Calibration method, processing device, QKD system and communication method thereof

Abstract

The invention discloses a calibration method, a processing device, a QKD system and a communication method thereof. The calibration method comprises the following steps: drawing a first curve and a second curve; the first curve is a relation curve of a plurality of different delay positions and corresponding counts when the single-photon detector detects the first pulse signal; the second curve is a relation curve of a plurality of different delay positions and corresponding counts when the single-photon detector detects a second pulse signal; the second pulse signal and the first pulse signal have different average photon numbers per pulse; drawing a third curve based on the first curve and the second curve; wherein the third curve is a relation curve of a plurality of different delay positions and corresponding counting ratios; based on the third curve, determining an avalanche transition region of the single-photon detector; based on the avalanche transition region, after an effective working region of the single-photon detector is determined, a calibration result is stored to a signal receiving end; the calibration result includes at least one of an avalanche transition region and an effective working region.

Description

Technical Field

[0001] The present invention relates to the technical field of Quantum Key Distribution (QKD), and more specifically, to a calibration method, a processing device, a QKD system, and a communication method thereof. Background Art

[0002] The security of the QKD system has been strictly proven from the principles of quantum physics to the communication protocol. However, in actual engineering, due to the imperfections of the devices in the system, there are deviations from the theoretical assumptions in the proof process, which may become loopholes. To improve the security of the QKD system, it is necessary to discover and adopt appropriate countermeasures for defense. Such as preventing strong light attack schemes, anti-dead time attack schemes, anti-avalanche transition region attack schemes, etc.

[0003] The QKD system is composed of multiple components, and the single-photon detector is a very important component, and most of them work in the gated mode. For the gated single-photon detector, its working principle is as follows: when inside the gate, the single-photon detector is in the Geiger mode and can detect single photons; when outside the gate, the single-photon detector is in the linear mode and cannot detect single photons. Due to the imperfections of the device, both the rise and fall of the gate signal require a certain amount of time to complete the opening and closing actions. Therefore, during this period, the single-photon detector neither belongs to the Geiger mode that can detect single photons nor belongs to the linear mode that cannot detect single photons. This time region is called the avalanche transition region. In the avalanche transition region, the single-photon detector has superlinear characteristics, hardly responds to single-photon signals, but has a high response probability for signals exceeding a certain threshold, similar to the detection principle in the linear region, but the photon number threshold is much lower.

[0004] Based on the above description, it can be seen that the QKD system is vulnerable to external interference signals in the avalanche transition region of the single-photon detector. Therefore, in the avalanche transition region of the single-photon detector, how to avoid the influence of external signals on the communication result of the QKD system is an urgent problem to be solved in the QKD technical field. Summary of the Invention

[0005] In view of this, the present application provides a calibration method, a processing device, a QKD system, and a communication method thereof, and the solutions are as follows:

[0006] A calibration method for calibrating the avalanche transition region of a single-photon detector at the signal receiving end of a QKD system, the calibration method comprising:

[0007] Draw a first curve and a second curve; wherein, the first curve is a relationship curve between multiple different delay positions and corresponding counts when a single-photon detector detects a first pulse signal; the second curve is a relationship curve between multiple different delay positions and corresponding counts when the single-photon detector detects a second pulse signal; the second pulse signal has a different average number of photons per pulse from the first pulse signal.

[0008] Based on the first curve and the second curve, draw a third curve; wherein, the third curve is a relationship curve between multiple different delay positions and corresponding count ratios.

[0009] Based on the third curve, determine the avalanche transition region of the single-photon detector.

[0010] After determining the effective working region of the single-photon detector based on the avalanche transition region, store the calibration result in the signal receiving end; wherein, the calibration result includes at least one of the avalanche transition region and the effective working region.

[0011] Preferably, in the above calibration method, the method of drawing the first curve includes:

[0012] Configure the signal transmitting end in the QKD system to emit a first pulse signal.

[0013] Within a preset delay range, traverse multiple different delay positions; wherein, the delay range is the period of one gating signal of the single-photon detector.

[0014] Based on the built-in time-to-digital converter in the signal receiving end, record the counts corresponding to multiple delay positions when the single-photon detector detects the first pulse signal.

[0015] Based on the counts of the single-photon detector under the first pulse signal, draw the first curve.

[0016] Preferably, in the above calibration method, the method of drawing the second curve includes:

[0017] Configure the signal transmitting end to emit a second pulse signal.

[0018] Within a preset delay range, traverse multiple different delay positions; wherein, the delay range is the period of one gating signal of the single-photon detector.

[0019] Based on the built-in time-to-digital converter in the signal receiving end, record the counts corresponding to multiple delay positions when the single-photon detector detects the second pulse signal.

[0020] Based on the counts of the single-photon detector under the second pulse signal, draw the second curve.

[0021] Preferably, in the above calibration method, both the first curve and the second curve include the counts corresponding to the first delay position to the Nth delay position.

[0022] The method for drawing the third curve includes:

[0023] Determine the counting ratio of the first curve and the second curve at the same delay position;

[0024] Based on the counting ratios at each of the first delay position to the Nth delay position, draw a relationship curve between different delay positions and the corresponding counting ratios.

[0025] Preferably, in the above calibration method, in the third curve, the duration of the delay position interval corresponding to the counting ratio interval greater than the set protection threshold on the vertical axis on the horizontal axis is T'; the period of one gating signal of the single-photon detector is T;

[0026] τ = T - 2T';

[0027] Wherein, τ is the effective working area of the single-photon detector.

[0028] Preferably, in the above calibration method, it further includes:

[0029] Display calibration information;

[0030] Wherein, the calibration information includes at least one of: the first curve, the second curve, the third curve, the avalanche transition region, the effective working area, the configuration information of the signal receiving end, and the configuration information of the signal transmitting end in the QKD system.

[0031] Preferably, in the above calibration method, it further includes:

[0032] Based on the debugging host, control the signal transmitting end and the signal receiving end of the QKD system to enter the debugging mode;

[0033] After controlling the signal transmitting end and the signal receiving end to enter the debugging mode, input a control instruction;

[0034] Wherein, the debugging host can respond to the control instruction, automatically determine the avalanche transition region and the effective working area of the single-photon detector based on the calibration method, and then store the calibration result into the signal receiving end; the calibration result includes at least one of the avalanche transition region and the effective working area.

[0035] This application also provides a processing device for executing any one of the above calibration methods, including:

[0036] A configuration module, which is used to configure the signal transmitting end of the QKD system to emit the first pulse signal or the second pulse signal;

[0037] A drawing module, which is used to draw a first curve when a first pulse signal is emitted at the signal transmitting end based on the count of a single-photon detector, draw a second curve when a second pulse signal is emitted at the signal transmitting end, and draw a third curve based on the first curve and the second curve;

[0038] A processing module, which is used to determine the avalanche transition region of the single-photon detector based on the third curve, and after determining the effective working region of the single-photon detector based on the avalanche transition region, store the calibration result at the signal receiving end; the calibration result includes at least one of the avalanche transition region and the effective working region.

[0039] Preferably, in the above processing device, it further includes: a human-computer interaction module, which is used to obtain user input instructions;

[0040] The configuration module is further used to respond to the user input instructions and control the signal transmitting end and the signal receiving end in the QKD system to enter the debugging mode;

[0041] After the transmitting end and the signal receiving end enter the debugging mode, the processing module controls the processing device to execute the calibration method based on the built-in calibration software.

[0042] Preferably, in the above processing device, it further includes:

[0043] A display module, which is used to display calibration information;

[0044] Wherein, the calibration information includes at least one of the first curve, the second curve, the third curve, the avalanche transition region, the effective working region, the configuration information of the signal receiving end, and the configuration information of the signal transmitting end in the QKD system.

[0045] This application also provides a QKD system, including:

[0046] A signal transmitting end, which is used to transmit synchronous light and signal light;

[0047] A signal receiving end, which pre-stores the calibration result determined by any one of the above calibration methods; the signal receiving end is used to extract the detection result of the single-photon detector in the effective working region for code generation, and discard the detection result of the single-photon detector in the avalanche transition region.

[0048] Preferably, in the above QKD system, the signal receiving end is further used to perform abnormal warning based on the detection result of the single-photon detector in the avalanche transition region and the detection result in the effective working region.

[0049] Preferably, in the above QKD system, the single-photon detector has a first count result in the effective working region, a second count result in the avalanche transition region at the rising edge of the gating signal, and a third count result in the avalanche transition region at the falling edge of the gating signal;

[0050] After the ratio of the second counting result to the first counting result at the signal receiving end exceeds the set threshold, an abnormal warning is given;

[0051] And / or, after the ratio of the third counting result to the first counting result at the signal receiving end exceeds the set threshold, an abnormal warning is given.

[0052] This application also provides a communication method for a QKD system. The calibration result determined by any one of the above calibration methods is pre-stored in the signal receiving end of the QKD system;

[0053] The communication method includes:

[0054] Detect the synchronization light and signal light emitted by the signal transmitting end through a single-photon detector;

[0055] Extract the detection results of the single-photon detector in the effective working area for code generation, and discard the detection results of the single-photon detector outside the effective working area.

[0056] Preferably, in the above communication method, the communication method further includes:

[0057] Based on the detection results of the single-photon detector in the avalanche transition region and in the effective working area, an abnormal warning is given.

[0058] Preferably, in the above communication method, based on the detection results of the single-photon detector in the avalanche transition region and in the effective working area, giving an abnormal warning includes:

[0059] Obtain the first counting result of the single-photon detector in the effective working area, the second counting result in the avalanche transition region at the rising edge of the gating signal, and the third counting result in the avalanche transition region at the falling edge of the gating signal;

[0060] Based on the first counting result, the second counting result, and the third counting result, an abnormal warning is given;

[0061] Among them,

[0062] After the ratio of the second counting result to the first counting result exceeds the set threshold, an abnormal warning is given;

[0063] And / or, after the ratio of the third counting result to the first counting result exceeds the set threshold, an abnormal warning is given.

[0064] As can be seen from the above description, in the calibration method, processing device, QKD system and its communication method provided by the technical solution of the present application, the calibration method includes: plotting a first curve and a second curve; wherein, the first curve is a relationship curve between multiple different delay positions and corresponding counts when a single-photon detector detects a first pulse signal; the second curve is a relationship curve between multiple different delay positions and corresponding counts when the single-photon detector detects a second pulse signal; the second pulse signal has a different average number of photons per pulse from the first pulse signal; based on the first curve and the second curve, a third curve is plotted; wherein, the third curve is a relationship curve between multiple different delay positions and corresponding count ratios; based on the third curve, the avalanche transition region of the single-photon detector is determined; after determining the effective working region of the single-photon detector based on the avalanche transition region, the calibration result is stored in the signal receiving end; wherein, the calibration result includes at least one of the avalanche transition region and the effective working region. The technical solution of the present application can calibrate the effective working region of the single-photon detector, so that the QKD system can generate keys based on the count results of the single-photon detector in the pre-calibrated effective working region, thereby avoiding external signal interference in the avalanche transition region. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] In order to more clearly illustrate the technical solutions in the embodiments of the present application or related technologies, the following will briefly introduce the drawings required for use in the description of the embodiments or the prior art. Obviously, the drawings in the following description are only the embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on the provided drawings.

[0066] The structures, ratios, sizes, etc. shown in the drawings of this specification are only used to cooperate with the content disclosed in the specification for those skilled in this technology to understand and read, and are not used to limit the limited conditions under which the present application can be implemented. Therefore, they do not have a substantial technical meaning. Any modification of the structure, change of the proportional relationship, or adjustment of the size, without affecting the effects that the present application can produce and the purposes that can be achieved, should still fall within the scope covered by the technical content disclosed in the present application.

[0067] Figure 1 It is a schematic flowchart of a calibration method provided by an embodiment of the present application;

[0068] Figure 2 It is a flowchart of a method for plotting the first curve provided by an embodiment of the present application;

[0069] Figure 3 It is a flowchart of a method for plotting the second curve provided by an embodiment of the present application;

[0070] Figure 4 It is a flowchart of a method for plotting the third curve provided by an embodiment of the present application;

[0071] Figure 5 Schematic structural diagram of a processing device provided by an embodiment of the present application;

[0072] Figure 6 Schematic structural diagram of another processing device provided by an embodiment of the present application;

[0073] Figure 7 Schematic structural diagram of yet another processing device provided by an embodiment of the present application;

[0074] Figure 8 Schematic diagram of the principle for calibrating a single - photon detector in a QKD system provided by an embodiment of the present application;

[0075] Figure 9 Schematic structural diagram of a QKD system provided by an embodiment of the present application;

[0076] Figure 10 Schematic diagram of the detection pulse distribution of single - photon detection in a QKD system within a gating signal period provided by an embodiment of the present application;

[0077] Figure 11 Schematic flowchart of a communication method for a QKD system provided by an embodiment of the present application;

[0078] Figure 12 Schematic flowchart of another communication method for a QKD system provided by an embodiment of the present application;

[0079] Figure 13 Schematic flowchart of a method for anomaly early warning based on the detection results of a single - photon detector provided by an embodiment of the present application. Detailed implementation manners

[0080] Next, the embodiments in the present application will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present application.

[0081] Without departing from the spirit or scope of the present application, various modifications and changes can be made in the present application, which are obvious to those skilled in the art. Therefore, the present application is intended to cover the modifications and changes of the present application that fall within the scope of the corresponding claims (the claimed technical solutions) and their equivalents. It should be noted that the implementation manners provided by the embodiments of the present application can be combined with each other without contradiction.

[0082] The QKD system includes a signal transmitting end and a signal receiving end. The signal transmitting end can emit synchronous light and signal light, and the signal receiving end can detect the synchronous light and the signal light, and obtain the communication information contained in the signal light based on the detection result.

[0083] In the BB84 protocol, a third party uses a random basis vector to measure the quantum state sent by the signal transmitting end, and then the third party resends the measurement result. This measurement result is not a single photon, but a known optical pulse, called a trigger pulse. Then, if the third party uses a basis vector that matches the signal receiving end to detect, the trigger pulse sent by the third party will always be detected by the detector with the same coding value at the same basis vector end of the signal receiving end, and will not be detected by the detector with a different coding value. On the contrary, if the third party uses a basis vector that does not match the signal receiving end to measure the quantum state of the signal light sent by the signal transmitting end, the energy of its trigger pulse will be evenly distributed to the detectors with two coding values at different basis vector ends of the signal receiving end and will not be detected. In this case, the situation where the third party introduces an error code will not occur, and the signal receiving end will not monitor the error code introduced by the third party. At this time, the third party can obtain the key information without being discovered.

[0084] The avalanche transition region attack (ATR attack) is an attack method in which a third party uses the above method combined with the superlinear characteristics of the avalanche transition region to obtain the key of the QKD system without introducing an error code.

[0085] A scheme for defending against the ATR attack is to resist the ATR attack by monitoring the bias current of the avalanche photodiode (APD). When the third party uses the avalanche transition region of the detector to implement the ATR attack, if the number of photons sent is only a few hundred photons, since the reverse bias voltage of the APD is smaller than the voltage value during normal single-photon detection, the avalanche current amplification will also be smaller than that during normal detection. Therefore, the current flowing through the APD during the implementation of the ATR attack is basically equivalent to or even smaller than the avalanche current during normal single-photon detection. So, the method of judging whether there is an ATR attack based on the magnitude of the APD bias current cannot resist the ATR attack under weak light.

[0086] Another scheme for defending against the ATR attack is to resist the ATR attack based on the characteristics of active gate signal switching. This method requires a clock fan-out, a multiplexer, a delay module, and a random source device, and the system complexity is high and the engineering implementation difficulty is large.

[0087] Based on the above description, it can be seen that among the above two methods of resisting the ATR attack, this type of patchy defense measure based on monitoring the APD bias current parameter changes the original system relatively little and is easy to implement, but this type of defense measure does not completely plug the loophole. And the scheme of using the characteristics of active gate signal switching to resist the avalanche transition region attack has a higher complexity compared with the original system.

[0088] To solve the above problems, the inventors have studied and found that by using a time-to-digital converter (TDC) for measurement, it can be known that the distribution of the arrival times of normal detector pulses is different from that of detection pulses when performing an ATR attack using the superlinear characteristic, and there is a gap in the peak positions of the two types of pulses. Based on this, the technical solution of the application embodiment utilizes the function of the existing time-to-digital converter in the signal receiving end to achieve the detection and defense of the avalanche transition region attack. On the one hand, before the QKD system leaves the factory, the avalanche transition region of the single-photon detector in the signal receiving end is calibrated, and the effective working region of the single-photon detector is determined. On the other hand, in the normal operating state after the QKD system leaves the factory, based on the pre-calibrated effective working region, the attack pulses of the single-photon detector in the avalanche transition region can be filtered out. Moreover, it can also be combined with a real-time monitoring method to monitor and give a timely warning of the avalanche transition region attack that bypasses the defense scheme.

[0089] To make the above objects, features, and advantages of the present application more obvious and understandable, the present application will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0090] Refer to Figure 1 as shown in Figure 1 which is a schematic flowchart of a calibration method provided by an embodiment of the present application. The calibration method is used to calibrate the avalanche transition region of the single-photon detector in the signal receiving end of the QKD system. The calibration method includes:

[0091] Step S11: Draw a first curve and a second curve; wherein, the first curve is a relationship curve between multiple different delay positions and the corresponding counts when the single-photon detector detects the first pulse signal; the second curve is a relationship curve between multiple different delay positions and the corresponding counts when the single-photon detector detects the second pulse signal; the second pulse signal has a different average number of photons per pulse from the first pulse signal.

[0092] Step S12: Based on the first curve and the second curve, draw a third curve; wherein, the third curve is a relationship curve between multiple different delay positions and the corresponding count ratio.

[0093] Step S13: Based on the third curve, determine the avalanche transition region of the single-photon detector.

[0094] Step S14: After determining the effective working region of the single-photon detector based on the avalanche transition region, store the calibration result in the signal receiving end.

[0095] Wherein, the calibration result includes at least one of the avalanche transition region and the effective working region. The signal transmitting end of the QKD system can emit synchronous light and signal light. In the signal receiving end, there is a PIN photodiode for detecting synchronous light and an APD for detecting signal light. In the embodiments of the present application, the single-photon detector refers to a detector provided with an APD for detecting signal light.

[0096] Based on the calibration method provided by the embodiments of the present application, it is possible to calibrate the avalanche transition region of the single-photon detector in the signal receiving end before the QKD system leaves the factory, and then determine its effective working region. Thus, after the QKD system leaves the factory, when the QKD system is in a normal working state, it can extract the detection results of the single-photon detector in the effective working region based on the pre-stored effective working region of the single-photon detector for code generation, thereby defending against attacks on the avalanche transition region.

[0097] In the above step S11, the method of drawing the first curve can be as Figure 2 shown.

[0098] Refer to Figure 2 shown, Figure 2 which is a flowchart of a method for drawing the first curve provided by the embodiments of the present application. The method includes:

[0099] Step S21: Configure the first pulse signal emitted by the signal transmitting end in the QKD system.

[0100] In the embodiments of the present application, the calibration method can be executed based on a debugging host with calibration software. Through the calibration software, the signal transmitting end is configured with parameters so that it emits the first pulse signal. In this step, the frequency f L of the first pulse signal and the average number of photons per pulse μ1 can be configured based on requirements. Optionally, f L can be set to 625 KHz and μ1 = 100. Obviously, f L and μ1 can be set based on requirements, and the embodiments of the present application do not limit this.

[0101] Step S22: Traverse multiple different delay positions within a preset delay range; where the delay range is the period of a gating signal of the single-photon detector. Optionally, it can be set to have n different delay positions, and n is a positive integer greater than 1.

[0102] Set the period of the gating signal as T. For a given gating signal, T is a known constant. A delay step t can be set according to requirements. Based on the given constants T and t, n different delay positions can be determined, where n = T / t. In this step, the delay positions of the gating signal can be automatically traversed through the calibration software in the debugging host.

[0103] Step S23: Based on the built-in time-to-digital converter in the signal receiving end, record the counts corresponding to multiple delay positions when the single-photon detector detects the first pulse signal.

[0104] Set the above n delay positions as the 1st delay position S1 to the nth delay position S n, the count of the single - photon detector at the i - th delay position S i is denoted as Q i , where i = {1, 2, …, n}, that is, i is a positive integer not greater than n.

[0105] At the signal receiving end of the QKD system, a time - to - digital converter based on the internal delay chain counting of the FPGA is set. In the embodiments of the present application, the time - to - digital converter with a precision of η in the QKD system can be reused to record the counts of the single - photon detector at different delay positions.

[0106] Step S24: Draw a first curve based on the count of the single - photon detector under the first pulse signal.

[0107] Under the first pulse signal, after obtaining the counts at each delay position through the single - photon detector, the count results are uploaded to the debugging host. The calibration software in the debugging host can automatically draw a delay - position - count curve based on each delay position and its corresponding count as the first curve.

[0108] In the above step S11, the method of drawing the second curve can be as Figure 3 shown.

[0109] Refer to Figure 3 shown, Figure 3 which is a flowchart of a method for drawing the second curve provided by the embodiments of the present application. The method includes:

[0110] Step S31: Configure the signal transmitting end to emit a second pulse signal.

[0111] In this step, the signal transmitting end is also configured with parameters through the calibration software so that it emits a second pulse signal. The average number of photons per pulse μ2 of the second pulse signal can be configured based on requirements. Optionally, μ2 = 50. The frequency of the second pulse signal can be the same as that of the first pulse signal. It should be noted that when μ1≠μ2, the average number of photons per pulse of the first pulse signal and the second pulse signal can be set based on requirements, and the values of μ1 and μ2 in the embodiments of the present application are not limited.

[0112] Among them, μ1 can be used to simulate the signal light during the normal operation of the QKD system. μ2 can be used to simulate the attack pulse.

[0113] Step S32: Traverse multiple different delay positions within a preset delay range; where the delay range is the period of a gating signal of the single - photon detector. When the average number of photons per pulse is configured as μ2, this step is the same as the above step S22.

[0114] Step S33: Based on the built-in time-to-digital converter in the signal receiving end, record the counts corresponding to multiple delay positions when the single-photon detector detects the second pulse signal. When the average number of photons per pulse is configured to be μ2, this step is the same as the above-mentioned step S23.

[0115] Among them, when the average number of photons per pulse is configured to be μ2, the count of the single-photon detector at the i-th delay position S i is denoted as P i .

[0116] Step S34: Draw a second curve based on the counts of the single-photon detector under the second pulse signal.

[0117] Under the second pulse signal, after obtaining the counts of each delay position through the single-photon detector, upload the count results to the debugging host. The calibration software in the debugging host can automatically draw a delay position-count curve based on each delay position and its corresponding count as the second curve.

[0118] As described above, both the first curve and the second curve include the counts corresponding to the 1st delay position to the Nth delay position. In the first curve and the second curve, the horizontal axis is the delay position and the vertical axis is the count.

[0119] In the above-mentioned step S12, the method of drawing the third curve can be as Figure 4 shown.

[0120] Refer to Figure 4 shown, Figure 4 which is a flowchart of a method for drawing a third curve provided by an embodiment of the present application. The method includes:

[0121] Step S41: Determine the count ratio of the first curve and the second curve at the same delay position.

[0122] As described above, when the average number of photons per pulse is configured to be μ1, the count corresponding to the i-th delay position S i is Q i . When the average number of photons per pulse is configured to be μ2, the count corresponding to the i-th delay position S i is P i . Therefore, the count ratio at the i-th delay position S i is Q i / P i .

[0123] Step S42: Draw a relationship curve between different delay positions and the corresponding count ratios based on the count ratios of the 1st delay position S1 to the Nth delay position S n respectively.

[0124] The debugging host can automatically draw a third curve based on each delay position and its corresponding counting ratio. In the third curve, the horizontal axis represents the delay position, and the vertical axis represents the counting ratio.

[0125] In the third curve, the duration of the delay position interval corresponding to the counting ratio interval greater than the set protection threshold χ on the vertical axis is T' on the horizontal axis. That is to say, the duration of the delay position interval corresponding to the interval where the counting ratio on the vertical axis is greater than χ is T'. Among them, the protection threshold χ is a constant that can be set based on requirements. The delay position interval corresponding to the interval where the counting ratio on the vertical axis is greater than χ is marked as the non-linear transition region, that is, the duration of the avalanche transition region of the single-photon detector is T'.

[0126] The gating signal period of a single-photon detector is T. Set the effective working area of the single-photon detector as τ. Since both the rising edge and the falling edge of the gating signal have an avalanche transition region, τ satisfies the following relationship:

[0127] τ = T - 2T'

[0128] In the embodiments of the present application, the calibration method further includes: displaying calibration information; where the calibration information includes at least one of the first curve, the second curve, the third curve, the avalanche transition region, the effective working area, the configuration information of the signal receiving end, and the configuration information of the signal transmitting end in the QKD system. Thus, the calibration result can be displayed on the display interface of the calibration software built in the debugging host, so that the user can intuitively obtain relevant calibration information.

[0129] Based on the above description, it can be seen that the above calibration method can calibrate the position of the avalanche transition region and the position of the effective working area of the single-photon detector under the given gating signal of the single-photon detector, and store the calibration result in the signal receiving end of the QKD system.

[0130] Optionally, the calibration method further includes: controlling the signal transmitting end and the signal receiving end of the QKD system to enter the debugging mode based on the debugging host; after controlling the signal transmitting end and the signal receiving end to enter the debugging mode, inputting a control instruction; where the debugging host can respond to the control instruction, automatically determine the avalanche transition region and the effective working area of the single-photon detector based on the calibration method, and then store the calibration result in the signal receiving end; the calibration result includes at least one of the avalanche transition region and the effective working area. Thus, after automatically controlling the signal transmitting end and the signal receiving end to enter the debugging mode based on the debugging host with calibration software, by clicking the preset control button on the display interface of the calibration software, the automatic calibration process can be started, so that the above calibration method can be automatically executed by the debugging host to obtain the calibration result.

[0131] Based on the above calibration method, another embodiment of the present application further provides a processing device, which can execute the above calibration method, and the processing device can be as Figure 5 shown.

[0132] Referring to Figure 5 shown, Figure 5 FIG. 9 is a schematic structural diagram of a processing device provided by an embodiment of the present application. The shown processing device includes:

[0133] A configuration module 11, configured to configure the signal transmitting end in the QKD system to emit a first pulse signal or a second pulse signal;

[0134] A plotting module 12, configured to draw a first curve when the signal transmitting end emits a first pulse signal and draw a second curve when the signal transmitting end emits a second pulse signal based on the count of the single-photon detector, and draw a third curve based on the first curve and the second curve;

[0135] A processing module 13, configured to determine the avalanche transition region of the single-photon detector based on the third curve, and determine the effective working region of the single-photon detector based on the avalanche transition region, and then store the calibration result into the signal receiving end; the calibration result includes at least one of the avalanche transition region and the effective working region. Wherein, the processing module 13 is communicatively connected to the configuration module 11 and the plotting module 12 respectively.

[0136] In the embodiment of the present application, the processing device can execute the above calibration method. Under the given gating signal of the single-photon detector, it can calibrate the position of the avalanche transition region and the position of the effective working region of the single-photon detector, and store the calibration result into the signal receiving end of the QKD system.

[0137] Referring to Figure 6 shown, Figure 6 FIG. 10 is a schematic structural diagram of another processing device provided by an embodiment of the present application. On the basis of the manner shown in Figure 5 , Figure 6 the shown processing device further includes: a human-computer interaction module 14, configured to obtain a user input instruction. The human-computer interaction module 14 is communicatively connected to the processing module 13. The configuration module 11 is further configured to respond to the user input instruction and control the signal transmitting end and the signal receiving end in the QKD system to enter the debugging mode; after the signal transmitting end and the signal receiving end enter the debugging mode, the processing module 13 controls the processing device to execute the calibration method based on the built-in calibration software. It is easy to know that the processing device further includes a storage module communicatively connected to the processing module 13 for storing the calibration software.

[0138] Referring to Figure 7 shown, Figure 7Schematic diagram of another processing device provided by an embodiment of the present application. Based on the above embodiment, Figure 7 The processing device shown further includes: a display module 15, and the display module 15 is used to display calibration information; wherein, the calibration information includes at least one of: a first curve, a second curve, a third curve, an avalanche transition region, an effective working region, configuration information of a signal receiving end, and configuration information of a signal transmitting end in a QKD system.

[0139] Refer to Figure 8 shown, Figure 8 Schematic diagram of the principle for calibrating a single-photon detector in a QKD system provided by an embodiment of the present application. The QKD system has a signal transmitting end 21 and a signal receiving end 22. The debugging host 23 is respectively communicatively connected to the signal transmitting end 21 and the signal receiving end 22. Among them, the debugging host 23 includes the above-mentioned processing device.

[0140] The signal transmitting end 21 includes: a first service control module and an encoding module that are communicatively connected, and the two can interact with each other to exchange control, status, and response-related data. The signal receiving end 22 includes: a second service control module and a detection module that are communicatively connected, and the two can interact with each other to exchange control, status, and response-related data; the detection module includes a single-photon detector. The debugging host 23 is respectively communicatively connected to the first service control module and the second service control module, so as to respectively exchange control, status, and response-related data with the first service control module and the second service control module. There is a quantum optical channel between the detection module and the encoding module, and the quantum light includes signal light and synchronization light. There is a classical optical channel between the first service control module and the second service control module.

[0141] Based on Figure 8 the shown method, after setting the signal transmitting end and the signal receiving end to enter the debugging mode through the calibration software of the debugging host, click the preset control button on the display interface of the calibration software to start the automatic calibration process. The calibration information can be displayed on the display interface, and the calibration result can be stored in the signal receiving end through the debugging host for the counting statistics of the single-photon detector when the QKD system operates normally.

[0142] It can be seen from the description that the technical solution of the embodiment of the present application can realize the automatic calibration of the avalanche transition region and the effective working region of the single-photon detector. Before the signal receiving end leaves the factory, the avalanche transition region and the effective working region of the single-photon detector can be automatically calibrated based on the calibration software in the debugging host, without the need for other measurement tools, improving the calibration convenience and reducing the dependence of the calibration process on the environment. The calibration process is applicable to application scenarios such as field maintenance and equipment debugging. Moreover, the calibration result can be stored in the signal receiving end of the QKD system for extracting the detection count of the effective working region during the communication process of the QKD system.

[0143] Based on the calibration method and processing device provided in the above embodiments, another embodiment of the present application further provides a QKD system, which is as follows Figure 9 as shown.

[0144] Referring to Figure 9 as shown, Figure 9 FIG. is a schematic structural diagram of a QKD system provided by an embodiment of the present application. The QKD system includes:

[0145] A signal transmitting end 21, which is used to transmit synchronous light and signal light;

[0146] A signal receiving end 22, which pre-stores the calibration result determined by the above calibration method; the signal receiving end 22 is used to extract the detection result of the single-photon detector in the effective working area for code generation, and discard the detection result of the single-photon detector in the avalanche transition area.

[0147] The calibration result at least includes the effective working area of the single-photon detector. Based on this, when the QKD system is running normally, the signal receiving end 22 can only extract the detection result of the single-photon detector in the effective working area for code generation, and discard the detection result of the single-photon detector in the avalanche transition area. The attack data in the avalanche transition area will not enter the key extraction process, thereby realizing the attack defense against the avalanche transition area.

[0148] Referring to Figure 10 as shown, Figure 10 FIG. is a schematic diagram of the detection pulse distribution of single-photon detection in a gating signal period of a QKD system provided by an embodiment of the present application. When an attack is carried out using the avalanche transition area, the distribution of the detection pulses of the single-photon detector and the distribution of the normal detection pulses have a time difference on the time axis. The QKD system can be based on this to realize the attack defense against the avalanche transition area.

[0149] Within a gating signal period T, the detection pulses of the single-photon detector are divided into rising-edge pulses, effective working area pulses, and falling-edge pulses in terms of time distribution. Among them, both the rising-edge pulses and the falling-edge pulses are invalid areas of the detection pulses, and the effective working area pulses are the effective areas of the detection pulses. Using the pre-stored calibration result, the time periods T' corresponding to the rising-edge pulses and the falling-edge pulses and the time period τ corresponding to the effective working area pulses within a gating signal period T can be determined. Therefore, when the detection module of the signal receiving end extracts the detection count, based on the pre-stored calibration result, it extracts the effective area of the detection pulse for code generation and discards the invalid area of the detection pulse, thereby realizing the attack defense against the avalanche transition area.

[0150] In an actual QKD system, to ensure the security of the devices in the QKD system, while the signal receiving end 22 extracts the counting results of the single-photon detector, it monitors whether there is an attack behavior in the avalanche transition region and issues a warning message after detecting the attack behavior. Based on this, the signal receiving end 22 is also used to perform anomaly warning based on the detection results of the single-photon detector in the avalanche transition region and in the effective working region.

[0151] The single-photon detector has a first counting result C1 in the effective working region, a second counting result C2 in the avalanche transition region at the rising edge of the gating signal, and a third counting result C3 in the avalanche transition region at the falling edge of the gating signal. Among them, the first counting result C1 corresponds to the pulse in the effective working region of the single-photon detector in Figure 10 the effective working region, the second counting result C2 corresponds to the pulse in the rising edge of the single-photon detector in Figure 10 the rising edge, and the third counting result C3 corresponds to the pulse in the falling edge of the single-photon detector in Figure 10 the falling edge. After the ratio of the second counting result C2 to the first counting result C1 exceeds the set threshold β, the signal receiving end 22 performs anomaly warning; and / or, after the ratio of the third counting result C3 to the first counting result C1 exceeds the set threshold β, the signal receiving end 22 performs anomaly warning. The set threshold β is a configurable parameter and can be set based on requirements. The embodiments of the present application do not limit its value.

[0152] Specifically, the method for performing the above anomaly warning includes: obtaining a detection pulse through the single-photon detector in the signal receiving end 22; as Figure 10 shown, based on the pre-stored calibration results, the detection pulse of the single-photon detector is partitioned in time, and the first counting result C1 corresponding to the effective working region, the second counting result C2 corresponding to the rising edge avalanche transition region, and the third counting result C3 corresponding to the falling edge avalanche transition region are respectively counted; after the QKD system successfully generates a code, it enters the monitoring mode, and the changes of C2 / C1 and C3 / C1 are respectively monitored; when at least one of C2 / C1 and C3 / C1 exceeds the set threshold β, an anomaly warning is performed.

[0153] Based on the QKD system provided in the above embodiments, another embodiment of the present application also provides a communication method for a QKD system. The calibration results determined by the above calibration method are pre-stored in the signal receiving end of the QKD system. This communication method is as Figure 11 shown.

[0154] Refer to Figure 11 shown, Figure 11 which is a schematic flowchart of a communication method for a QKD system provided by an embodiment of the present application. The shown communication method includes:

[0155] Step S51: Detect the synchronization light and signal light emitted by the signal transmitting end through a single-photon detector.

[0156] Step S52: Extract the detection results of the single-photon detector in the effective working area for coding, and discard the detection results of the single-photon detector outside the effective working area.

[0157] Reference Figure 12 shown in Figure 12 is a schematic flowchart of another QKD system communication method provided by an embodiment of the present application. On the basis of the method shown in Figure 11 shown in Figure 12 the communication method further includes:

[0158] Step S53: Based on the detection results of the single-photon detector in the avalanche transition region and the detection results in the effective working area, perform abnormal early warning.

[0159] In Figure 12 the communication method shown, the method for performing abnormal early warning based on the detection results of the single-photon detector in the avalanche transition region and the detection results in the effective working area is as shown in Figure 13 shown in

[0160] Reference Figure 13 shown in Figure 13 is a flowchart of a method for performing abnormal early warning based on the detection results of a single-photon detector provided by an embodiment of the present application. The method includes:

[0161] Step S61: Obtain the first counting result of the single-photon detector in the effective working area, the second counting result in the avalanche transition region at the rising edge of the gating signal, and the third counting result in the avalanche transition region at the falling edge of the gating signal.

[0162] Step S62: Based on the first counting result, the second counting result, and the third counting result, perform abnormal early warning.

[0163] Among them, after the ratio of the second counting result to the first counting result exceeds the set threshold β, abnormal early warning is performed; and / or, after the ratio of the third counting result to the first counting result exceeds the set threshold β, abnormal early warning is performed.

[0164] In the signal receiving end of the QKD system, the detection efficiency of the single-photon detector is superlinear at the rising edge and falling edge of the gating signal. At the same time, the average number of photons per pulse corresponding to the detection pulse during the normal operation of the QKD system is different from that during an attack, and the time distribution of the detection count inside the gate of the single-photon detector is different. Generally, the time distribution of the detection count during an attack is wider. Therefore, by filtering the detection count in the avalanche transition region through the time window of the time-to-digital converter and only extracting the detection count in the effective working area, attacks against the avalanche transition region can be effectively defended.

[0165] In the QKD system and its communication method provided by the embodiments of the present application, it is possible to extract the counts of single-photon detectors in the effective working region based on pre-stored calibration results, thereby realizing the attack defense against the avalanche transition region. Moreover, based on the calibration results, it is also possible to respectively determine the count results of the detection pulses of the single-photon detectors in the effective working region, the rising-edge avalanche transition region, and the falling-edge avalanche transition region, so as to enable the QKD system to monitor the avalanche transition region attack during normal operation and give a warning prompt when an attack is detected.

[0166] The various embodiments in this specification are described in a progressive, or parallel, or a combination of progressive and parallel manners. The key point of each embodiment is to illustrate the differences from other embodiments. The same or similar parts among the embodiments can be referred to each other. The technical solutions of the embodiments of the present application can be applied to low-speed QKD systems and also to high-speed QKD systems.

[0167] It should be noted that in the description of the present application, it should be understood that the descriptions of the drawings and embodiments are illustrative rather than restrictive. The same reference numerals throughout the embodiments of the specification identify the same structures. Additionally, for the sake of understanding and ease of description, the drawings may exaggerate the thickness of some layers, films, panels, regions, etc. At the same time, it can be understood that when an element such as a layer, film, region, or substrate is referred to as being "on" another element, the element can be directly on the other element or there may be intermediate elements. Moreover, "on" means positioning the element on or below another element, but essentially does not mean positioning on the upper side of another element according to the direction of gravity.

[0168] The orientation or positional relationship indicated by terms such as "upper", "lower", "top", "bottom", "inner", "outer", etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and thus should not be construed as a limitation of the present application. When a component is considered to be "connected" to another component, it can be directly connected to the other component or there may be intermediate components present.

[0169] It should also be noted that in this text, relational terms such as first and second are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variant thereof is intended to cover non-exclusive inclusion, so that an article or device comprising a series of elements not only includes those elements, but also includes other elements not expressly listed, or elements inherent to such article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the article or device comprising the above elements.

[0170] The above description of the disclosed embodiments enables those skilled in the art to implement or use the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A calibration method, characterized in that, For calibrating the avalanche transition region of a single-photon detector at the signal receiving end in a QKD system, the calibration method includes: Plot a first curve and a second curve; wherein, the first curve is a relationship curve between multiple different delay positions and corresponding counts when the single-photon detector detects a first pulse signal; the second curve is a relationship curve between multiple different delay positions and corresponding counts when the single-photon detector detects a second pulse signal; the second pulse signal has a different average number of photons per pulse from the first pulse signal; Based on the first curve and the second curve, plot a third curve; wherein, the third curve is a relationship curve between the multiple different delay positions and corresponding count ratios; Based on the third curve, determine the avalanche transition region of the single-photon detector; After determining the effective working region of the single-photon detector based on the avalanche transition region, store the calibration result in the signal receiving end; wherein, the calibration result includes at least one of the avalanche transition region and the effective working region.

2. The calibration method according to claim 1, wherein The method for plotting the first curve includes: Configure the signal transmitting end in the QKD system to emit the first pulse signal; Within a preset delay range, traverse the multiple different delay positions; wherein, the delay range is the period of one gating signal of the single-photon detector; Based on the built-in time-to-digital converter in the signal receiving end, record the counts corresponding to the multiple delay positions when the single-photon detector detects the first pulse signal; Based on the counts of the single-photon detector under the first pulse signal, plot the first curve.

3. The calibration method according to claim 1, characterized in that, The method for plotting the second curve includes: Configure the signal transmitting end in the QKD system to emit a second pulse signal; Within a preset delay range, traverse the multiple different delay positions; wherein, the delay range is the period of one gating signal of the single-photon detector; Based on the built-in time-to-digital converter in the signal receiving end, record the counts corresponding to the multiple delay positions when the single-photon detector detects the second pulse signal; Based on the counts of the single-photon detector under the second pulse signal, plot the second curve.

4. The calibration method according to claim 1, wherein Both the first curve and the second curve include the counts corresponding to the 1st delay position to the Nth delay position; The method for plotting the third curve includes: Determine the count ratio of the first curve and the second curve at the same delay position; Based on the count ratios of the 1st delay position to the Nth delay position respectively, plot a relationship curve between different delay positions and corresponding count ratios.

5. The calibration method according to claim 1, characterized in that, In the third curve, the duration of the delay position interval on the horizontal axis corresponding to the count ratio interval greater than the set protection threshold on the vertical axis is T'; the period of one gating signal of the single-photon detector is T; τ = T - 2T'; Wherein, τ is the effective working region of the single-photon detector.

6. The calibration method according to claim 1, wherein It further includes: Display calibration information; Wherein, the calibration information includes at least one of the first curve, the second curve, the third curve, the avalanche transition region, the effective working region, the configuration information of the signal receiving end, and the configuration information of the signal transmitting end in the QKD system.

7. The calibration method according to any one of claims 1-6, characterized in that, It further includes: Based on a debug host, controlling the signal transmitter and signal receiver of the QKD system to enter a debug mode; After controlling the signal transmitter and the signal receiver to enter the debug mode, inputting a control instruction; Wherein, the debug host can respond to the control instruction, automatically determine the avalanche transition region and the effective working region of the single-photon detector based on the calibration method, and then store the calibration result into the signal receiver; the calibration result includes at least one of the avalanche transition region and the effective working region.

8. A processing device for performing the calibration method according to any one of claims 1-7, characterized in that, It includes: A configuration module, which is used to configure the signal transmitter in the QKD system to emit a first pulse signal or a second pulse signal; A plotting module, which is used to plot the first curve when the signal transmitter emits the first pulse signal and the second curve when the signal transmitter emits the second pulse signal based on the count of the single-photon detector, and plot the third curve based on the first curve and the second curve; A processing module, which is used to determine the avalanche transition region of the single-photon detector based on the third curve, and determine the effective working region of the single-photon detector based on the avalanche transition region, and then store the calibration result into the signal receiver; the calibration result includes at least one of the avalanche transition region and the effective working region.

9. The processing device according to claim 8, characterized in that, It further includes: A human-computer interaction module, which is used to obtain a user input instruction; The configuration module is further used to respond to the user input instruction and control the signal transmitter and signal receiver in the QKD system to enter the debug mode; After the transmitter and the signal receiver enter the debug mode, the processing module controls the processing device to execute the calibration method based on built-in calibration software.

10. The processing device according to claim 8, characterized in that, It further includes: A display module, which is used to display calibration information; Wherein, the calibration information includes at least one of the first curve, the second curve, the third curve, the avalanche transition region, the effective working region, the configuration information of the signal receiver, and the configuration information of the signal transmitter in the QKD system.

11. A QKD system, characterized in that, It includes: A signal transmitter, which is used to transmit synchronous light and signal light; A signal receiver, which pre-stores the calibration result determined by the calibration method according to any one of claims 1-7; the signal receiver is used to extract the detection result of the single-photon detector in the effective working region for code generation, and discard the detection result of the single-photon detector in the avalanche transition region.

12. The QKD system according to claim 11, wherein The signal receiver is further used to perform abnormal warning based on the detection result of the single-photon detector in the avalanche transition region and the detection result in the effective working region.

13. The QKD system according to claim 11, wherein, The single-photon detector has a first count result in the effective working region, a second count result in the avalanche transition region at the rising edge of the gating signal, and a third count result in the avalanche transition region at the falling edge of the gating signal; The signal receiver performs abnormal warning after the ratio of the second count result to the first count result exceeds a set threshold. And / or, after the ratio of the third counting result to the first counting result at the signal receiving end exceeds the set threshold, an abnormal warning is given.

14. A communication method for a QKD system, characterized in that, The calibration result determined by the calibration method according to any one of claims 1-7 is pre-stored in the signal receiving end of the QKD system; The communication method includes: Detecting the synchronization light and the signal light emitted by the signal transmitting end in the QKD system through a single-photon detector; Extracting the detection results of the single-photon detector in the effective working area for code generation, and discarding the detection results of the single-photon detector outside the effective working area.

15. The communication method according to claim 14, wherein The communication method further includes: Based on the detection results of the single-photon detector in the avalanche transition area and the detection results in the effective working area, an abnormal warning is given.

16. The communication method according to claim 15, wherein Based on the detection results of the single-photon detector in the avalanche transition area and the detection results in the effective working area, giving an abnormal warning includes: Obtaining the first counting result of the single-photon detector in the effective working area, the second counting result in the avalanche transition area at the rising edge of the gating signal, and the third counting result in the avalanche transition area at the falling edge of the gating signal; Based on the first counting result, the second counting result, and the third counting result, an abnormal warning is given; Wherein, After the ratio of the second counting result to the first counting result exceeds the set threshold, an abnormal warning is given; And / or, after the ratio of the third counting result to the first counting result exceeds the set threshold, an abnormal warning is given.

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