WO2020140850A1 - 一种基于量子纠缠的时钟同步系统与方法 - Google Patents

一种基于量子纠缠的时钟同步系统与方法 Download PDF

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WO2020140850A1
WO2020140850A1 PCT/CN2019/129494 CN2019129494W WO2020140850A1 WO 2020140850 A1 WO2020140850 A1 WO 2020140850A1 CN 2019129494 W CN2019129494 W CN 2019129494W WO 2020140850 A1 WO2020140850 A1 WO 2020140850A1
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clock synchronization
unit
beam splitter
photons
alice
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PCT/CN2019/129494
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French (fr)
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郭邦红
胡敏
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华南师范大学
广东尤科泊得科技发展有限公司
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0635—Clock or time synchronisation in a network
    • H04J3/0638—Clock or time synchronisation among nodes; Internode synchronisation
    • H04J3/0644—External master-clock
    • 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
    • H04J—MULTIPLEX COMMUNICATION
    • H04J3/00—Time-division multiplex systems
    • H04J3/02—Details
    • H04J3/06—Synchronising arrangements
    • H04J3/0635—Clock or time synchronisation in a network
    • H04J3/0682—Clock or time synchronisation in a network by delay compensation, e.g. by compensation of propagation delay or variations thereof, by ranging

Definitions

  • the invention relates to the technical field of quantum information and optical communication, and more specifically, to a clock synchronization system and method based on quantum entanglement.
  • Time is awareness of the most basic physical nature, 1967 Thirteenth CGPM decided International System of Units (SI), the definition of time in seconds (S) is: 133 C S atom State The duration of 9192631770 cycles of transition radiation between two ultra-fine energy levels. Because time is the basic physical quantity with the highest measurement accuracy, other physical quantities are often converted into time and frequency before measurement. For example, the length of a meter is defined as the distance traveled by light in a vacuum within a time interval of 1/299793458 seconds.
  • time frequency is a very important parameter; time frequency standard transmission is also very important in high-precision time service systems.
  • time frequency standard transmission is also very important in high-precision time service systems.
  • each device is controlled by an independent clock (crystal oscillator).
  • the initial calibration may be the same at the factory, due to different manufacturing processes, environmental conditions and other factors, the running time increases at any time, and the operating rules of each clock are different. Without timely comparison and calibration, the operation of each clock will be different, and the entire network will fall into chaos.
  • This comparison and calibration is clock synchronization.
  • Time-frequency synchronization technology refers to the process of comparing time-frequency signals generated by a clock in a different place by some means and forming a unified time-frequency reference.
  • Quantum key distribution is the closest technological achievement in the field of quantum information. After more than 30 years of development, it has now developed to the application stage of measurement device-independent protocols.
  • the measurement device-independent protocol is based on the Bell state measurement principle, and its code rate depends on the photon's Hong-Ou-Mandal (HOM) effect. This effect requires that the photons arrive at the HOM interferometer at the same time, otherwise they will not interfere and cause bit errors.
  • independent optical pulses of different wavelengths are generally used to achieve synchronization of both parties of communication by using wavelength division multiplexing, which consumes wavelength resources.
  • wavelength division multiplexing which consumes wavelength resources.
  • each wavelength is a precious resource, and the above method is obviously not economical and feasible.
  • the patent 201410337054.7 uses a multi-wavelength laser and a wavelength selective switch to achieve quantum key distribution and sharing among multiple users, but the synchronization problem is not considered.
  • the plug-and-play solution used does not guarantee a time-shift attack. Security.
  • Patent 201120311727.3 proposes to use quantum entanglement to achieve the time synchronization of the Beidou satellite, but the attenuation of photons in the atmosphere is large, and the alignment between the satellite and the ground station is more difficult.
  • the invention provides a clock synchronization system based on quantum entanglement.
  • the system uses quantum entangled states to realize clock synchronization between quantum and classical fusion networks.
  • Another object of the present invention is to provide a clock synchronization method based on quantum entanglement.
  • a clock synchronization system based on quantum entanglement including an entanglement source unit, a transmission unit, a synchronization unit Alice, Bob and a measurement unit connected in sequence;
  • the entanglement source unit includes a pump light, a non-linear crystal, and a first connected in sequence A narrowband filter and a second narrowband filter;
  • the transmission unit includes a first polarization beam splitter, a second polarization beam splitter, a controllable optical delay line, a manually adjustable optical delay line, and a first optical fiber link connected in sequence And the second optical fiber link;
  • the clock synchronization unit Alice includes a third narrow-band filter, a first beam splitter, a first Faraday mirror, a first optical isolator, and a first single photon detector connected in sequence;
  • the clock synchronization unit Alice includes A fourth narrow-band filter, a second beam splitter, a second Faraday mirror, a second optical isolator, and a second single-photon detector connected in
  • the pump light is a pulsed or continuous laser.
  • the laser wavelength of the pump light output is 790 nm.
  • the nonlinear crystal is a Type II PPKTP crystal.
  • a clock synchronization method based on quantum entanglement includes the following steps:
  • the transmission unit sets a controllable optical delay line delay, and the measurement unit obtains the photon count value by measuring the interference of entangled photon pairs;
  • the present invention uses single-polarized entangled photons to synchronize the optical fiber clock, avoiding the decrease in accuracy caused by polarization mode dispersion and reducing the number of single photon detectors required;
  • the Faraday mirror used in the present invention can realize the automatic compensation of polarization jitter in the optical fiber link, reduce the influence of optical fiber stress on photon transmission, and improve the interference contrast pair; 3.
  • the present invention uses the HOM interference effect based on entangled photon pairs , Can improve the clock synchronization accuracy.
  • FIG. 1 is a working principle diagram of the present invention
  • Figure 2 is a schematic diagram of the structure of the entangled source unit
  • Figure 3 is a schematic diagram of the structure of the transmission unit
  • FIGS. 4 and 5 are schematic diagrams of the structure of the clock synchronization unit
  • Figure 6 is a schematic diagram of the structure of the measuring unit
  • FIG. 7 is a schematic diagram of an embodiment of the present invention.
  • Entangled source unit-1' pump laser-101, nonlinear crystal-102, first narrow-band filter-103, second narrow-band filter-104;
  • Transmission unit-2' first polarization beam splitter-201, second polarization beam splitter-202, electrically controllable optical delay line-203, manually adjustable optical delay line-204, first optical fiber link-205, Second fiber link-206;
  • a clock synchronization system based on quantum entanglement includes an entanglement source unit 1', a transmission unit 2', a clock synchronization unit Alice 3', a clock synchronization unit Bob-4' and a measurement unit 5'.
  • the units are connected by optical fiber, among which:
  • the entangled source unit 1 includes a pump laser 101, a nonlinear crystal 102, a first narrow-band filter 103, and a second narrow-band filter 104;
  • the pump laser 101 is a laser with a wavelength of 790 nm, which is used to generate a pump laser,
  • the pump laser 101 can generate two signal entangled photon and idle frequency photon entangled photon pulses;
  • the nonlinear crystal 102 receives the pattern-matched wavelength and generates entangled photon pairs with frequency entanglement through parametric downconversion; wherein the nonlinear crystal 102 is Type II type PPKTP crystal.
  • the transmission unit 2' includes a first polarization beam splitter 201, a second polarization beam splitter 202, an electrically controllable optical delay line 203, a manually adjustable optical delay line 204, a first fiber link 205 and a second fiber link Road 206;
  • the first polarization beam splitter 201 receives the signal photons from the entangled source unit, transmits horizontally polarized light into the electrically controllable optical delay line 203, which is controlled by the host computer to precisely control the delay (resolution The rate can reach 1fs), and then transmitted to the clock synchronization unit Alice3' through the first optical fiber link 205;
  • the second polarization beam splitter 202 receives idle frequency photons from the entangled source unit 1', transmits horizontally polarized light and enters manually adjustable light
  • the delay line 204 is transmitted to the clock synchronization unit Bob4' through the second optical fiber link 206.
  • the clock synchronization unit Alice3' includes a third narrowband filter 301, a first beam splitter 302, a first Faraday mirror 303, a first optical isolator 304, a first single photon detector 305; a third narrowband filter 301 receives The signal photons from the transmission unit 2', after filtering the stray light, enter the first beam splitter 302, in which the transmitted photons enter the first Faraday mirror 303, the polarization rotates 90 degrees and returns according to the original optical path, and the reflected photons enter through the first optical isolator 304
  • the first single photon detector 305 performs detection for clock synchronization.
  • the clock synchronization unit Bob4′ includes a fourth narrowband filter 401, a second beam splitter 402, a second Faraday mirror 403, a second optical isolator 404 and a second single photon detector 405; the fourth narrowband filter 401 receives The idle frequency photons from the transmission unit 2', after filtering the stray light, enter the second beam splitter 402, where the transmitted photon enters the second Faraday mirror 403, the polarization is rotated 90 degrees, and returns according to the original optical path, and the reflected photon passes through the second optical isolator 404 Enter the second single photon detector 405 for detection, used for clock synchronization.
  • the measurement unit 5 includes a fifth narrow-band filter 501, a sixth narrow-band filter 502, a first polarization controller 503, a second polarization controller 504, a third beam splitter 505, and a third single photon detector 506, Fourth, the photon detector 507 and the coincidence counter 508;
  • the fifth narrow-band filter 501 receives the signal photons from the transmission unit, filters the stray light, and enters the first polarization controller 503, adjusts the polarization, and enters the third beam splitter 505;
  • the six narrow-band filter 502 receives idle frequency photons from the transmission unit, filters the stray light and enters the second polarization controller 504, adjusts the polarization, and enters the third beam splitter 505;
  • the signal photons and idle frequency photons are in the third beam splitter 505 HOM interference occurs, the event is recorded by the third single photon detector 506 and the fourth single photon detector 507, and the magnitude of the HOM interference effect is calculated by the coincidence
  • a clock synchronization method based on quantum entanglement includes the following steps:
  • the transmission unit is set with an electrically controllable optical delay line delay, and the measurement unit obtains the photon count value by measuring the interference of entangled photon pairs;
  • the pump laser 101 emits a pulsed laser near 790 nm, which is incident on a non-linear crystal (the non-linear crystal adopts PPKTP crystal) to generate frequency entangled signal photon and idle frequency photon pairs.
  • the two-photon state generated during spontaneous parametric down-conversion is expressed as:
  • A( ⁇ s , ⁇ i ) ⁇ ( ⁇ s , ⁇ i ) ⁇ L ( ⁇ s , ⁇ i ) is two-photon
  • the joint spectrum amplitude is determined by the spectral shape function ⁇ ( ⁇ s , ⁇ i ) of the pump light and the phase matching function ⁇ L ( ⁇ s , ⁇ i ) of the parametric down-conversion process.
  • the synchronization accuracy of the system depends on the interference result of the HOM interferometer, and this interference result depends on the spectral characteristics of the frequency entanglement source, and the interference intensity spectrum is proportional to:
  • A( ⁇ s , ⁇ i ) is the spectral function of entangled photon pairs, and ⁇ is the arrival delay of signal light and idle light.
  • the parametric down conversion process produces entangled photon pairs with similar frequencies.
  • Signal photons are sent to the clock synchronization unit Alice through the transmission unit, and idle frequency photons are sent to the clock synchronization unit Bob through the transmission unit.
  • the clock synchronization unit reflects back to the measurement unit, where the time data of the photons reaching the clock synchronization unit Alice and the clock synchronization unit Bob are respectively recorded as: with The time when the signal photons and idle frequency photons arrive at the clock synchronization unit Alice and the clock synchronization unit Bob respectively can be written as a function f(t):
  • Time offset can be It is determined that Alice and Bob are synchronized by adding a compensation amount ⁇ to the clock B.
  • the pump laser 101 selects a mode-locked titanium sapphire laser with a center wavelength of 790 nm; the nonlinear crystal is a Type II phase-matched PPKTP crystal. By reasonably designing a periodic structure, entangled photons with similar frequencies can be obtained from the pump laser Correct.
  • the first narrowband filter and the second narrowband filter are used to filter the pump light signal and stray light.
  • the transmission unit 2' is composed of a first polarization beam splitter 201, a second polarization beam splitter 202, an electrically controllable optical delay line 203, a manually adjustable optical delay line 204, a first optical fiber link 205 and a second optical fiber link Road 206 consists.
  • the first polarization beam splitter and the second polarization beam splitter transmit horizontally polarized light and reflect vertically polarized light.
  • the resolution of the electrically controllable optical delay line is 1fs.
  • the clock synchronization unit 3' includes a third narrow-band filter 301, a first beam splitter 302, a first Faraday mirror 303, a first optical isolator 304 and a first single photon detector 305.
  • the narrowband filter is selected according to the wavelength of the signal light.
  • the first beam splitter is a 50:50 beam splitter.
  • the first Faraday mirror can use a single-port fiber Faraday rotating mirror.
  • the first single photon detector is InGaAs. Near infrared single photon detector idQuantique id210.
  • the clock synchronization unit 4' includes a fourth narrow-band filter 401, a second beam splitter 402, a second Faraday mirror 403, a second optical isolator 404, and a second single photon detector 405.
  • the narrowband filter is selected according to the wavelength of the signal light.
  • the second beam splitter is a 50:50 fiber beam splitter.
  • the second Faraday mirror can use a single-port fiber Faraday rotating mirror.
  • the second single photon detector is selected as InGaAs near infrared single photon detector idQuantique id210.
  • the measurement unit 5 includes a fifth narrow-band filter 501, a sixth narrow-band filter 502, a first polarization controller 503, a second polarization controller 504, a third beam splitter 505, and a third single photon detector 506, Fourth but photon detection 507 and coincidence counter 508.
  • the narrowband filter is selected according to the wavelength of the signal light
  • the polarization controller is General Photonics MPC
  • the beam splitter is a 50:50 fiber beam splitter
  • the single-photon detector is selected as InGaAs near-infrared single-photon detector idQuantiqueid210
  • the compliance counter is standford SR620.
  • the system combines a laser with a wavelength near 790 nm, a nonlinear crystal, a polarization beam splitter, an electrically controllable optical delay line, and an optical fiber chain Roads, Faraday mirrors, single photon detectors, etc. are connected in sequence, and the lengths of the two optical paths to be synchronized are precisely adjusted through an electrically controllable optical delay line, so that the two parties to be synchronized reach the intermediate position at the same time, thereby achieving clock synchronization.
  • Using a single polarization photon and using a Faraday mirror to automatically compensate the polarization jitter of the fiber can improve the visibility of the HOM effect, thereby increasing the accuracy of time synchronization.

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Abstract

本发明公开了一种基于量子纠缠的时钟同步系统与方法，包括纠缠源单元，传输单元，时钟同步单元Alice，时钟同步单元Bob和测量单元，本发明采用单一偏振态的纠缠光子作为同步信号载体，利用法拉第镜及双向路径实现光纤中偏振抖动的自动补偿，由790nm激光泵浦II型相位匹配晶体形成频率近似的纠缠光子对，通过电可控光延迟线精密控制两条光路的延时，得到待时钟同步双方之间的HOM凹陷最大值，从而得到以中间单元为基准的准确时间差，再通过纠缠光子的直接测量实现双方的时钟同步。

Description

一种基于量子纠缠的时钟同步系统与方法 技术领域
本发明涉及量子信息与光通信技术领域，更具体地，涉及一种基于量子纠缠的时钟同步系统与方法。
背景技术
时间(频率)是人们认识自然界的最基本的物理量之一，1967年第十三届国际计量大会决定国际单位制(SI)中，时间单位秒(S)的定义为： 133C S原子基态的两个超精细能级间跃迁辐射的9192631770个周期的持续时间。因为时间是目前具有最高测量精度的基本物理量，所以其他物理量常常转化为时间频率后再进行测量，例如长度米的定义为真空中的光在1/299793458秒的时间间隔内所行经的距离。
在通信领域，时间频率是一个很重要的参数；时间频率标准传递在高精密授时系统中也至关重要。例如在SDH网络中，要求必须全网设备时钟同步，否则将导致数据紊乱，系统瘫痪。但是每台设备都是有独立时钟(晶振)控制的，虽然出厂时可能初次校准为一致，但是因为制造工艺，所处环境等因素不同，随时运行时间的增加，各台时钟运行规律不同，如果不及时进行比对校准，各台时钟运行就会有所差异，整个网络就会陷入混乱。这种比对和校准就是时钟同步。时频同步技术是指通过某种手段，将处于异地的时钟产生的时频信号进行比对，并形成统一时频基准的过程。
量子密钥分发作为量子信息领域最接近应用的技术成果，经过30多年的发展，目前已经发展到测量设备无关协议应用阶段。测量设备无关协议基于Bell态测量原理，其成码率依赖于光子的Hong-Ou-Mandal(HOM)效应。而该效应要求光子到达HOM干涉仪的时间一致，否则不能产生干涉而导致误码。目前一般采用不同波长的独立光脉冲利用波分复用来实现通信双方的同步，消耗了波长资源。然而网络用户的增加，尤其在经典和量子通信融合网络中，每一个波长都是宝贵的资源，上述方法显然不经济也不可行。
现有技术中，专利201410337054.7采用多波长激光器和波长选择开关实现多用户之间的量子密钥分发与共享，但是未考虑同步问题，所采用的即插即用方案并不能保证如时移攻击下的安全性。
利用量子纠缠的方法实现时间同步的思想最早来自2001年Giovannetti等人在《自然》 杂志上的论文“Quantum-enhanced positioning and clock synchronization”。利用量子纠缠态和量子压缩态可以突破散粒噪声的极限，实现亚皮秒甚至更精确的时钟同步。
专利201120311727.3提出了利用量子纠缠实现北斗卫星的时间同步，但是光子在大气中的衰减较大，卫星与地面站之间对准较为困难。
发明内容
本发明提供一种基于量子纠缠的时钟同步系统，该系统使用量子纠缠态实现量子与经典融合网络中的时钟同步。
本发明的又一目的在于提供一种基于量子纠缠的时钟同步方法。
为了达到上述技术效果，本发明的技术方案如下：
一种基于量子纠缠的时钟同步系统，包括依次连接的纠缠源单元、传输单元、同步单元Alice、Bob以及测量单元；所述纠缠源单元包括顺次连接的泵浦光、非线性晶体、第一窄带滤波器和第二窄带滤波器；所述传输单元包括顺次连接的第一偏振分束器、第二偏振分束、可控光延迟线、手动可调光延迟线、第一光纤链路和第二光纤链路；时钟同步单元Alice包括依次连接的第三窄带滤波器、第一分束器、第一法拉第镜、第一光隔离器和第一单光子探测器；时钟同步单元Alice包括依次连接的第四窄带滤波器、第二分束器、第二法拉第镜、第二光隔离器和第二单光子探测器；所述测量单元包括依次连接的第五窄带滤波器、第六窄带滤波器、第一偏振控制器、第二偏振控制器、第三分束器、第三单光子探测器、第四单光子探测器和符合计数器。
优选地，所述泵浦光为脉冲或者连续激光器。
优选地，所述泵浦光输出激光波长为790nm。
优选地，所述非线性晶体为Type II PPKTP晶体。
一种基于量子纠缠的时钟同步方法，包括以下步骤：
S1、系统初始化：检查纠缠源单元、传输单元、测量单元和时钟同步单元Alice、Bob的硬件设施，查看设备是否正常运转，设定初始条件；
S2、光路粗调：手动调节光纤延迟线的长度，保证测量单元到时钟同步单元Alice和时钟同步单元Bob的距离粗略相等；
S3、光路微调：传输单元设置可控光延迟线时延，测量单元通过测量纠缠光子对的干涉得到光子计数值；
S4、寻找HOM效应最大值：重复S3多次，逐步逼近HOM干涉条纹最大值；
S5、经S4得到最大值后，Alice和Bob通过各自单光子探测器校准本地时钟；
S6、系统定时重复S3～S5，实现时钟的实时同步。与现有技术相比，本发明技术方案的有益效果是：
1.本发明采用单一偏振态的纠缠光子进行光纤时钟同步，避免了偏振模色散导致的精度下降，减少了需要的单光子探测器数量；
2.本发明采用的法拉第镜可实现光纤链路中偏振抖动的自动补偿，降低了光纤应力作用对光子传输的影响，提高了干涉对比对；3.本发明采用基于纠缠光子对的HOM干涉效应，可提高时钟同步精度。
附图说明
图1为本发明的工作原理图；
图2为纠缠源单元的结构示意图；
图3为传输单元的结构示意图；
图4，5为时钟同步单元的结构示意图；
图6为测量单元的结构示意图；
图7为本发明实施例的示意图；
图8为本发明的工作流程图。
图中各部件对应的名称：
纠缠源单元-1’，泵浦激光器-101，非线性晶体-102，第一窄带滤波器-103，第二窄带滤波器-104；
传输单元-2’，第一偏振分束器-201，第二偏振分束器-202，电可控光延迟线-203，手动可调光延迟线-204，第一光纤链路-205，第二光纤链路-206；
时钟同步单元Alice-3’，第三窄带滤波器-301，第一分束器-302，第一法拉第镜-303，第一光隔离器-304，第一单光子探测器-305；
时钟同步单元Bob-4’，第四窄带滤波器-401，第二分束器-402，第二法拉第镜-403，第二光隔离器-404，第二单光子探测器-405；
测量单元-5’，第五窄带滤波器-501，第六窄带滤波器-502，第一偏振控制器-503，第二偏振控制器-504，第三分束器-505，第三单光子探测器-506，第四单光子探测-507，符 合计数器-508。
具体实施方式
附图仅用于示例性说明，不能理解为对本专利的限制。
为了更好说明本实施例，附图某些部件会有省略、放大或缩小，并不代表实际产品的尺寸；
对于本领域技术人员来说，附图中某些公知结构及其说明可能省略是可以理解的。
下面结合附图和实施例对本发明的技术方案做进一步的说明。
如图1-7示，一种基于量子纠缠的时钟同步系统，包括纠缠源单元1’、传输单元2’、时钟同步单元Alice3’、时钟同步单元Bob-4’和测量单元5’。所述各个单元之间通过光纤连接，其中：
所述纠缠源单元1’包括泵浦激光器101，非线性晶体102，第一窄带滤波器103，第二窄带滤波器104；泵浦激光器101为波长为790nm的激光器，用于产生泵浦激光，所述泵浦激光器101可产生信号光子和闲频光子两路纠缠光子脉冲；非线性晶体102接收模式匹配的波长，通过参量下转换(Parametric Downconversion)产生频率纠缠的纠缠光子对；其中非线性晶体102为TypeII类型的PPKTP晶体。
所述传输单元2’包括第一偏振分束器201，第二偏振分束器202，电可控光延迟线203，手动可调光延迟线204，第一光纤链路205和第二光纤链路206；第一偏振分束器201接收来自纠缠源单元的信号光子，透射水平偏振光进入电可控光延迟线203，电可控光延迟线203由上位机控制，精确控制延时(分辨率可达1fs)，然后通过第一光纤链路205传输到时钟同步单元Alice3’；第二偏振分束器202接收来自纠缠源单元1’的闲频光子，透射水平偏振光进入手动可调光延迟线204，通过第二光纤链路206传送到时钟同步单元Bob4’。
所述时钟同步单元Alice3’包括第三窄带滤波器301，第一分束器302，第一法拉第镜303，第一光隔离器304，第一单光子探测器305；第三窄带滤波器301接收来自传输单元2’的信号光子，过滤杂散光后进入第一分束器302，其中透射光子进入第一法拉第镜303后偏振旋转90度按原光路返回，反射光子经第一光隔离器304进入第一单光子探测器305进行探测，用于时钟同步。
所述时钟同步单元Bob4’包括第四窄带滤波器401，第二分束器402，第二法拉第镜 403，第二光隔离器404和第二单光子探测器405；第四窄带滤波器401接收来自传输单元2’的闲频光子，过滤杂散光后进入第二分束器402，其中透射光子进入第二法拉第镜403后偏振旋转90度按原光路返回，反射光子经第二光隔离器404进入第二单光子探测器405进行探测，用于时钟同步。
所述测量单元5’包括第五窄带滤波器501，第六窄带滤波器502，第一偏振控制器503，第二偏振控制器504，第三分束器505，第三单光子探测器506，第四但光子探测器507和符合计数器508；第五窄带滤波器501接收来自传输单元的信号光子，过滤杂散光后进入第一偏振控制器503，调节偏振后进入第三分束器505；第六窄带滤波器502接收来自传输单元的闲频光子，过滤杂散光后进入第二偏振控制器504，调节偏振后进入第三分束器505；信号光子与闲频光子在第三分束器505处发生HOM干涉，通过第三单光子探测器506和第四单光子探测器507记录事件，通过符合计数器508计算HOM干涉效应的大小。
如图8所示，一种基于量子纠缠的时钟同步方法，该方法上述的一种基于量子纠缠的时钟同步系统，包括以下步骤：
S1、系统初始化：检查纠缠源单元、传输单元、测量单元和时钟同步单元Alice和Bob的硬件设施，查看设备是否正常运转，设定初始条件；
S2、光路粗调：手动调节光纤延迟线的长度，保证时钟同步单元到测量单元的距离粗略相等；
S3、光路微调：传输单元设置电可控光延迟线时延，测量单元通过测量纠缠光子对的干涉得到光子计数值；
S4、寻找HOM效应最大值：重复S3多次，逐步逼近HOM干涉曲线最大值；
S5、经S4得到最大值后，Alice和Bob通过各自单光子探测器校准本地时钟；
S6、系统定时重复S3～S5，实现时钟的实时同步。
本发明工作时，所述泵浦激光器101发出790nm附近的脉冲激光，入射到非线性晶体(非线性晶体采用PPKTP晶体)产生频率纠缠的信号光子和闲频光子对。根据量子光学理论，自发参量下转换过程中产生的双光子态表示为：
Figure PCTCN2019129494-appb-000001
其中
Figure PCTCN2019129494-appb-000002
和
Figure PCTCN2019129494-appb-000003
分别为信号光和闲频光的产生算符，|0>为真空态，A(ω s,ω i)＝α(ω s,ω i)Φ L(ω s,ω i)为双光子的联合频谱振幅，由抽运光的谱形函数α(ω s,ω i)和 参量下转换过程的相位匹配函数Φ L(ω s,ω i)决定。
系统的同步精度取决于HOM干涉仪的干涉结果，而这个干涉结果依赖于频率纠缠源的谱特性，由干涉强度谱正比于：
∫∫dω sdω i(|A(ω s，ω i)| 2-|A(ω s，ω i)A(ω i，ω s)|cos[(ω s-ω i)τ])
其中，A(ω s，ω i)为纠缠光子对的谱函数，τ为信号光和闲置光的到达延时，通过理论和现有器件性能估计，合理优化A(ω s，ω i)可提高系统的同步精度。
参量下转换过程产生频率相近的纠缠光子对，信号光子通过传输单元发送到时钟同步单元Alice，闲频光子通过传输单元发送到时钟同步单元Bob。时钟同步单元反射回测量单元，其中光子到达时钟同步单元Alice和时钟同步单元Bob的时间数据分别记为：
Figure PCTCN2019129494-appb-000004
和
Figure PCTCN2019129494-appb-000005
信号光子和闲频光子的分别到达时钟同步单元Alice和时钟同步单元Bob时间可以写成函数f(t)：
Figure PCTCN2019129494-appb-000006
Figure PCTCN2019129494-appb-000007
计算两个函数之间的互相关以提取时间偏移：
Figure PCTCN2019129494-appb-000008
对时间积分：
Figure PCTCN2019129494-appb-000009
时间偏移可以由
Figure PCTCN2019129494-appb-000010
确定，通过对时钟B添加补偿量τ实现Alice和Bob的同步。
所述泵浦激光器101选择锁模钛宝石激光器，将中心波长为790nm；所述非线性晶体为TypeII相位匹配的PPKTP晶体，通过合理设计周期性结构，能够由泵浦激光得到频率相近的纠缠光子对。
所述第一窄带滤波器和第二窄带滤波器用于过滤泵浦光信号和杂散光。
所述传输单元2’由第一偏振分束器201，第二偏振分束器202，电可控光延迟线203，手动可调光延迟线204，第一光纤链路205和第二光纤链路206组成。第一偏振分束器和第二偏振分束透射水平偏振光，反射垂直偏振光，电可控光延迟线的分辨率为1fs。
所述时钟同步单元3’包括第三窄带滤波器301，第一分束器302，第一法拉第镜303，第一光隔离器304和第一单光子探测器305。本实施例中窄带滤波器根据信号光波长进行选择，第一分束器为50:50分束器，第一法拉第镜可采用单端口的光纤法拉第旋转镜，第一单光子探测器选择为InGaAs近红外单光子探测器idQuantique id210。
所述时钟同步单元4’包括第四窄带滤波器401，第二分束器402，第二法拉第镜403，第二光隔离器404和第二单光子探测器405。本实施例中窄带滤波器根据信号光波长进行选择，第二分束器为50:50光纤分束器，第二法拉第镜可采用单端口的光纤法拉第旋转镜，第二单光子探测器选择为InGaAs近红外单光子探测器idQuantique id210。
所述测量单元5’包括第五窄带滤波器501，第六窄带滤波器502，第一偏振控制器503，第二偏振控制器504，第三分束器505，第三单光子探测器506，第四但光子探测507和符合计数器508。本实施例中窄带滤波器根据信号光波长进行选择，偏振控制器为General Photonics MPC，分束器为50:50光纤分束器，单光子探测器选择为InGaAs近红外单光子探测器idQuantique id210，符合计数器为standford SR620。
通过上述具体实施方式的说明，我们提出的一种基于纠缠的时钟同步系统与方法，该系统将波长为790nm附近的激光器、非线性晶体、偏振分束器、电可控光延迟线、光纤链路、法拉第镜、单光子探测器等依次连接起来，通过电可控光延迟线精密调节待同步的两条光路的长度，使得待同步双方同时到达中间位置，以此实现时钟同步。采用单一偏振态光子并利用法拉第镜自动补偿光纤的偏振抖动，能够提高HOM效应的可见度，从而增加时间同步的精度。
相同或相似的标号对应相同或相似的部件。
根据上述说明书的揭示和教导，本发明所属领域的技术人员还可以对上述实施方式进行变更和修改。因此，本发明并不局限于上面揭示和描述的具体实施方式，对发明的一些修改和变更也应当落入本发明的权利要求的保护范围内。此外，尽管本说明书中使用了一些特定的术语，但这些术语只是为了方便说明，并不对发明构成任何限制。

Claims (10)

  1. 一种基于量子纠缠的时钟同步系统，其特征在于：包括纠缠源单元，传输单元，时钟同步单元Alice，时钟同步单元Bob和测量单元，其中：
    所述纠缠源单元发射信号光子和闲频光子相互纠缠的两路纠缠光子脉冲，信号光子和闲频光子经传输单元分别传送至时钟同步单元Alice和时钟同步单元Bob，并在所述时钟同步单元Alice和Bob进行反射，反射后的脉冲经传输单元发送到所述测量单元；
    所述测量单元接收由所述传输单元发送过来两路纠缠光子脉冲并对其进行测量；
    所述传输单元多次调节两路纠缠光子脉冲光路之间的延时并通过符合计数得到HOM干涉曲线；
    获取HOM干涉曲线的最大值，在最大值时刻，两路纠缠光子脉冲到达时钟同步单元Alice和Bob的时间相同，所述时钟同步单元Alice和Bob通过单光子探测器进行时间同步；
    信号光子和闲频光子的分别到达时钟同步单元Alice和时钟同步单元Bob时间为函数f(t)：
    Figure PCTCN2019129494-appb-100001
    Figure PCTCN2019129494-appb-100002
    其中，其中
    Figure PCTCN2019129494-appb-100003
    和
    Figure PCTCN2019129494-appb-100004
    表示信号光子和闲频光子分别到达时钟同步单元Alice和时钟同步单元Bob的时间数据，N表示测量次数。
  2. 根据权利要求1所述的基于量子纠缠的时钟同步系统，其特征在于：所述纠缠源单元包括泵浦激光器、非线性晶体、第一窄带滤波器和第二窄带滤波器；
    所述泵浦激光器产生泵浦激光，泵浦激光进入到非线性晶体产生信号光子和闲频光子相互纠缠的两路纠缠光子脉冲，其中信号光子进入第一窄带滤波器后发送到传输单元，闲频光子进入第二窄带滤波器后发送到所述传输单元。
  3. 根据权利要求2所述的基于量子纠缠的时钟同步系统，其特征在于：所述泵浦光为脉冲或者连续激光器；
    所述泵浦光输出激光波长为790nm；
    所述非线性晶体为Type II PPKTP晶体；
    所述泵浦光为脉冲激光器时，探测器工作在门控模式下；
    所述泵浦光为连续激光器时，探测器工作在连续模式下。
  4. 根据权利要求2所述的基于量子纠缠的时钟同步系统，其特征在于：所述传输单元包括第一偏振分束器、第二偏振分束器、电可控光延迟线、手动可调光延迟线、第一光纤 链路和第二光纤链路；
    所述传输单元接收来自纠缠源单元的信号光子，进入所述第一偏振分束器，经第一偏振分束器透射水平偏振光，再进入所述电可控光延迟线，经过所述电可控光延迟线调节时延后进入第一光纤链路，经第一光纤链路发送到时钟同步单元Alice；
    所述传输单元接收来自纠缠源单元的闲频光子，进入所述第二偏振分束器，经第二偏振分束器透射水平偏振光，再进入所述手动可调光延迟线，经过所述手动可调光延迟线调节时延后进入第二光纤链路，经第二光纤链路发送到时钟同步单元Bob。
  5. 根据权利要求4所述的基于量子纠缠的时钟同步系统，其特征在于：所述电可控光延迟线用于精密控制光程；所述手动可调光延迟线用于粗略控制光程。
  6. 根据权利要求1所述的基于量子纠缠的时钟同步系统，其特征在于：所述时钟同步单元Alice包括第三窄带滤波器、第一分束器、第一法拉第镜、第一光隔离器和第一单光子探测器；
    所述时钟同步单元Alice接收来自传输单元的信号光子，经第三窄带滤波器过滤杂散光后进入第一分束器，在第一分束器处进行透射和反射，其中透射光子进入第一法拉第镜后偏振旋转90度按原光路返回；反射光子经第一光隔离器进入第一单光子探测器进行探测，用于时钟同步；
    所述第一分束器为50:50分束器，第一法拉第镜采用单端口的光纤法拉第旋转镜，第一单光子探测器为近红外单光子探测器。
  7. 根据权利要求1所述的基于量子纠缠的时钟同步系统，其特征在于：所述时钟同步单元Bob包括第四窄带滤波器、第二分束器、第二法拉第镜、第二光隔离器和第二单光子探测器；
    所述时钟同步单元Bob接收来自传输单元的闲频光子，经第四窄带滤波器过滤杂散光后进入第二分束器，在第二分束器处进行透射和反射，其中透射光子进入第二法拉第镜后偏振旋转90度按原光路返回；反射光子经第二光隔离器进入第二单光子探测器进行探测，用于时钟同步；
    所述第二分束器为50:50分束器，第二法拉第镜可采用单端口的光纤法拉第旋转镜，第二单光子探测器为近红外单光子探测器。
  8. 根据权利要求6或7所述的基于量子纠缠的时钟同步系统，其特征在于：所述传输单元接收来自所述时钟同步单元Alice和Bob反射回的垂直偏振信号光子和闲频光子，其 中信号光子进入第一偏振分束器，反射光经过第一环形器发送到测量单元，闲频光子进入第二偏振分束器，反射光经过第二环形器发送到测量单元。
  9. 根据权利要求8所述的基于量子纠缠的时钟同步系统，其特征在于：所述测量单元包括第五窄带滤波器、第六窄带滤波器、第一偏振控制器、第二偏振控制器、第三分束器、第三单光子探测器、第四单光子探测器和符合计数器；
    第五窄带滤波器接收来自所述传输单元的信号光子过滤杂散光后，经过第一偏振控制器调节偏振后进入第三分束器，第六窄带滤波器接收来自所述传输单元的闲频光子过滤杂散光后，经过第二偏振控制器调节偏振后进入第三分束器；信号光子与闲频光子在第三分束器产生干涉，由第三单光子探测器和第四单光子探测器分别记录并发送至符合计数器。
  10. 一种基于量子纠缠的时钟同步方法，该方法应用于权利要求1-9任一所述的一种基于量子纠缠的时钟同步系统，其特征在于：包括以下步骤：
    S1、系统初始化：检查纠缠源单元、传输单元、测量单元和时钟同步单元Alice和Bob的硬件设施，查看设备是否正常运转，设定初始条件；
    S2、光路粗调：手动调节光纤延迟线的长度，保证测量单元到时钟同步单元Alice和时钟同步单元Bob的距离粗略相等；
    S3、光路微调：传输单元设置电可控光延迟线时延，测量单元通过测量纠缠光子对的干涉得到光子计数值；
    S4、寻找HOM效应最大值：重复S3多次，逐步逼近HOM干涉曲线最大值；
    S5、经S4得到最大值后，Alice和Bob通过各自单光子探测器校准本地时钟；
    S6、系统定时重复S3～S5，实现时钟的实时同步。
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EP3943877A1 (en) * 2020-07-22 2022-01-26 Honeywell International Inc. Dynamic optical interferometer locking using entangled photons
EP3943878A1 (en) * 2020-07-22 2022-01-26 Honeywell International Inc. Direct measurement of imbalanced optical paths using entangled photons
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US11962353B2 (en) 2022-04-06 2024-04-16 Qubit Moving And Storage, Llc Method and system for identifying entangled photons with one-way classical information sharing
EP4277165A1 (en) * 2022-05-10 2023-11-15 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Quantum time reference synchronization
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US12003625B2 (en) 2023-02-26 2024-06-04 Qubit Moving And Storage, Llc Receiver for verification using entangled photons
CN116192320A (zh) * 2023-04-26 2023-05-30 军事科学院系统工程研究院网络信息研究所 波分复用的量子时间同步控制方法
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