A dual-field quantum key distribution method and system

Abstract

This invention discloses a dual-field quantum key distribution method, comprising: transmitting a first optical signal generated by a first transmitter to a detector via a first channel; and transmitting a second optical signal generated by a second transmitter to a detector via a second channel. The first and second optical signals include a quantum frame portion for encoding and a reference frame portion not used for encoding. The quantum frame portion includes an X basis vector and a Z basis vector representing the original key. The first and second optical signals are processed by the detector to obtain single-photon detection information of the optical signals and a global phase difference of the quantum frames. The global phase difference is then transmitted to the first and second transmitters via an authenticated classical channel. Based on the global phase difference and the single-photon detection information of the optical signals, the first and second transmitters respectively process their respective random numbers to obtain a secure shared key. This invention also discloses a dual-field quantum key distribution system.

Description

Technical Field

[0001] This invention relates to the field of quantum key distribution, and in particular to a two-field quantum key distribution method, electronic device, and storage medium. Background Technology

[0002] Quantum Key Distribution (QKD) utilizes the properties of quantum mechanics to ensure communication security. It enables both parties in a communication to generate and share a random, secure key to encrypt and decrypt messages. QKD has gained increasing attention from researchers due to its unconditional security. It solves the security problem of key distribution and, combined with one-time pad encryption, guarantees unconditional secure communication between the two parties. Therefore, this technology can be widely used in highly confidential organizations.

[0003] Since the first QKD protocol was developed, long-distance communication using QKD has been a key focus and challenge in the field of quantum communication. Because the security of QKD stems from the no-cloning principle, it cannot utilize optical amplifiers for signal amplification as in classical communication. Therefore, the photon signal transmitted from one side will inevitably attenuate as the channel length increases. Researchers in this field have provided an upper bound for the key generation rate R in relay-free point-to-point QKD with respect to the channel transmittance η. When the distance is relatively long, i.e., η << 1, This theoretically limits the maximum communication distance achievable by practical QKD. Related experiments also show that in a measurement-device-independent QKD experiment at 404 km, the data accumulation time was as long as 3 months, with a code rate of only 3.2 × 10⁻⁶. -4 The bps value illustrates the difficulty of implementing long-distance QKD.

[0004] In recent years, to address the challenges of long-distance quantum communication using QKD, researchers in this field have proposed a novel QKD protocol, namely the dual-field quantum key distribution protocol; the key generation rate of this protocol is [not specified]. It is expected to double the coding distance of existing QKD. Meanwhile, dual-field QKD possesses the characteristic of being measurement-device independent. With the help of dual-field QKD, the number of trusted relays in trusted relay schemes can be significantly reduced, and the coding rate is also improved by an order of magnitude over the same distance (>300km). However, quantum communication schemes based on dual-field quantum key distribution protocols require the use of light source phase-locked loop (PLL) technology and fiber optic phase compensation technology. Existing PLL technologies require the establishment of additional servo channels for transmitting phase-locked light, and the user-held transmitter requires an additional PLL device, which greatly limits the practical development of dual-field QKD. Summary of the Invention

[0005] In view of the above problems, the present invention provides a dual-field quantum key distribution method and system, which aims to solve at least one of the above problems.

[0006] According to a first aspect of the present invention, a dual-field quantum key distribution method is provided, comprising:

[0007] A first optical signal generated by a first transmitter is transmitted to a probe via a first channel, and a second optical signal generated by a second transmitter is transmitted to the probe via a second channel. The first and second transmitters have optical fields with random phases, which are determined based on random numbers held by each. The first and second optical signals include a quantum frame portion for encoding and a reference frame portion not used for encoding. The quantum frame portion includes an X basis vector and a Z basis vector representing the original key.

[0008] The first optical signal and the second optical signal are processed by the detection end to obtain the single-photon detection information of the optical signal and the global phase difference of the quantum frame, and the global phase difference is sent to the first transmitter and the second transmitter through the certified classical channel.

[0009] Based on the global phase difference and the single-photon detection information of the optical signal, the first transmitter and the second transmitter respectively perform key filtering, key error correction and key privacy amplification on the random numbers they hold to obtain a secure shared key.

[0010] According to an embodiment of the present invention, based on the aforementioned global phase difference and the single-photon detection information of the aforementioned optical signal, the first transmitting end and the second transmitting end respectively perform key filtering, key error correction, and key privacy amplification on the random numbers they hold to obtain a secure shared key, including:

[0011] Based on the single-photon detection information of the reference frame portion, the detection end performs frequency recovery on the single-frequency beat frequency signal and recovers the initial phase of the first optical signal and the second optical signal to obtain the global phase difference between the first optical signal and the second optical signal. The single-photon detection information of the optical signal includes the single-photon detection information of the reference frame portion and the single-photon detection information of the quantum frame portion.

[0012] The first transmitter and the second transmitter respectively filter the random numbers they hold based on the single-photon detection information of the quantum frame portion and the global phase difference to obtain the original key. They then use the global phase difference to filter the original key, correct key errors, and amplify key privacy to obtain a secure shared key.

[0013] According to an embodiment of the present invention, based on the single-photon detection information of the reference frame portion, the detection end performs frequency recovery on the single-frequency beat frequency signal and recovers the initial phase of the first optical signal and the second optical signal to obtain the global phase difference between the first optical signal and the second optical signal, including:

[0014] The first transmitting end and the second transmitting end respectively perform numerical conversion on the single-photon detection information of the reference frame portion to obtain the numerical conversion result;

[0015] According to the preset sampling time window, the first transmitting end and the second transmitting end respectively sample the numerical conversion result and perform calculations on the sampled result to obtain a discrete array;

[0016] According to preset conditions, the above-mentioned detection end preprocesses the above-mentioned discrete values, and performs Fourier transform on the above-mentioned preprocessing results to obtain the spectrum of the above-mentioned single-frequency beat frequency signal.

[0017] According to the preset screening conditions, the detection end filters the spectrum of the single-frequency beat frequency signal and obtains the global phase difference between the first optical signal and the second optical signal based on the screening results and the initial phase of the first optical signal and the second optical signal.

[0018] According to an embodiment of the present invention, the preprocessing of the discrete values ​​by the detection end according to preset conditions includes:

[0019] If the amount of data information in the discrete array is insufficient to obtain the beat frequency signal of the single frequency and the initial phase of the first optical signal and the second optical signal, the detection end merges the single-photon detection information of the reference frame portion of other time windows in order to increase the amount of data information in the discrete array.

[0020] If the length of the discrete array is less than the preset length, the probe performs zero-padding on the discrete array.

[0021] According to an embodiment of the present invention, the above-mentioned preset screening conditions are determined by the following formula:

[0022] |cos(2πνt+φ0+(φ a -φ b ))|≥Δ

[0023] Where v represents the frequency of the single-frequency beat signal, φ0 is the initial phase difference between the first optical signal and the second optical signal, and φ a and φ b These represent the random phases of the first and second transmitters, respectively, and Δ is a parameter obtained based on code rate optimization.

[0024] According to an embodiment of the present invention, the first transmitting end and the second transmitting end respectively filter the random numbers they hold based on the single-photon detection information of the quantum frame portion and the global phase difference to obtain the original key, and respectively use the global phase difference to filter the original key, correct key errors, and amplify key privacy to obtain a secure shared key, including:

[0025] The aforementioned detectors publish single-photon response events through the aforementioned certified classical channels;

[0026] Based on the above single-photon response event, the first transmitter filters its own basis information and the basis information corresponding to the second optical signal, and retains the random number corresponding to the part of the two basis information that is the same as the original key.

[0027] Based on the aforementioned single-photon response event, the second transmitting end filters its own basis information with the published basis information corresponding to the first optical signal, and retains the random number corresponding to the part of the two basis information that is the same as the original key.

[0028] The first transmitter and the second transmitter respectively use the global phase difference to filter their respective basis vector information to obtain data for parameter estimation;

[0029] The first and second sending ends respectively calculate the preset security key amount using the data used for parameter estimation;

[0030] The first sending end and the second sending end respectively use the preset security key amount to perform error correction and privacy amplification on the original key to obtain the secure shared key.

[0031] According to a second aspect of the present invention, a dual-field quantum key distribution system is provided, which is applied to a dual-field quantum key distribution method, including a first transmitting end, a second transmitting end, and a detector end;

[0032] The first transmitting end and the second transmitting end have the same structure, including a quantum random number generator, a light source, a phase modulator, an intensity modulator, and an optical attenuator;

[0033] The aforementioned detection end includes a polarization controller, a dense wavelength division multiplexer, a polarization beam splitter, a beam splitter with a preset splitting ratio, and a single-photon detector.

[0034] According to an embodiment of the present invention, the light source generator of the first transmitting end generates continuous weak coherent light to obtain an optical signal for encoding;

[0035] The first intensity modulator at the first transmitting end performs chopping processing on the optical signal to obtain a pulsed optical signal for quantum key distribution;

[0036] The second intensity modulator at the first transmitting end performs decoy-state intensity random modulation on the pulsed optical signal to obtain the intensity of the pulsed optical signal with multiple amplitude values;

[0037] The third intensity modulator of the first transmitting end decomposes the pulsed optical signal in the time domain to obtain the phase reference frame and quantum frame of the pulsed optical signal.

[0038] According to the preset optical signal amplitude range and the preset number of equal divisions, the first phase modulator and the second phase modulator of the first transmitting end perform phase randomization and phase encoding on the pulse optical signal to obtain a pulse optical signal with intensity and phase encoding.

[0039] The attenuator at the first transmitting end attenuates the pulsed optical signal with intensity and phase encoding to obtain a first optical signal at the single-photon level.

[0040] According to an embodiment of the present invention, the polarization controller of the above-mentioned detection end performs polarization reference system alignment processing on the first optical signal and the second optical signal, wherein the first optical signal is generated by the first transmitting end and the second optical signal is generated by the second transmitting end;

[0041] The polarization beam splitter at the above-mentioned detection end splits the first optical signal and the second optical signal after alignment processing respectively to obtain the first part and the second part of the first optical signal after alignment processing, as well as the first part and the second part of the second optical signal after alignment processing.

[0042] The photodetector at the detection end measures the first part of the first optical signal after alignment processing and the first part of the second optical signal after alignment processing, and feeds back the detection results to the polarization controller at the detection end.

[0043] The beam splitter with a preset splitting ratio at the above-mentioned detection end performs interference processing on the second part of the first optical signal after alignment processing and the second part of the second optical signal after alignment processing, respectively, to obtain interference results;

[0044] The single-photon detectors at the aforementioned detection ends detect the aforementioned interference results, obtain single-photon detection information, and transmit the obtained single-photon detection information to the aforementioned first transmitting end and the aforementioned second transmitting end through the certified classical channel.

[0045] According to an embodiment of the present invention, the detection events obtained by the single-photon detector at the detection end are used for coding, and the detection events obtained by the photodetector at the detection end are used for polarization feedback and delay alignment.

[0046] The dual-field quantum key distribution method and system provided by this invention, compared with the existing dual-field QKD method, reduces the system complexity and cost caused by the phase-locked light source in traditional dual-field QKD, eliminates the need for an additional phase-locked optical path, reduces the demand for optical fiber channels, and is easy to expand; at the same time, the frequency and phase estimation algorithm based on fast Fourier transform can obtain a higher signal-to-noise ratio with small samples, which is conducive to achieving fast and accurate frequency estimation; in addition, there is no need to perform phase modulation and chopping on the phase reference light, which reduces the modulation complexity and the peak power of the reference light, and helps to reduce scattering noise. Attached Figure Description

[0047] Figure 1 This is a flowchart of a dual-field quantum key distribution method according to an embodiment of the present invention;

[0048] Figure 2 This is a flowchart of obtaining a secure shared key according to an embodiment of the present invention;

[0049] Figure 3 This is a flowchart of obtaining the global phase difference according to an embodiment of the present invention;

[0050] Figure 4 This is a data processing flowchart for obtaining the global phase difference according to an embodiment of the present invention;

[0051] Figure 5 This is a flowchart of the basis vector alignment according to an embodiment of the present invention;

[0052] Figure 6 This is a schematic diagram of the structure of a dual-field quantum key distribution system according to an embodiment of the present invention. Detailed Implementation

[0053] To make the objectives, technical solutions, and advantages of the present invention clearer, the present invention will be further described in detail below with reference to specific embodiments and accompanying drawings.

[0054] The technical difficulty of dual-field QKD experiments is much higher than that of traditional point-to-point QKD, and there is still a certain distance to go before it can be truly put into practical use. The biggest difficulty in dual-field QKD experiments lies in the single-photon interference between two independent light sources, which requires the following two conditions to be met: (1) The phases of the two light sources need to be correlated. At present, the main way to achieve phase correlation is through laser phase locking, including optical phase-locked loops, time-frequency transfer technology, and injection locking technology. Among them, time-frequency transfer technology requires an ultra-stable cavity and has a high technical difficulty; injection locking technology is less difficult, but because it directly controls the phase of the internal light source through the external light source, there is a large risk to its actual security; while optical phase-locked loop technology has moderate difficulty and does not have the above-mentioned security risks; (2) The phase change after transmission through optical fiber can be estimated or compensated. In order to compensate for the influence of optical fiber on the phase, there are two schemes: real-time compensation and post-selection. These two schemes divide the transmitted pulse light into phase reference light and quantum light for coding. In order to accumulate enough counts in a short time, the intensity of the reference light is large. The real-time compensation scheme uses a phase modulator at the detector end to ensure the phase reference light is always in a fully constructive state, establishing the same phase reference frame between the two transmitters and the detector. Phase selection does not require real-time feedback; instead, the phase difference of the phase reference light is estimated during post-processing, achieving the same compensation purpose. Existing technologies offer a scheme for wavelength division multiplexing of the phase reference strong light and quantum light, reducing fiber scattering noise of the phase reference strong light and further improving the coding distance.

[0055] In summary, light source phase-locked loop (PLL) technology and fiber optic phase compensation technology are the key technologies and core challenges of dual-field QKD experimental schemes. Existing PLL technologies all require the establishment of additional servo channels for transmitting phase-locked light, and the user-owned transmitter needs an additional PLL device, which greatly limits the practical development of dual-field QKD.

[0056] To address the practical challenges of phase-locked loop (PLL) in dual-field QKD, this invention proposes a phase-locked dual-field QKD scheme. This scheme reduces the complexity of the dual-field QKD transmitter device and the use of optical fiber channels, expanding its application scenarios, such as integrated chip transmitters and free-space dual-field QKD. This further promotes the practical application of dual-field QKD and provides a feasible technical route for long-distance QKD.

[0057] The user end, or transmitter, comprises a light source, a quantum random number generator, a phase modulator, an intensity modulator, and an attenuator. The light source generates continuous, weakly coherent light, which is then chopped by the first intensity modulator. The second intensity modulator performs decoy state modulation, generating random intensity levels. The third intensity modulator divides the transmitted light into a phase reference frame and a quantum frame in the time domain. The first and second phase modulators are used together for phase randomization and phase encoding. The attenuator reduces the light intensity to the single-photon level. The transmitted quantum state is transmitted through a single-mode fiber to the detector end for interference and single-photon detection.

[0058] The detection end includes an electrically controlled polarization controller, a dense wavelength division multiplexer, a polarization beamsplitter, a 50:50 beam splitter, and single-photon detectors. Detection events from the first and second single-photon detectors are used for coding. Detection events from the third and fourth single-photon detectors are used for polarization feedback and delay alignment. The user filters, corrects errors, and amplifies the privacy of the original key according to the QKD protocol, ultimately generating a secure shared key.

[0059] Figure 1 This is a flowchart of a dual-field quantum key distribution method according to an embodiment of the present invention.

[0060] like Figure 1 As shown, the above-mentioned dual-field quantum key distribution method includes operations S110 to S130.

[0061] In operation S110, a first optical signal generated by a first transmitter is sent to the detector via a first channel, and a second optical signal generated by a second transmitter is sent to the detector via a second channel. The first transmitter and the second transmitter have optical fields with random phases, which are determined according to random numbers held by each. The first optical signal and the second optical signal include a quantum frame portion for coding and a reference frame portion not used for coding. The quantum frame portion includes an X basis vector and a Z basis vector representing the original key.

[0062] The dual-field quantum key distribution method provided by this invention requires two transmitters and one detector. The two transmitters are held by two users who need to establish a shared key. Each transmitter sends a strength- and phase-encoded quantum state to the detector for single-photon detection. This quantum state can be a first optical signal and a second optical signal corresponding to the first and second transmitters, respectively. The quantum state consists of a quantum frame and a reference frame. The X basis vector in the quantum frame is used to filter valid single-photon response events (detection results), while the Z basis vector in the quantum frame is used by the transmitter to generate the final secure key based on the detection results through a dual-field QKD protocol, including filtering, error correction, and privacy amplification.

[0063] The two user ends, i.e., the transmitting ends, include components such as a light source, a quantum random number generator, a phase modulator, an intensity modulator, and an attenuator. The light source generates continuous, weakly coherent light, which is then chopped by the first intensity modulator. The second intensity modulator performs decoy state modulation, generating random intensity levels of various amplitudes. The third intensity modulator divides the transmitted light into a phase reference frame and a quantum frame in the time domain. The first and second phase modulators are used together for phase randomization and phase encoding. The attenuator reduces the light intensity to the single-photon level. The transmitted quantum state is transmitted through a single-mode fiber (either the first or second channel) to the detector end for interference and single-photon detection. The quantum random number generator produces random numbers, which can be used to determine the optical field at the transmitting end and generate the original key, such as the intensity and phase modulation magnitude of the transmitting end.

[0064] The optical signals transmitted by the two transmitters contain intensity and phase information. The reference frame uses continuous light and requires no intensity or phase modulation. The transition region uses pulse modulation but not phase modulation. The quantum frame performs both intensity and phase modulation simultaneously. The intensity and phase modulation are determined by random numbers generated by quantum random number generators in both the first and second transmitters; these random numbers are generated independently of each other.

[0065] In operation S120, the first optical signal and the second optical signal are processed by the detection end to obtain the single-photon detection information of the optical signal and the global phase difference of the quantum frame, and the global phase difference is sent to the first transmitter and the second transmitter through the certified classical channel.

[0066] The aforementioned detection end includes an electrically controlled polarization controller, a dense wavelength division multiplexer, a polarization beamsplitter, a beamsplitter with a preset splitting ratio (e.g., 50:50 splitting ratio), and single-photon detectors. Detection events from the first and second single-photon detectors are used for coding. Detection events from the third and fourth single-photon detectors are used for polarization feedback and delay alignment.

[0067] In operation S130, based on the global phase difference and single-photon detection information of the optical signal, the first transmitter and the second transmitter respectively perform key filtering, key error correction and key privacy amplification on the random numbers they hold to obtain a secure shared key.

[0068] Based on the QKD protocol, the user end filters, corrects errors, and amplifies the privacy of the original key according to the global phase difference and single-photon detection information of the optical signal, and finally generates a secure shared key. The original key includes Z basis vectors determined by the random number held.

[0069] The dual-field quantum key distribution method and system provided by this invention, compared with the existing dual-field QKD method, reduces the system complexity and cost caused by the phase-locked light source in traditional dual-field QKD, eliminates the need for an additional phase-locked optical path, reduces the demand for optical fiber channels, and is easy to expand; at the same time, the frequency and phase estimation algorithm based on fast Fourier transform can obtain a higher signal-to-noise ratio with small samples, which is conducive to achieving fast and accurate frequency estimation; in addition, there is no need to perform phase modulation and chopping on the phase reference light, which reduces the modulation complexity and the peak power of the reference light, and helps to reduce scattering noise.

[0070] Figure 2 This is a flowchart of obtaining a secure shared key according to an embodiment of the present invention.

[0071] like Figure 2 As shown, based on the global phase difference and single-photon detection information of the optical signal, the first transmitter and the second transmitter respectively perform key filtering, key error correction and key privacy amplification on the random numbers they hold to obtain a secure shared key, including operations S310 to S320.

[0072] In operation S310, based on the single-photon detection information of the reference frame portion, the detection end performs frequency recovery on the single-frequency beat frequency signal and recovers the initial phase of the first optical signal and the second optical signal to obtain the global phase difference between the first optical signal and the second optical signal. The single-photon detection information of the optical signal includes the single-photon detection information of the reference frame portion and the single-photon detection information of the quantum frame portion.

[0073] In operation S320, the first and second transmitters respectively filter the random numbers they hold based on the single-photon detection information and global phase difference of the quantum frame portion to obtain the original key. They then use the global phase difference to filter the original key, correct key errors, and amplify key privacy to obtain a secure shared key.

[0074] By using the above method, the random numbers held by each of the two sending ends are filtered to generate the original key. The original key is then filtered, corrected, and its privacy is amplified to obtain a secure shared key.

[0075] The key to the secure shared key acquisition process described above lies in key screening, which includes basis vector matching and frequency and phase recovery.

[0076] The following is combined Figure 3 and Figure 4 The process of frequency and phase recovery is explained in detail.

[0077] Figure 3 This is a flowchart for obtaining the global phase difference according to an embodiment of the present invention.

[0078] like Figure 3 As shown, based on the single-photon detection information of the reference frame portion, the detection end performs frequency recovery on the single-frequency beat frequency signal and recovers the initial phase of the first optical signal and the second optical signal to obtain the global phase difference between the first optical signal and the second optical signal, including operations S410 to S440.

[0079] In operation S410, the first transmitter and the second transmitter respectively perform numerical conversion on the single-photon detection information of the reference frame portion to obtain the numerical conversion result.

[0080] During operation S420, according to the preset sampling time window, the first and second transmitting ends sample the numerical conversion results respectively, and perform calculations on the sampled results to obtain a discrete array.

[0081] During operation of S430, the detector preprocesses the discrete values ​​according to preset conditions, and performs Fourier transform on the preprocessing results to obtain the spectrum of the single-frequency beat frequency signal.

[0082] During operation of S440, the detector end filters the spectrum of the single-frequency beat frequency signal according to the preset filtering conditions, and obtains the global phase difference between the first optical signal and the second optical signal based on the filtering results and the initial phase of the first optical signal and the second optical signal.

[0083] According to an embodiment of the present invention, the preprocessing of discrete values ​​by the detection end according to preset conditions includes:

[0084] When the amount of data information in the discrete array is insufficient to obtain the beat frequency signal and the initial phase of the first and second optical signals, the detector end merges the single-photon detection information of the reference frame portion of other time windows in order to increase the amount of data information in the discrete array.

[0085] If the length of the discrete array is less than the preset length, the probe will pad the discrete array with zeros.

[0086] According to an embodiment of the present invention, the above-mentioned preset screening conditions are determined by formula (1):

[0087] |cos(2πνt+φ0+(φ a -φ b ))|≥Δ (1),

[0088] Where v represents the frequency of the single-frequency beat signal, φ0 is the initial phase difference between the first and second optical signals, and φ a and φ b These represent the phases of the first and second transmitters, respectively. Δ is a parameter obtained through code rate optimization, and here it can be taken as... The global phase difference is 2πνt+φ0.

[0089] The reference frame is used to recover the phase difference between the optical fields transmitted by the two transmitters when they interfere at the first optical beam splitter at the detector. The reference frame is not used for coding, while the quantum frame is used for coding. The phase recovered by the reference frame affects the filtering of the original key in the manner shown in Equation (1), and obtains valid X basis events (i.e., single-photon response events).

[0090] Figure 4 This is a data processing flowchart for obtaining the global phase difference according to an embodiment of the present invention.

[0091] Transmitter A (i.e., the first transmitter mentioned above) and transmitter B (i.e., the second transmitter mentioned above) recover the initial phase between the optical signals of the two transmitters based on the single-photon detection information within the reference frame. Within a short time, such as 5 μs, light source 1 in transmitter A and light source 12 in transmitter B can be considered stable. Therefore, the global phase difference between the two optical signals can be considered as a single-frequency beat frequency signal. By recovering the frequency and initial phase of the beat frequency signal based on the single-photon detection information within the reference frame, the global phase difference between the entire reference frame and the quantum frame can be obtained. The specific process is as follows: Figure 4 As shown. First, transmitters A and B convert the single-photon detection information in all reference frames into an easily processed numerical form x. i If in t i If the response of the first single-photon detector at the time-sensing end is given, then x is taken. i =1; if at t i The response of the second single-photon detector at the time detection end is taken as x. i =-1. Then, transmitter A and transmitter B select a suitable sampling time window size T, and add together the single-photon detection event information at different times within the same time window to obtain a discrete array, as shown in formula (2):

[0092]

[0093] To further increase the accuracy of frequency and phase recovery and reduce phase estimation errors and the corresponding error rate, X can be... k Selective preprocessing is performed. First, determine X. k If the data within the frame is insufficient to recover the accurate frequency and phase, then X can be increased by merging single-photon detection information from multiple reference frames. k The amount of data within. Next, determine X. k Is the data length sufficient, if X k If the data length is insufficient, you can add zeros at the end to increase the value by X. k The data length is increased, thereby increasing the spectral resolution of the recovered image. Finally, for X... kPerforming a Fourier transform yields the spectrum of the beat frequency signal, from which the frequency component with the largest amplitude can be selected as the frequency recovery result. The argument corresponding to the amplitude is used as the initial phase recovery result. Thus, the global phase reference is finally obtained, as shown in formula (3):

[0094]

[0095] Figure 5 This is a flowchart of the basis vector alignment according to an embodiment of the present invention.

[0096] like Figure 5 As shown, the first and second transmitters respectively filter the random numbers they hold based on the single-photon detection information and global phase difference of the quantum frame portion to obtain the original key, and respectively use the global phase difference to filter the original key, correct the key error and amplify the key privacy to obtain a secure shared key, including operations S610 to S660.

[0097] When operating the S610, the detector publishes single-photon response events through a certified classical channel.

[0098] In operation of S620, based on the single-photon response event, the first transmitter filters its own basis information with the published basis information corresponding to the second optical signal, and retains the random number corresponding to the part that is the same in the two basis information (e.g., two Z basis vectors) as the original key.

[0099] In operation S630, based on the single-photon response event, the second transmitter filters its own basis information with the published basis information corresponding to the first optical signal, and retains the random number corresponding to the part that is the same in the two basis information (e.g., two Z basis vectors) as the original key.

[0100] In operation S640, the first and second transmitters respectively use the global phase difference to filter their respective basis vector information to obtain data for parameter estimation.

[0101] In operation S650, the first and second transmitters respectively calculate the preset security key amount using the data used for parameter estimation.

[0102] When operating the S660, the first and second transmitting ends respectively use a preset amount of security key to perform error correction and privacy amplification on the original key to obtain a secure shared key.

[0103] In the aforementioned basis vector matching process, sender A (i.e., the first sender) and sender B (i.e., the second sender) publicly disclose single-photon response events through an authenticated classical channel, and obtain the corresponding original key and data for parameter estimation. The expected amount of secure keys to be generated is calculated through parameter estimation, and the original key undergoes error correction and privacy amplification to ultimately generate a secure shared key. The specific key selection, error correction, and privacy amplification processes are related to the actual implementation of the dual-field QKD protocol; here, the send-no-send (SNS-dual-field QKD) protocol is used as an example for explanation.

[0104] In the SNS-Dual-Field QKD protocol, both sender A (the first sender mentioned above) and sender B (the second sender mentioned above) retain the random codes corresponding to the probe events for which they both choose the Z basis vector as the original key. Sender A (and sender B) treats the vacuum state (non-vacuum state) as bit 0 (bit 1), and the non-vacuum state (vacuum state) as bit 1 (bit 0). Both sender A and sender B use the phase modulation selection φ corresponding to the probe events for which they both choose the X basis vector. a (φ b This is made public for parameter estimation to calculate the amount of leaked information and the expected amount of secure keys that can be generated. During parameter estimation, sender A and sender B select probe events for which they both choose the X basis vector and use the same intensity modulation. Further, based on the global phase reference recovered from the reference frame... And according to the conditions shown in formula (4):

[0105]

[0106] Valid X basis events were obtained through screening, where φ a (φ b The phase modulation selections for transmitters A and B are respectively. In a valid X-basis event, the first single-photon detector at the detector responds and Or the second single-photon detector at the detection end responds and For each correct event, the others are considered incorrect events. Based on the number of correct and incorrect events in the valid X-basis events, and combined with the single-photon detection information corresponding to each intensity combination of the Z-basis and X-basis, sender A and sender B perform finite code length analysis and parameter estimation to obtain the secure single-photon contribution and the corresponding single-photon phase error rate, thereby calculating the expected amount of secure key that can be generated. Then, sender A and sender B, based on the parameter estimation results, perform error correction and privacy amplification on the retained original Z-basis key, ultimately generating a secure shared key.

[0107] According to a second aspect of the present invention, a dual-field quantum key distribution system is provided, which is applied to the above-described dual-field quantum key distribution method, characterized in that it includes a first transmitting end, a second transmitting end, and a detecting end;

[0108] The first and second transmitters have the same structure, including a quantum random number generator, a light source, a phase modulator, an intensity modulator, and an optical attenuator.

[0109] The detection end includes a polarization controller, a dense wavelength division multiplexer, a polarization beam splitter, a beam splitter with a preset splitting ratio, and a single-photon detector.

[0110] According to an embodiment of the present invention, the light source generator at the first transmitting end generates continuous weak coherent light to obtain an optical signal for encoding;

[0111] The first intensity modulator at the first transmitting end performs chopping on the optical signal to obtain a pulsed optical signal for quantum key distribution;

[0112] The second intensity modulator at the first transmitting end performs decoy state intensity random modulation on the pulsed optical signal to obtain the intensity of the pulsed optical signal with multiple amplitude values;

[0113] The third intensity modulator at the first transmitter decomposes the pulsed optical signal in the time domain to obtain the phase reference frame and quantum frame of the pulsed optical signal;

[0114] According to the preset optical signal amplitude range and the preset number of equal divisions, the first phase modulator and the second phase modulator of the first transmitting end perform phase randomization and phase encoding on the pulse optical signal to obtain a pulse optical signal with intensity and phase encoding.

[0115] The attenuator at the first transmitting end attenuates the pulsed optical signal with intensity and phase encoding to obtain a first optical signal at the single-photon level.

[0116] According to an embodiment of the present invention, the polarization controller at the detection end performs polarization reference system alignment processing on the first optical signal and the second optical signal, wherein the first optical signal is generated by the first transmitting end and the second optical signal is generated by the second transmitting end;

[0117] The polarization beam splitter at the detector end splits the aligned first optical signal and the aligned second optical signal into beams, respectively, to obtain the first part and the second part of the aligned first optical signal, as well as the first part and the second part of the aligned second optical signal.

[0118] The photodetector at the detection end measures the first part of the first optical signal after alignment and the first part of the second optical signal after alignment, and feeds back the detection results to the polarization controller at the detection end.

[0119] The beam splitter with a preset splitting ratio at the detector end performs interference processing on the second part of the aligned first optical signal and the second part of the aligned second optical signal respectively to obtain the interference result;

[0120] The single-photon detectors at the detection end detect the interference results, obtain single-photon detection information, and send the obtained single-photon detection information to the first and second transmitters through a certified classical channel.

[0121] According to an embodiment of the present invention, the detection events obtained by the single-photon detector at the detection end are used for coding, and the detection events obtained by the photodetector at the detection end are used for polarization feedback and delay alignment.

[0122] To better assist those skilled in the art in understanding the aforementioned dual-field quantum key distribution system, this invention combines... Figure 6 The above-described dual-field quantum key distribution system will be described in further detail.

[0123] Figure 6 This is a schematic diagram of the structure of a dual-field quantum key distribution system according to an embodiment of the present invention.

[0124] like Figure 6 As shown, the aforementioned dual-field quantum key distribution system includes transmitter A, transmitter B, and detector C. Transmitters A and B each include a light source, an intensity modulator, a phase modulator, and an optical attenuator. Taking transmitter A transmitting optical quantum signals as an example, the light source 1 of transmitter A generates continuous weakly coherent light. The optical signal used for encoding is chopped by the first intensity modulator 2 of transmitter A to obtain pulsed optical signals for quantum key distribution. The second intensity modulator 3 of transmitter A performs decoy state intensity modulation, randomly modulating to obtain multiple amplitudes. The third intensity modulator 4 of transmitter A divides the time domain into a phase reference frame and a quantum frame. Then, the optical signal undergoes phase randomization and phase encoding within the range of 0-2π in 16 equal parts by the first phase modulator 5 and the second phase modulator 6 of transmitter A, and is attenuated to the single-photon level by the attenuator 7 of transmitter A. The modulated optical signal is then transmitted through the first channel 8. The transmitter B has the same device structure as the transmitter A, including a light source 12, a first intensity modulator 13, a second intensity modulator 14, a third intensity modulator 15, a first phase modulator 16, a second phase modulator 17, and an attenuator 18. The generated photons are sent to the detector C through the second channel 19.

[0125] Photons emitted by transmitters A and B are detected at detector C via channels 8 and 19, respectively, and their polarization reference frames are aligned by a first polarization controller 9 and a second polarizer 20. The two optical signals are then split into two parts by a first polarization beamsplitter 10 and a second polarization beamsplitter 21. A small portion is measured by a first photodetector 11 and a second photodetector 22, and the measurement result is fed back to the first polarization controller 9 and the second polarizer 20 to compensate for random polarization drift in the optical fiber. The remaining portion of the two optical signals is interfered with by a 50:50 optical beamsplitter 23 and then detected by a first single-photon detector 24 and a second single-photon detector 25. The measured single-photon detection information is sent to transmitters A and B via an authenticated classical channel. Transmitters A and B perform key filtering, error correction, and privacy amplification on the original key according to the QKD protocol, ultimately generating a secure shared key.

[0126] The above specific embodiments further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above are merely specific embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A dual-field quantum key distribution method, characterized in that, include: A first optical signal generated by a first transmitter is transmitted to a probe via a first channel, and a second optical signal generated by a second transmitter is transmitted to the probe via a second channel. The first transmitter and the second transmitter have optical fields with random phases, which are determined according to random numbers held by each. The first optical signal and the second optical signal include a quantum frame portion for coding and a reference frame portion not used for coding. The quantum frame portion includes an X basis vector and a Z basis vector representing the original key. The first optical signal and the second optical signal are processed by the detection end to obtain the single-photon detection information of the optical signal and the global phase difference of the quantum frame, and the global phase difference is sent to the first transmitter and the second transmitter through the certified classical channel; Based on the global phase difference and the single-photon detection information of the optical signal, the first transmitter and the second transmitter respectively perform key filtering on the random numbers they hold, and perform finite code length analysis and parameter estimation on the single-photon detection information corresponding to the X basis vector obtained by key filtering and the Z basis vector. Based on the obtained secure single-photon contribution and the corresponding single-photon phase error rate, the secure key quantity is calculated, and the secure key quantity is used to perform key error correction and key privacy amplification on the original key to obtain a secure shared key.

2. The method according to claim 1, characterized in that, Based on the global phase difference and the single-photon detection information of the optical signal, the first transmitter and the second transmitter respectively perform key filtering on their respective random numbers to conduct finite code length analysis and parameter estimation on the single-photon detection information corresponding to the X basis vector obtained by key filtering and the Z basis vector. Based on the obtained secure single-photon contribution and the corresponding single-photon phase error rate, the secure key quantity is calculated, and key error correction and key privacy amplification are performed to obtain a secure shared key, including: Based on the single-photon detection information of the reference frame portion, the detection end performs frequency recovery on the single-frequency beat frequency signal and recovers the initial phase of the first optical signal and the second optical signal to obtain the global phase difference between the first optical signal and the second optical signal. The single-photon detection information of the optical signal includes the single-photon detection information of the reference frame portion and the single-photon detection information of the quantum frame portion. The first transmitter and the second transmitter respectively filter the random numbers they hold based on the single-photon detection information of the quantum frame portion and the global phase difference to obtain the original key, and respectively use the global phase difference to filter the original key, correct key errors, and amplify key privacy to obtain a secure shared key.

3. The method according to claim 2, characterized in that, Based on the single-photon detection information of the reference frame portion, the detection end performs frequency recovery on the single-frequency beat frequency signal and recovers the initial phase of the first optical signal and the second optical signal to obtain the global phase difference between the first optical signal and the second optical signal, including: The first transmitting end and the second transmitting end respectively perform numerical conversion on the single-photon detection information of the reference frame portion to obtain the numerical conversion result; According to the preset sampling time window, the first transmitting end and the second transmitting end respectively sample the numerical conversion result and perform calculations on the sampling result to obtain a discrete array; According to preset conditions, the detection end preprocesses the discrete array and performs Fourier transform on the preprocessing result to obtain the spectrum of the single-frequency beat frequency signal; According to preset screening conditions, the detection end filters the spectrum of the single-frequency beat frequency signal, and obtains the global phase difference between the first optical signal and the second optical signal based on the screening results and the initial phase of the first optical signal and the second optical signal.

4. The method according to claim 3, characterized in that, According to preset conditions, the detection end preprocesses the discrete array, including: If the amount of data information in the discrete array is insufficient to obtain the beat frequency signal of the single frequency and the initial phase of the first optical signal and the second optical signal, the detection end merges the single-photon detection information of the reference frame portion of other time windows in order to increase the amount of data information in the discrete array; If the length of the discrete array is less than the preset length, the probe performs zero-padding on the discrete array.

5. The method according to claim 3, characterized in that, The preset screening conditions are determined by formula (1): （1）， in, This indicates the frequency of the single-frequency beat signal. It is the initial phase difference between the first optical signal and the second optical signal. and These represent the random phases of the first transmitter and the second transmitter, respectively. These parameters are obtained by optimizing the bitrate.

6. The method according to claim 2, characterized in that, The first and second transmitters, respectively, filter their random numbers based on the single-photon detection information of the quantum frame portion and the global phase difference to obtain the original key. They then utilize the global phase difference to filter, correct, and amplify the privacy of the original key, respectively, to obtain a secure shared key, including: The detector transmits a single-photon response event through the certified classical channel; Based on the single-photon response event, the first transmitting end filters its own basis information and the basis information corresponding to the second optical signal, and retains the random number corresponding to the part of the two basis information that is the same as the original key. Based on the single-photon response event, the second transmitting end filters its own basis information with the published basis information corresponding to the first optical signal, and retains the random number corresponding to the part of the two basis information that is the same as the original key. The first transmitting end and the second transmitting end respectively use the global phase difference to filter their respective basis vector information to obtain data for parameter estimation; The first and second sending ends respectively calculate a preset security key amount using the data used for parameter estimation; The first sending end and the second sending end respectively use the preset security key amount to perform error correction and privacy amplification on the original key to obtain the secure shared key.

7. A dual-field quantum key distribution system, applied to the method of any one of claims 1-6, characterized in that, Includes a first transmitter, a second transmitter, and a probe; The first transmitting end and the second transmitting end have the same structure, including a quantum random number generator, a light source, a phase modulator, an intensity modulator, and an optical attenuator; The detection end includes a polarization controller, a dense wavelength division multiplexer, a polarization beam splitter, a beam splitter with a preset splitting ratio, and a single-photon detector.

8. The system according to claim 7, characterized in that, The light source generator at the first transmitting end generates continuous weak coherent light to obtain an optical signal for encoding; The first intensity modulator at the first transmitting end performs chopping processing on the optical signal to obtain a pulsed optical signal for quantum key distribution; The second intensity modulator at the first transmitting end performs decoy state intensity random modulation on the pulsed optical signal to obtain the intensity of the pulsed optical signal with multiple amplitude values; The third intensity modulator at the first transmitting end decomposes the pulsed optical signal in the time domain to obtain the phase reference frame and quantum frame of the pulsed optical signal; According to the preset optical signal amplitude range and the preset number of equal divisions, the first phase modulator and the second phase modulator of the first transmitting end perform phase randomization and phase encoding on the pulse optical signal to obtain a pulse optical signal with intensity and phase encoding. The attenuator at the first transmitting end attenuates the pulsed optical signal with intensity and phase encoding to obtain a first optical signal at the single-photon level.

9. The system according to claim 7, characterized in that, The polarization controller at the detection end performs polarization reference system alignment processing on the first optical signal and the second optical signal, wherein the first optical signal is generated by the first transmitting end and the second optical signal is generated by the second transmitting end; The polarization beam splitter at the detection end splits the aligned first optical signal and the aligned second optical signal into beams, respectively, to obtain a first part of the aligned first optical signal and a second part of the aligned first optical signal, as well as a first part of the aligned second optical signal and a second part of the aligned second optical signal. The photodetector at the detection end measures the first part of the first optical signal after alignment and the first part of the second optical signal after alignment, and feeds back the detection results to the polarization controller at the detection end. The beam splitter with a preset splitting ratio at the detection end performs interference processing on the second part of the aligned first optical signal and the second part of the aligned second optical signal respectively to obtain the interference result; The single-photon detectors at the detection end detect the interference results respectively, obtain single-photon detection information, and send the obtained single-photon detection information to the first transmitter and the second transmitter through an authenticated classical channel.

10. The system according to claim 8, characterized in that, The detection events obtained by the single-photon detector at the detection end are used for coding, and the detection events obtained by the photodetector at the detection end are used for polarization feedback and delay alignment.

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