A terminal quantum time synchronization network method and system

Abstract

The application provides a terminal quantum time synchronization network method and system, comprising: a center node uses an integrated microcavity optical frequency comb as an entanglement source to obtain a plurality of pairs of signal light and idle light, which are used for time synchronization of each node; separated signal light reaches a terminal node after transmission through an optical fiber link; the terminal node has a probability of absorbing or reflecting the signal light, so that the signal light reenters the center node; the idle light has a probability of generating sum frequency effect with the reflected signal light in a sum frequency module; a computer of the center node dynamically adjusts the clock difference settlement according to the sum frequency signal, so that the separated signal light and the idle light experience the same propagation time when being transmitted in the optical fiber, and clock difference settlement is realized. The application realizes time synchronization of multiple terminals at the same time; clock difference between two places is detected by using sum frequency effect, which is performed in an optical domain, and time precision is high, which is femtosecond order; the integrated microcavity optical frequency comb is used as the entanglement source, a large number of entanglement pairs can be provided at the same time, and the network scale is convenient to expand and the topology is flexible.

Description

Technical Field

[0001] This invention relates to the field of quantum time synchronization technology, and more specifically, to a terminal quantum time synchronization network method and system. Background Technology

[0002] Time, as a fundamental physical quantity, is crucial for advancing fundamental physics research and ensuring the efficient operation of human society through improved time synchronization accuracy. Among various noises affecting the accuracy of time synchronization methods, noise generated by arrival time measurement is the fundamental noise, i.e., the shot noise limit. Quantum time synchronization is an emerging technology that utilizes quantum light sources and quantum measurement techniques in time synchronization systems, enabling the measurement accuracy of signal arrival time to surpass the classical limit. Furthermore, quantum time synchronization systems can further utilize physical laws such as the no-cloning theorem, incorporating the concept of quantum security to achieve a level of security that is difficult to achieve with traditional time synchronization methods. Parties involved in time synchronization can synchronize with quantum entangled photon pairs and perform Bell measurements to verify the reliability of each photon's source. If the signal is cloned or the degree of quantum entanglement is interfered with, the degree of interference can be constrained by Bell's inequality. Adding Bell measurement results to time information transmitted through classical channels holds promise for solving the spoofing problem in current classical time synchronization protocols.

[0003] Common quantum time synchronization protocols include: single-vector quantum time synchronization protocols based on coincidence measurement of entangled photon pairs, time synchronization protocols based on second-order quantum coherent coincidence measurement of entangled photons, and bidirectional quantum time synchronization protocols. Coincidence measurement of photon arrival times is crucial in quantum time synchronization. Common methods include time interval detection of the output electrical signals from single-photon detectors and Hong Ou-Mandel (HOM) second-order quantum interference. Although HOM interference provides more precise coincidence measurement than electrical methods, it is still limited to the sub-picosecond level. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the purpose of this invention is to provide a terminal quantum time synchronization network method and system.

[0005] According to one aspect of the present invention, a terminal quantum time synchronization network method is provided, comprising:

[0006] The central node extracts multiple pairs of entangled photons from the integrated microcavity quantum optical frequency comb. The entangled photons are separated into two paths: a signal light and an idle light. The signal light is input to the terminal node, and the idle light is input to the central node itself.

[0007] In the terminal node, a portion of the signal light is used to generate a sequence of terminal node detection events and is fed back to the central node through a classical channel, while another portion is reflected to the ultrafast coincidence module of the central node.

[0008] In the central node, part of the idle light is used to generate a central node detection event sequence, and the other part, after time delay and dispersion control, enters the ultrafast coincidence module of the central node.

[0009] In the ultrafast convergence module, the incoming signal light and the idle light are combined to obtain another central node detection event sequence;

[0010] Based on the terminal node detection event sequence and all the central node detection event sequences, clock bias is calculated to obtain the clock bias;

[0011] Based on the clock difference, the delay and dispersion control of the idle light are adjusted to ensure that the idle light and the signal light experience the same propagation time, thereby achieving time synchronization of multiple terminal nodes.

[0012] Preferably, the optical frequency comb has a center frequency of f. s0 The repetition frequency is f sr The multiple entangled sources, wherein the symmetrical comb teeth of the center frequency fs0 are a pair of entangled photons;

[0013] The optical frequency comb is edited by an arbitrary optical waveform editor W0 and then combined with f. s0 The symmetrical comb teeth on both sides are divided into two paths: the signal light and the idle light.

[0014] The signal light is transmitted sequentially through a circulator and an optical fiber link to the terminal node.

[0015] Preferably, in the terminal node, a portion of the signal light is used to generate a sequence of terminal node detection events and fed back to the central node via a classical channel, while another portion is reflected to the ultrafast reconciliation module of the central node, comprising:

[0016] The signal light is split into two paths by a beam splitter. One path is reflected back to the circulator and arbitrary light waveform editor at the central node by the Faraday mirror FM and then enters the ultrafast convergence module.

[0017] Another path is time-stamped via a single-photon detection module (SPD) and a time-to-digital converter (TDC) to form a sequence of detection events at the terminal node. The synchronization signal of the single-photon detection module (TDC) is provided by the terminal clock.

[0018] Preferably, in the central node, a portion of the idle light is used to generate a central node detection event sequence, and another portion, after time delay and dispersion control, enters the ultrafast coincidence module of the central node, including:

[0019] The idle light is split into two paths by a beam splitter. One path is received by the single-photon detection module (SPD) to form a detection event sequence of the idle light. The other path, after time delay and dispersion by the arbitrary light waveform editor, enters the ultrafast convergence module.

[0020] Preferably, in the ultrafast coincidence module, the signal light and the idle light are combined and frequency-matched to obtain another central node detection event sequence, including:

[0021] The signal light and the idle light output by the arbitrary light waveform editor enter the sum-frequency module SPF to generate a sum-frequency effect and obtain a sum-frequency signal;

[0022] The silicon single-photon detection module (SiSPD) detects the sum-frequency signal and outputs it to the time-to-digital converter (TDC) at the central node for time stamping, thereby obtaining the central node's detection event sequence. The synchronization signal of the central node's time-to-digital converter (TDC) is provided by the central clock.

[0023] Preferably, the step of calculating the clock bias based on the terminal node detection event sequence and the central node detection event sequence to obtain the clock bias includes:

[0024] The correlation function between the detection event sequences of the central node and the terminal node is c(τ) = F -1 [F * [s]·F[b]] is obtained from the probe event sequence through fast Fourier transform and its inverse transform: where a and b represent the probe event sequences of the central node and the terminal node, respectively; τ is the time offset;

[0025] The time offset is found by searching for the maximum value in the correlation function c(τ) through time delay control;

[0026] If the correlation function between the central node and the terminal node reaches its maximum at τ1, and the sum-frequency signal at the central node reaches its maximum at τ2, then the clock error δ is calculated from τ1 and τ2:

[0027] Preferably, the step of adjusting the delay and dispersion control of the idle light based on the clock difference to ensure that the idle light and the signal light experience the same propagation time, thereby achieving time synchronization of multiple terminal nodes, includes:

[0028] Based on the clock error, the clock error is eliminated by optical delay line (ODL), and the dispersion of the compensation fiber is adjusted by dispersion compensation fiber (DCF) to achieve time synchronization between the central node and a terminal node.

[0029] Quantum time synchronization between multiple terminal nodes can be achieved by switching the communication optical path of the current node to the communication optical path of the terminal node to be synchronized, or by using another pair of frequency-entangled photons.

[0030] According to a second aspect of the present invention, a terminal quantum time synchronization network system is provided, comprising a central node and multiple terminal nodes;

[0031] Each terminal node and the central node are connected via a single optical fiber;

[0032] Alternatively, multiple terminal nodes can share a single fiber optic link with the central node via wavelength division multiplexing (WDM), and an arrayed waveguide grating can be inserted in front of the terminal nodes for wavelength demultiplexing, in conjunction with the central node for WDM and demultiplexing of any optical waveform editor.

[0033] According to a third aspect of the present invention, a terminal is provided, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor, when executing the program, can be used to execute any of the terminal quantum time synchronization network methods described in the present invention, or to run the terminal quantum time synchronization network system described in the present invention.

[0034] According to a fourth aspect of the present invention, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, can be used to run any of the terminal quantum time synchronization network methods described above, or to run the terminal quantum time synchronization network system described above.

[0035] Compared with the prior art, the embodiments of the present invention have at least one of the following beneficial effects:

[0036] The terminal quantum time synchronization network method and system provided in this invention use an integrated microcavity optical frequency comb as an entanglement source, which has abundant spectrum resources, thus preparing for large-scale quantum time synchronization in terms of quantum entanglement resources.

[0037] The terminal quantum time synchronization network method and system provided in this invention utilize sum-frequency crystal coincidence detection technology, which can greatly improve the detection bandwidth and achieve a higher time resolution than HOM interferometry, reaching the femtosecond level. Simultaneously, the phase-match-free sum-frequency crystal can cover a very wide spectral region, thus enabling the measurement of ultrashort correlation times, thereby improving the accuracy of time synchronization.

[0038] The terminal quantum time synchronization network method and system provided in this invention can reduce the number of entangled photon pairs that need to be sent from the central node each time by using time division multiplexing, thereby reducing the number of sum-frequency modules and single-photon detection modules required, and thus compressing the manufacturing cost of the central node.

[0039] The terminal quantum time synchronization network method and system provided in this invention are compatible with wavelength division multiplexing and can adapt to various physical structures of fiber optic fixed networks, greatly enhancing the adaptability and compatibility of quantum time synchronization methods.

[0040] The terminal quantum time synchronization network method and system provided in this invention can achieve the tilted allocation of quantum entanglement resources of key nodes through program control of arbitrary optical waveform editor at the central node; and after simple modification, the terminal node can be changed to the next level central node, thereby providing compatibility guarantee for network cascading mode and facilitating further expansion of the scale of quantum time synchronization network. Attached Figure Description

[0041] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0042] Figure 1 This is a schematic diagram of the terminal quantum time synchronization network method in an embodiment of the present invention;

[0043] Figure 2 This is a schematic diagram of the terminal quantum time synchronization network method according to a specific embodiment of the present invention;

[0044] Figure 3 This is a schematic diagram illustrating the clock error calculation principle in a specific embodiment of the present invention;

[0045] Figure 4 This is a schematic diagram of a terminal quantum time synchronization network method according to another specific embodiment of the present invention. Detailed Implementation

[0046] The present invention will now be described in detail with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the present invention, but do not limit the invention in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present invention. These all fall within the protection scope of the present invention. Parts not described in detail in the following embodiments can be achieved using existing technology.

[0047] See Figure 1 This invention provides a terminal quantum time synchronization network method, the specific process of which is as follows:

[0048] S100: The central node extracts multiple pairs of entangled photons from the integrated microcavity quantum optical frequency comb. The entangled photons are separated into two paths: signal light and idle light. The signal light is input to the terminal node, and the idle light is input to the central node itself.

[0049] S200, in the terminal node, part of the signal light is used to generate a sequence of terminal node detection events and is fed back to the central node through a classical channel, while the other part is reflected to the ultrafast coincidence module of the central node.

[0050] In the S300, at the central node, part of the idle light is used to generate a sequence of central node detection events, and the other part, after time delay and dispersion control, enters the ultrafast coincidence module of the central node.

[0051] S400, in the ultrafast coincidence module, the incoming signal light and idle light and frequency are combined to obtain another central node detection event sequence;

[0052] S500 calculates the clock difference based on the terminal node detection event sequence and all central node detection event sequences of S300 and S400.

[0053] The S600, based on clock bias, adjusts the delay and dispersion control of idle light to ensure that idle light and signal light experience the same propagation time, thereby achieving time synchronization of multiple terminal nodes.

[0054] This invention enables multiple terminals to synchronize their time simultaneously. The method utilizes the sum-frequency effect to detect the clock difference between two locations in the optical domain, achieving high time accuracy on the order of femtoseconds. By using an integrated microcavity optical frequency comb as the entanglement source, a large number of entangled pairs can be provided simultaneously, making the network scale easily expandable and the topology flexible.

[0055] In a preferred embodiment of the present invention, S100 is implemented as follows:

[0056] S101, the central node generates an optical frequency comb as a multi-entanglement source, specifically a comb with a center frequency of f. s0 An optical frequency comb with a repetition frequency of fsr serves as a multi-entanglement source, and the comb teeth symmetrically arranged according to the center frequency form a pair of entangled photons.

[0057] The optical frequency combs of S102 and S101 are coupled with f by the arbitrary optical waveform editor W0. s0 The symmetrical comb teeth on both sides are divided into two paths: signal light and idle light.

[0058] The signal light obtained from S103 and S102 is transmitted to the corresponding terminal node through the circulator and fiber optic link in sequence;

[0059] The idle light obtained in S104 and S102 is input to the central node itself, and its delay is controlled before entering the ultrafast convergence module.

[0060] This embodiment uses an integrated microcavity optical frequency comb as the entanglement source, which has abundant spectrum resources, thus preparing the quantum entanglement resources for large-scale quantum time synchronization.

[0061] In a preferred embodiment of the present invention, S200 is implemented, and the specific process is as follows.

[0062] S201, in the terminal node, the signal light is split and output by a beam splitter;

[0063] S202, part of which is reflected by the Faraday mirror FM;

[0064] S203, another part sequentially passes through the single-photon detection module SPD and the time-to-digital converter module TDC to form a terminal node detection sequence, and the synchronization signal of the time-to-digital converter module TDC is provided by the terminal clock;

[0065] The reflected signals from S204 and S202 pass through the fiber optic link again, and then at the central node, via a circulator and an arbitrary optical waveform editor, they are connected to the ultrafast matching module.

[0066] In this embodiment, the terminal node detection sequence is the detection sequence left after the signal light reaches the terminal node. It is used in the subsequent central node calculation. Therefore, the terminal node will communicate with the central node through a traditional channel to transmit this terminal node detection sequence to the central node.

[0067] In a preferred embodiment of the present invention, S300 is implemented as follows:

[0068] At the central node S301, the idle light of entangled photons is output through the beam splitter. The idle light has a probability of being received by the single photon detection module SPD (generating a detection event sequence of idle light at point E), or it has a probability of entering the ultrafast coincidence module after passing through the time delay and dispersion of the arbitrary light waveform editor.

[0069] In a preferred embodiment of the present invention, S400 is implemented as follows:

[0070] S401, the signal light output by the arbitrary optical waveform editor and the idle light (i.e., the idle light after time delay control) enter the sum-frequency module to generate a sum-frequency signal;

[0071] S402, Silicon Single Photon Detection Module (SiSPD) detects the sum-frequency signal after filtering by short-pass filter (SPF);

[0072] S403, the silicon single-photon detector module (SiSPD) outputs to the time-to-digital converter (TDC) of the central node for time marking. The synchronization signal of the TDC of the central node is provided by the central clock of the central node.

[0073] This embodiment utilizes sum-frequency crystal coincidence detection technology, which can significantly improve the detection bandwidth and achieve a higher time resolution than HOM interferometry, reaching the femtosecond level. Simultaneously, the unmatched sum-frequency crystal can cover a wide spectral region, thus enabling the measurement of ultra-short correlation times and improving the accuracy of time synchronization.

[0074] In a preferred embodiment of the present invention, S500 is implemented as follows:

[0075] S501, the terminal node detection sequence obtained in S203 above is communicated with the central node via the classical channel;

[0076] S502, the central node computer calculates the coincidence count of the detection event sequences at the central node and the terminal node;

[0077] S503, the computer at the central node uses the coincidence count signal derived from the sum-frequency effect at the central node;

[0078] S504 dynamically adjusts the delay and dispersion of the arbitrary optical waveform editor to ensure that the separated signal light and idle light experience the same propagation time when transmitted in the optical fiber, thereby realizing clock error calculation.

[0079] Furthermore, the cross-correlation calculation is performed on the detection event sequences of the central node and the terminal node. By changing the time delay, the time difference 1 is found when the correlation is at its maximum. Similarly, the time delay 2 when the sum-frequency signal is at its maximum is found. The clock difference is then uniquely determined by the two. Based on the obtained clock difference solution signal, the ODL time delay is controlled to eliminate the clock difference, and the DCF is controlled to adjust and compensate for fiber dispersion, so that the dispersion broadening of the light is smaller and the time synchronization accuracy is improved.

[0080] That is, the specific process of clock error calculation is as follows:

[0081] The correlation function between the detection event sequences of the central node and the terminal node is c(τ)=F -1 [F * [a]·F[b]] is obtained from the sequence of probe events through fast Fourier transform and its inverse transform: where a and b represent the sequence of probe events of the central node and the terminal node, respectively; τ is the time offset.

[0082] The time offset is found by searching for the maximum value in the correlation function c(τ) through time delay control;

[0083] If the correlation function between the central node and the terminal node reaches its maximum at τ1, and the sum-frequency signal at the central node reaches its maximum at τ2, then the clock error δ is calculated from τ1 and τ2:

[0084] In a preferred embodiment of the present invention, S600 specifically includes the following steps:

[0085] S601, based on the clock error calculated by S500, eliminates the clock error through optical delay line (ODL) and adjusts the dispersion of the compensation fiber (DCF) to achieve time synchronization between the central node and a terminal node.

[0086] S602 switches the communication optical path of the current node to the communication optical path of the terminal node to be synchronized, or uses another pair of frequency-entangled photons to achieve quantum time synchronization between multiple terminal nodes.

[0087] In the above embodiment, the computer at the central node dynamically adjusts the clock difference calculated from the sum-frequency signal so that the separated signal light and idle light experience the same propagation time when transmitted in the optical fiber, thereby realizing clock difference calculation and enabling multiple terminals to synchronize their time simultaneously.

[0088] In other preferred embodiments of the present invention, a corresponding quantum security monitoring method is provided, which involves the central node randomly controlling W1 and W2 to switch the optical path to the CHSH inequality test module to ensure the security of the method. If quantum time synchronization between terminal nodes is required, it is only necessary to switch the optical path or use another pair of frequency-entangled photons and repeat the above steps to achieve quantum time synchronization between the central node and the terminal nodes. Thus, quantum time synchronization between one central node and multiple terminal nodes can ultimately be completed and security ensured.

[0089] Figure 2 This is a schematic diagram of a specific embodiment of the present invention. Figure 2 As shown, this embodiment is a point-to-point quantum time synchronization scheme for synchronizing a central node E with a single terminal A. The central node E and the terminal node A are connected via an optical fiber network and can also communicate through a classical channel; E and A are linearly connected.

[0090] The central node includes an integrated microcavity optical frequency comb quantum entanglement source, an arbitrary optical waveform editor (Waveshaper, W0 and W1), a circulator, a beam splitter, a tunable optical delay line (ODL), a dispersion-compensating fiber (DCF), a sum-frequency module, a short-pass filter (SPF), a silicon single-photon detection module (Si SPD), a single-photon detection module (SPD), a time-to-digital converter (TDC), a central clock, a CHSH inequality test module, and a computer; the fiber optic network is a standard single-mode fiber optic communication link; the terminal node (A) includes a beam splitter, a Faraday mirror (FM), a single-photon detection module (SPD), a TDC, and a terminal clock.

[0091] The specific implementation of the E-to-A point-to-point quantum time synchronization network method provided in this embodiment is as follows:

[0092] S11, the central node extracts a pair of entangled photons (+1 and -1) from the integrated microcavity quantum optical frequency comb. The entangled photon pair is separated into two paths by the arbitrary optical waveform editor W0 and then sent to the two paths respectively.

[0093] S12, the obtained signal light is transmitted sequentially through circulator C1 and fiber optic link to node A; the transmitted signal light is reflected or absorbed at the terminal node. Specifically, at a certain terminal node, the signal light is input into a 10:90 beam splitter. 90% of the output of the beam splitter is connected to a Faraday mirror FM to reflect the signal light, and 10% of the output is connected to a single-photon detection module (SPD). The output signal of the single-photon detection module SPD is time-stamped by the terminal node's time-to-digital converter (TDC) to form the detection sequence at point A. The synchronization signal of the terminal node's time-to-digital converter (TDC) is provided by the node's terminal clock.

[0094] S13, the signal light reflected by the Faraday mirror FM at the terminal node passes through the optical fiber link again, and then enters the arbitrary optical waveform editor W1 at the central node via the circulator C1.

[0095] S14, the corresponding idle light passes through a 50:50 splitter. One output of the splitter is connected to a single photon detection module (SPD) and the other is connected to an adjustable optical delay line (ODL). This makes it possible for the idle light to be received by the single photon detection module (SPD) (generating a detection event sequence of the idle light at point E), or to enter the adjustable optical delay line and reach the arbitrary light waveform editor (W1).

[0096] S15, the optical signal reflected back to the central node from the terminal node A is output by the arbitrary optical waveform editor W1. If the corresponding idle light reaches the arbitrary optical waveform editor W1, W1 outputs a signal. After the optical delay line (ODL) supplements the time delay and the dispersion compensation fiber (DCF) nonlocally compensates for the dispersion of the optical fiber link, the two signals enter the sum-frequency module to generate a sum-frequency signal. The silicon single-photon detection module (Si SPD) detects the sum-frequency signal filtered by the short-pass filter (SPF) and outputs it to the time-to-digital converter (TDC) of the central node for time marking, thus obtaining another event sequence of the central node. The synchronization signal of the time-to-digital converter (TDC) of the central node is provided by the central clock of the central node.

[0097] Figure 3 This is a schematic diagram illustrating the clock bias calculation principle in this embodiment. The sum-frequency effect calculation method mainly involves the terminal node communicating its signal optical detection event sequence with the central node via a classical channel. The central node can then calculate the coincidence count between the detection event sequences at both the central node and the terminal node. For example... Figure 3 As shown, the specific principle and method of clock error calculation provided in this embodiment are as follows:

[0098] Let the time of the central node E be t, the time of the terminal node A be t0, and the clock difference between the two locations be δ. Let the time for a photon to travel from E to A be Δt. EA The time it takes for a photon to travel from A to E is Δt. AE The detection event sequences for nodes E and A are respectively a(t) = ∑ i δ(tt i ), and b(t)=∑ j δ(tt j ), t i t j Let represent the time of the detection pulse for each photon. The correlation function between the two sequences is c(τ) = ∫a(t)b(t+τ)dt. c(τ) has a peak at τ = Δt, due to the correlated photodetector events above the independent background noise baselines on both sides. Therefore, the time offset Δt can be easily found by searching for the maximum value in c(τ) through time delay control. A discrete array c(τ) of length N can be efficiently obtained from the sequence of detection events using fast Fourier transform and their inverse transform: c(τ) = F -1 [F * [a]·F[b]]. The correlation function between nodes E and A in τ EA =Δt EA The sum-frequency signal R(τ) at E reaches a maximum at +δ, and at τ... EE =Δt EA +Δt AE It reaches its maximum value at Δt. EA =Δt AEThen the clock difference can be expressed by τ EA and τ EE Calculated as follows:

[0099] After obtaining the clock difference between the central node E and the terminal node A, the computer at the central node E dynamically adjusts the delay and dispersion of the arbitrary optical waveform editor W1 according to the clock difference to ensure that the separated signal light and idle light experience the same propagation time when they are transmitted in the optical fiber.

[0100] The specific implementation of this invention includes point-to-point quantum security monitoring, mainly by the central node E randomly controlling whether W1 switches the optical path to the CHSH inequality test module to ensure the security of the scheme.

[0101] Here, the CHSH inequality describes the entanglement property of photons. Specifically, if the physical quantities of a photon satisfy the CHSH inequality, then no entanglement has occurred; otherwise, entanglement is present. Therefore, if the optical path is not switched, the normal time synchronization procedure will still be followed. When the optical path is switched, the photon pairs enter the CHSH inequality test module to test their safety.

[0102] Figure 4 This is a schematic diagram of a specific embodiment two of the present invention. Figure 4 As shown, the method includes a central node E, four terminal nodes A, B, C, and D, an optical fiber network, and a classical channel. The optical fiber network connects each node to the central node in various ways, forming a star structure; the classical channel connects the nodes, allowing them to communicate with each other. Specifically, terminal nodes A and B are each connected to the central node E via an optical fiber link, while terminal nodes C and D share a single optical fiber link with the central node E via wavelength division multiplexing.

[0103] The central node includes an integrated microcavity optical frequency comb quantum entanglement source, an arbitrary optical waveform editor (Waveshaper, W0 and W1), a circulator, a beam splitter, a tunable optical delay line (ODL), a dispersion-compensating fiber (DCF), a sum-frequency module, a short-pass filter (SPF), a silicon single-photon detection module (Si SPD), a single-photon detection module (SPD), a time-to-digital converter (TDC), a central clock, a CHSH inequality test module, and a computer; the fiber optic network is a standard single-mode fiber optic communication link; the terminal node (A) includes a beam splitter, a Faraday mirror (FM), a single-photon detection module (SPD), a TDC, and a terminal clock.

[0104] The specific implementation of the multi-terminal quantum time synchronization network method provided in this embodiment is as follows: Figure 4 As shown, it includes the following steps:

[0105] S21, the central node uses an integrated microcavity quantum optical frequency comb to generate an optical frequency comb as a multi-entanglement source. Specifically, it is an optical frequency comb with a center frequency of fs0 and a repetition frequency of fsr as a multi-entanglement source. The comb teeth symmetrical according to the center frequency are a pair of entangled photons. The optical frequency comb is divided into two paths, signal light and idle light, by an arbitrary optical waveform editor W0.

[0106] S22, the obtained signal light is transmitted sequentially through circulator C1 and fiber optic link to the corresponding nodes. That is, the signal light in the nth pair of comb teeth is transmitted to the nth node using arbitrary optical waveform editor W0. For nodes A and B, the transmitted signal light is reflected or absorbed at the terminal node. Specifically, at a certain terminal node, the signal light is input into a 10:90 splitter. The 90% output of the splitter is connected to the Faraday mirror FM to reflect the signal light, and the 10% output is connected to a single-photon detection module. The output signal of the single-photon detection module SPD is time-stamped by the terminal node TDC to form a detection sequence. The synchronization signal of the terminal node TDC is provided by the terminal clock of the node. The signal light reflected by the Faraday mirror FM at the terminal node passes through the fiber optic link again, and then enters the arbitrary optical waveform editor W2 at the central node via circulator C1. For nodes C and D, an arrayed waveguide grating needs to be inserted in front of the terminal node for wavelength demultiplexing. With the wavelength division multiplexing and demultiplexing of arbitrary optical waveform editors W0 and W2 at the central node E, the scheme can work normally.

[0107] S23, the idle light corresponding to the node passes through a 50:50 splitter. One output of the splitter is connected to a single photon detection module and the other is connected to the ODL, so that the idle light has a probability of being received by the single photon detection module SPD (generating a detection event sequence of the idle light at point E), and also has a probability of entering the tunable optical delay line ODL and reaching the arbitrary optical waveform editor W1.

[0108] S24, the signal light reflected back to the central node at the terminal node is output by the arbitrary optical waveform editor W2. If the corresponding idle light reaches the arbitrary optical waveform editor W1, W1 outputs a signal. After the optical delay line ODL supplements the time delay and the dispersion compensation fiber DCF nonlocally compensates the dispersion of the optical fiber link, the two signals enter the sum-frequency module to generate a sum-frequency signal. The silicon single-photon detection module detects the sum-frequency signal filtered by the short-pass filter SPF and outputs it to the TDC of the central node for time marking. The synchronization signal of the TDC of the central node is provided by the central clock of the central node.

[0109] Using the clock error calculation method described in Specific Embodiment 1, the computer of the central node E controls the ODL delay to eliminate clock error and controls the DCF non-local dispersion compensation to improve time synchronization accuracy based on the obtained clock error calculation signal.

[0110] For simultaneous time synchronization of four nodes or time synchronization of any number of nodes, after the central node E synchronizes with the terminal node A, it also synchronizes with the terminal node B, thereby achieving bidirectional quantum time synchronization between terminal nodes A and B, and thus enabling the quantum synchronization process of all nodes.

[0111] The specific implementation of this invention includes quantum security monitoring, which mainly involves the central node E randomly controlling whether W1 and W2 switch the optical path to the CHSH inequality test module to ensure the security of the scheme.

[0112] In this embodiment, time-division multiplexing reduces the number of entangled photon pairs that need to be sent from the central node each time, thereby reducing the number of sum-frequency modules and single-photon detection modules required, and thus compressing the manufacturing cost of the central node. It is compatible with wavelength-division multiplexing, adapting to various physical structures of fiber optic fixed networks, greatly enhancing the adaptability and compatibility of the quantum time synchronization method. Since the quantum optical frequency comb can generate multiple pairs of entangled photons, the central node can also achieve tilted allocation of quantum entanglement resources at key nodes through program control of an arbitrary optical waveform editor. Furthermore, with simple modifications, the terminal node can be changed to the next-level central node, providing compatibility guarantees for network cascading modes and facilitating further expansion of the quantum time synchronization network.

[0113] Based on the same inventive concept, in other embodiments of the present invention, a multi-terminal quantum time synchronization network system is provided, including a central node and multiple terminal nodes; each terminal node is connected to the central node via a single optical fiber; or, multiple terminal nodes are connected to the central node via wavelength division multiplexing (WDM) using a shared optical fiber link, and an arrayed waveguide grating is inserted in front of the terminal nodes for wavelength demultiplexing, cooperating with the central node for WDM and demultiplexing of arbitrary optical waveform editors. The above-described multi-terminal quantum time synchronization network method is implemented between the central node and the multiple terminal nodes.

[0114] The specific technical features of the central node and multiple terminal nodes of the system in this embodiment correspond to the multi-terminal quantum time synchronization network method in the above embodiments, and will not be repeated here.

[0115] Based on the same inventive concept, in other embodiments of the present invention, a terminal is provided, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the program, it can be used to execute the multi-terminal quantum time synchronization network method in any of the above embodiments, or to run the multi-terminal quantum time synchronization network system described above.

[0116] Optionally, the memory is used to store programs; the memory may include volatile memory, such as random-access memory (RAM), such as static random-access memory (SRAM), double data rate synchronous dynamic random-access memory (DDR SDRAM), etc.; the memory may also include non-volatile memory, such as flash memory. The memory is used to store computer programs (such as application programs, functional modules, etc. that implement the above methods), computer instructions, etc., and the aforementioned computer programs, computer instructions, etc., can be partitioned and stored in one or more memories. Furthermore, the aforementioned computer programs, computer instructions, data, etc., can be accessed by the processor.

[0117] The aforementioned computer programs, computer instructions, etc., can be stored in partitions within one or more memory locations. Furthermore, the aforementioned computer programs, computer instructions, data, etc., can be accessed by a processor.

[0118] A processor is used to execute a computer program stored in memory to implement the various steps of the methods involved in the above embodiments. For details, please refer to the relevant descriptions in the preceding method embodiments.

[0119] The processor and memory can be separate structures or integrated structures. When the processor and memory are separate structures, they can be coupled together via a bus.

[0120] Based on the same inventive concept, in other embodiments of the present invention, a computer-readable storage medium is provided having a computer program stored thereon, which, when executed by a processor, can be used to perform the above-described method or to run the above-described system.

[0121] Computer-readable media include computer storage media and communication media, wherein communication media include any medium that facilitates the transfer of computer programs from one place to another. Storage media can be any available medium accessible to a general-purpose or special-purpose computer. An exemplary storage medium is coupled to a processor, enabling the processor to read information from and write information to the storage medium. Of course, the storage medium can also be a component of the processor. The processor and storage medium can reside in an ASIC. Alternatively, the ASIC can reside in a user device. Of course, the processor and storage medium can also exist as discrete components in a communication device.

[0122] Those skilled in the art will understand that embodiments of this application can be provided as methods, systems, or computer program products. Therefore, this application can take the form of a completely hardware embodiment, a completely software embodiment, or an embodiment combining software and hardware aspects. Furthermore, this application can take the form of a computer program product embodied 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.

[0123] This application is described with reference to flowchart illustrations and / or block diagrams of methods, apparatus (systems), and computer program products according to this application. It should 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. Figure 1 One or more processes and / or boxes Figure 1 A device that provides the functions specified in one or more boxes.

[0124] 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.

[0125] 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 1One or more processes and / or boxes Figure 1 The steps of the function specified in one or more boxes.

[0126] Specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention. The above preferred features can be used in any combination without conflict.

Claims

1. A terminal quantum time synchronization network method, characterized in that, include: The central node extracts multiple pairs of entangled photons from the integrated microcavity quantum optical frequency comb. The entangled photons are separated into two paths: a signal light and an idle light. The signal light is input to the terminal node, and the idle light is input to the central node itself. In the terminal node, a portion of the signal light is used to generate a sequence of terminal node detection events and is fed back to the central node through a classical channel, while another portion is reflected to the ultrafast coincidence module of the central node. In the central node, part of the idle light is used to generate a central node detection event sequence, and the other part, after time delay and dispersion control, enters the ultrafast coincidence module of the central node. In the ultrafast convergence module, the incoming signal light and the idle light are combined to obtain another central node detection event sequence; Based on the terminal node detection event sequence and all the central node detection event sequences, clock bias is calculated to obtain the clock bias; Based on the clock difference, the delay and dispersion control of the idle light are adjusted to ensure that the idle light and the signal light experience the same propagation time, thereby achieving time synchronization of multiple terminal nodes.

2. The terminal quantum time synchronization network method according to claim 1, characterized in that, The optical frequency comb has a center frequency of f. s0 The repetition frequency is f sr Multiple entangled sources, the center frequency f s0 The symmetrical comb teeth are a pair of entangled photons; The optical frequency comb is edited by an arbitrary optical waveform editor W0 and then combined with f. s0 The symmetrical comb teeth on both sides are divided into two paths: the signal light and the idle light. The signal light is transmitted sequentially through a circulator and an optical fiber link to the terminal node.

3. The terminal quantum time synchronization network method according to claim 2, characterized in that, In the terminal node, a portion of the signal light is used to generate a sequence of terminal node detection events and fed back to the central node via a classical channel, while another portion is reflected to the ultrafast reconciliation module of the central node, including: The signal light is split into two paths by a beam splitter. One path is reflected back to the central node by a Faraday mirror (FM), and then enters the ultrafast convergence module after passing through the circulator and the arbitrary light waveform editor. Another path is time-stamped via a single-photon detection module (SPD) and a time-to-digital converter (TDC) to form a sequence of detection events at the terminal node. The synchronization signal of the single-photon detection module (TDC) is provided by the terminal clock.

4. The terminal quantum time synchronization network method according to claim 2, characterized in that, In the central node, a portion of the idle light is used to generate a central node detection event sequence, and another portion, after time delay and dispersion control, enters the ultrafast convergence module of the central node, including: The idle light is split into two paths by a beam splitter. One path is received by the single-photon detection module (SPD) to form a detection event sequence of the idle light. The other path, after time delay and dispersion by the arbitrary light waveform editor, enters the ultrafast convergence module.

5. The terminal quantum time synchronization network method according to claim 1, characterized in that, In the ultrafast convergence module, the signal light and the idle light are combined and frequency-matched to obtain another central node detection event sequence, including: The signal light and the idle light output by the arbitrary light waveform editor enter the sum-frequency module SPF to generate a sum-frequency effect and obtain a sum-frequency signal; The silicon single-photon detection module (SiSPD) detects the sum-frequency signal and outputs it to the time-to-digital converter (TDC) at the central node for time stamping, thereby obtaining the central node's detection event sequence. The synchronization signal of the central node's time-to-digital converter (TDC) is provided by the central clock.

6. The terminal quantum time synchronization network method according to claim 1, characterized in that, The step of calculating the clock bias based on the terminal node detection event sequence and all the central node detection event sequences includes: The correlation function between the probe event sequences of the central node and the terminal node is obtained from the probe event sequence through Fast Fourier Transform and its inverse transform. , where a and b represent the detection event sequences of the central node and the terminal node, respectively; This is the time offset; The correlation function is searched using time delay control. Find the time offset by the maximum value in the range; The correlation function is obtained in The sum-frequency signal at the central node reaches its maximum value. When the value reaches its maximum, the clock difference is obtained. : .

7. The terminal quantum time synchronization network method according to claim 1, characterized in that, The step of adjusting the delay and dispersion control of the idle light based on the clock difference to ensure that the idle light and the signal light experience the same propagation time, thereby achieving time synchronization of multiple terminal nodes, includes: Based on the clock error, the clock error is eliminated by optical delay line (ODL), and the dispersion of the compensation fiber is adjusted by dispersion compensation fiber (DCF) to achieve time synchronization between the central node and a terminal node. Quantum time synchronization between multiple terminal nodes can be achieved by switching the communication optical path of the current node to the communication optical path of the terminal node to be synchronized, or by using another pair of frequency-entangled photons.

8. A terminal quantum time synchronization network system, characterized in that, It includes a central node and multiple terminal nodes; the central node and the multiple terminal nodes implement the multi-terminal quantum time synchronization network method according to any one of claims 1-7, wherein: Each terminal node and the central node are connected via a single optical fiber; Alternatively, multiple terminal nodes can share a single fiber optic link with the central node via wavelength division multiplexing (WDM), and an arrayed waveguide grating can be inserted in front of the terminal nodes for wavelength demultiplexing, in conjunction with the central node for WDM and demultiplexing of any optical waveform editor.

9. A terminal, comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the program, it can be used to perform the method of any one of claims 1-7.

10. A computer-readable storage medium having a computer program stored thereon, characterized in that, When executed by a processor, the program can be used to perform the method of any one of claims 1-7.

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