A single photon detection method and system

Abstract

The application provides a single photon detection method and system, polling delay scanning is performed, in a noise-free interval, a point corresponding to a detection count of a gate signal delay value is determined, the detection count is greater than or equal to a set threshold, until the total number of the determined points is greater than or equal to a set value; the delay value of each determined point meeting the number requirement and the corresponding detection count are fitted to obtain a fitting curve; a point, in which the fitting curve is a maximum value and the gate signal delay value is an integer, is determined as an optimal point, the gate signal delay value of the point is taken as an optimal delay value, and single photon position calibration is performed. The application is based on the characteristics of a scanning gate signal delay value-detection count curve, combines a curve fitting method and an interval approximation method, can quickly and completely calibrate the single photon detection position, and overcomes the influence caused by the noise of a detector.

Description

Technical Field

[0001] This invention belongs to the field of quantum secure communication technology, specifically relating to a single-photon detection method and system. Background Technology

[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.

[0003] In quantum key distribution (QKD) systems, it is often necessary to calibrate the detection position of gated detectors. For gated detectors, the gate signal passes through an adjustable delay chip. By adjusting the delay setting of the delay chip, the gate signal of the detector is moved. Therefore, calibration requires finding a suitable delay value for the gate signal, where "suitable" means that the maximum photon detection count can be collected at that point.

[0004] Based on the above objectives, current single-photon detection methods mainly determine the minimum adjustable step of the delay chip based on hardware circuit design and delay chip device selection. Within the range of the delay chip, the delay chip setting value of the gate signal is scanned point by point with the above minimum step to obtain the delay value-detection count curve and find the maximum detection count value. The delay value corresponding to the maximum detection count value is then determined to be the appropriate delay value for the gate signal.

[0005] It can be seen that although the existing detection methods are relatively accurate and do not have problems with missed or incorrect detection, the whole process is time-consuming. After the delay chip sends the delay value, the stabilization of the gating signal takes a certain amount of time, and the detection counting also takes a certain amount of time, making the total time even longer. In addition, frequent optical switching is required, which is very inefficient for systems with very small minimum step values, and can easily affect the efficiency and performance of quantum key distribution. Summary of the Invention

[0006] To address the aforementioned problems, this invention proposes a single-photon detection method and system. Based on the characteristics of the scanning gate signal delay value-detection count curve, this invention combines curve fitting and interval approximation methods to quickly and completely calibrate the single-photon detection position while overcoming the influence of detector noise floor.

[0007] According to some embodiments, the present invention adopts the following technical solution:

[0008] A single-photon detection method includes the following steps:

[0009] Perform polling and delayed scanning, and within the noise-free interval, determine the points whose detection counts corresponding to the gate signal delay value are greater than or equal to the set threshold, until the total number of determined points is greater than or equal to the set value;

[0010] The delay values ​​of each determined point that meets the number requirement are fitted with the corresponding detection count to obtain the fitting curve;

[0011] The point where the fitted curve has a maximum value and the gate signal delay value is an integer is determined as the optimal point. The gate signal delay value at this point is used as the optimal delay value for single-photon position calibration.

[0012] As an alternative implementation, the threshold setting is determined based on the dark count value of the detector.

[0013] As an alternative implementation, the magnitude of the set value is determined based on the power of the fitted curve, and the set value is at least the power plus one.

[0014] As an alternative implementation, the fitting is a Taylor series fitting.

[0015] As an alternative implementation method, the specific process of performing polling delayed scanning includes:

[0016] Set the initial value for the gate control signal delay and send it out;

[0017] Obtain the probe count n corresponding to the delay value t, and determine the next delay value t1 based on the probe count n;

[0018] If the detection count n is less than the set threshold, then the interval or the vicinity of the delay value t contains background noise, and the next delay value t1 is the current delay value t plus the first step.

[0019] Otherwise, determine that the point meets the requirements, record the current delay value t and the corresponding probe count n, and the next delay value t1 is the current delay value t plus the second step;

[0020] Use the updated delay value as the latest delay value, and repeat the update and recording process in a loop;

[0021] The delay continues until the updated delay value is greater than or equal to the set threshold or the total number of recorded points is greater than or equal to the set value.

[0022] As a further limitation, the first step is greater than the second step.

[0023] As a further limitation, the set threshold is T-1, where T is the maximum value of the delay range.

[0024] As a further limitation, if the updated delay value is greater than or equal to the set threshold, and the total number of recorded points is zero at this time, a fault information is reported.

[0025] As a further limitation, if the updated delay value is greater than or equal to the set threshold, and there are recorded points at this time, but the total number of recorded points is less than the set value, the second round of delayed scanning process is started.

[0026] As a further limitation, the second polling delayed scanning process specifically includes:

[0027] (1) Statistically analyze the points recorded during the existing polling delay scan process and their probe counts, and determine the delay value corresponding to the maximum probe count;

[0028] (2) Delineate an interval centered on the delay value, and within the interval, take multiple delay values ​​in the third step and send them to the detector to obtain the detection count, and record the points where the detector count value is greater than the set threshold.

[0029] (3) Determine whether the total number of points recorded in steps (1) and (2) is greater than or equal to the set value. If yes, end. Otherwise, within the interval, take multiple delay values ​​in the fourth step. The fourth step is less than the third step and send them to the detector to obtain the detection count. Record the points whose detector count value is greater than the set threshold and does not repeat with step (2) until the total number of points recorded is greater than or equal to the set value.

[0030] A single-photon detection system, comprising:

[0031] The polling delay scanning module is configured to perform polling delay scanning, and within an interval without background noise, determine the points whose detection counts corresponding to the gate signal delay value are greater than or equal to the set threshold, until the total number of determined points is greater than or equal to the set value.

[0032] The fitting module is configured to fit the delay values ​​of each determined point that meets the number requirement with the corresponding probe count to obtain a fitting curve;

[0033] The detection calibration module is configured to determine the point where the fitted curve has a maximum value and the gate signal delay value is an integer as the optimal point, and use the gate signal delay value of that point as the optimal delay value to perform single-photon detection position calibration.

[0034] A quantum key distribution system, wherein the receiver is a gated detector, and the above method is used for single-photon detection or includes the above system.

[0035] An electronic device includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor, wherein the computer instructions, when executed by the processor, perform the steps in the method described above.

[0036] A computer-readable storage medium for storing computer instructions, which, when executed by a processor, perform the steps in the above method.

[0037] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0038] This invention is applicable to all quantum key distribution (QKD) systems where the receiver is a gated detector.

[0039] This invention eliminates the influence of detector noise floor when determining the optimal value of gating delay.

[0040] This invention provides an algorithm for finding extreme values ​​using interval approximation and curve fitting based on the characteristics of the curve. This algorithm can quickly calibrate the single-photon detector position, reduce the startup time of the QKD system, improve the response time of the QKD network, and reduce the calibration time of the single-photon detector position during anomaly handling, thereby improving the code generation rate.

[0041] This invention can be implemented without modifying the hardware, only through firmware upgrades, without increasing hardware costs, and the update or upgrade process is simple and easy to operate.

[0042] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described below in detail with reference to the accompanying drawings. Attached Figure Description

[0043] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.

[0044] Figure 1 This is a quantum key distribution system according to at least one embodiment of the present invention;

[0045] Figure 2 The scanning gating signal delay value-detection count curve is shown in at least one embodiment of the present invention.

[0046] Figure 3 This is a flowchart of at least one embodiment of the present invention. Detailed implementation method:

[0047] The present invention will be further described below with reference to the accompanying drawings and embodiments.

[0048] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.

[0049] It should be noted that the terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention. As used herein, the singular form is intended to include the plural form as well, unless the context clearly indicates otherwise. Furthermore, it should be understood that when the terms "comprising" and / or "including" are used in this specification, they indicate the presence of features, steps, operations, devices, components, and / or combinations thereof.

[0050] like Figure 1 As shown, for a quantum key distribution system with a gated detector at the receiver, the detection circuit includes a delay module, and a fast delay scanning scheme is introduced during system operation. By calibrating the phase shifter in the delay module to adjust the delay position of the gated signal, the optimal gated signal delay position that matches the input optical pulse signal is quickly found. The process for achieving the optimal gated signal delay position is as follows: the transmitter generates a delay scanning test light, and the receiver automatically adjusts the delay position of the gated signal by detecting the detection count of the gated single-photon detector, so that the detection count of the gated single-photon detector reaches its maximum, and locks the gated signal delay position corresponding to the maximum detection count.

[0051] like Figure 2 As shown, it should be noted that Figure 2 This is just one example. The specific range of detection count and delay value will be determined according to the specific design. The gate signal delay value-detection count curve is generally a monotonically increasing / decreasing single-peak curve. In some positions, such as the delay value of 33, the detection count has a small peak on the curve caused by background noise.

[0052] This invention provides a method that modifies the traversal delayed scanning method to a fast interval approximation and curve fitting method to find the optimal gating delay value, while overcoming the influence of detector noise floor.

[0053] Specifically, such as Figure 3 As shown, a threshold N is first set. In the partial implementation, N is a value that is about 2 to 3 times the dark count of the detector.

[0054] Specifically, the following steps are included:

[0055] Step 1: Collect 6 to 8 data points (gating signal delay value, detector count), and these 6 to 8 detector count values ​​are ≥ N;

[0056] Step 2: Fit the data collected in Step 1 using the Taylor formula (gating signal delay value X, detector count Y) to obtain the following curve formula:

[0057] f(x) = a0 + a1x + a2x 2 +a3x 3 +a4x 4 +a5x 5 ;

[0058] Step 3: Based on the fitting formula f(x) in Step 2, and assuming x is an integer, find the maximum value of formula f(x) and send down the corresponding gate signal delay value X.

[0059] It should be noted that this embodiment uses a fifth-power fitted curve as an example, so at least six data points need to be collected to obtain parameters a0-a5. In other embodiments, the power of the fitted curve can be adjusted. Generally, a higher power results in greater accuracy, but also a more complex and time-consuming calibration process. Generally, values ​​greater than or equal to the third power are more accurate. In specific applications, those skilled in the art can set the appropriate power according to the specific application.

[0060] Specifically, step 1 may include several rounds of delay value scanning process.

[0061] The first round of gating signal delay value scanning process specifically includes:

[0062] Step (1): Set the initial value t of the delay value (which can be 0 in this embodiment) and send the delay value;

[0063] Step (2): Obtain the detection count n corresponding to the delay value t in this round, and determine the delay value t1 for the next round based on n;

[0064] a. If n is less than N:

[0065] The delay value t1 for the next round is equal to the delay value t + T / 4 for the current round, where T is the maximum value within the delay range.

[0066] b. If n is greater than or equal to N:

[0067] The delay value t1 for the next round is equal to the delay value t + T / 8 for this round, and the (delay value, probe count) (t, n) for this round is recorded.

[0068] It should be noted that the recorded data are in pairs and can be labeled in the form of (X1,Y1), (X2,Y2), etc. Each time a new data is added that meets the condition that the detection count is greater than or equal to the set threshold N, a new data is added.

[0069] Step (3) sends down the delay value obtained in step (2) and repeats step (2) until the delay value t1≥T-1 stops. When t1≥T-1, if no gated delay value with a detection count greater than N is recorded, then report "Gated single-photon detector failure, calibration process failed".

[0070] Continue scanning the delay values ​​in the second round until 6 to 8 delay values ​​are obtained (and the detector count value corresponding to the delay value is ≥ N).

[0071] The second round of delay value scanning includes:

[0072] Step (1): Count the number of gated delay values ​​and probe counts ≥ N during the first round of delay value scanning: (X1, Y1), (X2, Y2) ... (X n-1,Y n-1 ), (X n ,Y n Find the maximum probe count Y. max The corresponding delay value X t ;

[0073] Step (2): Using the delay value X obtained in step (1) t Centered at (X) t-1 X t+1 In the interval, take several delay values ​​in step T / 16 and send them to the detector to obtain the detection count. Keep the (delay value, detection count) where the detector count value is ≥ N.

[0074] Step (3): If the total number of delay values ​​issued by the detector count obtained in steps (1) and (2) is less than 6, then the delay value X is used. t Centered on the interval, several delay values ​​are taken in increments of T / 32 and sent to the detector to obtain counts, until a total of 6 to 8 detector count values ​​≥ N are obtained. Of course, if there is a delay value that is the same as in step (2), it will not be sent again.

[0075] If the total number of delay values ​​issued by the detector count obtained in steps (1) and (2) is greater than N, then record (delay value, detector count).

[0076] If the above-mentioned delay value update process exceeds the range of [0, T-1] during the calculation process, it can be made to satisfy the range of [0, T-1] by increasing or decreasing the calculation of T.

[0077] Of course, the above step lengths are just examples and can be adjusted according to the hardware circuit design, delay chip selection and calibration requirements.

[0078] Step 2 includes:

[0079] In this embodiment, the curve obtained by fitting the acquisition points using Taylor's formula (gating signal delay value, detector count) is as follows: f(x)=a0+a1x+a2x 2 +a3x 3 +a4x 4 +a5x 5 ;

[0080] According to Taylor's formula, the curve representing (gating signal delay value, detector count) is a polynomial function: f(x) = a0 + a1x + a2x 2 +a3x 3 +a4x 4 +a5x 5 .

[0081] Collect six or more points (gating signal delay values, detector counts) for matrix solving. The following example uses six points: (X1, Y1), (X2, Y2), (X3, Y3), (X4, Y4), (X5, Y5), and (X6, Y6).

[0082] Construct the following matrices and solve them to obtain (a0, a1, a2, a3, a4, a5).

[0083]

[0084] Step 3 includes:

[0085] According to the fitting formula f(x), the extreme value is calculated and adjusted to (X, Y), where X must be an integer, and the gate signal delay value X is sent down.

[0086] Specifically, according to the formula y = f(x), x is in the range (0, T) and x is an integer. The value of x when y is at its maximum is the calibration value X of the gate signal delay value.

[0087] Send down the gating signal delay value X.

[0088] In some embodiments, a quantum key distribution system is provided, which initiates the aforementioned rapid delayed scanning process when the quantum key distribution system starts up and when an anomaly occurs in the quantum key distribution system, wherein the sending of delay values ​​and the acquisition of probe counts can reuse the firmware interface of the previous system.

[0089] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems, or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, the present invention can take the form of a computer program product embodied on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code.

[0090] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1A device that provides the functions specified in one or more boxes.

[0091] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0092] These computer program instructions may also be loaded onto a computer or other programmable data processing apparatus to cause a series of operational steps to be performed on the computer or other programmable apparatus to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable apparatus for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0093] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.

Claims

1. A single-photon detection method, characterized by: Includes the following steps: Perform polling and delayed scanning, and within the noise-free interval, determine the points whose detection counts corresponding to the gate signal delay value are greater than or equal to the set threshold, until the total number of determined points is greater than or equal to the set value; The delay values ​​of each determined point that meets the number requirement are fitted with the corresponding detection count to obtain the fitting curve; The point where the fitted curve has a maximum value and the gate signal delay value is an integer is determined as the optimal point. The gate signal delay value at this point is used as the optimal delay value for single-photon position calibration. The specific process of performing polling with delayed scanning includes: Set the initial value for the gate control signal delay and send it out; Obtain the probe count n corresponding to the delay value t, and determine the next delay value t1 based on the probe count n; If the detection count n is less than the set threshold, then the interval or the vicinity of the delay value t contains background noise, and the next delay value t1 is the current delay value t plus the first step. Otherwise, determine that the point meets the requirements, record the current delay value t and the corresponding probe count n, and the next delay value t1 is the current delay value t plus the second step; Use the updated delay value as the latest delay value, and repeat the update and recording process in a loop; Until the updated delay value is greater than or equal to the set threshold or the total number of recorded points is greater than or equal to the set value; If the updated delay value is greater than or equal to the set threshold, and the total number of recorded points is zero, report the fault information. If the updated delay value is greater than or equal to the set threshold, and there are recorded points at this time, but the total number of recorded points is less than the set value, the second round of delayed scanning process begins; The second polling delayed scan process specifically includes: (1) Statistically analyze the points recorded during the existing polling delay scan process and their probe counts, and determine the delay value corresponding to the maximum probe count; (2) Delineate an interval centered on the delay value, and within the interval, take multiple delay values ​​in the third step and send them to the detector to obtain the detection count, and record the points where the detector count value is greater than the set threshold. (3) Determine whether the total number of points recorded in steps (1) and (2) is greater than or equal to the set value. If yes, end. Otherwise, within the interval, take multiple delay values ​​in the fourth step. The fourth step is less than the third step and send them to the detector to obtain the detection count. Record the points whose detector count value is greater than the set threshold and does not repeat with step (2) until the total number of points recorded is greater than or equal to the set value.

2. The single-photon detection method as described in claim 1, characterized in that: The threshold value is determined based on the dark count value of the detector.

3. The single-photon detection method as described in claim 1, characterized in that: The magnitude of the set value is determined based on the power of the fitted curve, and the set value is at least the power plus one.

4. The single-photon detection method as described in claim 1, characterized in that: The fitting is a Taylor series fitting.

5. The single-photon detection method as described in claim 1, characterized in that: The first step is greater than the second step.

6. A single-photon detection method as described in claim 1 or 5, characterized in that: The set threshold is T-1, where T is the maximum value of the delay range.

7. A single-photon detection system, characterized in that: include: The polling delay scanning module is configured to perform polling delay scanning, and within an interval without background noise, determine the points whose detection counts corresponding to the gate signal delay value are greater than the set threshold, until the total number of determined points is greater than or equal to the set value. The fitting module is configured to fit the delay values ​​of each determined point that meets the number requirement with the corresponding probe count to obtain a fitting curve; The detection calibration module is configured to determine the point where the fitted curve has a maximum value and the gate signal delay value is an integer as the optimal point, and use the gate signal delay value of that point as the optimal delay value to perform single-photon detection position calibration; The specific process of performing polling with delayed scanning includes: Set the initial value for the gate control signal delay and send it out; Obtain the probe count n corresponding to the delay value t, and determine the next delay value t1 based on the probe count n; If the detection count n is less than the set threshold, then the interval or the vicinity of the delay value t contains background noise, and the next delay value t1 is the current delay value t plus the first step. Otherwise, determine that the point meets the requirements, record the current delay value t and the corresponding probe count n, and the next delay value t1 is the current delay value t plus the second step; Use the updated delay value as the latest delay value, and repeat the update and recording process in a loop; Until the updated delay value is greater than or equal to the set threshold or the total number of recorded points is greater than or equal to the set value; If the updated delay value is greater than or equal to the set threshold, and the total number of recorded points is zero, report the fault information. If the updated delay value is greater than or equal to the set threshold, and there are recorded points at this time, but the total number of recorded points is less than the set value, the second round of delayed scanning process begins; The second polling delayed scan process specifically includes: (1) Statistically analyze the points recorded during the existing polling delay scan process and their probe counts, and determine the delay value corresponding to the maximum probe count; (2) Delineate an interval centered on the delay value, and within the interval, take multiple delay values ​​in the third step and send them to the detector to obtain the detection count, and record the points where the detector count value is greater than the set threshold. (3) Determine whether the total number of points recorded in steps (1) and (2) is greater than or equal to the set value. If yes, end. Otherwise, within the interval, take multiple delay values ​​in the fourth step. The fourth step is less than the third step and send them to the detector to obtain the detection count. Record the points whose detector count value is greater than the set threshold and does not repeat with step (2) until the total number of points recorded is greater than or equal to the set value.

8. A quantum key distribution system, characterized in that: The receiving end is a gated detector, which performs single-photon detection using the method described in any one of claims 1-6 or includes the system described in claim 7.

9. An electronic device, characterized in that: It includes a memory and a processor, as well as computer instructions stored in the memory and running on the processor, which, when executed by the processor, perform the steps of the method according to any one of claims 1-6.

10. A computer-readable storage medium, characterized in that: Used to store computer instructions, which, when executed by a processor, complete the steps of the method according to any one of claims 1-6.

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