Photon intensity control method and device for bb84 decoy state quantum key distribution system

Abstract

The application discloses a photon intensity control method and device of a BB84 decoy state quantum key distribution system, and relates to the technical field of quantum communication photon intensity control. The photon intensity control method comprises the following steps: detecting the photon intensity of the photon state of a first beam splitting ratio after beam splitting; determining the average photon number ratio of the photon state according to the photon intensity of the photon state and the trigger number of the photon state; determining the control signal of the photon state according to the average photon number ratio of the photon state; and controlling the photon intensity of the photon state of a second beam splitting ratio after beam splitting in response to the control signal of the photon state, so as to control the photon intensity of the photon state of the second beam splitting ratio of the BB84 decoy state quantum key distribution system. The photon intensity control method can accurately control the photon intensity of the signal state, the photon intensity of the decoy state and the photon intensity of the vacuum state, and improve the feedback control precision.

Description

Technical Field

[0001] This application relates to the technical field of photon intensity control in quantum communication, and more specifically, to a method and apparatus for photon intensity control in a BB84 decoy state quantum key distribution system. Background Technology

[0002] In high-speed QKD systems, IM or IQ modulators are typically used to generate signal states and decoy states of varying intensities. The voltage-light intensity relationships of both the signal state and the decoy state must be rigorously calibrated to prevent exploitation by attackers. Due to environmental factors (such as temperature and mechanical vibration), voltage drift or noise can introduce light intensity fluctuations. Therefore, real-time monitoring combined with automatic feedback is necessary to ensure the stability of photon intensity across photon states (signal state, decoy state, and vacuum state).

[0003] In existing technologies, the photon intensity of photon states (signal state, decoy state, and vacuum state) can be monitored using direct optical power monitoring or passive compensation methods.

[0004] However, neither direct optical power monitoring nor passive compensation can detect photon intensity at the single-photon level, making it difficult to accurately distinguish light intensity fluctuations at the single-photon level (especially the slight difference between the signal state and the decoy state), and the feedback speed may be insufficient.

[0005] The content of the background section is merely technology known to the public and does not necessarily represent existing technology in the field. Summary of the Invention

[0006] This application aims to provide a photon intensity control method and apparatus for a BB84 decoy state quantum key distribution system, in order to solve the technical problems that neither the above-mentioned direct optical power monitoring nor passive compensation methods can detect photon intensity at the single-photon level, make it difficult to accurately distinguish light intensity fluctuations at the single-photon level, and may have insufficient feedback speed.

[0007] According to one aspect of this application, a photon intensity control method for a BB84 decoy state quantum key distribution system is provided. The photon intensity control method includes: detecting the photon intensity of photon states at a first split ratio after beam splitting by a beam splitter, wherein the photon states include signal states, decoy states, and vacuum states; determining an average photon number ratio of the photon states based on the photon intensity of the photon states and the trigger number of each photon state; determining a control signal for each photon state based on the average photon number ratio of the photon states; and controlling the photon intensity of photon states at a second split ratio after beam splitting by a beam splitter in response to the control signal of each photon state, so as to control the BB84 decoy state quantum key distribution system according to the photon intensity of the photon states at the second split ratio.

[0008] According to some embodiments of this application, the step of determining the average photon number ratio of photon states based on the photon intensity of the photon state and the triggering number of each photon state includes: determining the average photon number of each photon state based on the photon intensity of the photon state and the triggering number of each photon state; and determining the average photon number ratio of the photon states based on the average photon number of each photon state.

[0009] According to some embodiments of this application, the step of determining the average photon number ratio of photon states based on the average photon number of each photon state includes: determining the average photon number ratio of photon states based on the average photon number of each photon state and the noise count.

[0010] According to some embodiments of this application, after determining the average photon number ratio of a photon state based on the photon intensity and the triggering number of each photon state, the photon intensity control method further includes: determining the fluctuation range of each photon state based on the photon intensity and the triggering number of each photon state. The step of determining the control signal for each photon state based on the average photon number ratio includes: determining the control signal for each photon state based on the average photon number ratio and the fluctuation range of each photon state.

[0011] According to one aspect of this application, a photon intensity control device for a BB84 decoy state quantum key distribution system is provided. The photon intensity control device includes a photon detection module, a control module, and an adjustment circuit module. The photon detection module detects the photon intensity of photon states at a first split ratio after beam splitting by a beam splitter, wherein the photon states include signal states, decoy states, and vacuum states. The control module determines an average photon number ratio for each photon state based on its photon intensity and the trigger count of each photon state. The control module determines a control signal for each photon state based on the average photon number ratio. The adjustment circuit module, responding to the control signals of each photon state, controls the photon intensity of photon states at a second split ratio after beam splitting by the beam splitter, thereby controlling the BB84 decoy state quantum key distribution system according to the photon intensity of the photon states at the second split ratio.

[0012] According to some embodiments of this application, the control module determines the average number of photons for each photon state based on the photon intensity of the photon state and the triggering number of each photon state; the control module determines the average photon number ratio of the photon states based on the average number of photons for each photon state.

[0013] According to some embodiments of this application, the control module determines the average photon count ratio of each photon state based on the average photon count and noise count of each photon state.

[0014] According to some embodiments of this application, the control module determines the fluctuation range of each photon state based on the photon intensity of the photon state and the triggering number of each photon state; the control module determines the control signal of each photon state based on the average photon number ratio of the photon state and the fluctuation range of each photon state.

[0015] According to some embodiments of this application, the photon detection module is a single-photon detector.

[0016] According to some embodiments of this application, the single-photon detector is at least one of a photomultiplier tube, a single-photon avalanche diode, a Geiger-mode avalanche photodiode, a silicon photomultiplier tube, a multi-pixel photon counter, a superconducting nanowire single-photon detector, a superconducting phase transition edge single-photon detector, or a semiconductor upconversion single-photon detector.

[0017] Beneficial effects

[0018] This application can detect the photon intensity of photon states with a first beam split ratio after beam splitting by a beam splitter. This application can determine the average photon number ratio of photon states by using the photon intensity of each photon state and the trigger count of each photon state. This application can determine the control signal for each photon state by using the average photon number ratio of the photon states. This application can control the photon intensity of photon states with a second beam split ratio after beam splitting by a beam splitter in response to the control signals of each photon state, thereby controlling the BB84 decoy state quantum key distribution system based on the photon intensity of the photon states with the second beam split ratio.

[0019] This application can determine the average photon number ratio of photon states by detecting the photon intensity of the photon states after the beam splitter has split the light, thereby determining the control signals for the signal state, the decoy state, and the vacuum state. This allows for precise control of the photon intensity of the signal state, the decoy state, and the vacuum state, thus solving the technical challenge of the extremely high photon number ratio requirement of the decoy state BB84 protocol and improving the security and reliability of quantum key distribution.

[0020] This application enables the detection of photon intensity in photon states using a single-photon detector. The single-photon detector is small in size and can be integrated into a QKD system. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0022] Figure 1This diagram shows a schematic representation of a photon intensity control device according to an embodiment of the present application.

[0023] Figure 2 A schematic flowchart of a photon intensity control method 1000 according to an embodiment of this application is shown.

[0024] Figure 3 A flowchart illustrating step S120 according to an embodiment of this application is shown.

[0025] Figure 4 Another schematic flowchart of a photon intensity control method 1000 according to an embodiment of this application is shown;

[0026] Figure 5 This paper shows a bar chart of pulse counts and pulse sequences detected by a photon detection module according to an embodiment of the present application;

[0027] Figure 6 This is another bar chart showing the pulse count and pulse sequence detected by a photon detection module according to an embodiment of this application.

[0028] Explanation of reference numerals in the attached figures:

[0029] Photon intensity control device 200; photon detection module 210; control module 220; adjustment circuit module 230. Detailed Implementation

[0030] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this application will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0031] The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of these specific details, or other methods, components, materials, devices, etc. In these cases, well-known structures, methods, devices, implementations, materials, or operations will not be shown or described in detail.

[0032] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0033] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order.

[0034] The technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0035] The BB84 Decoy-State Protocol is a significant improvement over the original BB84 quantum key distribution (QKD) protocol. While the ideal BB84 protocol uses a single-photon source, weakly coherent laser pulses are commonly used in practice. Such sources may emit multi-photon pulses (i.e., a single pulse contains multiple photons), allowing an eavesdropper (Eve) to exploit photon number splitting attacks (PNS attacks). The BB84 Decoy-State Protocol addresses this security vulnerability.

[0036] In the BB84 decoy state protocol, the precise values ​​of the photon counts in the signal state, decoy state, and vacuum state have a significant impact on the security, transmission distance, and key generation rate of the quantum key distribution system.

[0037] The signal state is a high-intensity pulse used to transmit key information. The average photon number of the signal state is typically μ (e.g., 0.5 photons / pulse). When μ is too high, the proportion of multiphoton components increases. For example, when μ=1, according to the Poisson distribution formula, the multiphoton probability is approximately 26.4%, making it vulnerable to attackers using photon number splitting (PNS) attacks to steal information. Conversely, when μ is too low, the number of photons received by the detector decreases, shortening the effective transmission distance.

[0038] Decoy states are low-intensity pulses used to detect eavesdropping (the average photon count of a decoy state is typically ν, such as 0.1 photons / pulse). If an eavesdropper selectively intercepts multiphoton pulses, the statistical properties of the decoy state will become abnormal, thus detecting the eavesdropping. ν needs to be low enough to distinguish between single-photon and multiphoton events. However, too low a ν will lead to increased statistical fluctuations, reducing the accuracy of parameter estimation.

[0039] The vacuum state refers to a photon-free pulse (the average number of photons in the vacuum state is typically w), used to calibrate the detector's dark count and background noise. By optimizing the ratios of μ, ν, and w, and the light intensity, the secure key rate can be maximized at a given distance.

[0040] In high-speed QKD systems, IM or IQ modulators are typically used to generate signal states and decoy states of varying intensities. The voltage-light intensity relationships of both the signal state and the decoy state must be rigorously calibrated to prevent exploitation by attackers. Due to environmental factors (such as temperature and mechanical vibration), voltage drift or noise can introduce light intensity fluctuations. Therefore, real-time monitoring combined with automatic feedback is necessary to ensure the stability of photon intensity across photon states (signal state, decoy state, and vacuum state).

[0041] In existing technologies, the photon intensity of photon states (signal state, decoy state, and vacuum state) can be monitored using direct optical power monitoring or passive compensation methods.

[0042] However, neither direct optical power monitoring nor passive compensation can detect photon intensity at the single-photon level, resulting in the photon intensity control precision failing to meet the requirements at the single-photon level.

[0043] Direct optical power monitoring involves using photodiodes or power meters to monitor the output of a light source. Traditional power meters (such as photodiodes) are typically designed for milliwatt-level light intensity, while decoy-state protocols need to detect minute differences in light intensity at the nanowatt (nW) or even picowatt (pW) level.

[0044] Passive compensation compensates for slow drift of the light source through temperature control or pre-calibration, but it cannot cope with rapid fluctuations. For example, in the measurement of photon intensity at the single-photon level, passive compensation techniques (such as temperature control or pre-calibration) can alleviate slow drift of the light source (such as wavelength / power drift caused by changes in ambient temperature), but they have significant limitations when faced with rapid fluctuations (such as photon intensity jitter caused by external mechanical vibrations or electrical noise).

[0045] The English terms used in this application, their full English names, and their corresponding Chinese definitions are as follows:

[0046] PID stands for Proportional-Integral-Derivative.

[0047] QKD, Quantum Key Distribution;

[0048] IM, Intensity Modulator;

[0049] IQ Modulator, In-Phase and Quadrature Modulator;

[0050] PMT, Photomultiplier Tube;

[0051] SPAD, Single-Photon Avalanche Diode;

[0052] Gm-APD, Geiger-mode Avalanche Photodiode;

[0053] SiPM, Silicon Photomultiplier;

[0054] MPPC, Multi-Pixel Photon Counter;

[0055] SNSPD, Superconducting Nanowire Single-Photon Detector;

[0056] TES, Transition Edge Sensor, is a superconducting phase transition edge single-photon detector.

[0057] UCD, Upconversion Single-Photon Detector, is a semiconductor upconversion single-photon detector.

[0058] See Figure 1 The photon intensity control device 200 of the BB84 decoy state quantum key distribution system provided in this application includes a photon detection module 210, a control module 220 and an adjustment circuit module 230.

[0059] The following is combined with Figure 1 This application describes a photon intensity control method 1000 for a BB84 decoy state quantum key distribution system.

[0060] See Figure 2 The photon intensity control method 1000 may include steps S110-S140.

[0061] In step S110, the photon detection module 210 detects the photon intensity of the photon state of the first beam split ratio after the beam splitter.

[0062] According to an example embodiment, a beam splitter can be a device that splits an incident beam into two or more beams. A first beam splitting ratio can be the ratio of the intensity of the split beam used for monitoring after beam splitting to the total intensity of the beam received by the beam splitter. A second beam splitting ratio can be the ratio of the intensity of the split beam used for subsequent QKD encoding and decoding operations after beam splitting to the total intensity of the beam splitter.

[0063] According to an example embodiment, the photon state includes a signal state, a decoy state, and a vacuum state. The photon intensity of the photon state includes the photon intensity of the signal state, the photon intensity of the decoy state, and the photon intensity of the vacuum state. The photon intensity of the photon state can be determined by statistically counting the pulses of the signal state, the decoy state, and the vacuum state.

[0064] For example, a beam splitter can split an incident beam into two output beams. A laser can emit incident light, which is then modulated by a modulator to adjust the intensity ratios of the signal state, the decoy state, and the vacuum state.

[0065] One beam of light after being split by the beam splitter can be used as the monitoring light, i.e., the beam with the first beam splitting ratio. The other beam of light after being split by the beam splitter can be used for subsequent QKD encoding and decoding operations, i.e., the beam with the second beam splitting ratio. The first beam splitting ratio and the second beam splitting ratio can be 99:1.

[0066] The intensity of the monitoring light with the first beam splitting ratio can be relatively strong, but it cannot be too strong; exceeding the threshold will cause it to malfunction. If the intensity of the monitoring light with the first beam splitting ratio is too low, the signal-to-noise ratio will be poor, and the detection by the photon detection module 210 will be inaccurate.

[0067] Optionally, the photon detection module 210 can be a single-photon detector. Single-photon detectors have high sensitivity.

[0068] For example, in step S110, the photon detection module 210 can detect the photon intensity of the signal state, the photon intensity of the decoy state, and the photon intensity of the vacuum state of the beam after it has been split by the beam splitter at the first beam split ratio.

[0069] Alternatively, the single-photon detector can be a photomultiplier tube (PMT), a single-photon avalanche diode (SPAD), a Geiger-mode avalanche photodiode (Gm-APD), a silicon photomultiplier tube (SiPM), a multi-pixel photon counter (MPPC), a superconducting nanowire single-photon detector (SNSPD), a superconducting phase transition edge single-photon detector (TES), or a semiconductor upconversion single-photon detector (UCD), etc.

[0070] For example, in the actual detection process of the photon detection module 210, such as Figure 6 As shown, the states of a photon are generated randomly. Figure 6The vertical axis represents the exponent, and the rate can reach GHz levels. Traditional power meters cannot keep up with the rate of change of photon intensity in each photon state. The photon intensity measured by a traditional power meter will be the average of the signal state, decoy state, and vacuum state. However, a single-photon detector can count the value of each pulse in real time, thus determining the photon intensity of the signal state, decoy state, and vacuum state.

[0071] In step S120, the control module 220 determines the average photon number ratio of the photon states based on the photon intensity of the photon states and the triggering number of each photon state.

[0072] According to the example embodiment, the trigger count can be the number of trigger events for a photon state. A trigger event can be a sequence of pulses. The trigger count for each photon state includes the trigger count for the signal state, the trigger count for the decoy state, and the trigger count for the vacuum state.

[0073] The average photon count of a photon state can be the ratio of the photon intensity of the photon state to the number of triggers. The average photon count of a photon state can include the average photon count of the signal state, the average photon count of the decoy state, and the average photon count of the vacuum state.

[0074] The ratio of the average photon count in a photon state can be the ratio of the average photon count in the signal state, the average photon count in the decoy state, and the average photon count in the vacuum state.

[0075] For example, in step S120, the control module 220 can determine the average number of photons in the signal state based on the photon intensity of the signal state and the number of triggers in the signal state. The control module 220 can determine the average number of photons in the decoy state based on the photon intensity of the decoy state and the number of triggers in the decoy state. The control module 220 can determine the average number of photons in the vacuum state based on the photon intensity of the vacuum state and the number of triggers in the vacuum state. The control module 220 can determine the ratio of the average number of photons in the photon states to the average number of photons in the signal state, the average number of photons in the decoy state, and the average number of photons in the vacuum state.

[0076] In step S130, the control module 220 determines the control signal for each photon state based on the average photon number ratio of the photon states.

[0077] According to the example embodiment, the control signal for each photon state can be a voltage signal that controls the intensity of each photon state. The control signal for each photon state can include a control signal for the signal state, a control signal for the decoy state, and a control signal for the vacuum state.

[0078] For example, in step S130, the control module 220 can generate control signals for the signal state, decoy state, and vacuum state based on the average photon number ratio of the photon states.

[0079] In step S140, the adjustment circuit module 230 responds to the control signals of the respective photon states and controls the photon intensity of the photon states of the second split ratio after being split by the beam splitter, so as to control the BB84 decoy state quantum key distribution system according to the photon intensity of the photon states of the second split ratio.

[0080] According to an example embodiment, the adjustment circuit module 230 can be a PID control circuit. For example... Figure 1 As shown, the adjustment circuit module 230 can receive and respond to the voltages of the control signals for each photon state (i.e., the control signal for the signal state, the control signal for the decoy state, and the control signal for the vacuum state), adjusting the total light intensity emitted by the laser, as well as the intensity ratios of the signal state, the decoy state, and the vacuum state emitted by the modulator. That is, the adjustment circuit module 230 can control the photon intensity of the signal state, the photon intensity of the decoy state, and the photon intensity of the vacuum state in the second beam splitting ratio according to the control signals for each photon state.

[0081] A beam with a second beam ratio can be used for subsequent QKD encoding and decoding operations.

[0082] Through the above embodiments, this application can detect the photon intensity of photon states with a first beam split ratio after beam splitting by a beam splitter. This application can determine the average photon number ratio of photon states by using the photon intensity of each photon state and the trigger count of each photon state. This application can determine the control signal for each photon state by using the average photon number ratio of the photon states. This application can control the photon intensity of photon states with a second beam split ratio after beam splitting by a beam splitter in response to the control signals of each photon state, thereby controlling the BB84 decoy state quantum key distribution system based on the photon intensity of the photon states with the second beam split ratio.

[0083] This application can determine the average photon number ratio of photon states by detecting the photon intensity of the photon states after the beam splitter has split the light, thereby determining the control signals for the signal state, the decoy state, and the vacuum state. This allows for precise control of the photon intensity of the signal state, the decoy state, and the vacuum state, thus solving the technical challenge of the extremely high photon number ratio requirement of the decoy state BB84 protocol and improving the security and reliability of quantum key distribution.

[0084] This application enables the detection of photon intensity in photon states using a single-photon detector. The single-photon detector is small in size and can be integrated into a QKD system.

[0085] Optionally, see Figure 3 Step S120 may include steps S121-S122.

[0086] In step S121, the control module 220 determines the average number of photons for each photon state based on the photon intensity of the photon state and the triggering number of each photon state.

[0087] According to an example embodiment, the average number of photons in a photon state can be the ratio of the photon intensity of the photon state to the number of triggers. The average number of photons in a photon state can include the average number of photons in the signal state, the average number of photons in the decoy state, and the average number of photons in the vacuum state.

[0088] The average photon count in the signal state can be expressed as the ratio of the photon intensity of the signal state to the number of triggers in the signal state. The average photon count in the decoy state can be expressed as the ratio of the photon intensity of the decoy state to the number of triggers in the decoy state. The average photon count in the vacuum state can be expressed as the ratio of the photon intensity of the vacuum state to the number of triggers in the vacuum state.

[0089] For example, such as Figure 5 As shown, the photon detection module 210 detects the first trigger event as a signal state and measures the photon intensity of that first trigger event. The photon detection module 210 detects the second trigger event as a vacuum state and measures the photon intensity of that second trigger event. The photon detection module 210 detects the third trigger event as a signal state and measures the photon intensity of that third trigger event. The photon detection module 210 detects the fourth trigger event as a vacuum state and measures the photon intensity of that fourth trigger event. The photon detection module 210 detects the fifth trigger event as a decoy state and measures the photon intensity of that fifth trigger event. And so on, until the photon detection module 210 detects the eighth trigger event as a decoy state and measures the photon intensity of that eighth trigger event.

[0090] The control module 220 can determine that the number of triggers in the signal state is 2, the number of triggers in the decoy state is 4, and the number of triggers in the vacuum state is 2.

[0091] The control module 220 can calculate the average photon number of the signal state as the sum of the photon intensities of the two signal states divided by 2. The control module 220 can calculate the average photon number of the decoy state as the sum of the photon intensities of the four signal states divided by 4. The control module 220 can calculate the average photon number of the vacuum state as the sum of the photon intensities of the two signal states divided by 2.

[0092] In step S122, the control module 220 determines the average photon number ratio of each photon state based on the average photon number of each photon state.

[0093] According to the example embodiment, the control module 220 can determine the average photon number ratio of the photon states based on the ratio of the average photon number of the signal state, the average photon number of the decoy state, and the average photon number of the vacuum state.

[0094] For example, the ratio of the average number of photons in a photon state can be "the average number of photons in the signal state: the average number of photons in the decoy state: the average number of photons in the vacuum state".

[0095] Through the above embodiments, this application can determine the average photon count of each photon state by using the photon intensity of each photon state and the triggering quantity of each photon state. This application can determine the average photon count ratio of each photon state by using the average photon count of each photon state.

[0096] This application can improve the control accuracy of the photon state control signal by determining the average photon number ratio of the photon state.

[0097] Optionally, step S122 can specifically be: the control module 220 determines the average photon count ratio of each photon state based on the average photon count and noise count of each photon state.

[0098] According to the example embodiment, the noise count can be the noise count of the photon detection module 210 (single photon detector) itself (e.g., dark count, afterpulse, etc.).

[0099] When calculating the average photon count ratio of photon states, the control module 220 can discard noise counts from the average photon counts of each photon state, and then determine the average photon count ratio of the photon states based on the average photon counts of each photon state after discarding noise counts.

[0100] For example, the ratio of the average number of photons in a photon state can be "the average number of photons in the signal state after removing noise counting: the average number of photons in the decoy state after removing noise counting: the average number of photons in the vacuum state after removing noise counting".

[0101] This application can determine the average photon count ratio of photon states by using the average photon count and noise count of each photon state, thereby further improving the control accuracy of the photon state control signal.

[0102] Optionally, see Figure 4 After step S120, the photon intensity control method 1000 may further include step S120a.

[0103] In step S120a, the control module 220 determines the fluctuation range of each photon state based on the photon intensity of the photon state and the number of triggers of each photon state.

[0104] According to an example embodiment, the fluctuation range can be the range of amplitude changes in optical signal power (typically expressed in dBm or mW) over time. The fluctuation range can be determined by the standard deviation of the pulse counts of the photon states. The fluctuation ranges of each photon state include the fluctuation range of the signal state, the fluctuation range of the decoy state, and the fluctuation range of the vacuum state.

[0105] For example, control module 220 can determine the fluctuation range (standard deviation of the signal state) of the signal state based on the photon intensity of the signal state and the number of triggers of the signal state. Control module 220 can determine the fluctuation range (standard deviation of the decoy state) of the decoy state based on the photon intensity of the decoy state and the number of triggers of the decoy state. Control module 220 can determine the fluctuation range (standard deviation of the vacuum state) of the vacuum state based on the photon intensity of the vacuum state and the number of triggers of the vacuum state.

[0106] Step S130 can be specifically described as follows: The control module 220 determines the control signal for each photon state based on the average photon number ratio of the photon states and the fluctuation range of each photon state.

[0107] According to the example embodiment, the fluctuation range can measure the stability of the photon state. QKD requires that the smaller the fluctuations (i.e., standard deviations) of the signal state, decoy state, and vacuum state, the safer the QKD. The voltage of the control signal can take into account the stability of the fluctuation range, thereby stabilizing the photon intensities of the signal state, decoy state, and vacuum state of the beam with the second beam splitting ratio.

[0108] For example, control module 220 can determine the control signal for the signal state based on the average photon number ratio of the photon states and the fluctuation range of the signal state. Control module 220 can determine the control signal for the decoy state based on the average photon number ratio of the photon states and the fluctuation range of the decoy state. Control module 220 can determine the control signal for the vacuum state based on the average photon number ratio of the photon states and the fluctuation range of the vacuum state.

[0109] Through the above embodiments, this application can determine the fluctuation range of each photon state by the photon intensity of the photon state and the triggering number of each photon state. This application can determine the control signal of each photon state by the average photon number ratio of the photon states and the fluctuation range of each photon state, thereby stabilizing the photon intensity of the signal state, the photon intensity of the decoy state, and the photon intensity of the vacuum state of the beam with the second beam splitting ratio.

[0110] Alternatively, the photon detection module 210 can also be a high-bandwidth oscilloscope.

[0111] Finally, it should be noted that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions of the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for controlling photon intensity in a BB84 decoy state quantum key distribution system, characterized in that, The photon intensity control method includes: The photon intensity of the photon state of the first beam split ratio after the beam splitter is detected by a single photon detector, wherein the photon state includes a signal state, a decoy state, and a vacuum state; The average photon number ratio of each photon state is determined based on its photon intensity and the number of triggers for that photon state, including: The average number of photons for each photon state is determined based on the photon intensity of the photon state and the number of triggers for each photon state. The average photon number ratio of the photon states is determined based on their respective average photon numbers. Based on the average photon number ratio of the photon states, the control signal for each photon state is determined; In response to the control signals of the respective photon states, the photon intensity of the photon state after the beam splitter is controlled to a second split ratio, so as to control the BB84 decoy state quantum key distribution system according to the photon intensity of the photon state of the second split ratio.

2. The photon intensity control method according to claim 1, characterized in that, Determining the average photon number ratio of the photon states based on their respective average photon numbers includes: The average photon count ratio of each photon state is determined based on its average photon count and noise count.

3. The photon intensity control method according to claim 1, characterized in that, After determining the average photon number ratio of the photon states based on the photon intensity of each photon state and the triggering number of each photon state, the photon intensity control method further includes: The fluctuation range of each photon state is determined based on the photon intensity of the photon state and the number of triggers of each photon state. The step of determining the control signals for each photon state based on the average photon number ratio of the photon states includes: Based on the average photon number ratio of the photon states and the fluctuation range of each photon state, the control signal for each photon state is determined.

4. A photon intensity control device for a BB84 decoy state quantum key distribution system, characterized in that, The photon intensity control device includes: A photon detection module detects the photon intensity of the photon state of the first beam split ratio after the beam is split by the beam splitter. The photon state includes a signal state, a decoy state, and a vacuum state. The photon detection module is a single-photon detector. The control module determines the average photon number ratio of each photon state based on the photon intensity and the trigger count of each photon state, including: The control module determines the average number of photons for each photon state based on the photon intensity of the photon state and the triggering number of each photon state. The control module determines the average photon number ratio of the photon states based on their respective average photon numbers. The control module determines the control signal for each photon state based on the average photon number ratio of the photon states. The adjustment circuit module, in response to the control signals of the respective photon states, controls the photon intensity of the photon state with a second split ratio after being split by the beam splitter, so as to control the BB84 decoy state quantum key distribution system according to the photon intensity of the photon state with the second split ratio.

5. The photon intensity control device according to claim 4, characterized in that, The control module determines the average photon count ratio of each photon state based on the average photon count and noise count of each photon state.

6. The photon intensity control device according to claim 4, characterized in that, The control module determines the fluctuation range of each photon state based on the photon intensity of each photon state and the number of triggers for each photon state. The control module determines the control signal for each photon state based on the average photon number ratio of the photon states and the fluctuation range of each photon state.

7. The photon intensity control device according to claim 4, characterized in that, The single-photon detector is at least one of the following: photomultiplier tube, single-photon avalanche diode, Geiger-mode avalanche photodiode, silicon photomultiplier tube, multi-pixel photon counter, superconducting nanowire single-photon detector, superconducting phase transition edge single-photon detector, or semiconductor upconversion single-photon detector.

Images