluation method, which includes an initial test process, a calibration test process, a phase difference correction process, and an evaluation process; During the initial test, a measurement step is performed at the first modulation phase φ0 and the second modulation phase φ0 to obtain the count rate S 00 , at the first modulation phase φ0 and the second modulation phase φ " Perform the following measurement steps to obtain the count rate S 0" , at the first modulation phase φ " and performing the measurement step at the second modulation phase φ3 to obtain the count rate S "3 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ2 to obtain the count rate S 02 ; and by means of a phase difference evaluation step, using the counting rate S 00 、S 0" 、S "3 and S 02 , calculate the phase difference φ′0, φ′ " , φ′2 and φ′3; among them, The measurement step is configured to cause quantum light that first enters the ground / state preparation module 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; return the output first and second components to the ground / state preparation module, wherein a second modulation phase is applied to the second component; cause the first component loaded with the first modulation phase and the second component loaded with the second modulation phase to interfere with each other to generate an interference signal, and measure the interference signal using a light detector to obtain a count rate; The phase difference evaluation step is used to calculate the phase differences φ′0, φ′ " , φ′2 and φ′3, where φ′0=0, d is the dark count rate of the photodetector, η is the total channel efficiency; During the calibration test, the values of φ2 and φ3 are changed, and the measurement steps are performed at the first modulation phase φ0 and the second modulation phase φ0 to obtain the count rate S 00 , at the first modulation phase φ0 and the second modulation phase φ " Perform the following measurement steps to obtain the count rate S 0" , at the first modulation phase φ " and performing the measurement step at the second modulation phase φ3 to obtain the count rate S "3 , the measurement step is performed under the first modulation phase φ0 and the second modulation phase φ2 to obtain the count rate S 02 ; and by means of a phase difference evaluation step, using the counting rate S 00 、S 0" 、S "3 and S 02 , calculate the phase difference φ′0, φ′ " , φ′2 and φ′3; In the phase difference correction process, by comparing the values of φ′2 and φ′3 obtained in two different correction test processes, or comparing the values of φ′2 and φ′3 obtained in the correction test process with the values obtained in the initial test process, the monotonic change relationship of φ′2 with respect to φ2 and the monotonic change relationship of φ′3 with respect to φ3 are judged, and the monotonic change relationship of φ′2 with respect to φ2 and the monotonic change relationship of φ′3 with respect to φ3 are determined accordingly. or or Among them, φ′0=0, During the evaluation process, the phase differences φ′0, φ′1, φ′2, and φ′3 determined during the phase difference correction process are used to calculate the maximum conjugate error ∑=Max(|AE|,|BE|,|CE|,|DE|), and determine whether it meets the preset threshold requirements, where:
2. The QKD light source coding conjugation evaluation method according to claim 1, wherein: During the calibration test, φ2 is increased or decreased by δφ2, and φ3 is increased or decreased by δφ3, δφ2≤2(π-φ′2), δφ3≤2(π-φ′3); During the phase difference correction process, if the phase difference φ′2 obtained by increasing δφ2 corresponding to φ2 is smaller than the phase difference φ′2 obtained by corresponding to φ2, or the phase difference φ′2 obtained by decreasing δφ2 corresponding to φ2 is larger than the phase difference φ′2 obtained by corresponding to φ2, If the phase difference φ′3 obtained by increasing δφ3 corresponding to φ3 is smaller than the phase difference φ′3 obtained by corresponding to φ3, or the phase difference φ′3 obtained by decreasing δφ3 corresponding to φ3 is larger than the phase difference φ′3 obtained by corresponding to φ3, 3. The QKD light source coding conjugation evaluation method according to claim 1, wherein: During the calibration test, φ2 is increased and decreased by δφ2, and φ3 is increased and decreased by δφ3; During the phase difference correction process, if the phase difference φ′2 obtained by increasing δφ2 by φ2 is smaller than the phase difference φ′2 obtained by decreasing δφ2 by φ2, If the phase difference φ′3 obtained by increasing φ3 by δφ3 is smaller than the phase difference φ′3 obtained by decreasing φ3 by δφ3, 4. The QKD light source coding conjugation evaluation method according to claim 1, wherein: In the measurement step, for the quantum light entering the ground / state preparation module for the first time, the first component and the second component are transmitted along the first arm and the second arm of the unequal-arm interferometer respectively, and the first component is loaded with a first modulation phase on the first arm; The returned first component and second component are transmitted along the second arm and the first arm of the unequal-arm interferometer respectively, and the second component is loaded with a second modulation phase on the first arm.
5. The QKD light source coding conjugation evaluation method according to claim 1, wherein: In the measuring step, the phase modulation frequency is twice the repetition frequency of the quantum light, and / or a first component of one of two adjacent quantum lights interferes with a second component of the other.
6. The QKD light source coding conjugation evaluation method according to any one of claims 1 to 5, wherein: During the evaluation process, the relative error of conjugativity is also calculated And determine whether it meets the preset threshold requirement; and / or, the counting rate is the detection counts per second / the operating frequency of the light detector.
7. The QKD light source coding conjugation evaluation method according to any one of claims 1 to 5, wherein: The quantum light first enters the ground / state preparation module through the circulator, and the interference signal enters the light detector through the circulator; and / or, the first component and the second component are reflected back to the ground / state preparation module by means of a reflector.
8. The QKD light source coding conjugation evaluation method according to any one of claims 1 to 5, wherein: Modulation phase φ , 、φ1、φ2、φ * They are 0, π / 2, π, and 3π / 2 respectively.
9. The QKD light source coding conjugation evaluation method according to any one of claims 1 to 5, wherein: The light detector is a single-photon detector.
10. The QKD light source 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.