Quantum key distribution equipment and time calibration method thereof

Abstract

The invention discloses a quantum key distribution (QKD) device and a time calibration method thereof, in which the time calibration of the QKD device is realized by using the logical relationship between the detection data correlation and the light interference effect, thereby overcoming the problem of time alignment caused by insufficient detection efficiency, large statistical fluctuation, inconsistent data curves and the like. Therefore, the optimal coherent superposition of the optical signals is realized. Meanwhile, non-interference data of a monitoring channel can be used for replacing interference data of a data channel for delay difference tracking and control in the operation stage, independent real-time time calibration in the operation stage is achieved, and therefore the stability of the QKD system is improved.

Description

Technical Field

[0001] The present invention relates to the field of quantum key distribution (QKD), and more particularly to a time calibration method for a quantum key distribution device (such as TF-QKD, MDI-QKD, MP-QKD, etc.) with a two-arm channel structure and a corresponding quantum key distribution device. Background Art

[0002] A two-field quantum key distribution (TF-QKD) device is a long-distance QKD device developed based on the two-field quantum key distribution protocol, with measurement-device-independent security. During the operation of the two-field quantum key distribution device, the transmitting ends Alice and Bob respectively send optical (pulse) signals to the detecting end Charlie through optical fiber links. The optical signals from both ends interfere within the detecting end through beam combination. By analyzing the interference results at the detecting end, the information statistics of the signal state and the phase state are realized, and the generated code data is produced through data post-processing.

[0003] During the modulation process of the two-field quantum key distribution device, it is necessary to align the optical signals transmitted by the transmitting ends Alice and Bob in time. This alignment process is the time calibration process. The currently commonly used implementation scheme is to take the difference between the edge trigger positions or peak positions of the statistical data of the optical signals on both sides, and use a delay unit to adjust to achieve the time alignment of the optical signals. During the operation of the two-field quantum key distribution device, due to the influence of environmental factors such as temperature, the delay position will deviate, resulting in a deterioration of the interference effect. In view of this situation, it is also necessary to calibrate the time of the optical signals transmitted by the transmitting ends Alice and Bob in real time. For QKD devices with a two-arm channel structure, for example, TF-QKD devices and their related measurement-device-independent quantum key distribution (MDI-QKD) devices and mode-matching quantum key distribution (MP-QKD) devices all have such problems and requirements.

[0004] However, the inventors of the present application have noticed that in the existing time calibration modulation scheme, taking the difference between the edge trigger positions or peak positions of the statistical data of the optical signals on both sides will be affected by physical factors such as the acquisition accuracy of the time-to-digital converter (TDC), detection count fluctuations, and detection jitter, resulting in a calculation deviation in the alignment result, a deterioration of the interference result, and an increase in the error rate. During the operation, due to the influence of environmental factors such as temperature, the delay position will deviate, resulting in a deterioration of the interference effect, an increase in the error rate, and even an inability to generate codes normally. Summary of the Invention

[0005] In view of the above-mentioned defects of the prior art, the present invention proposes a time calibration method for a quantum key distribution device and a corresponding quantum key distribution device. In the present invention, the logical relationship between the correlation of detection data and the optical interference effect is utilized, and the time calibration of the QKD device is realized by means of the correlation analysis of the detection data, thereby overcoming the time alignment problems caused by insufficient detection efficiency, large statistical fluctuations, inconsistent data curves, etc., and thus realizing the optimal coherent superposition of optical signals. In the present invention, by means of the data normalization process before the data correlation analysis, the problem of inconsistent correlation data caused by insufficient detection efficiency and data fluctuations can be solved; and when adjusting the time positions of the sampling data of the transmitting ends Alice / Bob in the modulation and real-time calibration stages, the correlation coefficient method is used to obtain the time calibration delay difference according to the maximum value of the correlation coefficient for the delay control of the two optical signals, and the optimal interference position of the two optical signals can be found, which can solve the problem that the data curve difference affects the determination of the time position. At the same time, a specific optical path structure implemented by a multiplexing scheme such as polarization / wavelength division multiplexing can be adopted at the detection end, and the non-interference data of the monitoring channel can be used instead of the interference data of the data channel for delay difference tracking and control during the operation stage, realizing independent real-time time calibration during the operation stage, thereby improving the stability of the QKD system.

[0006] Specifically, a first aspect of the present invention relates to a time calibration method for a quantum key distribution device, wherein detectors D0 and D2 and D1 and D3 in the detection end Charlie are respectively used to detect the interference components and non-interference components of the first optical signal and the interference components and non-interference components of the second optical signal;

[0007] The time calibration method includes a detection data acquisition step, a data normalization step, a data correlation analysis step, and a delay control step;

[0008] The detection data acquisition step is used to collect the detection counts of the detectors by using a time-to-digital converter and statistically generate the corresponding detection data at each time position;

[0009] The data normalization step is used to normalize the detection data according to the maximum count in the detection data to generate the corresponding normalized data;

[0010] The data correlation analysis step is used to shift one of the two normalized data in the time position towards the other by ΔT(i), and calculate the Pearson correlation coefficient K(i) between the shifted normalized data and the other normalized data; and, set the shift amount ΔT(i) corresponding to the maximum value of the Pearson correlation coefficient K(i) as the time calibration delay difference δ;

[0011] The delay control step is used to adjust the delay amount of the first and / or second optical signals according to the time calibration delay difference δ; wherein,

[0012] In the modulation calibration stage, the transmitter Alice transmits the first optical signal alone, and the transmitter Bob transmits the second optical signal alone; by means of the detection data acquisition step, the detection data Fa0, Fa2, Fb1, and Fb3 corresponding to the detectors D0, D2, D1, and D3 are generated; by means of the data normalization step, the normalized data Fa0' and Fb1' are generated based on the detection data Fa0 and Fb1; by means of the data correlation analysis step, the time calibration delay difference δ is calculated based on the normalized data Fa0' and Fb1'; and, by means of the delay control step, the delay amounts of the first and / or second optical signals are adjusted until the time calibration delay difference δ is not greater than the preset threshold Tth;

[0013] Moreover, when the time calibration delay difference δ is not greater than the preset threshold Tth, by means of the data normalization step, the normalized data Fa2' and Fb3' are generated based on the detection data Fa2 and Fb3; by means of the data correlation analysis step, the time calibration delay difference δ is calculated based on the normalized data Fa2' and Fb3', and is set as the real-time time calibration offset δr;

[0014] In the real-time calibration stage, the transmitter Alice transmits the first optical signal, and at the same time the transmitter Bob transmits the second optical signal. By means of the detection data acquisition step, the detection data Fa2 and Fb3 are generated; by means of the data normalization step, the normalized data Fa2' and Fb3' are generated based on the detection data Fa2 and Fb3; by means of the data correlation analysis step, the time calibration delay difference δ is calculated based on the normalized data Fa2' and Fb3'; and, according to the difference Δδ between the time calibration delay difference δ and the real-time time calibration offset δr, the delay amounts of the first and / or second optical signals are adjusted until the difference Δδ is not greater than the preset threshold Tth.

[0015] Furthermore, in the data normalization step, the formula is used to normalize the detection data, where x i is the count in the detection data, and y i is the count after normalization.

[0016] Furthermore, in the data correlation analysis step, a plurality of translation amounts ΔT(i) are set within (δT - Δ, δT + Δ), where δT is the absolute difference between the time positions corresponding to the maximum counts in the two channels of normalized data, and Δ is a preset value.

[0017] Preferably, the translation amount ΔT(i) = δT + (i - N)*Tth, where i is 0, 1,..., 2N, and N = [Δ / Tth], and [] is the integer function.

[0018] Preferably, Δ can be set according to the pulse width of the optical signal.

[0019] Preferably, the preset threshold Tth is an adjustment step value for delay control.

[0020] The second aspect of the present invention relates to a quantum key distribution device capable of real-time time calibration, which includes a transmitting end Alice, a transmitting end Bob, and a detecting end Charlie;

[0021] The transmitting end Alice is configured to transmit a first optical signal, and the transmitting end Bob is configured to transmit a second optical signal;

[0022] The detecting end Charlie includes a beam combining module and a detecting module;

[0023] The detecting module includes detectors D0, D1, D2, and D3;

[0024] The beam combining module is configured to form an interference component and a non-interference component based on the first optical signal, and respectively send them into detectors D0 and D2, and form an interference component and a non-interference component based on the second optical signal, and respectively send them into detectors D1 and D3;

[0025] Wherein, the quantum key distribution device is configured to perform time calibration on the first and second optical signals in real time according to the above time calibration method.

[0026] Optionally, the beam combining module includes a first polarization multiplexing unit, a second polarization multiplexing unit, and an interference unit;

[0027] The first polarization multiplexing unit is configured to demultiplex the first optical signal into a first component and a second component, and transmit the first component as a non-interference component to detector D2, and transmit the second component as an interference component to the interference unit;

[0028] The second polarization multiplexing unit is configured to demultiplex the second optical signal into a first component and a second component, and transmit the first component as a non-interference component to detector D3, and transmit the second component as an interference component to the interference unit;

[0029] The interference unit is configured to allow the second components of the first optical signal and the second optical signal to interfere, and respectively transmit the interference results to detectors D0 and D1.

[0030] Optionally, the beam combining module includes a first wavelength division multiplexing unit, a second wavelength division multiplexing unit, and an interference unit;

[0031] The first wavelength division multiplexing unit is configured to demultiplex the first optical signal into a first component and a second component, and transmit the first component as a non-interference component to detector D2, and transmit the second component as an interference component to the interference unit;

[0032] The second wavelength division multiplexing unit is configured to demultiplex the second optical signal into a first component and a second component, transmit the first component as a non-interfering component to the detector D3, and transmit the second component as an interfering component to the interference unit;

[0033] The interference unit is configured to allow the second component of the first optical signal and the second component of the second optical signal to interfere, and transmit the interference results to the detectors D0 and D1 respectively.

[0034] Furthermore, the quantum key distribution device of the present invention can be a TF-QKD device, an MDI-QKD device or an MP-QKD device. Description of the Drawings

[0035] Figure 1 Schematically shows a partial optical path of the quantum key distribution device according to the present invention;

[0036] Figure 2 Schematically shows a polarization multiplexing scheme for the quantum key distribution device of the present invention;

[0037] Figure 3 Schematically shows a wavelength division multiplexing scheme for the quantum key distribution device of the present invention;

[0038] Figure 4 Schematically shows a flowchart of the time calibration method for the quantum key distribution device according to the present invention;

[0039] Figure 5 Schematically shows the normalized data of two-way detection data collected from the data channel before the time calibration is completed;

[0040] Figure 6 Schematically shows that by means of the data correlation analysis step, the Pearson correlation coefficient curves obtained by performing Pearson correlation analysis on the two-way normalized data in Figure 5 at multiple translation amounts ΔT(i);

[0041] Figure 7 Schematically shows the normalized data of two-way detection data collected from the data channel after the time calibration is completed. Detailed Description of the Invention

[0042] Hereinafter, the exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings. The following embodiments are provided by way of example so as to fully convey the spirit of the present invention to those skilled in the art to which the present invention pertains. Therefore, the present invention is not limited to the embodiments disclosed herein.

[0043] Figure 1The partial optical path of a quantum key distribution device according to the present invention is shown. In the present invention, the quantum key distribution device can be a TF-QKD device, an MDI-QKD device, or an MP-QKD device.

[0044] As Figure 1 shown, the quantum key distribution device may mainly include a transmitting end Alice, a transmitting end Bob, and a detecting end Charlie.

[0045] The transmitting ends Alice and Bob are used to respectively transmit optical signals, i.e., the first and second optical signals, to the detecting end Charlie.

[0046] The detecting end Charlie is used to make the first and second optical signals interfere through beam combination and detect the interference result. In the present invention, the detecting end may include a beam combination module, a detecting module, and a post-processing unit.

[0047] The detecting module may include four detectors D0, D1, D2, and D3. Among them, the detectors D0 and D1 are arranged to detect the interference result of the first and second optical signals, the detector D2 is arranged to detect the non-interference component of the first optical signal, and the detector D3 is arranged to detect the non-interference component of the second optical signal. Those skilled in the art know that the first and second optical signals in the detecting end Charlie should generally have the same or comparable intensity, which can be achieved, for example, through attenuation calibration, and will not be elaborated here.

[0048] To cooperate with the above functions of the detecting module, the beam combination module can be configured to respectively make the interference component and non-interference component of the first optical signal enter the detectors D0 and D2, and the interference component and non-interference component of the second optical signal enter the detectors D1 and D3. In the present invention, the beam combination module can be implemented by using various multiplexing schemes including polarization multiplexing and wavelength division multiplexing.

[0049] Figure 2 The polarization multiplexing scheme for the beam combination module used in the present invention is shown, which may include a first polarization multiplexing unit, a second polarization multiplexing unit, and an interference unit.

[0050] The first polarization multiplexing unit is used to demultiplex the first optical signal into a first component and a second component, and transmit the first component as the non-interference component to the detector D2 and the second component as the interference component to the interference unit.

[0051] The second polarization multiplexing unit is used to demultiplex the second optical signal into a first component and a second component, and transmit the first component as the non-interference component to the detector D3 and the second component as the interference component to the interference unit.

[0052] The interference unit is used to allow the second component of the first optical signal and the second component of the second optical signal to interfere, and is connected to detectors D0 and D1 through two output ends respectively to detect the interference result.

[0053] Figure 3 A wavelength division multiplexing scheme for the beam combining module of the present invention is shown, which may include a first wavelength division multiplexing unit, a second wavelength division multiplexing unit, and an interference unit.

[0054] The first wavelength division multiplexing unit is used to demultiplex the first optical signal into a first component and a second component, transmit the first component as a non-interference component to detector D2, and transmit the second component as an interference component to the interference unit.

[0055] The second wavelength division multiplexing unit can be used to demultiplex the second optical signal into a first component and a second component, transmit the first component as a non-interference component to detector D3, and transmit the second component as an interference component to the interference unit.

[0056] The interference unit is used to allow the second component of the first optical signal and the second component of the second optical signal to interfere, and is connected to detectors D0 and D1 through two output ends respectively to detect the interference result.

[0057] In the present invention, the post-processing unit is used to implement functions such as post-processing of detection data.

[0058] Based on Figures 1 - 3 It can be known that in the quantum key distribution device of the present invention, in addition to the data channels for interference data implemented by detectors D0 and D1, there is also a monitoring channel for non-interference data implemented by detectors D2 and D3. On this basis, the present invention further proposes a time calibration method for a quantum key distribution device, which, by means of time calibration parameters calculated by collecting data from the data channel and the monitoring channel during the modulation calibration stage, enables the use of non-interference data from the monitoring channel to replace the interference data from the data channel for tracking and control of the delay difference during the operation of the device, thereby accurately providing a real-time time calibration function without affecting the normal operation of the device.

[0059] For a better understanding of the present invention, the following will be combined with Figure 4 the flowchart shown to specifically describe the time calibration method for a quantum key distribution device according to the present invention.

[0060] As described above, in the detection end of the present invention, detectors D0 and D2 are respectively used to detect the interference component and non-interference component of the first optical signal, and detectors D1 and D3 are respectively used to detect the interference component and non-interference component of the second optical signal. At this time, there is a fixed synchronization relationship between the time delays of the two detection data (non-interference data) of the monitoring channel realized by detectors D2 and D3 and the time delays of the two detection data (interference data) of the data channel realized by detectors D0 and D1, that is, the difference between these two time delays is a constant. Based on the existence of this fixed synchronization relationship, it is allowed to use the non-interference data of the monitoring channel to replace the interference data of the data channel for time calibration during operation, so as to achieve a good interference effect.

[0061] In the time calibration method of the present invention, a modulation calibration stage and a real-time calibration stage are involved. Among them, the modulation calibration stage is used to calculate the real-time time calibration offset δr before the QKD device runs, so as to facilitate subsequent real-time time calibration with the help of the monitoring channel. The real-time calibration stage is used to perform real-time time calibration of the QKD device during the operation of the QKD device according to the real-time time calibration offset δr with the help of the non-interference data of the monitoring channel.

[0062] Specifically, the time calibration method of the present invention mainly includes steps such as detection data acquisition step, data normalization step, data correlation analysis step, and time delay control step, etc.

[0063] The detection data acquisition step is used to use the TDC to collect the detection counts of the detectors to obtain sample data, and then count the counts at each time position in the sample data according to the time position information, so as to obtain the corresponding detection data.

[0064] The data normalization step is used to normalize the detection data according to the maximum count in the detection data to generate the corresponding normalized data. By means of the data normalization step, the intensity and statistical differences of different detection channels (i.e., the channels for collecting detection counts through the TDC) can be effectively suppressed, providing necessary conditions for subsequent correlation analysis of the two detection data.

[0065] As an example, the normalization processing of the detection data can be realized by using the formula where: x i is the count at each time position in the detection data, y i is the corresponding normalized value, and the functions max and min are respectively used to calculate the maximum count and minimum count in the detection data.

[0066] On the basis of normalizing two-channel detection data (which, for example, come from a data channel or a monitoring channel), in the data correlation analysis step, multiple translation amounts ΔT(i) can be set according to the deviation in the time position of the two-channel normalized data. According to the translation amount ΔT(i), one of the two-channel normalized data is translated in the time position towards the other two-channel normalized data, and the Pearson correlation coefficient K(i) of the two-channel normalized data after translation is calculated corresponding to each translation amount ΔT(i). Thus, the maximum value of the Pearson correlation coefficient K(i) and the corresponding translation amount ΔT(i) are found as the time calibration delay difference (or time position offset) δ between the current two-channel detection data.

[0067] To improve efficiency, according to the absolute difference δT = |Ta - Tb| between the time positions (such as Ta and Tb) corresponding to the maximum counts (such as Va and Vb) in the two-channel detection data (normalized data) to be analyzed, a value range (δT - Δ, δT + Δ) for the translation amount ΔT(i) can be set, where the value of Δ can be preset according to experience.

[0068] As a preferred example, Δ is set according to the pulse width (i.e., the flat-top range) of the detected optical signal. For example, Δ is set to half of the pulse width.

[0069] Further, when multiple translation amounts ΔT(i) are set in (δT - Δ, δT + Δ), the adjustment step value Tth for delay control can preferably be used as the value step for the translation amount ΔT(i), that is: ΔT(i) = δT + (i - N)*Tth, i = 0, 1, …, 2N, N = [Δ / Tth].

[0070] Further, after one of the two-channel normalized data is translated in the time position according to the translation amount ΔT(i), the Pearson correlation coefficient K(i) of the translated normalized data and the other two-channel normalized data can be calculated using the following formula:

[0071]

[0072] where ρ(X,Y) is the Pearson correlation coefficient, the E(*) function is the expected value, X and Y are the two-channel normalized data after translation, and XY is the product of the two-channel normalized data at the corresponding time positions after translation.

[0073] After calculating the corresponding number (e.g., 2N + 1) of Pearson correlation coefficients K(i) corresponding to each translation amount, find the maximum value of the Pearson correlation coefficient K(i) and the corresponding translation amount ΔT(i), and set it as the time calibration delay difference δ between the current two-way detection data. Using the time calibration delay difference δ obtained based on the logical relationship between the Pearson correlation coefficient and optical interference to achieve the time calibration of the optical signal can effectively improve the accuracy of the optical signal interference result and reduce the influence of physical factors on the time calibration calculation.

[0074] After obtaining the time calibration delay difference δ between the current two-way detection data, the delay control step can be used to compensate for the time calibration delay difference between the two-way detection data by adjusting the delay amount for the first and / or second optical signal (e.g., according to the step value Tth).

[0075] Based on the above content, further refer to Figure 4 The flowchart shown specifically describes the specific implementation manners of the modulation calibration stage and the real-time calibration stage of the present invention.

[0076] As Figure 4 shown, in the modulation calibration stage, the transmitter Alice alone transmits the first optical signal, and the detection data Fa0 and Fa2 corresponding to the detectors D0 and D2 are generated by means of the detection data acquisition step.

[0077] The transmitter Bob alone transmits the second optical signal, and the detection data Fb1 and Fb3 corresponding to the detectors D1 and D3 are generated by means of the detection data acquisition step.

[0078] Subsequently, in the data normalization step, the maximum counts Va and Vb in the detection data Fa0 and Fb1 are respectively found, and the detection data Fa0 and Fb1 are normalized according to the maximum counts Va and Vb to obtain the corresponding normalized data Fa0' and Fb1'.

[0079] In the present invention, the absolute difference δT = |Ta - Tb| can also be calculated according to the time positions Ta and Tb corresponding to the maximum counts Va and Vb for subsequent use.

[0080] Based on the normalized data Fa0' and Fb1', the time calibration delay difference δ between the two-way detection data can be calculated by means of the data correlation analysis step.

[0081] Specifically, in the data correlation analysis step, a plurality of translation amounts ΔT(i) can be set first. For example, 2N + 1 translation amounts ΔT(i) are set by using the formula ΔT(i) = δT + (i - N) * Tth.

[0082] Therefore, according to each translation amount ΔT(i), the normalized data of one path (e.g., normalized data Fa0’) can be translated in the time position towards the normalized data of another path (e.g., normalized data Fb1’), and the Pearson correlation coefficient K(i) between the translated normalized data and the normalized data of another path can be calculated. Eventually, through multiple translations and calculations, multiple (e.g., 2N + 1) Pearson correlation coefficients K(i) are obtained.

[0083] At this time, find the maximum value among the multiple calculated Pearson correlation coefficients K(i), and set the translation amount ΔT(i) corresponding to the maximum value of the Pearson correlation coefficient K(i) as the time calibration delay difference δ between the current two sets of detection data.

[0084] After obtaining the time calibration delay difference δ, if the current time calibration delay difference δ is not greater than the adjustment step value Tth for delay control, it can be considered that the current two optical signals are already aligned in time, and the time calibration is completed.

[0085] Otherwise, in the delay control step, according to the current time calibration delay difference δ, for example, based on the step value Tth, adjust the delay amount for the first and / or second optical signals to compensate for this time calibration delay difference δ, so that the two are aligned in time to achieve time calibration.

[0086] Furthermore, after adjusting the delay amount by means of the delay control step, the detection data acquisition step can be re - executed to obtain the current detection data Fa0 and Fb1, and then the current time calibration delay difference δ can be calculated by means of the data normalization step, data correlation analysis step, etc., to determine whether the time calibration is achieved. Repeat this cycle until the time calibration is achieved.

[0087] According to the present invention, when realizing time calibration by means of the data (detection data Fa0 and Fb1) collected from the data channel in the modulation calibration stage, it is also necessary to collect the current data (detection data Fa2 and Fb3) from the monitoring channel, and calculate the time position offset between the two sets of detection data of the monitoring channel in the time calibration state, which is used as the real - time time calibration offset δr.

[0088] Specifically, when realizing time calibration in the modulation calibration stage (i.e., in the last modulation cycle), the detection data Fa2 and Fb3 can be obtained by means of the detection data acquisition step, and the time calibration delay difference δ between the detection data Fa2 and Fb3 can be calculated by using the data normalization step and the data correlation analysis step, and set it as the real - time time calibration offset δr.

[0089] At this point, those skilled in the art can understand that the real-time time calibration offset δr represents the time calibration delay difference δ between the two detection data (i.e., detection data Fa2 and Fb3) on the corresponding monitoring channel when the first and second optical signals are aligned in interference time.

[0090] After obtaining and setting the real-time time calibration offset δr, the QKD device can be started for code generation operation, and at the same time, enter the real-time calibration stage.

[0091] During the real-time calibration stage, the transmitters Alice and Bob will emit light simultaneously during normal operation. Among them, the detection data collected from detectors D0 and D1 are normally used for, for example, QKD code generation operations.

[0092] During this period, the detection data Fa2 and Fb3 of detectors D2 and D3 can be synchronously obtained by means of the detection data acquisition step, and the time calibration delay difference δ between the detection data Fa2 and Fb3 can be obtained in real time by using the data normalization step and the data correlation analysis step. Therefore, the difference Δδ between the time calibration delay difference δ obtained in real time by calculation and the real-time time calibration offset δr can be further used as the current delay control amount.

[0093] Similarly, if the current delay control amount Δδ is not greater than the adjustment step value Tth, it can be considered that the current two optical signals are aligned in time and the time calibration is completed; otherwise, according to the current delay control amount Δδ and the adjustment step value Tth, the delay amount for the first and / or second optical signals is adjusted to maintain the delay control amount Δδ within the adjustment step value Tth, that is, when Δδ is not greater than Tth, the real-time time calibration during the operation stage is achieved.

[0094] For ease of understanding the above content, a specific example of the time calibration method of the present invention will be further described below in conjunction with Figures 5 - 7 In this example, the transmitter of the TF-QKD device uses a light emission frequency of 625 MHz, the light emission interval is 1600 ps, the (first / second) optical signal has a pulse width (flat top) of 200 ps, and the adjustment step value Tth for delay control is 10 ps.

[0095] In the modulation calibration stage, the detection data Fa0 and Fb1 corresponding to detectors D0 and D1 are generated by means of the detection data acquisition step, and they are normalized by means of the data normalization step to generate two corresponding normalized data Fa0' and Fb1', as Figure 5 shown.

[0096] In the detection data Fa0 and Fb1, the time positions corresponding to the maximum counts are Ta = 800 and Tb = 1150 respectively. Therefore, δT = 350 can be calculated.

[0097] According to the pulse width of the detected optical signal, Δ = 100 can be set, and N = 10 can be calculated and obtained.

[0098] Therefore, 21 translation amounts can be set according to the formula ΔT(i) = δT + (i - N) * Tth: ΔT(0) = 350 - 100, ΔT(1) = 350 - 90,..., ΔT(10) = 350,..., ΔT(20) = 350 + 90, ΔT(21) = 350 + 100.

[0099] Therefore, in the data correlation analysis step, for each translation amount ΔT(i), the normalized data Fb1' can be translated in the time position towards the direction of the normalized data Fa0', and the Pearson correlation coefficient K(i) between the translated normalized data Fb1'' and the normalized data Fa0' can be calculated. Finally, 21 Pearson correlation coefficients K(i) corresponding to the 21 translation amounts ΔT(i) are calculated to form Figure 6 the correlation coefficient curve diagram shown.

[0100] From Figure 6 the correlation coefficient curve diagram, it can be determined that the time position corresponding to its maximum correlation coefficient is 790, that is, corresponding to the translation amount 360. Thus, it can be determined that the current time calibration delay difference δ is 360.

[0101] On this basis, with the help of the delay control step, such as adjusting the delay amounts of the transmitting ends Alice and / or Bob, the time calibration delay difference δ is compensated to achieve time calibration. At this time, the two-way normalized data Fa0' and Fb1' obtained with the help of the detection data acquisition step and the data normalization step will show coincidence in the time position, as Figure 7 shown.

[0102] In summary, in the time calibration scheme for quantum key distribution devices proposed in the present invention, by utilizing the logical relationship between the correlation of detection data and the optical interference effect, and based on the correlation analysis of detection data to achieve the time calibration of QKD devices, it is possible to effectively overcome the time alignment problems caused by insufficient detection efficiency, large statistical fluctuations, inconsistent data curves, etc., thereby achieving the optimal coherent superposition of optical signals. For example, by means of data normalization processing, it is possible to effectively solve the problem of inconsistent correlation data caused by insufficient detection efficiency and data fluctuations; when adjusting the time positions of the sampling data at the transmitting ends Alice / Bob in the modulation and real-time calibration stages, using the correlation coefficient method, the time calibration delay difference is obtained according to the maximum value of the correlation coefficient, which is used for the delay control of the two optical signals, and the best interference position of the two optical signals is found, which can solve the problem that the difference in data curves affects the determination of the time position. At the same time, in the detection end, a specific optical path structure implemented by a multiplexing scheme such as polarization / wavelength division multiplexing can use the non-interference data of the monitoring channel instead of the interference data of the data channel for delay difference tracking and control during the operation stage, achieving independent real-time time calibration during the operation stage, thereby improving the stability of the QKD system.

[0103] Although the present invention has been described above in conjunction with specific embodiments with reference to the accompanying drawings, it is easy for those skilled in the art to recognize that the above embodiments are merely exemplary and are used to illustrate the principles of the present invention, which will not limit the scope of the present invention. Those skilled in the art can make various combinations, modifications, and equivalent replacements of the above embodiments without departing from the spirit and scope of the present invention.

Claims

1. A time calibration method for a quantum key distribution device, wherein, The detectors D0 and D2, as well as D1 and D3 in the detection end Charlie, are respectively used to detect the interference components and non-interference components of the first optical signal and the interference components and non-interference components of the second optical signal; The time calibration method includes a detection data acquisition step, a data normalization step, a data correlation analysis step, and a delay control step; The detection data acquisition step is used to collect the detection counts of the detectors by using a time-to-digital converter, and count the counts at each time position to generate corresponding detection data; The data normalization step is used to normalize the detection data according to the maximum count in the detection data to generate corresponding normalized data; The data correlation analysis step is used to shift one of the two normalized data toward the other by ΔT(i) at the time position, and calculate the Pearson correlation coefficient K(i) between the shifted normalized data and the other normalized data; and, set the shift amount ΔT(i) corresponding to the maximum value of the Pearson correlation coefficient K(i) as the time calibration delay difference δ; The delay control step is used to adjust the delay amount of the first and / or second optical signals according to the time calibration delay difference δ; where, In the modulation calibration stage, the transmitting end Alice is made to transmit the first optical signal alone, and the transmitting end Bob is made to transmit the second optical signal alone; the detection data Fa0, Fa2, Fb1, and Fb3 corresponding to the detectors D0, D2, D1, and D3 are generated by means of the detection data acquisition step; by means of the data normalization step, the normalized data Fa0’ and Fb1’ are generated based on the detection data Fa0 and Fb1; by means of the data correlation analysis step, the time calibration delay difference δ is calculated based on the normalized data Fa0’ and Fb1’; and, by means of the delay control step, the delay amount of the first and / or second optical signals is adjusted until the time calibration delay difference δ is not greater than the preset threshold Tth; And, when the time calibration delay difference δ is not greater than the preset threshold Tth, by means of the data normalization step, the normalized data Fa2’ and Fb3’ are generated based on the detection data Fa2 and Fb3; by means of the data correlation analysis step, the time calibration delay difference δ is calculated based on the normalized data Fa2’ and Fb3’, and is set as the real-time time calibration offset δr; In the real-time calibration stage, the transmitting end Alice is made to transmit the first optical signal, and at the same time the transmitting end Bob is made to transmit the second optical signal, the detection data Fa2 and Fb3 are generated by means of the detection data acquisition step; by means of the data normalization step, the normalized data Fa2’ and Fb3’ are generated based on the detection data Fa2 and Fb3; by means of the data correlation analysis step, the time calibration delay difference δ is calculated based on the normalized data Fa2’ and Fb3’; and, according to the difference Δδ between the time calibration delay difference δ and the real-time time calibration offset δr, the delay amount of the first and / or second optical signals is adjusted until the difference Δδ is not greater than the preset threshold Tth.

2. The time calibration method according to claim 1, wherein, In the data normalization step, the formula is used to normalize the detection data, where x i is the count in the detection data and y i is the normalized count.

3. The time calibration method according to claim 1, wherein, In the data correlation analysis step, a plurality of translation amounts ΔT(i) are set within (δT - Δ, δT + Δ), where δT is the absolute difference between the time positions corresponding to the maximum counts in the two-channel normalized data, and Δ is a preset value.

4. The time calibration method according to claim 3, wherein, The translation amount ΔT(i) = δT + (i - N)*Tth, where i is 0, 1, …, 2N, N = [Δ / Tth], and [] is the rounding function.

5. The time calibration method according to claim 3 or 4, wherein, Δ is set according to the pulse width of the optical signal.

6. The time calibration method according to claim 1 or 4, wherein, The preset threshold Tth is the adjustment step value for delay control.

7. A quantum key distribution device capable of realizing real-time time calibration, which includes a transmitting end Alice, a transmitting end Bob, and a detecting end Charlie; The transmitting end Alice is configured to transmit a first optical signal, and the transmitting end Bob is configured to transmit a second optical signal; The detecting end Charlie includes a beam combining module and a detecting module; The detecting module includes detectors D0, D1, D2, and D3; The beam combining module is configured to form an interference component and a non-interference component based on the first optical signal and make them enter the detectors D0 and D2 respectively, and form an interference component and a non-interference component based on the second optical signal and make them enter the detectors D1 and D3 respectively; Among them, The quantum key distribution device is configured to perform real-time time calibration on the first and second optical signals according to the time calibration method described in any one of claims 1-6.

8. The quantum key distribution device according to claim 7, wherein, The beam combining module includes a first polarization multiplexing unit, a second polarization multiplexing unit, and an interference unit; The first polarization multiplexing unit is configured to demultiplex the first optical signal into a first component and a second component, transmit the first component as a non-interference component to the detector D2, and transmit the second component as an interference component to the interference unit; The second polarization multiplexing unit is configured to demultiplex the second optical signal into a first component and a second component, transmit the first component as a non-interference component to the detector D3, and transmit the second component as an interference component to the interference unit; The interference unit is configured to allow the second components of the first optical signal and the second optical signal to interfere with each other and transmit the interference results to the detectors D0 and D1 respectively.

9. The quantum key distribution device according to claim 7, wherein The beam combining module includes a first wavelength division multiplexing unit, a second wavelength division multiplexing unit, and an interference unit; The first wavelength division multiplexing unit is configured to demultiplex the first optical signal into a first component and a second component, transmit the first component as a non-interference component to the detector D2, and transmit the second component as an interference component to the interference unit; The second wavelength division multiplexing unit is configured to demultiplex the second optical signal into a first component and a second component, transmit the first component as a non-interference component to the detector D3, and transmit the second component as an interference component to the interference unit; The interference unit is configured to allow the second components of the first optical signal and the second optical signal to interfere with each other and transmit the interference results to the detectors D0 and D1 respectively.

10. The quantum key distribution device according to claim 7, which is a TF-QKD device, an MDI-QKD device, or an MP-QKD device.

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