Photon intensity control method and device of BB84 decoy state quantum key distribution system

Abstract

The invention 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 a photon state of a first beam splitting ratio after beam splitting by a beam splitter; determining an average photon number ratio of the photon states according to the photon intensity of the photon states and the respective triggering number of the photon states; determining respective control signals of the photon states according to the average photon number ratio of the photon states; and in response to respective control signals of the photon states, controlling the photon intensity of the photon state of the second beam splitting ratio after beam splitting 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 of the second beam splitting ratio. According to the photon intensity control method, the photon intensity of a signal state, the photon intensity of a decoy state and the photon intensity of a vacuum state can be accurately controlled, and the feedback control precision is improved.

Description

Technical Field

[0001] This application relates to the technical field of photon intensity control in quantum communication. Specifically, it relates to a method and device for photon intensity control in a BB84 decoy state quantum key distribution system. Background Art

[0002] In a high-speed QKD system, an IM or IQ modulator is usually used to generate signal states and decoy states with different intensities. The voltage-light intensity relationship of the signal state and the voltage-light intensity relationship of the decoy state need to be strictly calibrated to avoid being exploited by attackers. Due to environmental factors (such as temperature, mechanical vibration, etc.), voltage drift or noise will introduce light intensity fluctuations. Therefore, it is necessary to monitor in real time and combine automatic feedback to ensure the photon intensity stability of the photon states (signal state, decoy state, and vacuum state).

[0003] In the prior art, direct optical power monitoring or passive compensation methods can be used to monitor the photon intensity of photon states (signal state, decoy state, and vacuum state). However, neither of these two methods, direct optical power monitoring or passive compensation, can achieve the detection of photon intensity at the single-photon level, it is difficult to accurately distinguish the light intensity fluctuations at the single-photon level (especially the weak differences between the signal state / decoy state), and the feedback speed may be insufficient.

[0004] The content of the background art part is only the technology known to the applicant and does not of course represent the prior art in this field. Summary of the Invention

[0005] This application aims to provide a method and device for photon intensity control in a BB84 decoy state quantum key distribution system to solve the technical problems that neither of the two methods, direct optical power monitoring or passive compensation, can achieve the detection of photon intensity at the single-photon level, it is difficult to accurately distinguish the light intensity fluctuations at the single-photon level, and the feedback speed may be insufficient. According to one aspect of this application, this application provides a method for photon intensity control in a BB84 decoy state quantum key distribution system. The photon intensity control method includes: detecting the photon intensity of the photon state with the first beam splitting ratio after being split by a beam splitter, where the photon state includes a signal state, a decoy state, and a vacuum state; determining the average photon number ratio of the photon state according to the photon intensity of the photon state and the respective trigger numbers of the photon state; determining the respective control signals of the photon state according to the average photon number ratio of the photon state; and in response to the respective control signals of the photon state, controlling the photon intensity of the photon state with the second beam splitting ratio after being split by the beam splitter to control the BB84 decoy state quantum key distribution system according to the photon intensity of the photon state with the second beam splitting ratio.

[0006] According to some embodiments of the present application, the steps of determining the average photon number ratio of photon states according to the photon intensity of photon states and the respective trigger numbers of photon states include: determining the average photon number of each photon state according to the photon intensity of the photon state and the respective trigger numbers of the photon state; determining the average photon number ratio of the photon states according to the average photon number of each photon state.

[0007] According to some embodiments of the present application, the steps of determining the average photon number ratio of photon states according to the average photon number of each photon state include: determining the average photon number ratio of the photon states according to the average photon number of each photon state and the noise count.

[0008] According to some embodiments of the present application, after the steps of determining the average photon number ratio of photon states according to the photon intensity of photon states and the respective trigger numbers of photon states, the photon intensity control method further includes: determining the respective fluctuation ranges of photon states according to the photon intensity of photon states and the respective trigger numbers of photon states. The steps of determining the respective control signals of photon states according to the average photon number ratio of photon states include: determining the respective control signals of photon states according to the average photon number ratio of photon states and the respective fluctuation ranges of photon states.

[0009] According to one aspect of the present application, the present application provides a photon intensity control device for a BB84 decoy state quantum key distribution system. 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 the photon state of the first beam splitting ratio after being split by a beam splitter, where the photon state includes a signal state, a decoy state, and a vacuum state; the control module determines the average photon number ratio of the photon states according to the photon intensity of the photon state and the respective trigger numbers of the photon state; the control module determines the respective control signals of the photon states according to the average photon number ratio of the photon states; the adjustment circuit module controls the photon intensity of the photon state of the second beam splitting ratio after being split by the beam splitter in response to the respective control signals of the photon states, so as to control the BB84 decoy state quantum key distribution system according to the photon intensity of the photon state of the second beam splitting ratio.

[0010] According to some embodiments of the present application, the control module determines the average photon number of each photon state according to the photon intensity of the photon state and the respective trigger numbers of the photon state; the control module determines the average photon number ratio of the photon states according to the average photon number of each photon state.

[0011] According to some embodiments of the present application, the control module determines the average photon number ratio of the photon states according to the average photon number of each photon state and the noise count.

[0012] According to some embodiments of the present application, the control module determines the respective fluctuation ranges of the photon states according to the photon intensities of the photon states and the respective trigger numbers of the photon states; the control module determines the respective control signals of the photon states according to the average photon number ratios of the photon states and the respective fluctuation ranges of the photon states.

[0013] According to some embodiments of the present application, the photon detection module is a single-photon detector.

[0014] According to some embodiments of the present 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, 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.

[0015] Beneficial effects The present application can detect the photon intensity of the photon state of the first beam splitting ratio after beam splitting by a beam splitter. The present application can determine the average photon number ratio of the photon state according to the photon intensity of the photon state and the respective trigger numbers of the photon state. The present application can determine the respective control signals of the photon state according to the average photon number ratio of the photon state. The present application can control the photon intensity of the photon state of the second beam splitting ratio after beam splitting by a beam splitter in response to the respective control signals of the photon state, so as to control the BB84 decoy state quantum key distribution system according to the photon intensity of the photon state of the second beam splitting ratio.

[0016] The present application can determine the average photon number ratio of the photon state by detecting the photon intensity of the photon state of the first beam splitting ratio after beam splitting by a beam splitter, so as to determine the control signal of the signal state, the control signal of the decoy state, and the control signal of the vacuum state, and 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, thereby solving the technical problem that the decoy state BB84 protocol has extremely high requirements for the photon number ratio, and improving the security and reliability of quantum key distribution.

[0017] The present application can detect the photon intensity of the photon state by a single-photon detector. The single-photon detector has a small volume and can be integrated into the QKD system. Description of the drawings

[0018] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the following drawings are only some embodiments of the present application. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to these drawings.

[0019] Figure 1Shows a schematic structural diagram of a photon intensity control device according to an embodiment of the present application; Figure 2 Shows a schematic flowchart of a photon intensity control method 1000 according to an embodiment of the present application; Figure 3 Shows a schematic flowchart of step S120 according to an embodiment of the present application; Figure 4 Shows another schematic flowchart of a photon intensity control method 1000 according to an embodiment of the present application; Figure 5 Shows a bar chart of the pulse count detected by the photon detection module and the pulse sequence according to an embodiment of the present application; Figure 6 Shows another bar chart of the pulse count detected by the photon detection module and the pulse sequence according to an embodiment of the present application.

[0020] Description of reference numerals: Photon intensity control device 200; photon detection module 210; control module 220; adjustment circuit module 230. Detailed implementation manners

[0021] Example embodiments will now be described more fully with reference to the accompanying drawings. However, the example embodiments can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this application will be thorough and complete, and will fully convey the concept of the example embodiments to those skilled in the art. Like reference numerals in the figures denote like or similar parts, and thus their repetitive description will be omitted.

[0022] The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. In the following description, numerous specific details are provided to give a thorough understanding of the embodiments of the present disclosure. However, those skilled in the art will realize that the technical solutions of the present disclosure can be practiced without one or more of these specific details, or can be implemented in other ways, components, materials, devices, etc. In these cases, well-known structures, methods, devices, implementations, materials, or operations will not be shown or described in detail.

[0023] In addition, the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not limited to the listed steps or units, but may optionally further include steps or units not listed, or may optionally further include other steps or units inherent to these processes, methods, products, or devices.

[0024] In the description and claims of this application and the above-mentioned drawings, terms such as "first", "second", etc. are used to distinguish different objects, rather than to describe a specific order.

[0025] The following will clearly and completely describe the technical solutions of this application with reference to the accompanying drawings in the embodiments of this application. Obviously, the described embodiments are some, rather than all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments in this application without creative efforts fall within the scope of protection of this application.

[0026] The Decoy-State BB84 Protocol is an important improvement to the original BB84 quantum key distribution (QKD) protocol. The ideal BB84 protocol uses a single-photon source, but in practice, weak coherent laser pulses are commonly used. Such a light source may emit multi-photon pulses (i.e., a pulse contains multiple photons), so an eavesdropper (Eve) can use the photon number splitting attack (PNS attack). The BB84 decoy state protocol solves this security vulnerability.

[0027] In the BB84 decoy state protocol, the exact photon number values of the signal state, decoy state, and vacuum state have an important impact on the security, transmission distance, and key generation rate of the quantum key distribution system.

[0028] The signal state is a high-intensity pulse used to transmit key information. The average photon number of the signal state is usually μ, such as 0.5 photons / pulse). When μ is too high, the proportion of multi-photon components increases. For example, when μ = 1, according to the Poisson distribution formula, the multi-photon probability is about 26.4%, and it is easy for an attacker to use the photon number splitting (PNS) attack to steal information. While too low μ will result in a decrease in the number of photons received by the detector, shortening the effective transmission distance.

[0029] The decoy state is a low-intensity pulse used to detect eavesdropping (the average photon number of the decoy state is usually ν, such as 0.1 photons / pulse). If the eavesdropper selectively intercepts multi-photon pulses, it will cause abnormal statistical characteristics of the decoy state, thus detecting eavesdropping. ν needs to be low enough to distinguish single-photon and multi-photon events. But too low ν will lead to an increase in statistical fluctuations and reduce the accuracy of parameter estimation.

[0030] The vacuum state refers to a pulse without photons (the average photon number of the vacuum state is usually w), which is used to calibrate the dark count and background noise of the detector. By optimizing the ratio and light intensity of μ, ν, and w, the secure key rate can be maximized at a given distance.

[0031] In a high-speed QKD system, IM or IQ modulators are usually used to generate signal states and decoy states with different intensities. The voltage-light intensity relationships of the signal states and the decoy states need to be strictly calibrated to prevent attackers from exploiting them. Due to environmental factors (such as temperature, mechanical vibration, etc.), voltage drift or noise can introduce light intensity fluctuations. Therefore, real-time monitoring and automatic feedback are required to ensure the photon intensity stability of the photon states (signal states, decoy states, and vacuum states).

[0032] In the prior art, direct optical power monitoring or passive compensation methods can be used to monitor the photon intensities of photon states (signal states, decoy states, and vacuum states). However, neither direct optical power monitoring nor passive compensation can detect the photon intensity at the single-photon level, resulting in the control accuracy of the photon intensity not meeting the requirements at the single-photon level.

[0033] Direct optical power monitoring is to monitor the output of the light source using a photodiode or a power meter. Traditional power meters (such as photodiodes) are usually designed for light intensities in the milliwatt range, while the decoy state protocol requires detecting weak light intensity differences in the nanowatt (nW) or even picowatt (pW) range.

[0034] Passive compensation is to compensate for the 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, although passive compensation techniques (such as temperature control or pre-calibration) can alleviate the slow drift of the light source (such as wavelength / power drift caused by environmental temperature changes), they have obvious limitations when facing rapid fluctuations (such as photon intensity jitter caused by external mechanical vibration or electrical noise).

[0035] The English terms, their full English names, and corresponding Chinese interpretations involved in this application are as follows: PID, Proportional-Integral-Derivative, proportional-integral-derivative; QKD, Quantum Key Distribution, quantum key distribution; IM, Intensity Modulator, intensity modulator; IQ Modulator, In-Phase and Quadrature Modulator, in-phase and quadrature modulator; PMT, Photomultiplier Tube, photomultiplier tube; SPAD, Single-Photon Avalanche Diode, single-photon avalanche diode; Gm-APD, Geiger-mode Avalanche Photodiode, Geiger-mode avalanche photodiode; SiPM, Silicon Photomultiplier, silicon photomultiplier; MPPC, Multi-Pixel Photon Counter, multi-pixel photon counter; SNSPD, Superconducting Nanowire Single-Photon Detector, superconducting nanowire single-photon detector; TES, Transition Edge Sensor, superconducting transition edge single-photon detector; UCD, Upconversion Single-Photon Detector, semiconductor upconversion single-photon detector.

[0036] See Figure 1 , the photon intensity control device 200 of the BB84 decoy state quantum key distribution system provided by this application includes a photon detection module 210, a control module 220, and an adjustment circuit module 230.

[0037] The following combines Figure 1 , and describes a photon intensity control method 1000 of a BB84 decoy state quantum key distribution system provided by this application.

[0038] See Figure 2 , the photon intensity control method 1000 may include step S110-step S140.

[0039] In step S110, the photon detection module 210 detects the photon intensity of the photon state with the first beam splitting ratio after being split by the beam splitter.

[0040] According to the exemplary embodiment, the beam splitter may be a device that splits an incident light beam into two or more light beams. The first beam splitting ratio may be the ratio of the split light intensity used for monitoring after being split by the beam splitter to the total light intensity received by the beam splitter. The second beam splitting ratio may be the ratio of the split light intensity used for subsequent operations such as encoding and decoding of QKD after being split by the beam splitter to the total light intensity received by the beam splitter.

[0041] According to the exemplary 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 counting the pulses of the signal state, the pulses of the decoy state, and the pulses of the vacuum state.

[0042] For example, a beam splitter can split an incident light beam into two output light beams. A laser can emit the incident light, and the incident light also passes through a modulator to adjust the light intensity ratios of the signal state, the decoy state, and the vacuum state.

[0043] One of the light beams after being split by the beam splitter can be the monitoring light, that is, the light beam with the first beam splitting ratio. The other light beam after passing through the beam splitter can be used for subsequent operations such as encoding and decoding in QKD, that is, the light beam with the second beam splitting ratio. The first beam splitting ratio and the second beam splitting ratio can be 99:1.

[0044] The light intensity of the monitoring light with the first beam splitting ratio can be relatively strong, but not too strong, otherwise it will be damaged if it exceeds the threshold. If the light intensity of the monitoring light with the first beam splitting ratio is too small, the signal-to-noise ratio will be poor, and the detection of the photon detection module 210 will be inaccurate.

[0045] Optionally, the photon detection module 210 can be a single-photon detector. The single-photon detector has high sensitivity.

[0046] For example, in step S110, the photon detection module 210 can detect the photon intensities of the signal state, the decoy state, and the vacuum state of the light beam with the first beam splitting ratio after being split by the beam splitter.

[0047] Optionally, the single-photon detector can be of types such as a photomultiplier tube (PMT), a single-photon avalanche diode (SPAD), a Geiger-mode avalanche photodiode (Gm-APD), a silicon photomultiplier (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).

[0048] For example, during the actual detection process of the photon detection module 210, as Figure 6 shown, the states of each photon state are randomly generated ( Figure 6 the ordinate in is the exponent), and the rate can reach the GHz level. The traditional power meter will not be able to keep up with the change rate of the photon intensities of the states of each photon state, and the photon intensity of the photon state measured by the traditional power meter will be the average value of the signal state, the decoy state, and the vacuum state added together. While the single-photon detector can statistically count the number of counts of each pulse in real time, that is, it can determine the photon intensities of the signal state, the decoy state, and the vacuum state.

[0049] In step S120, the control module 220 determines the average photon number ratio of the photon states according to the photon intensities of the photon states and the respective trigger numbers of the photon states.

[0050] According to an exemplary embodiment, the trigger quantity may be the quantity of trigger events for the photon states. The trigger events may be a sequence of pulses. The trigger quantity for each of the photon states includes the trigger quantity for the signal state, the trigger quantity for the decoy state, and the trigger quantity for the vacuum state.

[0051] The average photon number of a photon state may be the ratio of the photon intensity of the photon state to the trigger quantity. The average photon number of a photon state may include 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.

[0052] The average photon number ratio of a photon state may be 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.

[0053] For example, in step S120, the control module 220 may determine the average photon number of the signal state according to the photon intensity of the signal state and the trigger quantity of the signal state. The control module 220 may determine the average photon number of the decoy state according to the photon intensity of the decoy state and the trigger quantity of the decoy state. The control module 220 may determine the average photon number of the vacuum state according to the photon intensity of the vacuum state and the trigger quantity of the vacuum state. The control module 220 may determine the average photon number ratio of the photon state according to 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.

[0054] In step S130, the control module 220 determines the control signals for each of the photon states according to the average photon number ratio of the photon state.

[0055] According to an exemplary embodiment, the control signals for each of the photon states may be voltage signals for controlling the intensity of each of the photon states. The control signals for each of the photon states may include the control signal for the signal state, the control signal for the decoy state, and the control signal for the vacuum state.

[0056] For example, in step S130, the control module 220 may generate the control signal for the signal state, the control signal for the decoy state, and the control signal for the vacuum state according to the average photon number ratio of the photon state.

[0057] In step S140, the adjustment circuit module 230 responds to the control signals for each of the photon states to control the photon intensity of the photon state with the second beam splitting ratio after beam splitting 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 beam splitting ratio.

[0058] According to an exemplary embodiment, the adjustment circuit module 230 may be a PID control circuit. As Figure 1As shown, the adjustment circuit module 230 can receive and respond to the voltages of the control signals for the respective photon states (i.e., the control signal for the signal state, the control signal for the decoy state, and the control signal for the vacuum state), adjust the total light intensity emitted by the laser, and modulate the light 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 intensities of the signal state, the decoy state, and the vacuum state of the second beam splitting ratio according to the control signals for the respective photon states.

[0059] The light beam with the second beam ratio can be used for subsequent operations such as encoding and decoding in QKD.

[0060] Through the above embodiments, the present application can detect the photon intensities of the photon states of the first beam splitting ratio after being split by the beam splitter. The present application can determine the average photon number ratio of the photon states based on the photon intensities of the photon states and the respective trigger numbers of the photon states. The present application can determine the control signals for the respective photon states based on the average photon number ratio of the photon states. The present application can control the photon intensities of the photon states of the second beam splitting ratio after being split by the beam splitter by responding to the control signals for the respective photon states, so as to control the BB84 decoy state quantum key distribution system according to the photon intensities of the photon states of the second beam splitting ratio.

[0061] The present application can detect the photon intensities of the photon states of the first beam splitting ratio after being split by the beam splitter, determine the average photon number ratio of the photon states, thereby determining the control signals for the signal state, the decoy state, and the vacuum state, and can precisely control the photon intensities of the signal state, the decoy state, and the vacuum state, thus solving the technical problem of the extremely high requirement for the photon number ratio in the decoy state BB84 protocol and improving the security and reliability of quantum key distribution.

[0062] The present application can detect the photon intensities of the photon states through single-photon detectors. The single-photon detectors are small in volume and can be integrated into the QKD system.

[0063] Optionally, referring to Figure 3 , step S120 may include steps S121 - S122.

[0064] In step S121, the control module 220 determines the average photon numbers for the respective photon states based on the photon intensities of the photon states and the respective trigger numbers of the photon states.

[0065] According to the exemplary embodiments, the average photon number of a photon state can be the ratio of the photon intensity of the photon state to the trigger number. The average photon numbers of the photon states can include 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.

[0066] The average number of photons in the signal state can be the ratio of the photon intensity of the signal state to the number of triggers of the signal state. The average number of photons in the decoy state can be the ratio of the photon intensity of the decoy state to the number of triggers of the decoy state. The average number of photons in the vacuum state can be the ratio of the photon intensity of the vacuum state to the number of triggers of the vacuum state.

[0067] For example, as Figure 5 shown, the photon detection module 210 detects that the first trigger event is a signal state and detects the photon intensity of the first trigger event. The photon detection module 210 detects that the second trigger event is a vacuum state and detects the photon intensity of the second trigger event. The photon detection module 210 detects that the third trigger event is a signal state and detects the photon intensity of the third trigger event. The photon detection module 210 detects that the fourth trigger event is a vacuum state and detects the photon intensity of the fourth trigger event. The photon detection module 210 detects that the fifth trigger event is a decoy state and detects the photon intensity of the fifth trigger event. And so on, the photon detection module 210 detects that the eighth trigger event is a decoy state and detects the photon intensity of the eighth trigger event.

[0068] The control module 220 can determine that the number of triggers of the signal state is 2, the number of triggers of the decoy state is 4, and the number of triggers of the vacuum state is 2.

[0069] Then the control module 220 can calculate that the average number of photons in the signal state is the sum of the photon intensities of the two signal states divided by 2. The control module 220 can calculate that the average number of photons in the decoy state is the sum of the photon intensities of the four signal states divided by 4. The control module 220 can calculate that the average number of photons in the vacuum state is the sum of the photon intensities of the two signal states divided by 2.

[0070] In step S122, the control module 220 determines the average photon number ratio of the photon states according to the average photon number of each photon state.

[0071] According to the exemplary embodiment, the control module 220 can determine the average photon number ratio of the photon states according to 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.

[0072] For example, the average photon number ratio of the photon states can be "average photon number of the signal state: average photon number of the decoy state: average photon number of the vacuum state".

[0073] Through the above embodiments, the present application can determine the average photon number of each photon state through the photon intensity of the photon state and the number of triggers of each photon state. The present application can determine the average photon number ratio of the photon states through the average photon number of each photon state.

[0074] This application can improve the control accuracy of the control signal for the photon state by determining the average photon number ratio of the photon states.

[0075] Optionally, step S122 can be specifically: The control module 220 determines the average photon number ratio of the photon states according to the average photon number and noise count of each photon state.

[0076] According to the exemplary embodiment, the noise count can be the noise count of the photon detection module 210 (single-photon detector) itself (for example, dark count, afterpulse, etc.).

[0077] When calculating the average photon number ratio of the photon states, the control module 220 can subtract the noise count from the average photon number of each photon state, and then determine the average photon number ratio of the photon states according to the average photon number of each photon state after subtracting the noise count.

[0078] For example, the average photon number ratio of the photon states can be "the average photon number of the signal state after subtracting the noise count: the average photon number of the decoy state after subtracting the noise count: the average photon number of the vacuum state after subtracting the noise count".

[0079] This application can determine the average photon number ratio of the photon states according to the average photon number and noise count of each photon state, and further improve the control accuracy of the control signal for the photon state.

[0080] Optionally, referring to Figure 4 , after step S120, the photon intensity control method 1000 can further include step S120a.

[0081] In step S120a, the control module 220 determines the fluctuation range of each photon state according to the photon intensity of the photon state and the trigger count of each photon state.

[0082] According to the exemplary embodiment, the fluctuation range can be the amplitude range of the optical signal power (usually expressed in dBm or mW) changing with time. The fluctuation range can be determined by the standard deviation of the pulse count of the photon state. The fluctuation range of each photon state includes the fluctuation range of the signal state, the fluctuation range of the decoy state, and the fluctuation range of the vacuum state.

[0083] For example, the control module 220 can determine the fluctuation range of the signal state (the standard deviation of the signal state) according to the photon intensity of the signal state and the trigger count of the signal state. The control module 220 can determine the fluctuation range of the decoy state (the standard deviation of the decoy state) according to the photon intensity of the decoy state and the trigger count of the decoy state. The control module 220 can determine the fluctuation range of the vacuum state (the standard deviation of the vacuum state) according to the photon intensity of the vacuum state and the trigger count of the vacuum state.

[0084] Step S130 may be specifically as follows: The control module 220 determines the respective control signals of the photon states according to the average photon number ratio of the photon states and the respective fluctuation ranges of the photon states.

[0085] According to the exemplary embodiment, the fluctuation range can measure the stability of the photon state. The smaller the fluctuations (i.e., the standard deviations) of the signal state, the decoy state, and the vacuum state are required for QKD, the safer the QKD is. The voltage of the control signal can consider the stability of the fluctuation range, so as to stabilize the photon intensity of the signal state, the photon intensity of the decoy state, and the photon intensity of the vacuum state of the light beam with the second beam splitting ratio.

[0086] For example, the control module 220 can determine the control signal of the signal state according to the average photon number ratio of the photon states and the fluctuation range of the signal state. The control module 220 can determine the control signal of the decoy state according to the average photon number ratio of the photon states and the fluctuation range of the decoy state. The control module 220 can determine the control signal of the vacuum state according to the average photon number ratio of the photon states and the fluctuation range of the vacuum state.

[0087] Through the above embodiments, the present application can determine the respective fluctuation ranges of the photon states through the photon intensity of the photon states and the respective triggering numbers of the photon states. The present application can determine the respective control signals of the photon states according to the average photon number ratio of the photon states and the respective fluctuation ranges of the photon states, so as to stabilize the photon intensity of the signal state, the photon intensity of the decoy state, and the photon intensity of the vacuum state of the light beam with the second beam splitting ratio.

[0088] Optionally, the photon detection module 210 may also be a high-bandwidth oscilloscope.

[0089] Finally, it should be noted that the above are only the preferred embodiments of the present application and are not used to limit the present application. Although the present 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 perform equivalent replacements on some of the technical features. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A method for controlling the photon intensity of a BB84 decoy state quantum key distribution system, characterized in that, The photon intensity control method includes: Detecting the photon intensity of the photon state with the first beam splitting ratio after being split by a beam splitter, where the photon state includes a signal state, a decoy state, and a vacuum state; Determining the average photon number ratio of the photon states according to the photon intensity of the photon states and the respective trigger numbers of the photon states; Determining the respective control signals of the photon states according to the average photon number ratio of the photon states; In response to the respective control signals of the photon states, controlling the photon intensity of the photon state with the second beam splitting ratio after being split by the beam splitter to control the BB84 decoy state quantum key distribution system according to the photon intensity of the photon state with the second beam splitting ratio.

2. The photon intensity control method according to claim 1, wherein The determining the average photon number ratio of the photon states according to the photon intensity of the photon states and the respective trigger numbers of the photon states includes: Determining the respective average photon numbers of the photon states according to the photon intensity of the photon states and the respective trigger numbers of the photon states; Determining the average photon number ratio of the photon states according to the respective average photon numbers of the photon states.

3. The photon intensity control method according to claim 1, characterized in that, The determining the average photon number ratio of the photon states according to the respective average photon numbers of the photon states includes: Determining the average photon number ratio of the photon states according to the respective average photon numbers of the photon states and the noise count.

4. The photon intensity control method according to claim 1, characterized in that After determining the average photon number ratio of the photon states according to the photon intensity of the photon states and the respective trigger numbers of the photon states, the photon intensity control method further includes: Determining the respective fluctuation ranges of the photon states according to the photon intensity of the photon states and the respective trigger numbers of the photon states; The determining the respective control signals of the photon states according to the average photon number ratio of the photon states includes: Determining the respective control signals of the photon states according to the average photon number ratio of the photon states and the respective fluctuation ranges of the photon states.

5. 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 that detects the photon intensity of the photon state with the first beam splitting ratio after being split by a beam splitter, where the photon state includes a signal state, a decoy state, and a vacuum state; A control module that determines the average photon number ratio of the photon states according to the photon intensity of the photon states and the respective trigger numbers of the photon states; The control module determines the respective control signals of the photon states according to the average photon number ratio of the photon states; An adjustment circuit module that, in response to the respective control signals of the photon states, controls the photon intensity of the photon state with the second beam splitting ratio after being split by the beam splitter to control the BB84 decoy state quantum key distribution system according to the photon intensity of the photon state with the second beam splitting ratio.

6. The photon intensity control device according to claim 5, wherein, The control module determines the respective average photon numbers of the photon states according to the photon intensity of the photon states and the respective trigger numbers of the photon states; The control module determines the average photon number ratio of the photon states according to the respective average photon numbers of the photon states.

7. The photon intensity control device according to claim 5, characterized in that The control module determines the average photon number ratio of the photon states according to the average photon numbers and noise counts of the respective photon states.

8. The photon intensity control device according to claim 5, characterized in that, The control module determines the respective fluctuation ranges of the photon states according to the photon intensities of the photon states and the respective trigger numbers of the photon states; The control module determines the respective control signals of the photon states according to the average photon number ratio of the photon states and the respective fluctuation ranges of the photon states.

9. The photon intensity control device according to claim 5, characterized in that, The photon detection module is a single-photon detector.

10. The photon intensity control device according to claim 9, characterized in that, 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, 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.

Images