A method and system for self-referenced time synchronization of entanglement distribution networks

Abstract

The application discloses a self-reference time synchronization method and system for an entanglement distribution network, and relates to the technical field of quantum communication; the method comprises the following steps: acquiring real-time timestamp data of two single-photon detectors for two sites in the network which are paired to form Franson interference measurement branches, and collecting and generating a coincidence count histogram of a two-photon arrival time difference; dividing time windows corresponding to left and right edge peaks based on a preset arm length difference delay, calculating real-time estimation values of the center positions of the left and right edge peaks and a comprehensive clock-link delay between the two sites; performing translation compensation on original timestamps of any one site based on the comprehensive clock-link delay, and completing single time synchronization; and cyclically executing the above process, tracking changes in the comprehensive clock-link delay in real time, and ensuring that time synchronization is continuously effective. The method realizes high-precision time synchronization of a quantum entanglement distribution network without introducing classical noise and without additionally occupying fiber channel resources.

Description

Technical Field

[0001] This invention belongs to the field of quantum communication technology, specifically relating to a self-reference time synchronization method and system for entanglement distribution networks. Background Technology

[0002] Thanks to the inherent robustness of energy-time entanglement to fiber optic link loss and decoherence effects, energy-time entanglement-based quantum entanglement distribution networks have attracted widespread attention. Franson interference, a quantum interference phenomenon based on energy-time entanglement, plays a crucial role in quantum entanglement distribution networks. This interference scheme utilizes entangled photon pairs passed through two unequal-arm Mach-Zehnder interferometers, forming high-contrast interference fringes by precisely controlling the time delay between photons. In quantum entanglement distribution networks, entangled photon pairs need to be efficiently distributed to distant nodes to establish quantum channels, and Franson interference is the core tool for verifying whether these entangled pairs maintain quantum correlation. By analyzing interference visibility, the network system can monitor entanglement quality in real time, ensuring the reliability of the distribution process, which is crucial for applications such as quantum key distribution and long-range state transmission. In terms of security, the sensitivity of Franson interference means that any third-party eavesdropping attempt will disturb the system and reduce interference visibility, thus being detected immediately, which strengthens the unconditional security foundation of quantum communication.

[0003] Time synchronization is a prerequisite for achieving efficient quantum entanglement distribution, especially in field experiments. Differences in the reference clocks of two users located in different places, along with link transmission delays, will cause random fluctuations in the arrival time difference of the two photons, making stable interferometric measurements impossible. Current quantum entanglement distribution systems typically employ classical time synchronization schemes, which involve transmitting additional laser pulses through a separate optical fiber or by sharing an optical fiber with the quantum signal to achieve clock synchronization between the two locations.

[0004] However, the above-mentioned solutions have significant limitations: first, they require dedicated fiber optic resources, increasing the cost and complexity of network deployment; second, the additional laser pulses can interfere with the weak quantum signals, thereby reducing the performance of applications such as key distribution. Furthermore, classical time synchronization methods introduce additional noise sources, affecting the quality and stability of quantum entanglement distribution.

[0005] Therefore, there is an urgent need to develop a time synchronization technology that is highly compatible with existing energy-time entanglement distribution networks, so as to achieve high-precision time synchronization of quantum entanglement distribution networks without introducing classical noise or occupying additional fiber optic channel resources. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides a self-reference time synchronization method and system for entanglement distribution networks. In a first aspect, this invention proposes a self-reference time synchronization method for entanglement distribution networks, wherein the entanglement distribution network is an energy-time entanglement distribution network based on Franson interferometry, comprising an energy-time entangled photon source and multiple stations; the energy-time entangled photon source is connected to the multiple stations via fiber optic links; each station is equipped with an UMZI (Unbalanced Mach-Zehnder Interferometer), a single-photon detector, and a time-to-digital converter; any two stations are paired to form a Franson interferometric branch, and the UMZIs configured at the two stations in the same branch have the same fixed arm length difference time delay; the method includes the following steps: S1. For any two stations on a branch, obtain the timestamp data of the two single-photon detectors collected in real time by the time-to-digital converter configured at each station, and summarize them to generate a coincidence count histogram of the time difference of arrival of two photons. Among them, the histogram of coincidence counts shows a three-peak structure, namely the central interference main peak formed by the coherent superposition of the short arm path of two photons traveling in the same UMZI and the long arm path of two photons traveling in the same UMZI, and the left and right non-interference side peaks formed by the two types of paths, one photon traveling in the short arm and the other photon traveling in the long arm. S2. On the coincidence count histogram, the time window corresponding to the left and right non-interference side peaks is defined based on the preset arm length difference time delay; within the time window, the peak finding algorithm is used to calculate the real-time estimated value of the center position of the left and right non-interference side peaks respectively. S3. Calculate the combined clock-link delay between the two stations based on the real-time estimated values ​​of the center positions of the two non-interference side peaks on the left and right. S4. Based on the comprehensive clock-link delay, set the compensation amount, and perform translation compensation on the original timestamp of either of the two stations according to the compensation amount, so that the timestamps of the two stations are synchronized to the same time base, and complete a single time synchronization. S5. Repeatedly execute S1 to S4 to track the changes in the integrated clock-link delay in real time, so as to dynamically update the compensation amount and ensure that time synchronization is continuously effective.

[0007] Secondly, this invention proposes a self-reference time synchronization system for entanglement distribution networks, used to implement the method provided in the first aspect of this invention. The entanglement distribution network is an energy-time entanglement distribution network based on Franson interferometry, comprising an energy-time entangled photon source and multiple stations; the energy-time entangled photon source is connected to the multiple stations via fiber optic links; each station is equipped with a UMZI, a single-photon detector, and a time-to-digital converter; any two stations are paired to form a Franson interferometry branch, and the UMZIs configured at the two stations in the same branch have the same fixed arm length difference time delay; the system includes: The histogram generation unit is used to acquire the timestamp data of the two single-photon detectors collected in real time by the time-to-digital converters configured at each of the two stations of any branch, and to summarize and generate a coincidence count histogram of the time difference of arrival of two photons. The coincidence count histogram has a three-peak structure, namely the central interference main peak formed by the coherent superposition of the short arm path and the long arm path of the two photons traveling in the same UMZI, and the two non-interference side peaks formed by the two types of paths, one photon traveling in the short arm and the other photon traveling in the long arm. The first calculation unit is used to delineate the time windows corresponding to the left and right non-interference side peaks on the coincidence count histogram based on the preset arm length difference time delay; within the time window, the peak finding algorithm is used to calculate the real-time estimated values ​​of the center positions of the left and right non-interference side peaks respectively. The second calculation unit is used to calculate the integrated clock-link delay between the two stations based on the real-time estimated values ​​of the center positions of the left and right non-interference side peaks; The time synchronization unit is used to set the compensation amount based on the comprehensive clock-link delay, and to perform translation compensation on the original timestamp of either of the two stations according to the compensation amount, so that the timestamps of the two stations are synchronized to the same time base, thus completing a single time synchronization.

[0008] Thirdly, the present invention proposes an electronic device, including a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; Memory is used to store computer programs; The processor is used to execute a program stored in memory to implement the method steps provided in the first aspect of the present invention.

[0009] Fourthly, the present invention provides a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the method steps provided in the first aspect of the present invention.

[0010] Compared with the prior art, the beneficial effects of the present invention are as follows: The self-reference time synchronization method for entangled distribution networks provided by this invention first acquires real-time timestamp data of two single-photon detectors for two stations in any branch, and aggregates them to generate a coincidence count histogram of the two-photon arrival time difference. Then, based on a preset arm length difference delay, time windows corresponding to the left and right non-interference peaks are defined on this coincidence count histogram. Within these time windows, a peak-finding algorithm is used to calculate the real-time estimates of the center positions of the left and right non-interference peaks. Next, the combined clock-link delay between the two stations is calculated based on the real-time estimates of the center positions of the left and right non-interference peaks. Finally, a compensation amount is set based on the combined clock-link delay to shift and compensate the original timestamp of either station, synchronizing the timestamps of the two stations to the same time base, thus completing a single time synchronization. By repeatedly executing the above process, the changes in the combined clock-link delay are tracked in real time to dynamically update the compensation amount, ensuring continuous and effective time synchronization. This method utilizes two naturally occurring, constant-amplitude non-interference peaks of the Franson interference as a self-reference time delay benchmark. It reuses the original entangled photon coincidence count data to complete the comprehensive clock-link time delay calculation. It eliminates the need for additional synchronizing lasers, dedicated synchronizing fibers, or new complex optical modules, thus reducing network deployment complexity and saving costs. Furthermore, the peak spacing is determined solely by the time delay of the fixed arm length difference of the UMZI, and is unaffected by clock drift and fiber delay fluctuations, ensuring a stable synchronization benchmark. It does not introduce classical synchronization noise throughout the process and does not occupy additional channels, achieving high-precision time synchronization for quantum entanglement distribution networks.

[0011] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0012] Figure 1 A typical framework diagram of an energy-time entanglement distribution network based on Franson interferometry provided for embodiments of the present invention; Figure 2 This is a schematic diagram of a histogram of coincidence counts provided in an embodiment of the present invention; Figure 3 A flowchart illustrating a self-reference time synchronization method for entanglement distribution networks provided in an embodiment of the present invention; Figure 4 This is a structural block diagram of a self-reference time synchronization system for entanglement distribution networks provided in an embodiment of the present invention. Detailed Implementation

[0013] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the embodiments described below are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0014] The first aspect of the present invention provides a self-reference time synchronization method for an entanglement distribution network, wherein the entanglement distribution network is an energy-time entanglement distribution network based on Franson interferometry, including an energy-time entangled photon source and multiple stations; the energy-time entangled photon source is connected to the multiple stations via optical fiber links; wherein each station is configured with a UMZI, a single-photon detector and a time-to-digital converter; any two stations are paired to form a Franson interferometric branch, and the UMZIs configured in the two stations of the same branch have the same fixed arm length difference time delay.

[0015] Please see Figure 1 , Figure 1 The diagram illustrates a typical framework of an energy-time entangled distribution network based on Franson interferometry, as provided in this embodiment of the invention. It shows that a typical energy-time entangled distribution network includes one energy-time entangled photon source and two stations (also called network nodes). The energy-time entangled photon source is connected to the first and second stations via fiber optic links. Each station contains a UMZI (Uninterruptible Multi-Interferometer), with its long arm denoted as L and its short arm as S. The time delay due to the arm length difference between the two interferometers is fixed. Furthermore, the time delay of the arm length difference is much greater than the coherence time of the entangled photons, so as to ensure that the quantum states of the long and short paths are distinguishable in time.

[0016] Energy-time entangled photon pairs generated by an energy-time entangled photon source , The entangled photons are distributed to two sites via fiber optic links. Each site is equipped with a UMZI (Unified Memory Injector) that couples the incident entangled photons to a corresponding single-photon detector via a split-path transmission. The single-photon detectors collect and record the arrival time of the entangled photons based on their respective reference clocks and generate local raw timestamps using time-to-digital converters. and This refers to the timestamp data of a single-photon detector.

[0017] By performing coincidence counts on the detection events at the two sites, a coincidence count histogram of the two-photon arrival time difference can be constructed. (See [link to relevant documentation]). Figure 2 , Figure 2This is a schematic diagram of the coincidence count histogram provided in an embodiment of the present invention. In the figure, the horizontal axis represents the arrival time difference of the two photons, and the vertical axis represents the coincidence count. It can be seen that three coincidence peaks appear in this histogram: When both photons pass through the short arm (SS) or the long arm (LL) in the UMZI, their quantum states are indistinguishable, interference occurs, and a central main peak that varies with the phase, also known as the central interference main peak, is formed. Its peak height varies with the phase difference of the interferometer. When one photon passes through the short arm S and the other photon passes through the long arm, that is, when the photon's path in the UMZI is SL / LS, two side peaks with fixed time delays are generated, located on the left and right sides of the central interference main peak, respectively, also known as the left and right non-interference side peaks, or simply the left peak (or left side peak) and the right peak (or right side peak).

[0018] It is understandable that the clock difference between the reference clocks of the two stations... Link delay introduced by fiber optic links Fluctuations can cause the coincidence peaks to shift, but the three peaks as a whole will shift. Theoretically, the center of the left peak will shift. The center of the right peak It can be represented as: ; ; In the formula, The clock difference between the reference clocks of the two stations. Link delay introduced by fiber optic links, The known UMZI arm length difference time delay.

[0019] Since the edge peaks originate from distinguishable path combinations, they are non-interference peaks, and their peak height does not change with phase, thus serving as a stable time delay reference. This invention utilizes this characteristic to propose a self-reference time synchronization method for entangled distribution networks. This method dynamically acquires the combined changes in clock difference and link delay by real-time monitoring the positions of the left and right edge peaks, thereby adaptively adjusting the timestamp data to achieve high-precision energy-time entanglement distribution time synchronization.

[0020] For details, please see Figure 3 , Figure 3 This invention provides a flowchart illustrating a self-reference time synchronization method for entanglement distribution networks, comprising: S1. For any two stations on any branch, obtain the timestamp data of the two single-photon detectors collected in real time by the time-to-digital converter configured at each station, and summarize them to generate a coincidence count histogram of the time difference of arrival of two photons.

[0021] Among them, the coincidence count histogram forms a three-peak structure, namely the central interference main peak formed by the coherent superposition of the short arm path of two photons traveling in the same UMZI and the long arm path of two photons traveling in the same UMZI, and the left and right non-interference side peaks formed by the two types of paths, one photon traveling in the short arm and the other photon traveling in the long arm.

[0022] S2. On the coincidence count histogram, the time window corresponding to the left and right non-interference side peaks is defined based on the preset arm length difference time delay; within the time window, the peak finding algorithm is used to calculate the real-time estimated value of the center position of the left and right non-interference side peaks respectively.

[0023] First, based on the known arm length difference time delay on the coincidence count histogram. Alternatively, historical data can be used to preset the time windows for the appearance of left and right peaks.

[0024] Specifically, on the horizontal axis of the two-photon arrival time difference conforming to the counting histogram, with the time difference position corresponding to the central main peak as the reference, based on the pre-known UMZI arm length difference time delay... Shifting in the positive and negative time delay directions respectively The theoretical centers of the two non-interference side peaks are obtained. A preset time margin is added on both sides of each theoretical center, and candidate time windows that surround the two non-interference side peaks are defined as the appearance time windows of the preset left and right side peaks. Only the histogram sampling data within the window is retained for subsequent peak finding processing.

[0025] Then, the peak-finding algorithm is used to accurately calculate the real-time estimated values ​​of the center positions of the two non-interference side peaks on the left and right.

[0026] Optionally, in this embodiment, the peak finding algorithm can be a Gaussian fitting method.

[0027] Specifically, within the candidate time window, noise is first filtered out based on a preset counting threshold; then, a local maximum count value is searched within the window using threshold peak detection, and a narrow interval near the peak value is extracted centered on this local maximum count value; within this narrow interval, Gaussian fitting is used to perform least-squares fitting on the discrete sampling points in the figure, i.e., the two-photon arrival time difference distribution, such as... Figure 2 As shown by the black lines in the diagram, by solving for the optimal fitting parameters, the real-time estimated values ​​of the center positions of the two non-interference side peaks are obtained, denoted as follows: and .

[0028] Furthermore, after obtaining the real-time estimates of the center positions of the two non-interference side peaks on the left and right, the following is also included: The working status of UMZI is verified based on the real-time estimated values ​​of the center positions of the two non-interference side peaks on the left and right and the preset arm length difference time delay.

[0029] In this embodiment, the working status of UMZI is verified, including: The difference between the real-time estimated values ​​of the center positions of the two non-interference side peaks on the left and right is compared with a time delay of twice the preset arm length difference. If the deviation between the two exceeds a predetermined threshold, the UMZI is determined to be abnormal.

[0030] Specifically, based on the center position of the left peak mentioned above and the center position of the right peak The theoretical formulas are: ; ; Subtracting the two equations above, we have: .

[0031] Based on this, the real-time estimated values ​​of the center positions of the two non-interference side peaks obtained by the peak-finding algorithm are... and If satisfied If the condition is met, it indicates that the UMZI is working normally; if not, the UMZI is considered abnormal when the deviation between the left and right sides of the equation exceeds a predetermined threshold.

[0032] When an anomaly is detected in the UMZI, the parameters are indicated as unreasonable. The UMZI arm length difference needs to be readjusted so that the time delay of the arm length difference is much greater than the coherence time of the entangled photons, so as to ensure that the quantum states of the long and short paths are distinguishable in time.

[0033] It should be noted that, in order to adapt to the slow drift of clock difference and link delay, a sliding time window can be used to continuously update the histogram and continuously output the real-time estimated values ​​of the center positions of the left and right non-interference side peaks.

[0034] S3. Calculate the combined clock-link delay between the two stations based on the real-time estimated values ​​of the center positions of the two non-interference side peaks on the left and right.

[0035] Specifically, the formula for calculating the combined clock-link delay is as follows: ; In the formula, Indicates the combined clock-link delay. This represents the real-time estimate of the center position of the left non-interference edge peak. This represents a real-time estimate of the location of the center of the right non-interfering edge peak. This represents the clock difference between the reference clocks of two stations. This indicates the link delay introduced by the fiber optic link.

[0036] S4. Based on the comprehensive clock-link delay setting compensation amount, and according to the compensation amount, the original timestamp of either of the two stations is shifted and compensated so that the timestamps of the two stations are synchronized to the same time base, thus completing a single time synchronization.

[0037] Specifically, after obtaining the comprehensive clock-link delay Then, arbitrarily select one of the two sites, keeping the original timestamp of the selected site unchanged, and designate the other site as the site to be compensated. Using the comprehensive clock-link delay as the compensation amount, compensate the original timestamp of the site to be compensated. For example, keep the original timestamp of site 1 unchanged. The original timestamp of site 2 remains unchanged. Compensation shall be made according to the following formula: ; In the formula, This indicates the timestamp of site 2 after compensation.

[0038] After compensation, the timestamps of the two stations were synchronized to the same time base.

[0039] Furthermore, after completing a single time synchronization, the coincidence count histogram is updated. When reconstructed within the coincidence count histogram, the central interference peak automatically aligns with the zero-delay position, meaning the central interference peak of the coincidence count histogram stabilizes near zero time difference. Based on the updated coincidence count histogram, Franson interference curves are extracted from the central interference peak region for use in quantum key distribution or entanglement verification.

[0040] S5. Repeatedly execute S1 to S4 to track the changes in the integrated clock-link delay in real time, so as to dynamically update the compensation amount and ensure that time synchronization is continuously effective.

[0041] By continuously repeating steps S1 to S4, the integrated clock-link delay can be tracked in real time. The changes in the clock frequency cause dynamic updates to the timestamp compensation. When the fiber optic link experiences a gradually varying delay due to temperature, stress, etc., the positions of the left and right side peaks shift as a whole, but their spacing and height remain stable. The calculated overall clock-link delay is then adjusted accordingly. This will accurately reflect the change and ensure that time synchronization remains effective.

[0042] It should be noted that for the energy-time entangled distribution network based on Franson interferometry, which includes multiple sites, a wavelength division multiplexing (WDM) beam splitter is also configured. The energy-time entangled photon source outputs multiple entangled photon pairs through the WDM beam splitter. Each entangled photon pair is assigned to an independent pair of paired sites, forming multiple Franson interferometry branches. Time synchronization can be achieved for each Franson interferometry branch using the above method, thereby achieving a unified time reference calibration for the entire network.

[0043] This invention utilizes two naturally occurring, constant-amplitude non-interference peaks of the Franson interference as a self-reference time delay benchmark. It reuses the existing entangled photon coincidence count data to complete the comprehensive clock-link time delay calculation, eliminating the need for additional synchronizing lasers, dedicated synchronizing fibers, or new complex optical modules, thus reducing network deployment complexity and saving costs. Furthermore, the peak spacing is determined solely by the difference in the fixed arm length of the UMZI, remaining unaffected by clock drift and fiber delay fluctuations, ensuring a stable synchronization benchmark. It introduces no classical synchronization noise throughout the process and does not occupy additional channels, achieving high-precision time synchronization in quantum entanglement distribution networks.

[0044] Based on the same inventive concept, a second aspect of the present invention also provides a self-reference time synchronization system for entanglement distribution networks. Similarly, this system is configured in an energy-time entanglement distribution network based on Franson interferometry, the network comprising energy-time entangled photon sources and multiple stations; the energy-time entangled photon sources are connected to the multiple stations via fiber optic links; each station is configured with a UMZI, a single-photon detector, and a time-to-digital converter; any two stations are paired to form a Franson interferometry branch, and the UMZIs configured at the two stations in the same branch have the same fixed arm length difference time delay.

[0045] Please see Figure 4 , Figure 4 A structural block diagram of a self-reference time synchronization system for entanglement distribution networks provided in an embodiment of the present invention, the system comprising: The histogram generation unit is used to collect the timestamp data of the two single-photon detectors in real time through the time-to-digital converters configured at each of the two stations of any branch, and summarize them to generate a coincidence count histogram of the time difference of arrival of two photons. The coincidence count histogram has a three-peak structure, namely the central interference main peak formed by the coherent superposition of the short arm path and the long arm path of the two photons traveling in the same UMZI, and the left and right non-interference side peaks formed by the two types of paths, one photon traveling in the short arm and the other photon traveling in the long arm. The first calculation unit is used to delineate the time windows corresponding to the left and right non-interference side peaks on the coincidence count histogram based on the preset arm length difference time delay; within the time window, the peak finding algorithm is used to calculate the real-time estimated values ​​of the center positions of the left and right non-interference side peaks respectively. The second calculation unit is used to calculate the integrated clock-link delay between the two stations based on the real-time estimated values ​​of the center positions of the left and right non-interference side peaks; The time synchronization unit is used to set the compensation amount based on the comprehensive clock-link delay, and to perform translation compensation on the original timestamp of either of the two stations according to the compensation amount, so that the timestamps of the two stations are synchronized to the same time base, thus completing a single time synchronization.

[0046] Based on the same inventive concept, a third aspect of the present invention also provides an electronic device, which includes a processor, a communication interface, a memory, and a communication bus; wherein the processor, the communication interface, and the memory communicate with each other through the communication bus. Memory is used to store computer programs; When the processor executes a program stored in memory, it implements the method steps provided in the first aspect of the present invention.

[0047] Based on the same inventive concept, a fourth aspect of the present invention also proposes a computer-readable storage medium storing a computer program, which, when executed by a processor, implements the method steps provided in the first aspect of the present invention.

[0048] It should be noted that the descriptions of the system, electronic device, and storage medium embodiments are relatively simple because they are fundamentally similar to the method embodiments; relevant details can be found in the descriptions of the method embodiments. Therefore, all embodiments of the self-reference time synchronization method for entanglement distribution networks described above are applicable to the system, electronic device, and storage medium, and all can achieve the same or similar beneficial effects.

[0049] Those skilled in the art will understand that embodiments of the present invention can be provided as methods, systems (devices), or computer program products. Therefore, the present invention can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects, all of which are collectively referred to herein as "modules" or "units." Furthermore, the present invention can take the form of a computer program product implemented on one or more computer-usable storage media (including, but not limited to, disk storage, CD-ROM, optical storage, etc.) containing computer-usable program code. The computer program may be stored / distributed in a suitable medium, provided with or as part of other hardware, or may be distributed in other forms, such as via the Internet or other wired or wireless telecommunications systems.

[0050] This invention is described with reference to flowchart illustrations and / or block diagrams of methods, systems (apparatus), and computer program products according to embodiments of the invention. It will be understood that each block of the flowchart illustrations and / or block diagrams, and combinations of blocks in the flowchart illustrations and / or block diagrams, can be implemented by computer program instructions. These computer program instructions can be provided to a processor of a general-purpose computer, special-purpose computer, embedded processor, or other programmable data processing apparatus to produce a machine, such that the instructions, which execute via the processor of the computer or other programmable data processing apparatus, generate instructions for implementing the flowchart illustrations and / or block diagrams. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0051] These computer program instructions may also be stored in a computer-readable storage medium that can direct a computer or other programmable data processing device to function in a particular manner, such that the instructions stored in the computer-readable storage medium produce an article of manufacture including instruction means, which are implemented in a process Figure 1 One or more processes and / or boxes Figure 1 The function specified in one or more boxes.

[0052] These computer program instructions may also be loaded onto a computer or other programmable data processing equipment to cause a series of operational steps to be performed on the computer or other programmable equipment to produce a computer-implemented process, thereby providing instructions that execute on the computer or other programmable equipment for implementing the process. Figure 1 One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0053] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A self-reference time synchronization method for entangled distribution networks, characterized in that, The entanglement distribution network is an energy-time entanglement distribution network based on Franson interferometry, comprising an energy-time entangled photon source and multiple stations; the energy-time entangled photon source is connected to the multiple stations via fiber optic links; each station is equipped with a UMZI, a single-photon detector, and a time-to-digital converter; any two stations are paired to form a Franson interferometric measurement branch, and the UMZIs configured in the two stations of the same branch have the same fixed arm length difference time delay; the method includes the following steps: S1. For any two stations on a branch, obtain the timestamp data of the two single-photon detectors collected in real time by the time-to-digital converter configured at each station, and summarize them to generate a coincidence count histogram of the time difference of arrival of two photons. The coincidence count histogram has a three-peak structure, namely the central interference peak formed by the coherent superposition of the short arm path of two photons traveling in the same UMZI and the long arm path of two photons traveling in the same UMZI, and the left and right non-interference side peaks formed by the two types of paths, one photon traveling in the short arm and the other photon traveling in the long arm. S2. On the coincidence count histogram, a time window is defined for the two non-interference side peaks on the left and right based on the preset arm length difference time delay; within the time window, the peak finding algorithm is used to calculate the real-time estimated value of the center position of the two non-interference side peaks on the left and right respectively. S3. Calculate the combined clock-link delay between the two stations based on the real-time estimated values ​​of the center positions of the two non-interference side peaks on the left and right. S4. Based on the comprehensive clock-link delay, set a compensation amount, and perform translation compensation on the original timestamp of either of the two stations according to the compensation amount, so that the timestamps of the two stations are synchronized to the same time base, thus completing a single time synchronization. S5. Repeatedly execute S1 to S4 to track the changes in the integrated clock-link delay in real time, so as to dynamically update the compensation amount and ensure that time synchronization remains effective.

2. The self-reference time synchronization method for entangled distribution networks according to claim 1, characterized in that, In S2, within the time window, a peak-finding algorithm is used to calculate the real-time estimated positions of the center positions of the left and right non-interference side peaks, including: Within the time window, the two-photon arrival time difference distribution in the coincidence count histogram is fitted with a Gaussian function using least squares to obtain real-time estimates of the center positions of the left and right non-interference side peaks.

3. The self-reference time synchronization method for entangled distribution networks according to claim 1, characterized in that, After obtaining the real-time estimates of the center positions of the two non-interfering side peaks in S2, the following is also included: The working status of the UMZI is verified based on the real-time estimated values ​​of the center positions of the two non-interference side peaks on the left and right and the preset arm length difference time delay.

4. The self-reference time synchronization method for entangled distribution networks according to claim 3, characterized in that, Verification of the working status of the UMZI includes: The difference between the real-time estimated values ​​of the center positions of the two non-interference side peaks on the left and right is compared with a time delay of twice the preset arm length difference. If the deviation between the two exceeds a predetermined threshold, the UMZI is determined to be abnormal.

5. A self-reference time synchronization method for entangled distribution networks according to claim 1, characterized in that, In S3, the formula for calculating the integrated clock-link delay is: ； In the formula, Indicates the combined clock-link delay. This represents the real-time estimate of the center position of the left non-interference edge peak. This represents a real-time estimate of the location of the center of the right non-interfering edge peak. This represents the clock difference between the reference clocks of two stations. This indicates the link delay introduced by the fiber optic link.

6. The self-reference time synchronization method for entangled distribution networks according to claim 1, characterized in that, S4 includes: Choose one of the two sites arbitrarily, keeping the original timestamp of the selected site unchanged, and use the integrated clock-link delay as the compensation amount to compensate the original timestamp of the other site according to the following formula: ； In the formula, This indicates the timestamp of site 2 after compensation. This represents the original timestamp of site 2 to be compensated. This represents the combined clock-link delay.

7. A self-reference time synchronization method for entangled distribution networks according to claim 1, characterized in that, Also includes: After a single time synchronization is completed, the coincidence count histogram is updated. Based on the updated coincidence count histogram, the Franson interference curve is extracted from the central interference peak region for quantum key distribution or entanglement verification.

8. A self-reference time synchronization system for entanglement distribution networks, used to implement the method according to any one of claims 1-7, characterized in that, The entanglement distribution network is an energy-time entanglement distribution network based on Franson interferometry, comprising an energy-time entangled photon source and multiple stations; the energy-time entangled photon source is connected to the multiple stations via fiber optic links; each station is equipped with a UMZI, a single-photon detector, and a time-to-digital converter; any two stations are paired to form a Franson interferometric measurement branch, and the UMZIs configured in the two stations of the same branch have the same fixed arm length difference time delay; the system includes: The histogram generation unit is used to acquire the timestamp data of two single-photon detectors collected in real time by the time-to-digital converters configured at each of the two stations of any branch, and to summarize and generate a coincidence count histogram of the time difference of arrival of two photons; wherein, the coincidence count histogram forms a three-peak structure, namely, the central interference main peak formed by the coherent superposition of the short arm path of the two photons traveling in the same UMZI and the long arm path of the two photons traveling in the same UMZI, and the left and right non-interference side peaks formed by the two types of paths, one photon traveling in the short arm and the other photon traveling in the long arm; The first calculation unit is used to delineate the time windows corresponding to the left and right non-interference side peaks on the coincidence count histogram based on a preset arm length difference time delay; within the time window, the peak finding algorithm is used to calculate the real-time estimated values ​​of the center positions of the left and right non-interference side peaks respectively. The second calculation unit is used to calculate the integrated clock-link delay between the two stations based on the real-time estimated values ​​of the center positions of the two non-interference side peaks on the left and right. The time synchronization unit is used to set a compensation amount based on the integrated clock-link delay, and to perform translation compensation on the original timestamp of either of the two stations according to the compensation amount, so that the timestamps of the two stations are synchronized to the same time base, thus completing a single time synchronization.

9. An electronic device, characterized in that, It includes a processor, a communication interface, a memory, and a communication bus, wherein the processor, the communication interface, and the memory communicate with each other through the communication bus; Memory is used to store computer programs; The processor is used to execute a program stored in memory to implement the steps of the method described in any one of claims 1-7.

10. A computer-readable storage medium, characterized in that, The computer-readable storage medium stores a computer program that, when executed, performs the steps of the method described in any one of claims 1-7.

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