CN115001596B - Gating signal tuning method and device for quantum communication system - Google Patents

Gating signal tuning method and device for quantum communication system Download PDF

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CN115001596B
CN115001596B CN202210939560.8A CN202210939560A CN115001596B CN 115001596 B CN115001596 B CN 115001596B CN 202210939560 A CN202210939560 A CN 202210939560A CN 115001596 B CN115001596 B CN 115001596B
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CN115001596A (en
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王其兵
王林松
陈柳平
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Guokaike Quantum Technology Beijing Co Ltd
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B10/00—Transmission systems employing electromagnetic waves other than radio-waves, e.g. infrared, visible or ultraviolet light, or employing corpuscular radiation, e.g. quantum communication
    • H04B10/70—Photonic quantum communication
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
    • H04L9/0852—Quantum cryptography
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04L—TRANSMISSION OF DIGITAL INFORMATION, e.g. TELEGRAPHIC COMMUNICATION
    • H04L9/00—Cryptographic mechanisms or cryptographic arrangements for secret or secure communications; Network security protocols
    • H04L9/08—Key distribution or management, e.g. generation, sharing or updating, of cryptographic keys or passwords
    • H04L9/0816—Key establishment, i.e. cryptographic processes or cryptographic protocols whereby a shared secret becomes available to two or more parties, for subsequent use
    • H04L9/0852—Quantum cryptography
    • H04L9/0858—Details about key distillation or coding, e.g. reconciliation, error correction, privacy amplification, polarisation coding or phase coding

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  • Theoretical Computer Science (AREA)
  • Computer Security & Cryptography (AREA)
  • Optics & Photonics (AREA)
  • Optical Communication System (AREA)

Abstract

The invention provides a gating signal tuning method and a device for a quantum communication system, wherein the method comprises the following steps: outputting optical pulses synchronous with the encoding clock period of the quantum communication system to an optical decoding unit through a phase-based light source, and carrying out time-delay scanning on a single-photon detector for detecting the phase-based optical pulses to obtain the single-photon count scanned for the single-photon detector in a time-delay scanning period; if three peak counts are scanned in one delay scanning period and the interval between two adjacent peak counts is the optical path difference of the unequal arm interferometer, determining the delay position of the middle peak count as the delay position of the phase base optical pulse; the delay position of the gating signal is adjusted until the gating signal is aligned with the delay position of the phase base light pulse. The method not only can rapidly position and align the delay position of the optical pulse to be detected by the single photon detector, but also can remarkably improve the code rate of the quantum communication system.

Description

Gating signal tuning method and device for quantum communication system
Technical Field
The invention relates to the technical field of quantum communication, in particular to a gating signal tuning method and device for a quantum communication system.
Background
In general, in a quantum communication system, different light sources are used to prepare light pulses carrying different information, as shown in fig. 1, in a quantum communication system based on time-phase encoding, a phase-based light source Laser0 may be used to prepare a phase-based light pulse X0, a phase-based light source Laser1 may be used to prepare a phase-based light pulse X1, and a time-based light source Laser2 may be used to prepare a time-based light pulse Z0 or Z1, and the delay positions of the light pulses are aligned before the light pulses are transmitted to a receiving end, so that the light pulses are combined into a beam and transmitted to the receiving end. However, after reaching the receiving end, the optical pulses enter different single photon detectors through different optical paths, and the delay positions of the optical pulses cannot be aligned due to different lengths of the optical paths, so that the gate control signal (electrical pulse) for the single photon detector cannot be aligned with the optical pulses received by the single photon detector, that is, the gate control of the single photon detector cannot be opened at a proper time to detect the received optical pulses, which results in a decrease in the rate of finished code of the quantum communication system.
Disclosure of Invention
The invention aims to provide a gating signal tuning method and a gating signal tuning device for a quantum communication system.
According to an aspect of the present invention, there is provided a gating signal tuning method for a quantum communication system, the method comprising: outputting an optical pulse synchronized with an encoding clock cycle of the quantum communication system to an optical decoding unit of the quantum communication system through a phase-based light source in the optical encoding unit of the quantum communication system, wherein an optical path of the optical pulse reaching a single photon detector for detecting the phase-based optical pulse in the optical decoding unit comprises an unequal arm interferometer in the optical encoding unit and an unequal arm interferometer in the optical decoding unit, and an optical path difference between a long arm and a short arm of the unequal arm interferometer in the optical encoding unit is the same as an optical path difference between the long arm and the short arm of the unequal arm interferometer in the optical decoding unit; performing time-delay scanning on the single-photon detector to acquire a single-photon count scanned for the single-photon detector in a time-delay scanning period; determining a delay position of a middle peak count of the three peak counts as a delay position of the phase-based light pulse if three peak counts are scanned in the acquired single photon counts and an interval between two adjacent peak counts among the three peak counts is an optical path difference between a long arm and a short arm of the unequal-arm interferometer; adjusting a delay position of a gating signal for the single photon detector until the gating signal for the single photon detector aligns with a delay position of the phase-based light pulse.
According to an embodiment of the invention, before adjusting the delay position of the gating signal for the single-photon detector, the method further comprises: if two peak counts are scanned in the acquired single photon counts and an interval between the two peak counts is twice an optical path difference between a long arm and a short arm of the unequal arm interferometer, a voltage of a phase shifter provided on the long arm of the unequal arm interferometer in the optical decoding unit is adjusted until three peak counts are scanned in the acquired single photon counts and an interval between adjacent two of the three peak counts is an optical path difference between the long arm and the short arm of the unequal arm interferometer.
According to one embodiment of the invention, before adjusting the delay position of the gating signal for the single photon detector, the method further comprises: determining a delay position of an intermediate peak count of the first three peak counts as a delay position of the phase-based light pulse if four peak counts are scanned in the acquired single photon counts and an interval between adjacent two peak counts of only the first three peak counts among the four peak counts is an optical path difference between a long arm and a short arm of the unequal-arm interferometer; or if four peak counts are scanned in the acquired single photon counts and the interval between adjacent two of only the last three of the four peak counts is the optical path difference between the long and short arms of the unequal arm interferometer, determining the delay position of the middle one of the last three peak counts as the delay position of the phase-based light pulse.
According to an embodiment of the invention, before adjusting the delay position of the gating signal for the single-photon detector, the method further comprises: if four peak counts are scanned in the acquired single photon counts and only an interval between the first two peak counts and an interval between the second two peak counts among the four peak counts is an optical path difference between the long arm and the short arm of the unequal arm interferometer, determining a delay position of the former one of the first two peak counts or a delay position of the latter one of the second two peak counts as a delay position of the phase base light pulse.
According to one embodiment of the invention, the delayed scan period is greater than the encoding clock period.
According to another aspect of the present invention, there is provided a gating signal tuning method for a quantum communication system, the method comprising: outputting, by a phase-based light source in an optical encoding unit of the quantum communication system, a light pulse synchronized with an encoding clock cycle of the quantum communication system to an optical decoding unit of the quantum communication system, the light pulse reaching a single photon detector for detecting a time-based light pulse in the optical decoding unit, the light pulse including an unequal-arm interferometer in the optical encoding unit but not including the unequal-arm interferometer in the optical decoding unit, wherein an optical path difference between a long arm and a short arm of the unequal-arm interferometer in the optical encoding unit is the same as an optical path difference between the long arm and the short arm of the unequal-arm interferometer in the optical decoding unit; performing time-delay scanning on the single-photon detector to acquire a single-photon count scanned for the single-photon detector in a time-delay scanning period; determining a delay position of one of two peak counts as a delay position of the time base light pulse according to a delay position of the time base light pulse relative to another time base light pulse if two peak counts are scanned in the acquired single photon counts and an interval between the two peak counts is an optical path difference between a long arm and a short arm of the unequal arm interferometer; adjusting a delay position of a gating signal for the single photon detector until the gating signal for the single photon detector aligns with a delay position of the temporal base light pulse.
According to an embodiment of the invention, before adjusting the delay position of the gating signal for the single-photon detector, the method further comprises: if three peak counts are scanned in the acquired single photon counts, determining a delay position of one of two adjacent peak counts spaced by an optical path difference between a long arm and a short arm of the unequal arm interferometer as a delay position of the time base light pulse according to the delay position of the time base light pulse relative to the other time base light pulse.
According to an embodiment of the invention, before adjusting the delay position of the gating signal for the single-photon detector, the method further comprises: if four peak counts are scanned in the acquired single photon counts and a first peak count and a fourth peak count of the four peak counts are located at the beginning and the end of the delay scanning period, respectively, determining a delay position of one of a second peak count and a third peak count of the four peak counts as a delay position of the time base light pulse according to the delay position of the time base light pulse relative to another time base light pulse.
According to one embodiment of the invention, the delayed scan period is greater than the encoding clock period.
According to another aspect of the present invention, there is provided a gating signal tuning apparatus for a quantum communication system, the apparatus comprising: a light source preparation unit configured to output, to an optical decoding unit of the quantum communication system, a light pulse synchronized with an encoding clock cycle of the quantum communication system through a phase-based light source in an optical encoding unit of the quantum communication system, the light pulse including an unequal arm interferometer in the optical encoding unit and an unequal arm interferometer in the optical decoding unit on an optical path to a single photon detector in the optical decoding unit for detecting the phase-based light pulse, wherein an optical path difference between a long arm and a short arm of the unequal arm interferometer in the optical encoding unit is the same as an optical path difference between the long arm and the short arm of the unequal arm interferometer in the optical decoding unit; a time-delay scanning unit configured to time-delay scan the single-photon detector to acquire single-photon counts scanned for the single-photon detector within one time-delay scanning period; a position determination unit configured to determine a delay position of a middle peak count of three peak counts as a delay position of the phase base light pulse if three peak counts are scanned in the acquired single photon counts and an interval between adjacent two of the three peak counts is an optical path difference between a long arm and a short arm of the unequal arm interferometer; a signal tuning unit configured to adjust a delay position of a gating signal for the single photon detector until the gating signal for the single photon detector aligns with a delay position of the phase-based light pulse.
According to an embodiment of the invention, the apparatus further comprises: a phase adjusting unit configured to adjust a voltage of a phase shifter provided on a long arm of the unequal arm interferometer in the optical decoding unit until three peak counts are scanned in the acquired single photon counts and an interval between adjacent two of the three peak counts is an optical path difference between the long arm and the short arm of the unequal arm interferometer, if two peak counts are scanned in the acquired single photon counts and the interval between the two peak counts is twice the optical path difference between the long arm and the short arm of the unequal arm interferometer.
According to an embodiment of the present invention, the position determination unit is further configured to determine a delay position of an intermediate peak count of the first three peak counts as the delay position of the phase base light pulse if four peak counts are scanned in the acquired single photon counts and an interval between adjacent two peak counts of only the first three peak counts of the four peak counts is an optical path difference between the long arm and the short arm of the unequal arm interferometer; or if four peak counts are scanned in the acquired single photon counts and the interval between adjacent two of only the last three of the four peak counts is the optical path difference between the long and short arms of the unequal arm interferometer, determining the delay position of the middle one of the last three peak counts as the delay position of the phase-based light pulse.
According to an embodiment of the present invention, the position determination unit is further configured to determine a delay position of a previous peak count of the previous two peak counts or a delay position of a subsequent peak count of the subsequent two peak counts as the delay position of the phase base light pulse if four peak counts are scanned in the acquired single photon counts and only an interval between the first two peak counts and an interval between the subsequent two peak counts of the four peak counts are optical path differences between the long arm and the short arm of the unequal arm interferometer.
According to one embodiment of the invention, the delayed scan period is greater than the encoding clock period.
According to another aspect of the present invention, there is provided a gating signal tuning apparatus for a quantum communication system, the apparatus comprising: a light source preparation unit configured to output, to an optical decoding unit of the quantum communication system, a light pulse synchronized with an encoding clock cycle of the quantum communication system through a phase-based light source in the optical encoding unit of the quantum communication system, the light pulse reaching a single photon detector for detecting a time-based light pulse in the optical decoding unit including an unequal arm interferometer in the optical encoding unit but not including the unequal arm interferometer in the optical decoding unit, wherein an optical path difference between a long arm and a short arm of the unequal arm interferometer in the optical encoding unit is the same as an optical path difference between the long arm and the short arm of the unequal arm interferometer in the optical decoding unit; a time-delay scanning unit configured to time-delay scan the single-photon detector to acquire a single-photon count scanned for the single-photon detector within a time-delay scanning period; a position determination unit configured to determine a delay position of one of two peak counts as a delay position of the time base light pulse according to a delay position of the time base light pulse with respect to another time base light pulse if two peak counts are scanned in the acquired single photon counts and an interval between the two peak counts is an optical path difference between a long arm and a short arm of the unequal arm interferometer; a signal tuning unit configured to adjust a delay position of a gating signal for the single photon detector until the gating signal for the single photon detector aligns with a delay position of the temporal base light pulse.
According to an embodiment of the present invention, the position determination unit is further configured to determine, as the delay position of the time base light pulse, a delay position of one of two adjacent peak counts spaced by an optical path difference between a long arm and a short arm of the unequal arm interferometer according to a delay position of the time base light pulse relative to another time base light pulse, if three peak counts are scanned in the acquired single photon counts.
According to an embodiment of the present invention, the position determination unit is further configured to determine the delay position of one of the second and third peak counts of the four peak counts as the delay position of the time base light pulse according to the delay position of the time base light pulse with respect to another time base light pulse if four peak counts are scanned in the acquired single photon counts and the first and fourth peak counts of the four peak counts are located at the start and end of the delay scan period, respectively.
According to one embodiment of the invention, the delayed scan period is greater than the encoding clock period.
The gating signal tuning method and the gating signal tuning device for the quantum communication system can not only quickly position and align the delay position of the optical pulse to be detected by the single-photon detector, but also obviously improve the code rate of the quantum communication system.
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The above objects and features of the present invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.
Fig. 1 shows a schematic diagram of a quantum communication system based on time phase encoding.
Fig. 2 shows a schematic diagram of aligning the delay positions of the light pulses from different light sources in the transmitting end of the quantum communication system shown in fig. 1.
Fig. 3 shows a schematic flow diagram of a gating signal tuning method for a quantum communication system according to an exemplary embodiment of the present invention.
Fig. 4 shows another schematic flow diagram of a gating signal tuning method for a quantum communication system according to an exemplary embodiment of the present invention.
Fig. 5 shows a schematic block diagram of a gating signal tuning apparatus for a quantum communication system according to an exemplary embodiment of the present invention.
Figure 6 shows a schematic diagram of single photon counts of individual single photon detectors scanned by light pulses output by a phase based light source according to an exemplary embodiment of the present invention.
Figure 7A shows a schematic diagram of a delayed scan of single photon detectors X0-SPD to determine the delayed position of phase-based optical pulses X0 by optical pulses output by phase-based optical source Laser0, according to an exemplary embodiment of the present invention.
Figure 7B shows another schematic diagram of a delayed scan of the single photon detectors X0-SPD to determine the delayed position of the phase-based optical pulses X0 by the optical pulses output by the phase-based optical source Laser0 according to an exemplary embodiment of the present invention.
Figure 7C shows another schematic diagram of a delayed scan of the single photon detectors X0-SPD to determine the delayed position of the phase-based optical pulses X0 by the optical pulses output by the phase-based optical source Laser0 according to an exemplary embodiment of the present invention.
Figure 7D shows another schematic diagram of a delayed scan of single photon detectors X0-SPD to determine the delayed position of phase-based optical pulses X0 by optical pulses output by phase-based optical source Laser0, according to an exemplary embodiment of the present invention.
Figure 7E shows another schematic diagram of a delayed scan of the single photon detectors X0-SPD to determine the delayed position of the phase-based optical pulses X0 by the optical pulses output by the phase-based optical source Laser0 according to an exemplary embodiment of the present invention.
Figure 7F shows a schematic diagram of a delayed scan of single-photon detectors Z0-SPD to determine the delayed position of time-based optical pulses Z0 by optical pulses output by phase-based optical source Laser0, according to an exemplary embodiment of the present invention.
Figure 7G shows another schematic diagram of a delayed scan of the single photon detectors Z0-SPD to determine the delayed position of time-based optical pulses Z0 by optical pulses output by phase-based optical source Laser0, according to an exemplary embodiment of the present invention.
Figure 7H shows another schematic diagram of a delayed scan of the single photon detectors Z0-SPD to determine the delayed position of time-based optical pulses Z0 by optical pulses output by phase-based optical source Laser0, according to an exemplary embodiment of the present invention.
Detailed Description
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings.
Fig. 1 shows a schematic diagram of a quantum communication system based on temporal phase encoding.
Referring to FIG. 1, a quantum communication system based on time phase encoding may include transmissionA terminal Alice and a receiving terminal Bob, wherein the optical coding unit is included in the transmitting terminal Alice, the optical decoding unit is included in the receiving terminal Bob, and the unequal arm interferometer M-Z in the optical coding unit is included 1 And an unequal arm interferometer M-Z included in the optical decoding unit 2 The optical path difference between the long arm and the short arm is the same.
In the transmitting end Alice shown in FIG. 1, the phase-based light source laser0 included in the optical encoding unit may be via an unequal arm interferometer M-Z included in the optical encoding unit 1 Outputting the phase-based light pulse X0 to the receiving end Bob, wherein the phase-based light source Laser1 included in the optical encoding unit can be obtained by an unequal arm interferometer M-Z included in the optical encoding unit 1 And outputting the phase-based optical pulse X1 to the receiving end Bob, wherein the time-based light source Laser2 included in the optical coding unit may output the time-based optical pulse Z0 to the receiving end Bob and may also output the time-based optical pulse Z1 to the receiving end Bob.
In the receiving end Bob shown in fig. 1, the single-photon detectors X0-SPD included in the optical decoding unit may be used to detect the phase-based optical pulse X0, the single-photon detectors X1-SPD included in the optical decoding unit may be used to detect the phase-based optical pulse X1, the single-photon detectors Z0-SPD included in the optical decoding unit may be used to detect the time-based optical pulse Z0, and the single-photon detectors Z1-SPD included in the optical decoding unit may be used to detect the time-based optical pulse Z1. After the phase-based optical pulse X0, the phase-based optical pulse X1, the time-based optical pulse Z0, and the time-based optical pulse Z1 (i.e., coded light) reach the receiving end Bob, gating signals synchronized with the coded clock period of the quantum communication system are applied to the single-photon detectors X0-SPD, X1-SPD, Z0-SPD, and Z1-SPD to control the gating of the single-photon detectors X0-SPD, X1-SPD, Z0-SPD, and Z1-SPD to be turned on, so that the single-photon detectors X0-SPD, X1-SPD, Z0-SPD, and Z1-SPD detect the respective received optical pulses in a geiger mode.
In order to enable the single-photon detectors X0-SPD, X1-SPD, Z0-SPD, and Z1-SPD to open their gates at appropriate timings so as to detect the optical pulses received by them in the geiger mode, in the transmitting end Alice shown in fig. 1, the delay positions of the phase base optical pulses X0, X1, Z0, and Z1 may be aligned before combining and transmitting the phase base optical pulses X0, X1, Z0, and Z1, so that the delay position of the gating signal synchronized with the encoding clock cycle of the quantum communication system can be simultaneously kept consistent with the delay positions of the phase base optical pulses X0, X1, Z0, and Z1.
Fig. 2 shows a schematic diagram of aligning the delay positions of individual light pulses from different light sources in the transmitting end of the quantum communication system shown in fig. 1.
Referring to fig. 2, the first row shows phase-based light pulse X0 output from phase-based light source laser0, the second row shows phase-based light pulse X1 output from phase-based light source laser1, the third row shows time-based light pulse Z0 output from time-based light source laser2, and the fourth row shows time-based light pulse Z1 output from time-based light source laser 2.
In each optical pulse shown in fig. 2, the delay position of the phase base optical pulse X0 may be aligned with the delay position of the phase base optical pulse X1, the delay position of the time base optical pulse Z0 may be aligned with the delay position of the previous optical pulse in the phase base optical pulses X0 and X1, and the delay position of the time base optical pulse Z1 may be aligned with the delay position of the subsequent optical pulse in the phase base optical pulses X0 and X1, in which case, the delay position of the gate signal synchronized with the encoding clock period of the quantum communication system may be simultaneously aligned with the delay position of each optical pulse.
Although the alignment mode can keep the delay positions of the optical pulses from different light sources consistent, after the optical pulses enter the receiving end Bob, the optical pulses from different light sources enter the single-photon detectors X0-SPD, X1-SPD, Z0-SPD and Z1-SPD through different optical paths, and the different optical paths cause that the gating signals cannot simultaneously align the optical pulses received by the single-photon detectors X0-SPD, X1-SPD, Z0-SPD and Z1-SPD, so that the gating signals cannot be opened at proper time for each single-photon detector to detect the optical pulses received by the single-photon detector, thereby not only increasing the error rate of the quantum communication system, but also reducing the code rate of the quantum communication system.
To this end, the present invention proposes hereinafter a gating signal tuning method and apparatus for a quantum communication system, so that each single-photon detector (such as, but not limited to, the single-photon detectors X0-SPD, X1-SPD, Z0-SPD, and Z1-SPD shown in fig. 1) included in an optical decoding unit can turn on its gate at an appropriate timing to detect optical pulses that it receives.
Fig. 3 shows a schematic flow diagram of a gating signal tuning method for a quantum communication system according to an exemplary embodiment of the present invention.
Referring to fig. 3, the method illustrated in fig. 3 may include the following steps.
In step 301, an optical pulse synchronized with an encoding clock cycle of the quantum communication system may be output by a phase-based light source in an optical encoding unit of the quantum communication system to an optical decoding unit of the quantum communication system, and an optical path on which the optical pulse reaches a single photon detector for detecting the phase-based optical pulse in the optical decoding unit includes an unequal arm interferometer in the optical encoding unit and an unequal arm interferometer in the optical decoding unit, wherein an optical path difference between a long arm and a short arm of the unequal arm interferometer in the optical encoding unit is the same as an optical path difference between the long arm and the short arm of the unequal arm interferometer in the optical decoding unit.
In step 302, the single photon detectors may be scanned in a delayed manner to obtain single photon counts scanned for the single photon detectors within a delayed scan period. Heretofore, the single photon counts detected by the single photon detector at each delay position may be counted by a delay scanning device provided for the single photon detector in the quantum communication system to obtain the single photon counts detected by the single photon detector at each delay position, and then the single photon counts detected at each delay position may be fitted to a curve varying with the delay position for easy observation. The delay scanning device can include, but is not limited to, a delay device, a gate control signal generation circuit, a counting module, and the like, wherein the delay device can be used for setting a delay position of a gate control signal output by the gate control signal generation circuit, and the counting module can be used for counting single photons detected by the single photon detector at the set delay position. The change of the single photon counting of the single photon detector in a delay scanning period can be obtained through the delay scanning device.
In step 303, if three peak counts are scanned in the acquired single photon counts and the interval between two adjacent peak counts among the three peak counts is the optical path difference between the long and short arms of the unequal arm interferometer, the delay position of the middle peak count among the three peak counts is determined as the delay position of the phase-based light pulse.
In another example, if two peak counts are scanned in the acquired single photon counts and an interval between the two peak counts is twice an optical path difference between a long arm and a short arm of the unequal arm interferometer, a voltage of a phase shifter disposed on the long arm of the unequal arm interferometer in the optical decoding unit is adjusted until three peak counts are scanned in the acquired single photon counts and an interval between adjacent two of the three peak counts is an optical path difference between the long arm and the short arm of the unequal arm interferometer.
In another example, if four peak counts are scanned in the acquired single photon counts and the interval between adjacent two of only the first three of the four peak counts is the optical path difference between the long and short arms of the unequal arm interferometer, the delay position of the middle of the first three peak counts is determined as the delay position of the phase base light pulse.
In another example, if four peak counts are scanned in the acquired single photon counts and the interval between adjacent two of only the last three of the four peak counts is the optical path difference between the long and short arms of the unequal arm interferometer, the delay position of the middle of the last three peak counts is determined as the delay position of the phase base light pulse.
In another example, if four peak counts are scanned in the acquired single photon counts and only the interval between the first two peak counts and the interval between the last two peak counts in the four peak counts are the optical path difference between the long and short arms of the unequal arm interferometer, the delay position of the previous one of the first two peak counts or the delay position of the next one of the last two peak counts is determined as the delay position of the phase base light pulse.
In step 304, the delay position of the gating signal for the single photon detector may be adjusted until the gating signal for the single photon detector aligns with the delay position of the phase base light pulse.
Additionally, in the method illustrated in FIG. 3, the delayed scan period may be greater than the encoding clock period to ensure that the desired waveform is scanned.
Fig. 4 shows another schematic flow diagram of a gating signal tuning method for a quantum communication system according to an exemplary embodiment of the present invention.
Referring to fig. 4, the method illustrated in fig. 4 may include the following steps.
In step 401, an optical pulse synchronized with an encoding clock cycle of the quantum communication system may be output by an optical decoding unit of the vector sub-communication system through a phase-based light source in an optical encoding unit of the quantum communication system, and an optical path of the optical pulse reaching a single photon detector for detecting a time-based optical pulse in the optical decoding unit includes an unequal arm interferometer in the optical encoding unit but does not include the unequal arm interferometer in the optical decoding unit, wherein an optical path difference between a long arm and a short arm of the unequal arm interferometer in the optical encoding unit is the same as an optical path difference between the long arm and the short arm of the unequal arm interferometer in the optical decoding unit.
In step 402, the single photon detectors may be scanned in a delayed manner to obtain single photon counts scanned for the single photon detectors within a delayed scan period. Here, the time-lapse scanning process for the single-photon detector for detecting the time-base light pulse is the same as the time-lapse scanning process for the single-photon detector for detecting the phase-base light pulse, and a description thereof will not be repeated.
At step 403, if two peak counts are scanned in the acquired single photon counts and the interval between the two peak counts is the optical path difference between the long and short arms of the unequal arm interferometer, the delay position of one of the two peak counts is determined as the delay position of the time base light pulse from the delay position of the time base light pulse relative to the other time base light pulse.
In another example, if three peak counts are scanned in the acquired single photon counts, the delay position of one of the two adjacent peak counts spaced by the optical path difference between the long and short arms of the unequal arm interferometer is determined as the delay position of the time base light pulse according to the delay position of the time base light pulse relative to the other time base light pulse.
In another example, if four peak counts are scanned in the acquired single photon counts and a first peak count and a fourth peak count of the four peak counts are located at a start point and an end point of the delay scan period, respectively, a delay position of one of a second peak count and a third peak count of the four peak counts is determined as a delay position of the time base light pulse according to a delay position of the time base light pulse relative to the other time base light pulse.
In step 404, the delay position of the gating signal for the single photon detector may be adjusted until the gating signal for the single photon detector aligns with the delay position of the temporal base light pulse.
Additionally, in the method illustrated in FIG. 4, the delayed scan period may be greater than the encoding clock period to ensure that the desired waveform is scanned.
Fig. 5 shows a schematic block diagram of a gating signal tuning apparatus for a quantum communication system according to an exemplary embodiment of the present invention.
Referring to fig. 5, a gating signal tuning apparatus for a quantum communication system according to an exemplary embodiment of the present invention may include at least a light source preparation unit 501, a delay scanning unit 502, a position determination unit 503, and a signal tuning unit 504.
In the apparatus shown in fig. 5, the light source preparation unit 501 may be configured to output, by the phase-based light source in the optical encoding unit of the quantum communication system, a light pulse synchronized with an encoding clock cycle of the quantum communication system to the optical decoding unit of the vector sub-communication system, and an optical path on which the light pulse reaches the single photon detector for detecting the phase-based light pulse in the optical decoding unit includes the unequal arm interferometer in the optical encoding unit and the unequal arm interferometer in the optical decoding unit, wherein an optical path difference between a long arm and a short arm of the unequal arm interferometer in the optical encoding unit is the same as an optical path difference between a long arm and a short arm of the unequal arm interferometer in the optical decoding unit; the delayed scanning unit 502 can be configured to delay scan the single photon detectors to obtain single photon counts scanned for the single photon detectors within one delayed scanning period; the position determination unit 503 may be configured to determine a delay position of an intermediate peak count of the three peak counts as a delay position of the phase base light pulse if three peak counts are scanned in the acquired single photon counts and an interval between adjacent two of the three peak counts is an optical path difference between a long arm and a short arm of the unequal arm interferometer; the signal tuning unit 504 may be configured to adjust the delay position of the gating signal for the single photon detector until the gating signal for the single photon detector aligns with the delay position of the phase-based optical pulse.
In the apparatus illustrated in fig. 5, a phase adjustment unit (not shown) may be further included, and the phase adjustment unit may be configured to adjust a voltage of a phase shifter disposed on the long arm of the unequal arm interferometer in the optical decoding unit until three peak counts are scanned in the acquired single photon counts and an interval between adjacent two of the three peak counts is an optical path difference between the long arm and the short arm of the unequal arm interferometer, if two peak counts are scanned in the acquired single photon counts and the interval between the two peak counts is twice the optical path difference between the long arm and the short arm of the unequal arm interferometer.
In the above example, the position determination unit 503 may be further configured to determine the delay position of the middle peak count of the first three peak counts as the delay position of the phase-based light pulse if four peak counts are scanned in the acquired single photon counts and an interval between adjacent two peak counts of only the first three peak counts of the four peak counts is an optical path difference between the long arm and the short arm of the unequal arm interferometer; alternatively, if four peak counts are scanned in the acquired single photon counts and the interval between adjacent two of only the last three of the four peak counts is the optical path difference between the long and short arms of the unequal arm interferometer, the delay position of the middle one of the last three peak counts is determined as the delay position of the phase-based light pulse.
In the above example, the position determination unit 503 may be further configured to determine the delay position of the previous peak count of the previous two peak counts or the delay position of the next peak count of the next two peak counts as the delay position of the phase base light pulse if four peak counts are scanned in the acquired single photon counts and only an interval between the first two peak counts and an interval between the next two peak counts of the four peak counts are optical path differences between the long arm and the short arm of the unequal arm interferometer.
In addition, in the apparatus shown in fig. 5, the light source preparation unit 501 may be further configured to output, by the phase-based light source in the optical encoding unit of the quantum communication system, a light pulse synchronized with the encoding clock cycle of the quantum communication system to the optical decoding unit of the quantum communication system, the light pulse reaching the single-photon detector for detecting the time-based light pulse in the optical decoding unit including the unequal arm interferometer in the optical encoding unit but not including the unequal arm interferometer in the optical decoding unit, wherein an optical path difference between the long arm and the short arm of the unequal arm interferometer in the optical encoding unit is the same as an optical path difference between the long arm and the short arm of the unequal arm interferometer in the optical decoding unit; the time-delay scanning unit 502 can also be configured to time-delay scan the single-photon detectors to acquire the single-photon counts scanned for the single-photon detectors within one time-delay scanning period; the position determining unit 503 may be further configured to determine a delay position of one of the two peak counts as a delay position of the time base light pulse according to the delay position of the time base light pulse relative to the other time base light pulse if two peak counts are scanned in the acquired single photon counts and an interval between the two peak counts is an optical path difference between the long arm and the short arm of the unequal arm interferometer; the signal tuning unit 504 may also be configured to adjust the delay position of the gating signal for the single-photon detector until the gating signal for the single-photon detector aligns with the delay position of the temporal base light pulse.
In the above example, the position determining unit 503 may be further configured to determine, as the delay position of the time base light pulse, the delay position of one of the two adjacent peak counts spaced by the optical path difference between the long arm and the short arm of the unequal arm interferometer according to the delay position of the time base light pulse relative to the other time base light pulse, if three peak counts are scanned in the acquired single photon counts.
In the above example, the position determining unit 503 may be further configured to determine the delay position of one of the second peak count and the third peak count of the four peak counts as the delay position of the time base light pulse according to the delay position of the time base light pulse relative to another time base light pulse if four peak counts are scanned in the acquired single photon counts and the first peak count and the fourth peak count of the four peak counts are located at the start point and the end point of the delay scanning period, respectively.
Additionally, in the apparatus shown in FIG. 5, the delayed scan period may be greater than the encoding clock period to ensure that the desired waveform is scanned.
Figure 6 shows a schematic diagram of single photon counts of individual single photon detectors scanned by light pulses output by a phase based light source according to an exemplary embodiment of the present invention.
Referring to fig. 6, the first row shows an optical pulse X output by the phase-based light source Laser0 shown in fig. 1 in synchronization with the encoding clock period T0 of the quantum communication system; second line of drawingsWhat is shown is an unequal arm interferometer M-Z illustrated by FIG. 1 1 Splitting the light pulse X output by the phase-based light source Laser0 into phase-based light pulses X0; the third row shows the single photon counts X0-DET output by time-delayed scanning of the single photon detectors X0-SPD shown in FIG. 1; the fourth row shows the single photon counts X1-DET output by time-lapse scanning of the single photon detectors X1-SPD shown in FIG. 1; the fifth row shows the single photon counts Z0-DET output by time-delayed scanning of the single photon detectors Z0-SPD shown in FIG. 1; the sixth row shows the single-photon counts Z1-DET output by time-delayed scanning of the single-photon detectors Z1-SPD shown in figure 1.
Next, a specific implementation process of determining the delay positions of the phase-based light pulse X0, the phase-based light pulse X1, the time-based light pulse Z0, and the time-based light pulse Z1 by performing delay scanning on the single-photon detector will be described in further detail with reference to fig. 7A to 7H.
In the example shown in FIGS. 7A-7H, the OPD is an unequal arm interferometer M-Z 1 Or M-Z 2 And the optical path difference between the long arm and the short arm is the same (hereinafter, both referred to as the optical path difference between the long arm and the short arm of the unequal arm interferometer), T0 is the encoding clock period of the quantum communication system based on time phase encoding, and T1 is the delay scanning period, where T0 is 4 times the OPD and T1 is 5 times the OPD.
Figure 7A shows a schematic diagram of a delayed scan of the single photon detectors X0-SPD to determine the delayed position of a phase-based optical pulse X0 by an optical pulse output by a phase-based optical source Laser0 according to an exemplary embodiment of the present invention.
In the example shown in fig. 7A, if three peak counts are scanned within one delay scan period T1 and the interval between adjacent two of the three peak counts is the optical path difference OPD between the long and short arms of the unequal arm interferometer, the delay position of the middle one of the three peak counts is determined as the delay position of the phase base light pulse X0. In FIG. 7A, the interval between two adjacent peak counts is the optical path difference OPD between the long and short arms of the unequal-arm interferometerInterferometer M-Z with three peak values counted as unequal arms 1 And M-Z 2 Interference results. Interferometer M-Z with unequal arms 1 And M-Z 2 In the best interference condition, the middle of the three peak counts may be significantly higher than the left and right of the three peak counts. When the three peak counts of the interference phase rise are scanned, the delay position of the middle peak count of the three peak counts may be determined as the delay position of the phase-based light pulse X0.
Figure 7B shows another schematic diagram of a delayed scan of the single photon detectors X0-SPD to determine the delayed position of the phase-based optical pulses X0 by the optical pulses output by the phase-based optical source Laser0 according to an exemplary embodiment of the present invention.
In the example shown in FIG. 7B, if two peak counts are scanned within one delay scan period T1 and the interval between the two peak counts is 2 times the optical path difference OPD between the long and short arms of the unequal arm interferometer, the unequal arm interferometer M-Z provided in the optical decoding unit is adjusted 2 Until three peak counts are swept within one delay sweep period T1 and the interval between two adjacent peak counts of the three peak counts is the optical path difference OPD between the long and short arms of the unequal-arm interferometer. In FIG. 7B, two peak counts spaced 2 times the optical path difference OPD between the long and short arms of the unequal-arm interferometer may be the unequal-arm interferometer M-Z 1 And M-Z 2 As a result of the destructive interference, in this case, it will be difficult to identify the delayed position of the phase base light pulse X0, and therefore the voltage of the phase shifter PM can be increased or decreased until three peak counts of the destructive interference are scanned within one delayed scan period T1. After scanning the three peak counts of the interference phase shown in fig. 7A, the delay position of the middle peak count of the three peak counts may be determined as the delay position of the phase base light pulse X0.
Figure 7C shows another schematic diagram of a delayed scan of single photon detectors X0-SPD to determine the delayed position of phase-based optical pulses X0 by optical pulses output by phase-based optical source Laser0, according to an exemplary embodiment of the present invention.
In the example shown in fig. 7C, if four peak counts are scanned within one delay scan period T1 and the interval between adjacent two of only the first three of the four peak counts is the optical path difference OPD between the long and short arms of the unequal arm interferometer, the delay position of the middle one of the first three peak counts is determined as the delay position of the phase base light pulse X0.
Figure 7D shows another schematic diagram of a delayed scan of single photon detectors X0-SPD to determine the delayed position of phase-based optical pulses X0 by optical pulses output by phase-based optical source Laser0, according to an exemplary embodiment of the present invention.
In the example shown in fig. 7D, if four peak counts are scanned within one delay scan period T1 and the interval between adjacent two of only the last three of the four peak counts is the optical path difference OPD between the long and short arms of the unequal arm interferometer, the delay position of the middle one of the last three peak counts is determined as the delay position of the phase-based light pulse X0.
Figure 7E shows another schematic diagram of a delayed scan of single photon detectors X0-SPD to determine the delayed position of phase-based optical pulses X0 by optical pulses output by phase-based optical source Laser0, in accordance with an exemplary embodiment of the present invention.
In the example shown in fig. 7E, if four peak counts are scanned within one delay scan period T1 and only the interval between the first two peak counts and the interval between the second two peak counts among the four peak counts are the optical path difference OPD between the long arm and the short arm of the unequal arm interferometer, the delay position of the first one of the first two peak counts or the delay position of the second one of the second two peak counts is determined as the delay position of the phase base light pulse X0.
Similarly, single-photon detectors X1-SPD may be scanned with time delays by light pulses output by phase-based light source Laser0 to determine the time-delayed positions of time-based light pulses X1.
If three peak counts are scanned within one delay scan period T1 and the interval between adjacent two of the three peak counts is the optical path difference OPD between the long and short arms of the unequal arm interferometer, the delay position of the middle one of the three peak counts is determined as the delay position of the phase base optical pulse X1.
If two peak counts are scanned within one delay scanning period T1 and the interval between the two peak counts is 2 times the optical path difference OPD between the long arm and the short arm of the unequal arm interferometer, the unequal arm interferometer M-Z disposed in the optical decoding unit is adjusted 2 Until three peak counts are swept within one delay sweep period T1 and the interval between two adjacent peak counts among the three peak counts is the optical path difference OPD between the long and short arms of the unequal arm interferometer. After scanning the three peak counts of the rising interference, the delay position of the middle peak count of the three peak counts may be determined as the delay position of the phase base light pulse X1.
If four peak counts are scanned within one delay scan period T1 and the interval between adjacent two of only the first three of the four peak counts is the optical path difference OPD between the long and short arms of the unequal arm interferometer, the delay position of the middle of the first three peak counts is determined as the delay position of the phase base optical pulse X1.
If four peak counts are scanned within one delay scan period T1 and the interval between adjacent two of only the last three of the four peak counts is the optical path difference OPD between the long and short arms of the unequal arm interferometer, the delay position of the middle of the last three peak counts is determined as the delay position of the phase base optical pulse X1.
If four peak counts are scanned within one delay scan period T1 and only the interval between the first two peak counts and the interval between the last two peak counts among the four peak counts are the optical path difference OPD between the long arm and the short arm of the unequal arm interferometer, the delay position of the former one of the first two peak counts or the delay position of the latter one of the last two peak counts is determined as the delay position of the phase base light pulse X1.
Figure 7F shows a schematic diagram of a delayed scan of single-photon detectors Z0-SPD to determine the delayed position of time-based optical pulses Z0 by optical pulses output by phase-based optical source Laser0, according to an exemplary embodiment of the present invention.
In the example shown in fig. 7F, if two peak counts are scanned within one delay scanning period T1 and the interval between the two peak counts is the optical path difference OPD between the long arm and the short arm of the unequal arm interferometer, the delay position of the previous one of the two peak counts is determined as the delay position of the time base light pulse Z0 from the delay position of the time base light pulse Z0 with respect to the time base light pulse Z1.
Figure 7G shows another schematic diagram of a delayed scan of the single photon detectors Z0-SPD to determine the delayed position of time-based optical pulses Z0 by optical pulses output by phase-based optical source Laser0, according to an exemplary embodiment of the present invention.
In the example shown in fig. 7G, if three peak counts are scanned within one delay scanning period T1, the delay position of the previous peak count of the two adjacent peak counts spaced by the optical path difference OPD between the long arm and the short arm of the unequal arm interferometer is determined as the delay position of the time base light pulse Z0 according to the delay position of the time base light pulse Z0 with respect to the time base light pulse Z1.
Figure 7H shows another schematic diagram of a delayed scan of the single photon detectors Z0-SPD to determine the delayed position of time-based optical pulses Z0 by optical pulses output by phase-based optical source Laser0, according to an exemplary embodiment of the present invention.
In the example shown in fig. 7H, if four peak counts are scanned within one delay scanning period T1 and the first and fourth peak counts of the four peak counts are located at the start and end points of the delay scanning period, respectively, the delay position in the third peak count of the four peak counts is determined as the delay position of the time base light pulse Z0 according to the delay position of the time base light pulse Z0 with respect to the time base light pulse Z1.
Similarly, the single-photon detectors Z1-SPD may be scanned in a delayed manner by the optical pulses output by the phase-based light source Laser0 to determine the delayed positions of the time-based optical pulses Z1.
However, if two peak counts are scanned within one delay scanning period T1 and the interval between the two peak counts is the optical path difference OPD between the long arm and the short arm of the unequal arm interferometer, the delay position of the latter one of the two peak counts is determined as the delay position of the time base light pulse Z1 from the delay position of the time base light pulse Z1 with respect to the time base light pulse Z0.
However, if three peak counts are scanned within one delay scanning period T1, the delay position of the latter one of the adjacent two peak counts spaced by the optical path difference OPD between the long arm and the short arm of the unequal arm interferometer is determined as the delay position of the time base light pulse Z1 from the delay position of the time base light pulse Z1 with respect to the time base light pulse Z0.
However, if four peak counts are scanned within one delay scan period T1 and the first and fourth of the four peak counts are located at the start and end of the delay scan period, respectively, the delay position of the second of the four peak counts is determined as the delay position of the time base light pulse Z1 based on the delay position of the time base light pulse Z1 with respect to the time base light pulse Z0.
It can be seen that the method and apparatus for tuning a gating signal for a quantum communication system according to the exemplary embodiments of the present invention not only can rapidly locate and align the delay position of an optical pulse to be detected by a single-photon detector, but also can significantly improve the rate of finished bits of the quantum communication system.
There may also be provided a computer-readable storage medium storing a computer program according to an exemplary embodiment of the present invention. The computer readable storage medium stores a computer program which, when executed by a processor, causes the processor to perform a gating signal tuning method for a quantum communication system according to the present invention. The computer readable recording medium is any data storage device that can store data which can be read by a computer system. Examples of the computer-readable recording medium include: read-only memory, random access memory, compact disc read-only memory, magnetic tape, floppy disk, optical data storage device, and carrier wave (such as data transmission through the internet via a wired or wireless transmission path).
A computer apparatus may also be provided according to an exemplary embodiment of the present invention. The computer device includes a processor and a memory. The memory is for storing a computer program. The computer program is executed by a processor such that the processor performs the gate signal tuning method for a quantum communication system according to the invention.
While the present application has been shown and described with reference to the preferred embodiments, it will be understood by those skilled in the art that various changes and modifications may be made to these embodiments without departing from the spirit and scope of the present application as defined by the appended claims.

Claims (18)

1. A gating signal tuning method for a quantum communication system, comprising:
outputting an optical pulse synchronized with an encoding clock cycle of the quantum communication system to an optical decoding unit of the quantum communication system through a phase-based light source in the optical encoding unit of the quantum communication system, wherein an optical path of the optical pulse reaching a single photon detector for detecting the phase-based optical pulse in the optical decoding unit comprises an unequal arm interferometer in the optical encoding unit and an unequal arm interferometer in the optical decoding unit, and an optical path difference between a long arm and a short arm of the unequal arm interferometer in the optical encoding unit is the same as an optical path difference between the long arm and the short arm of the unequal arm interferometer in the optical decoding unit;
performing time-delay scanning on the single-photon detector to acquire a single-photon count scanned for the single-photon detector in a time-delay scanning period;
determining a delay position of a middle peak count of the three peak counts as a delay position of the phase-based light pulse if three peak counts are scanned in the acquired single photon counts and an interval between two adjacent peak counts among the three peak counts is an optical path difference between a long arm and a short arm of the unequal-arm interferometer;
adjusting a delay position of a gating signal for the single photon detector until the gating signal for the single photon detector aligns with a delay position of the phase-based light pulse.
2. The method of gating signal tuning of claim 1, further comprising, prior to adjusting the delay position of the gating signal for the single photon detector:
if two peak counts are scanned in the acquired single photon counts and the interval between the two peak counts is twice the optical path difference between the long and short arms of the unequal arm interferometer, adjusting the voltage of a phase shifter provided on the long arm of the unequal arm interferometer in the optical decoding unit until three peak counts are scanned in the acquired single photon counts and the interval between two adjacent peak counts in the three peak counts is the optical path difference between the long and short arms of the unequal arm interferometer.
3. The method of gating signal tuning of claim 1, further comprising, prior to adjusting the delay position of the gating signal for the single photon detector:
determining a delay position of an intermediate peak count of the first three peak counts as a delay position of the phase-based light pulse if four peak counts are scanned in the acquired single photon counts and an interval between adjacent two peak counts of only the first three peak counts among the four peak counts is an optical path difference between a long arm and a short arm of the unequal-arm interferometer; or
Determining a delay position of a middle peak count of the last three peak counts as a delay position of the phase base light pulse if four peak counts are scanned in the acquired single photon counts and an interval between adjacent two of only the last three peak counts of the four peak counts is an optical path difference between a long arm and a short arm of the unequal arm interferometer.
4. The gating signal tuning method of claim 1, further comprising, prior to adjusting the delay position of the gating signal for the single photon detector:
if four peak counts are scanned in the acquired single photon counts and only an interval between the first two peak counts and an interval between the second two peak counts among the four peak counts is an optical path difference between the long arm and the short arm of the unequal arm interferometer, determining a delay position of the former one of the first two peak counts or a delay position of the latter one of the second two peak counts as a delay position of the phase-based light pulse.
5. The method of any of claims 1 to 4, wherein the delay sweep period is greater than the encoding clock period.
6. A method for tuning a gating signal for a quantum communication system, comprising:
outputting, by a phase-based light source in an optical encoding unit of the quantum communication system, a light pulse synchronized with an encoding clock cycle of the quantum communication system to an optical decoding unit of the quantum communication system, the light pulse reaching a single photon detector for detecting a time-based light pulse in the optical decoding unit, the light pulse including an unequal-arm interferometer in the optical encoding unit but not including the unequal-arm interferometer in the optical decoding unit, wherein an optical path difference between a long arm and a short arm of the unequal-arm interferometer in the optical encoding unit is the same as an optical path difference between the long arm and the short arm of the unequal-arm interferometer in the optical decoding unit;
performing time-delay scanning on the single-photon detector to acquire single-photon counts scanned for the single-photon detector in a time-delay scanning period;
determining a delay position of one of two peak counts as a delay position of the time base light pulse according to the delay position of the time base light pulse relative to another time base light pulse if two peak counts are scanned in the acquired single photon counts and an interval between the two peak counts is an optical path difference between a long arm and a short arm of the unequal arm interferometer;
adjusting a delay position of a gating signal for the single photon detector until the gating signal for the single photon detector aligns with the delay position of the temporal base light pulse.
7. The method of gating signal tuning of claim 6, further comprising, prior to adjusting the delay position of the gating signal for the single photon detector:
if three peak counts are scanned in the acquired single photon counts, determining a delay position of one of two adjacent peak counts separated by an optical path difference between a long arm and a short arm of the unequal arm interferometer as the delay position of the time base light pulse according to the delay position of the time base light pulse relative to the other time base light pulse.
8. The method of gating signal tuning of claim 6, further comprising, prior to adjusting the delay position of the gating signal for the single photon detector:
if four peak counts are scanned in the acquired single photon counts and a first peak count and a fourth peak count of the four peak counts are located at the beginning and the end of the delay scanning period, respectively, determining a delay position of one of a second peak count and a third peak count of the four peak counts as a delay position of the time base light pulse according to the delay position of the time base light pulse relative to another time base light pulse.
9. The method of any of claims 6 to 8, wherein the delay sweep period is greater than the encoding clock period.
10. A gating signal tuning apparatus for a quantum communication system, comprising:
a light source preparation unit configured to output, to an optical decoding unit of the quantum communication system, a light pulse synchronized with an encoding clock cycle of the quantum communication system through a phase-based light source in an optical encoding unit of the quantum communication system, the light pulse including an unequal arm interferometer in the optical encoding unit and an unequal arm interferometer in the optical decoding unit on an optical path to a single photon detector in the optical decoding unit for detecting the phase-based light pulse, wherein an optical path difference between a long arm and a short arm of the unequal arm interferometer in the optical encoding unit is the same as an optical path difference between the long arm and the short arm of the unequal arm interferometer in the optical decoding unit;
a time-delay scanning unit configured to time-delay scan the single-photon detector to acquire a single-photon count scanned for the single-photon detector within a time-delay scanning period;
a position determination unit configured to determine a delay position of a middle peak count of three peak counts as a delay position of the phase base light pulse if three peak counts are scanned in the acquired single photon counts and an interval between adjacent two of the three peak counts is an optical path difference between a long arm and a short arm of the unequal arm interferometer;
a signal tuning unit configured to adjust a delay position of a gating signal for the single photon detector until the gating signal for the single photon detector aligns with a delay position of the phase-based light pulse.
11. The gating signal tuning apparatus of claim 10, further comprising:
a phase adjusting unit configured to adjust a voltage of a phase shifter provided on a long arm of the unequal arm interferometer in the optical decoding unit until three peak counts are scanned in the acquired single photon counts and an interval between adjacent two peak counts among the three peak counts is an optical path difference between the long arm and the short arm of the unequal arm interferometer if two peak counts are scanned in the acquired single photon counts and the interval between the two peak counts is twice the optical path difference between the long arm and the short arm of the unequal arm interferometer.
12. The gating signal tuning apparatus of claim 10, wherein the location determination unit is further configured to determine the location of the first object based on the position of the first object
Determining a delay position of an intermediate peak count of the first three peak counts as a delay position of the phase-based light pulse if four peak counts are scanned in the acquired single photon counts and an interval between adjacent two peak counts of only the first three peak counts among the four peak counts is an optical path difference between a long arm and a short arm of the unequal-arm interferometer; or
Determining a delay position of an intermediate peak count of the last three peak counts as a delay position of the phase-based light pulse if four peak counts are scanned in the acquired single photon counts and an interval between adjacent two peak counts of only the last three peak counts of the four peak counts is an optical path difference between a long arm and a short arm of the unequal-arm interferometer.
13. The gating signal tuning apparatus of claim 10, wherein the position determining unit is further configured to determine the position of the gating signal tuning apparatus
If four peak counts are scanned in the acquired single photon counts and only an interval between the first two peak counts and an interval between the second two peak counts among the four peak counts is an optical path difference between the long arm and the short arm of the unequal arm interferometer, determining a delay position of the former one of the first two peak counts or a delay position of the latter one of the second two peak counts as a delay position of the phase base light pulse.
14. The gating signal tuning apparatus of any one of claims 10 to 13, wherein the delay sweep period is greater than the encoding clock period.
15. A gating signal tuning apparatus for a quantum communication system, comprising:
a light source preparation unit configured to output, to an optical decoding unit of the quantum communication system, a light pulse synchronized with an encoding clock cycle of the quantum communication system through a phase-based light source in the optical encoding unit of the quantum communication system, the light pulse including an unequal arm interferometer in the optical encoding unit but not including an unequal arm interferometer in the optical decoding unit on an optical path to a single photon detector for detecting a temporal base light pulse in the optical decoding unit, wherein an optical path difference between a long arm and a short arm of the unequal arm interferometer in the optical encoding unit is the same as an optical path difference between the long arm and the short arm of the unequal arm interferometer in the optical decoding unit;
a time-delay scanning unit configured to time-delay scan the single-photon detector to acquire a single-photon count scanned for the single-photon detector within a time-delay scanning period;
a position determination unit configured to determine a delay position of one of two peak counts as a delay position of the time base light pulse according to a delay position of the time base light pulse with respect to another time base light pulse if two peak counts are scanned in the acquired single photon counts and an interval between the two peak counts is an optical path difference between a long arm and a short arm of the unequal arm interferometer;
a signal tuning unit configured to adjust a delay position of a gating signal for the single photon detector until the gating signal for the single photon detector aligns with a delay position of the temporal base light pulse.
16. The gating signal tuning apparatus of claim 15, wherein the location determination unit is further configured to determine the location of the first object based on the position of the first object
If three peak counts are scanned in the acquired single photon counts, determining a delay position of one of two adjacent peak counts separated by an optical path difference between a long arm and a short arm of the unequal arm interferometer as the delay position of the time base light pulse according to the delay position of the time base light pulse relative to the other time base light pulse.
17. The gating signal tuning apparatus of claim 15, wherein the position determining unit is further configured to determine the position of the gating signal tuning apparatus
If four peak counts are scanned in the acquired single photon counts and a first peak count and a fourth peak count of the four peak counts are located at the start and end of the delay scan period, respectively, determining a delay position of one of a second peak count and a third peak count of the four peak counts as a delay position of the time base light pulse according to a delay position of the time base light pulse relative to another time base light pulse.
18. The gating signal tuning device of any of claims 15 to 17, wherein the delay sweep period is greater than the encoding clock period.
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