Composite bidirectional quantum time synchronization method and system

Abstract

The embodiment of the application provides a kind of composite bidirectional quantum time synchronization method and system, the system includes: reference end and to be synchronized end, the reference end includes first frequency entanglement source, first optical module, first detection module and first event timer, the to be synchronized end includes second frequency entanglement source, second optical module, second detection module and second event timer;The first optical module connects the first frequency entanglement source and first detection module, and is connected second optical module by quantum link;Second optical module connects the second frequency entanglement source and second detection module, and is connected first optical module by quantum link.The embodiment of the application provides a kind of composite bidirectional quantum time synchronization method and system by superimposing twice bidirectional time synchronization result to eliminate wavelength non reciprocity, can improve the precision and stability of long distance quantum time synchronization.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of time frequency, in particular to a composite bidirectional quantum time synchronization system. BACKGROUND

[0002] Compared with the classical bidirectional time synchronization, the bidirectional quantum time synchronization based on the energy-time entanglement source has the natural advantages of high precision and security. At present, the synchronization precision of the bidirectional quantum time synchronization can reach picosecond to sub-picosecond. However, in the process of generating entangled photons, the output wavelength of the entangled photons is subject to jitter due to the high sensitivity of the temperature of the nonlinear crystal and other factors.

[0003] The existing scheme actively controls the temperature of the nonlinear crystal through the feedback mechanism of monitoring the output entangled photon wavelength, so as to realize the stability of the output wavelength of the entangled photons, but has defects such as increase of system cost and complexity. SUMMARY

[0004] The embodiment of the present application expects to provide a composite bidirectional quantum time synchronization system, which can improve the time synchronization precision and stability.

[0005] The technical scheme of the present application is implemented as follows:

[0006] In a first aspect, the embodiment provides a composite bidirectional quantum time synchronization system, comprising: a reference end and a to-be-synchronized end, the reference end comprising a first frequency entanglement source, a first optical module, a first detection module and a first event timer, and the to-be-synchronized end comprising a second frequency entanglement source, a second optical module, a second detection module and a second event timer.

[0007] The first frequency entanglement source is configured to generate a first pair of frequency anti-correlated photons.

[0008] The first optical module is connected to the first frequency entanglement source and the first detection module, and is connected to the second optical module through a quantum link, and is configured to process the first pair of photons and send at least part of the first mixed photons to the first detection module, so that the first detection module detects the arrival of the first mixed photons and records the first arrival time of the signal photons and the second arrival time of the idle photons in at least part of the first mixed photons through the first event timer, and transmits at least another part of the first mixed photons to the second optical module. Correspondingly, the second detection module is also configured to detect the arrival of at least another part of the first mixed photons and record the third arrival time of the signal photons and the fourth arrival time of the idle photons in at least another part of the first mixed photons through the second event timer.

[0009] The second frequency entanglement source is used to generate a second pair of frequency anti-correlated photons, wherein the second frequency entanglement source is the same as the laser frequency of the first frequency entanglement source.

[0010] The second optical module is connected to the second frequency entanglement source and a second detection module, and is connected to the first optical module through a quantum link, and is used to transmit at least part of the second mixed photons to the second detection module after processing the second pair of photons, so that the second detection module detects that at least part of the second mixed photons arrives, and records the fifth arrival time of the signal photons and the sixth arrival time of the idle photons in at least part of the second mixed photons through a second event timer, and transmits at least another part of the second mixed photons to the first optical module, and correspondingly, the first detection module is also used to detect that at least another part of the second mixed photons arrives, and records the seventh arrival time of the signal photons and the eighth arrival time of the idle photons in at least another part of the second mixed photons through the first event timer.

[0011] The first arrival time, the second arrival time, the third arrival time, the fourth arrival time, the fifth arrival time, the sixth arrival time, the seventh arrival time and the eighth arrival time are used to calculate the clock difference of the composite two-way quantum time synchronization.

[0012] In one specific embodiment, the first optical module includes a first single-mode optical fiber, a first polarization beam combiner, a first beam splitter and a first loopback device connected in sequence, and the first loopback device is connected to the second optical module through a quantum link.

[0013] The first polarization beam combiner is used to receive the idle photons in the first pair of photons transmitted by the first frequency entanglement source and the signal photons in the first pair of photons delayed by the first single-mode optical fiber, and to combine the idle photons in the first pair of photons and the signal photons in the first pair of photons to obtain first mixed photons.

[0014] The first beam splitter is used to transmit at least part of the first mixed photons to the first detection module, and transmit at least another part of the first mixed photons to the first loopback device to transmit at least another part of the first mixed photons to the second optical module through the quantum link.

[0015] In one specific embodiment, the first detection module includes a third single-photon detector and a second single-photon detector, the third single-photon detector is connected to the first beam splitter, and the second single-photon detector is connected to the first loopback device.

[0016] The third single-photon detector is configured to record a first arrival time of a signal photon and a second arrival time of an idle photon in the first mixed photon through a first event timer after the first mixed photon is detected to arrive;

[0017] The second single-photon detector is configured to record a third arrival time of a signal photon and a fourth arrival time of an idle photon in the at least another part of the second mixed photon through a first event timer after the at least another part of the second mixed photon is detected to arrive.

[0018] In one specific embodiment, the second optical module comprises a second single-mode optical fiber, a second polarization beam combiner, a second beam splitter and a second circulator connected in sequence, and the second circulator is connected to the first optical module through a quantum link;

[0019] The second polarization beam combiner is configured to receive an idle photon in a second two-photon pair sent by the second frequency entanglement source and a signal photon in the second two-photon pair delayed through the second single-mode optical fiber, and combine the idle photon in the second two-photon pair and the signal photon in the second two-photon pair to obtain a second mixed photon;

[0020] The second beam splitter is configured to transmit at least a part of the second mixed photon to a second detection module, and transmit at least another part of the second mixed photon to the second circulator to transmit the at least another part of the second mixed photon to the first optical module through the quantum link.

[0021] In one specific embodiment, the second detection module comprises a first single-photon detector and a fourth single-photon detector, the fourth single-photon detector is connected to the second beam splitter, and the first single-photon detector is connected to the second circulator;

[0022] The fourth single-photon detector is configured to record a fifth arrival time of a signal photon and a sixth arrival time of an idle photon in the second mixed photon through a second event timer after the second mixed photon is detected to arrive;

[0023] The first single-photon detector is configured to record a seventh arrival time of a signal photon and an eighth arrival time of an idle photon in the at least another part of the first mixed photon through a second event timer after the at least another part of the first mixed photon is detected to arrive.

[0024] In one specific embodiment, the formula for calculating the clock difference of the composite bidirectional quantum time synchronization is:

[0025] wherein, the third arrival time of the signal photon in the at least another part of the first mixed photon, a fourth arrival time of an idler photon in at least another portion of the first mixed photons; a seventh arrival time of a signal photon in at least another portion of the second mixed photons; an eighth arrival time of an idler photon in at least another portion of the second mixed photons; a first arrival time of a signal photon in at least a portion of the first mixed photons; a second arrival time of an idler photon in at least a portion of the first mixed photons; a fifth arrival time of a signal photon in at least a portion of the second mixed photons; a sixth arrival time of an idler photon in at least a portion of the second mixed photons.

[0026] In one specific embodiment, the quantum link comprises a dispersion-compensated optical fiber.

[0027] In one specific embodiment, further comprising: a reference clock connected to the first event timer for providing a time reference of the first event timer; a clock to be synchronized connected to the second event timer for providing a time reference of the second event timer, and calibrated according to the clock difference of the composite bidirectional quantum time synchronization.

[0028] In a second aspect, the embodiment provides a composite bidirectional quantum time synchronization method, which is applied to the composite bidirectional quantum time synchronization system described above, and the method comprises:

[0029] generating a first pair of bi-photons with frequency anti-correlation;

[0030] After processing the first pair of bi-photons, at least a portion of the first mixed photons is sent to the first detection module, so that the first detection module detects the arrival of the first mixed photons, and records the first arrival time of a signal photon and the second arrival time of an idler photon in at least a portion of the first mixed photons through the first event timer, and at least another portion of the first mixed photons is transmitted to the second optical module, and correspondingly, the second detection module detects the arrival of at least another portion of the first mixed photons, and records the third arrival time of a signal photon and the fourth arrival time of an idler photon in at least another portion of the first mixed photons through the second event timer;

[0031] generating a second pair of bi-photons with frequency anti-correlation, wherein the laser frequency of the second frequency entanglement source is the same as that of the first frequency entanglement source;

[0032] After processing the second two-photon pair, at least a part of the second mixed photons is sent to the second detection module, so that the second detection module detects the arrival of at least a part of the second mixed photons, and records the fifth arrival time of the signal photons and the sixth arrival time of the idle photons in at least a part of the second mixed photons through the second event timer after the arrival of at least a part of the second mixed photons, and at least another part of the second mixed photons is transmitted to the first optical module, and correspondingly, the first detection module detects the arrival of at least another part of the second mixed photons, and records the seventh arrival time of the signal photons and the eighth arrival time of the idle photons in at least another part of the second mixed photons through the first event timer after the arrival of at least another part of the second mixed photons.

[0033] Wherein, the first arrival time, the second arrival time, the third arrival time, the fourth arrival time, the fifth arrival time, the sixth arrival time, the seventh arrival time and the eighth arrival time are used to calculate the clock difference of the composite two-way quantum time synchronization.

[0034] The embodiment of the application provides a composite bidirectional quantum time synchronization system, comprising: a reference end and a to-be-synchronized end, wherein the reference end comprises a first frequency entanglement source, a first optical module, a first detection module and a first event timer, the to-be-synchronized end comprises a second frequency entanglement source, a second optical module, a second detection module and a second event timer; the first frequency entanglement source is used for generating a first pair of frequency anti-correlated double photons; the first optical module is connected with the first frequency entanglement source and the first detection module, and is connected with the second optical module through a quantum link, and is used for transmitting at least part of first mixed photons to the first detection module after processing the first pair of double photons, so that the first detection module records a first arrival time of a signal photon and a second arrival time of an idle photon in at least part of the first mixed photons after detecting the arrival of the first mixed photons, and transmits at least another part of the first mixed photons to the second optical module, and correspondingly, the second detection module is also used for recording a third arrival time of a signal photon and a fourth arrival time of an idle photon in at least another part of the first mixed photons after detecting the arrival of at least another part of the first mixed photons; the second frequency entanglement source is used for generating a second pair of frequency anti-correlated double photons, wherein the laser frequency of the second frequency entanglement source is the same as that of the first frequency entanglement source; the second optical module is connected with the second frequency entanglement source and the second detection module, and is connected with the first optical module through a quantum link, and is used for transmitting at least part of second mixed photons to the second detection module after processing the second pair of double photons, so that the second detection module records a fifth arrival time of a signal photon and a sixth arrival time of an idle photon in at least part of the second mixed photons after detecting the arrival of at least part of the second mixed photons, and transmits at least another part of the second mixed photons to the first optical module, and correspondingly, the first detection module is also used for recording a seventh arrival time of a signal photon and an eighth arrival time of an idle photon in at least another part of the second mixed photons after detecting the arrival of at least another part of the second mixed photons; wherein the first arrival time, the second arrival time, the third arrival time, the fourth arrival time, the fifth arrival time, the sixth arrival time, the seventh arrival time and the eighth arrival time are used for calculating a clock difference of the composite bidirectional quantum time synchronization. In the above scheme, the wavelength non-reciprocity is eliminated by superimposing twice the bidirectional time synchronization result, and the precision and stability of long-distance quantum time synchronization can be improved. BRIEF DESCRIPTION OF DRAWINGS

[0035] The drawings in the accompanying drawings are incorporated into the specification and form a part of the specification, which show embodiments consistent with the present application, and together with the specification serve to explain the technical solutions of the present application. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor on the basis of these drawings.

[0036] The flowchart shown in the drawings is only an exemplary description, and is not necessarily to include all contents and operations / steps, nor is it necessarily executed in the order described. For example, some operations / steps can be further decomposed, and some operations / steps can be combined or partially combined, so that the actual execution order can be changed according to the actual situation.

[0037] Figure 1 A composite bidirectional quantum time synchronization system module block diagram is provided for the embodiments of the present application.

[0038] Figure 2 Another composite bidirectional quantum time synchronization system module block diagram is provided for the embodiments of the present application. DETAILED DESCRIPTION

[0039] In order to make the purpose, technical solutions and advantages of the embodiments of the present application more clear, the specific technical solutions of the present application will be further described in detail below in combination with the drawings in the embodiments of the present application. The following embodiments are used to illustrate the present application, but not to limit the scope of the present application.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which the present application belongs. The terms used herein are only for the purpose of describing the embodiments of the present application, and are not intended to limit the present application.

[0041] In the following description, "some embodiments", "the embodiment", "the embodiments of the present application" and the like are described, which describe a subset of all possible embodiments, but it can be understood that "some embodiments" can be the same subset or different subset of all possible embodiments, and can be combined with each other without conflict.

[0042] If the application file appears "first / second" similar description, the following description is added, in the following description, the terms "first\second\third" are only to distinguish similar objects, and do not represent the specific order of the objects. It can be understood that "first\second\third" can be interchanged in the specific order or sequence as allowed, so that the embodiments of the present application described herein can be implemented in an order other than that illustrated or described herein.

[0043] Please refer to Figure 1This embodiment provides a composite bidirectional quantum time synchronization system, including: a reference end 10 and a synchronization end 20. The reference end 10 includes a first frequency entanglement source 11, a first optical module 12, a first detection module 13 and a first event timer 14. The synchronization end 20 includes a second frequency entanglement source 21, a second optical module 22, a second detection module 23 and a second event timer 24.

[0044] The first frequency entanglement source 11 is used to generate a first frequency-anticorrelated two-photon pair; specifically, it can be generated by exciting a periodically polarized lithium niobate crystal or other crystals with a pump laser to induce a nonlinear effect of spontaneous parametric down-conversion.

[0045] The first optical module 12 is connected to the first frequency entanglement source 11 and the first detection module 13, and is connected to the second optical module 22 via a quantum link. It is used to process the first two-photon pair and send at least a portion of the first mixed photons to the first detection module 13, so that after the first detection module 13 detects the arrival of the first mixed photons, it records the first arrival time of the signal photon and the second arrival time of the idle photon in the at least a portion of the first mixed photons through the first event timer 14, and transmits at least another portion of the first mixed photons to the second optical module 22. Correspondingly, the second detection module 23 is also used to detect the arrival of at least another portion of the first mixed photons and record the third arrival time of the signal photon and the fourth arrival time of the idle photon in the at least another portion of the first mixed photons through the second event timer 24.

[0046] The second frequency entanglement source 21 is used to generate a second two-photon pair with anti-correlation in frequency, wherein the second frequency entanglement source 21 has the same laser frequency as the first frequency entanglement source 11;

[0047] The second optical module 22 is connected to the second frequency entanglement source 21 and the second detection module 23, and is connected to the first optical module 12 via a quantum link. It is used to process the second two-photon pair and send at least a portion of the second mixed photons to the second detection module 23. After the second detection module 23 detects the arrival of at least a portion of the second mixed photons, it records the fifth arrival time of the signal photon and the sixth arrival time of the idle photon in at least a portion of the second mixed photons through the second event timer 24. It also transmits at least another portion of the second mixed photons to the first optical module 12. Correspondingly, the first detection module 13 is also used to detect the arrival of at least another portion of the second mixed photons and record the seventh arrival time of the signal photon and the eighth arrival time of the idle photon in at least another portion of the second mixed photons through the first event timer 14.

[0048] The first arrival time, the second arrival time, the third arrival time, the fourth arrival time, the fifth arrival time, the sixth arrival time, the seventh arrival time and the eighth arrival time are used to calculate the clock difference of the composite two-way quantum time synchronization.

[0049] In one embodiment, the first optical module 12 comprises a first single-mode optical fiber 121, a first polarization beam combiner 122, a first beam splitter 123 and a first circulator 124 connected in sequence, and the first circulator 124 is connected to the second optical module 22 through a quantum link.

[0050] The first polarization beam combiner 122 is configured to receive an idle photon in a first two-photon pair sent by the first frequency entanglement source 11 and a signal photon in the first two-photon pair delayed through the first single-mode optical fiber 121, and combine the idle photon in the first two-photon pair and the signal photon in the first two-photon pair to obtain a first mixed photon.

[0051] The first beam splitter 122 is configured to transmit at least part of the first mixed photon to the first detection module 13 and transmit at least another part of the first mixed photon to the first circulator 124 to transmit the at least another part of the first mixed photon to the second optical module 22 through the quantum link.

[0052] In one embodiment, the first detection module 13 comprises a third single-photon detector 131 and a second single-photon detector 132, the third single-photon detector 131 is connected to the first beam splitter 122, and the second single-photon detector 132 is connected to the first circulator 124.

[0053] The third single-photon detector 131 is configured to detect the arrival of the first mixed photon and record the first arrival time of the signal photon and the second arrival time of the idle photon in the first mixed photon through the first event timer 14.

[0054] The second single-photon detector 132 is configured to detect the arrival of the at least another part of the second mixed photon and record the third arrival time of the signal photon and the fourth arrival time of the idle photon in the at least another part of the second mixed photon through the first event timer 14.

[0055] In one embodiment, the second optical module 22 comprises a second single-mode optical fiber 221, a second polarization beam combiner 222, a second beam splitter 223 and a second circulator 224 connected in sequence, and the second circulator 224 is connected to the first optical module 12 through a quantum link.

[0056] The second polarization beam combiner 222 is configured to receive an idle photon in a second two-photon pair sent by the second frequency entanglement source 21 and a signal photon in the second two-photon pair delayed by the second single-mode optical fiber 221, and combine the idle photon in the second two-photon pair and the signal photon in the second two-photon pair to obtain a second mixed photon;

[0057] The second beam splitter 223 is configured to transmit at least part of the second mixed photon to the second detection module 23 and transmit at least another part of the second mixed photon to the second circulator 224 to transmit the at least another part of the second mixed photon to the first optical module 12 through the quantum link.

[0058] It should be noted that the splitting ratios of the first beam splitter and the second beam splitter in the embodiment can be adjusted according to actual conditions under the premise of meeting the measurement requirements and accuracy requirements, for example, a 90 / 10 beam splitter is selected.

[0059] In one specific embodiment, the second detection module 23 includes a fourth single-photon detector 231 and a first single-photon detector 232, the fourth single-photon detector 231 is connected to the second polarization beam combiner 222, and the first single-photon detector 232 is connected to the second circulator 224.

[0060] The fourth single-photon detector 231 is configured to detect the arrival of the second mixed photon and record a fifth arrival time of a signal photon and a sixth arrival time of an idle photon in the second mixed photon through the second event timer 24;

[0061] The first single-photon detector 232 is configured to detect the arrival of the at least another part of the first mixed photon and record a seventh arrival time of a signal photon and an eighth arrival time of an idle photon in the at least another part of the first mixed photon through the second event timer 24.

[0062] In one specific embodiment, the calculation formula of the clock difference of the composite two-way quantum time synchronization is:

[0063] , wherein, the third arrival time of the signal photon in the at least another part of the first mixed photon is represented by T1, the fourth arrival time of the idle photon in the at least another part of the first mixed photon is represented by T2; the seventh arrival time of the signal photon in the at least another part of the second mixed photon is represented by T5, the eighth arrival time of the idle photon in the at least another part of the second mixed photon is represented by T6. a first arrival time of a signal photon in at least a portion of the first hybrid photons; a second arrival time of an idler photon in at least a portion of the first hybrid photons; a fifth arrival time of a signal photon in at least a portion of the second hybrid photons; a sixth arrival time of an idler photon in at least a portion of the second hybrid photons.

[0064] The derivation process of the clock difference calculation formula of the above composite two-way quantum time synchronization is as follows:

[0065] The coincidence measurement of the signal photon and idler photon arrival time of the third single photon detector and the first single photon detector can reflect the sum of the clock difference and the link delay information as follows:

[0066] (1)

[0067] (2)

[0068] wherein, is the reference time of the clock to be synchronized located at the to-be-synchronized end, is the reference time of the reference clock located at the reference end, and are the first-order dispersion experienced by the entangled photons in the single-mode fiber medium and the dispersion compensation fiber medium, respectively, and are the lengths of the single-mode fiber and the dispersion elimination fiber, respectively, is the center frequency of the entangled photons, represents the signal photon frequency of the first frequency entanglement source, represents the idler photon frequency of the first frequency entanglement source.

[0069] Similarly, the coincidence measurement of the photon arrival time of the fourth single photon detector and the second single photon detector can reflect the sum of the clock difference and the link delay information as follows:

[0070] (3)

[0071] (4)

[0072] represents the signal photon frequency of the second frequency entanglement source, represents the idler photon frequency of the second frequency entanglement source. By subtracting (3) from the above formula (1), the following formula (5) can be obtained:

[0073] (5)

[0074] wherein, The clock difference of the two-way quantum time synchronization 1 can be obtained by simplifying the above formula (5):

[0075] (6)

[0076] Similarly, the clock difference of the two-way quantum time synchronization 2 can be obtained by subtracting formula (4) from formula (2):

[0077] (7)

[0078] The clock difference of the two-way quantum time synchronization 2 can be obtained by simplifying the above formula (7):

[0079] (8)

[0080] The clock difference of the two-way quantum time synchronization 1 and the clock difference of the two-way quantum time synchronization 2 can be calculated to obtain the clock difference of the composite two-way quantum time synchronization:

[0081] (9)

[0082] Since the first frequency entanglement source and the second frequency entanglement source have the same pump light frequency, the following formula (10) is obtained:

[0083] (10)

[0084] According to formula (10), formula (9) can be simplified as:

[0085] (11)

[0086] That is, the embodiment realizes the composite two-way quantum time synchronization by transmitting and processing the entangled two photons of the frequency entanglement two photon source without distinction on the basis of the protocol of the two-way quantum time synchronization, and can effectively resist the transmission wavelength related time delay non-reciprocity, thereby improving the quantum time synchronization performance.

[0087] In one specific embodiment, the quantum link includes a dispersion compensation fiber.

[0088] In one specific embodiment, it further includes a reference clock 15 connected to the first event timer 14 for providing a time reference of the first event timer, a to-be-synchronized clock 25 connected to the second event timer 24 for providing a time reference of the second event timer, and calibrating according to the clock difference of the composite two-way quantum time synchronization.

[0089] In a second aspect, the embodiment provides a composite two-way quantum time synchronization method, which is applied to the composite two-way quantum time synchronization system described above, and the method comprises:

[0090] generating a first pair of two-photon with frequency anti-correlation;

[0091] after processing the first pair of two-photon, sending at least part of the first mixed photons to the first detection module, so that the first detection module detects the arrival of the first mixed photons, and records the first arrival time of the signal photons and the second arrival time of the idle photons in the at least part of the first mixed photons by the first event timer, and transmits at least another part of the first mixed photons to the second optical module, and correspondingly, the second detection module detects the arrival of the at least another part of the first mixed photons, and records the third arrival time of the signal photons and the fourth arrival time of the idle photons in the at least another part of the first mixed photons by the second event timer;

[0092] generating a second pair of two-photon with frequency anti-correlation, wherein the second frequency entanglement source has the same laser frequency as the first frequency entanglement source;

[0093] after processing the second pair of two-photon, sending at least part of the second mixed photons to the second detection module, so that the second detection module detects the arrival of the at least part of the second mixed photons, and records the fifth arrival time of the signal photons and the sixth arrival time of the idle photons in the at least part of the second mixed photons by the second event timer, and transmits at least another part of the second mixed photons to the first optical module, and correspondingly, the first detection module detects the arrival of the at least another part of the second mixed photons, and records the seventh arrival time of the signal photons and the eighth arrival time of the idle photons in the at least another part of the second mixed photons by the first event timer;

[0094] wherein the first arrival time, the second arrival time, the third arrival time, the fourth arrival time, the fifth arrival time, the sixth arrival time, the seventh arrival time and the eighth arrival time are used to calculate the clock difference of the composite two-way quantum time synchronization.

[0095] The embodiment of the present application provides a composite bidirectional quantum time synchronization system, comprising: a reference end and a to-be-synchronized end, wherein the reference end comprises a first frequency entanglement source, a first optical module, a first detection module and a first event timer, and the to-be-synchronized end comprises a second frequency entanglement source, a second optical module, a second detection module and a second event timer; the first frequency entanglement source is used for generating a first pair of frequency anti-correlated two photons; the first optical module is connected with the first frequency entanglement source and the first detection module, and is connected with the second optical module through a quantum link, and is used for transmitting at least part of first mixed photons to the first detection module after processing the first pair of two photons, so that the first detection module records a first arrival time of a signal photon and a second arrival time of an idle photon in at least part of the first mixed photons after detecting the arrival of the first mixed photons, and transmits at least another part of the first mixed photons to the second optical module, and correspondingly, the second detection module is also used for recording a third arrival time of a signal photon and a fourth arrival time of an idle photon in at least another part of the first mixed photons after detecting the arrival of at least another part of the first mixed photons; the second frequency entanglement source is used for generating a second pair of frequency anti-correlated two photons, wherein the laser frequency of the second frequency entanglement source is the same as that of the first frequency entanglement source; the second optical module is connected with the second frequency entanglement source and the second detection module, and is connected with the first optical module through a quantum link, and is used for transmitting at least part of second mixed photons to the second detection module after processing the second pair of two photons, so that the second detection module records a fifth arrival time of a signal photon and a sixth arrival time of an idle photon in at least part of the second mixed photons after detecting the arrival of at least part of the second mixed photons, and transmits at least another part of the second mixed photons to the first optical module, and correspondingly, the first detection module is also used for recording a seventh arrival time of a signal photon and an eighth arrival time of an idle photon in at least another part of the second mixed photons after detecting the arrival of at least another part of the second mixed photons; wherein the first arrival time, the second arrival time, the third arrival time, the fourth arrival time, the fifth arrival time, the sixth arrival time, the seventh arrival time and the eighth arrival time are used for calculating a clock difference of the composite bidirectional quantum time synchronization. In the above scheme, the wavelength non-reciprocity is eliminated by superimposing twice the bidirectional time synchronization result, and the precision and stability of long-distance quantum time synchronization can be improved.

[0096] In addition, each functional module in the embodiment of the present application can be integrated in one processing unit, or each unit can exist physically independently, or two or more units can be integrated in one unit. The integrated unit can be realized in the form of hardware or in the form of a software functional module.

[0097] If the integrated unit is implemented in the form of a software function module and is not sold or used as an independent product, it can be stored in a computer readable storage medium based on such understanding. The technical solutions of the embodiments can essentially or contribute to the prior art or all or part of the technical solutions can be embodied in the form of a software product. The computer software product is stored in a storage medium and includes a plurality of instructions for causing a computer device (which can be a personal computer, a server, or a network device, etc.) or a processor to execute all or part of the steps of the embodiments. The aforementioned storage medium includes a U disk, a mobile hard disk, a read-only memory (ROM), a random access memory (RAM), a magnetic disk or an optical disk, and various media that can store program codes.

[0098] It should be understood that the "one embodiment" or "an embodiment" or "some embodiments" mentioned throughout the specification means that the specific features, structures or characteristics related to the embodiments are included in at least one embodiment of the present application. Therefore, "in one embodiment" or "in an embodiment" or "in some embodiments" appearing throughout the specification does not necessarily refer to the same embodiment. In addition, these specific features, structures or characteristics can be combined in one or more embodiments in any suitable manner. It should be understood that in various embodiments of the present application, the size of the sequence number of the above processes does not mean the execution order, and the execution order of the processes should be determined according to its function and inherent logic, and should not constitute any limitation on the implementation process of the embodiments of the present application. The above sequence number of the embodiments of the present application is only for description, not representing the advantages and disadvantages of the embodiments. The above description of each embodiment tends to emphasize the differences between each embodiment, and the same or similar parts can be referred to each other. For the sake of brevity, this paper will not repeat here.

[0099] The above modules described as separate components can or can not be physically separated, and the components displayed as modules can or can not be physical modules; they can be located in one place or distributed on multiple network units; part or all of the modules can be selected according to actual needs to achieve the purpose of the embodiments.

[0100] In addition, each functional module in each embodiment of the present application can be integrated in one processing unit, or each module can be a separate unit, or two or more modules can be integrated in one unit. The integrated module can be realized in the form of hardware or hardware plus software function unit.

[0101] Those skilled in the art can understand that all or part of the steps of the above-mentioned method embodiments can be completed by relevant hardware of program instructions, the foregoing program can be stored in a computer readable storage medium, and the program executes the steps of the method embodiments when executed.

[0102] The methods disclosed in the several method embodiments provided by the embodiments of the present application can be combined arbitrarily without conflict to obtain new method embodiments.

[0103] The features disclosed in the several product embodiments provided by the embodiments of the present application can be combined arbitrarily without conflict to obtain new product embodiments.

[0104] The features disclosed in the several method or device embodiments provided by the embodiments of the present application can be combined arbitrarily without conflict to obtain new method or device embodiments.

[0105] The above merely describes the implementation manners of the embodiments of the present application, but the protection scope of the embodiments of the present application is not limited to this. Any person skilled in the art can easily think of changes or replacements within the technical range disclosed by the present application, which should be covered in the protection scope of the embodiments of the present application. Therefore, the protection scope of the embodiments of the present application should be subject to the protection scope of the claims.

Claims

1. A composite bidirectional quantum time synchronization system, characterized in that, include: The system includes a reference end and a synchronization end. The reference end includes a first frequency entanglement source, a first optical module, a first detection module, and a first event timer. The synchronization end includes a second frequency entanglement source, a second optical module, a second detection module, and a second event timer. The first frequency entanglement source is used to generate a first two-photon pair with anti-correlation in frequency; The first optical module is connected to the first frequency entanglement source and the first detection module, and is connected to the second optical module via a quantum link. It is used to process the first two-photon pair and send at least a portion of the first mixed photons to the first detection module, so that after the first detection module detects the arrival of the first mixed photons, it records the first arrival time of the signal photon and the second arrival time of the idle photon in the at least a portion of the first mixed photons through a first event timer. It also transmits at least another portion of the first mixed photons to the second optical module. Correspondingly, the second detection module is also used to detect the arrival of at least another portion of the first mixed photons and record the third arrival time of the signal photon and the fourth arrival time of the idle photon in the at least another portion of the first mixed photons through a second event timer. The second frequency entanglement source is used to generate a second two-photon pair with anti-correlated frequencies, wherein the laser frequency of the second frequency entanglement source is the same as that of the first frequency entanglement source; The second optical module is connected to the second frequency entanglement source and the second detection module, and is connected to the first optical module via a quantum link. It is used to process the second two-photon pair and send at least a portion of the second mixed photons to the second detection module. After the second detection module detects the arrival of at least a portion of the second mixed photons, it records the fifth arrival time of the signal photon and the sixth arrival time of the idle photon in at least a portion of the second mixed photons through a second event timer. It also transmits at least another portion of the second mixed photons to the first optical module. Correspondingly, the first detection module is also used to detect the arrival of at least another portion of the second mixed photons and record the seventh arrival time of the signal photon and the eighth arrival time of the idle photon in at least another portion of the second mixed photons through a first event timer. The first arrival time, second arrival time, third arrival time, fourth arrival time, fifth arrival time, sixth arrival time, seventh arrival time, and eighth arrival time are used to calculate the clock difference of the composite two-way quantum time synchronization. The formula for calculating the clock difference in composite two-way quantum time synchronization is: wherein denotes a third arrival time of a signal photon in at least another portion of the first mixed photons, denotes a fourth arrival time of an idler photon in at least another portion of the first mixed photons; denotes a seventh arrival time of a signal photon in at least another portion of the second mixed photons; denotes an eighth arrival time of an idler photon in at least another portion of the second mixed photons; denotes a first arrival time of a signal photon in at least a portion of the first mixed photons; denotes a second arrival time of an idler photon in at least a portion of the first mixed photons; denotes a fifth arrival time of a signal photon in at least a portion of the second mixed photons; denotes a sixth arrival time of an idler photon in at least a portion of the second mixed photons.

2. The composite two-way quantum time synchronization system of claim 1, wherein, The first optical module includes a first single-mode fiber, a first polarization combiner, a first beam splitter, and a first circulator connected in sequence. The first circulator is connected to the second optical module via a quantum link. The first polarization beam combiner is used to receive the idle photon in the first two-photon pair sent by the first frequency entanglement source, and the signal photon in the first two-photon pair after being delayed by the first single-mode fiber, and to combine the idle photon in the first two-photon pair and the signal photon in the first two-photon pair to obtain the first mixed photon. The first beam splitter is configured to transmit at least a part of the first mixed photons to a first detection module, and transmit at least another part of the first mixed photons to a first circulator to transmit the at least another part of the first mixed photons to a second optical module through a quantum link.

3. The composite two-way quantum time synchronization system of claim 2, wherein, The first detection module comprises a third single-photon detector and a second single-photon detector, the third single-photon detector is connected to the first beam splitter, and the second single-photon detector is connected to the first circulator. The third single-photon detector is configured to detect arrival of the first mixed photons and record a first arrival time of a signal photon and a second arrival time of an idle photon in the first mixed photons through a first event timer. The second single-photon detector is configured to detect arrival of the at least another part of the second mixed photons and record a third arrival time of a signal photon and a fourth arrival time of an idle photon in the at least another part of the second mixed photons through a first event timer.

4. The composite two-way quantum time synchronization system of claim 1, wherein, The second optical module comprises a second single-mode optical fiber, a second polarization beam combiner, a second beam splitter and a second circulator connected in sequence, and the second circulator is connected to the first optical module through a quantum link. The second polarization beam combiner is configured to receive an idle photon in a second two-photon pair sent by the second frequency entanglement source and a signal photon in the second two-photon pair delayed by the second single-mode optical fiber, combine the idle photon in the second two-photon pair and the signal photon in the second two-photon pair to obtain second mixed photons. The second beam splitter is configured to transmit at least a part of the second mixed photons to a second detection module, and transmit at least another part of the second mixed photons to the second circulator to transmit the at least another part of the second mixed photons to the first optical module through a quantum link.

5. The composite two-way quantum time synchronization system of claim 4, wherein, The second detection module comprises a first single-photon detector and a fourth single-photon detector, the fourth single-photon detector is connected to the second beam splitter, and the first single-photon detector is connected to the second circulator. The fourth single-photon detector is configured to detect arrival of the second mixed photons and record a fifth arrival time of a signal photon and a sixth arrival time of an idle photon in the second mixed photons through a second event timer. The first single-photon detector is configured to detect arrival of the at least another part of the first mixed photons and record a seventh arrival time of a signal photon and an eighth arrival time of an idle photon in the at least another part of the first mixed photons through a second event timer.

6. The composite two-way quantum time synchronization system of claim 1, wherein, The quantum link comprises a dispersion-compensated optical fiber.

7. The composite two-way quantum time synchronization system of claim 1, wherein, Further comprising: a reference clock connected to the first event timer, configured to provide a time reference of the first event timer; a clock to be synchronized connected to the second event timer, configured to provide a time reference of the second event timer, and calibrated according to a clock difference of the composite bidirectional quantum time synchronization.

8. A composite two-way quantum time synchronization method, characterized in that, The method is applied to the composite bidirectional quantum time synchronization system of any one of claims 1-7, and the method comprises: generating a first two-photon pair of frequency anti-correlation; After processing the first two-photon pair, at least part of the first mixed photons is sent to the first detection module, so that the first detection module detects the arrival of the first mixed photons, and records the first arrival time of the signal photons and the second arrival time of the idle photons in at least part of the first mixed photons through the first event timer, and at least another part of the first mixed photons is transmitted to the second optical module, and correspondingly, after the second detection module detects the arrival of at least another part of the first mixed photons, the third arrival time of the signal photons and the fourth arrival time of the idle photons in at least another part of the first mixed photons are recorded through the second event timer; The second two-photon pair with frequency anti-correlation is generated, wherein the laser frequency of the second frequency entanglement source is the same as that of the first frequency entanglement source; After processing the second two-photon pair, at least part of the second mixed photons is sent to the second detection module, so that the second detection module detects the arrival of at least part of the second mixed photons, and records the fifth arrival time of the signal photons and the sixth arrival time of the idle photons in at least part of the second mixed photons through the second event timer, and at least another part of the second mixed photons is transmitted to the first optical module, and correspondingly, after the first detection module detects the arrival of at least another part of the second mixed photons, the seventh arrival time of the signal photons and the eighth arrival time of the idle photons in at least another part of the second mixed photons are recorded through the first event timer; The first arrival time, the second arrival time, the third arrival time, the fourth arrival time, the fifth arrival time, the sixth arrival time, the seventh arrival time and the eighth arrival time are used to calculate the clock difference of the composite two-way quantum time synchronization.

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