WO2021068129A1 - 量子存储装置 - Google Patents

量子存储装置 Download PDF

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WO2021068129A1
WO2021068129A1 PCT/CN2019/110139 CN2019110139W WO2021068129A1 WO 2021068129 A1 WO2021068129 A1 WO 2021068129A1 CN 2019110139 W CN2019110139 W CN 2019110139W WO 2021068129 A1 WO2021068129 A1 WO 2021068129A1
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storage
quantum
crystal
light
signal
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PCT/CN2019/110139
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French (fr)
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周宗权
李传锋
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中国科学技术大学
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Priority to PCT/CN2019/110139 priority Critical patent/WO2021068129A1/zh
Priority to US17/281,931 priority patent/US11328773B2/en
Publication of WO2021068129A1 publication Critical patent/WO2021068129A1/zh

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    • G—PHYSICS
    • G11—INFORMATION STORAGE
    • G11C—STATIC STORES
    • G11C13/00—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00
    • G11C13/04—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using optical elements ; using other beam accessed elements, e.g. electron or ion beam
    • G11C13/047—Digital stores characterised by the use of storage elements not covered by groups G11C11/00, G11C23/00, or G11C25/00 using optical elements ; using other beam accessed elements, e.g. electron or ion beam using electro-optical elements
    • G—PHYSICS
    • G06—COMPUTING; CALCULATING OR COUNTING
    • G06N—COMPUTING ARRANGEMENTS BASED ON SPECIFIC COMPUTATIONAL MODELS
    • G06N10/00—Quantum computing, i.e. information processing based on quantum-mechanical phenomena
    • G06N10/40—Physical realisations or architectures of quantum processors or components for manipulating qubits, e.g. qubit coupling or qubit control
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01S—DEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00—Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005—Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0085—Modulating the output, i.e. the laser beam is modulated outside the laser cavity

Definitions

  • the present disclosure relates to the field of quantum information technology, and in particular to a quantum storage device.
  • the ultimate goal of quantum communication development is to build a large-scale quantum communication network across the country and even across continents.
  • the main challenge facing quantum communication is to realize long-distance quantum communication.
  • Photons are the natural carrier of quantum information transmission.
  • the transmission loss of photons in optical fibers increases exponentially with the transmission distance, even with the use of ultra-low loss optical fibers in the communication band, the current transmission distance is limited to less than 500 kilometers. Due to the law of unclonability of quantum states, the method of using amplifiers to directly amplify signals in classical communication is also not suitable for quantum communication.
  • a feasible remote quantum communication scheme is the quantum encrypted USB flash drive. It first stores the photons in the ultra-long-life transportable quantum memory (or called the quantum encrypted USB flash drive), and then uses the classical transportation means to transport the quantum encrypted USB flash drive. Realize the long-distance transmission of photons. Considering the transmission distance of 1,000 kilometers and the transportation speed of 300 kilometers/hour, the quantum encrypted U disk needs to support at least an hour-level storage life and support photon storage with a high signal-to-noise ratio.
  • the present invention discloses a quantum storage device, including: a sample cavity for loading storage crystals and filter crystals and for cooling the storage crystals and filter crystals to a preset temperature; a laser control system for generating control light and signal light to realize the Signal light quantum storage based on spin population locking; quantum state encoding and analysis system for encoding and analyzing signal photons; filtering system for suppressing noise introduced by control light and extracting signal photons.
  • the sample chamber includes: a cryogenic chamber for cooling the storage crystal to a preset temperature; and a vibration synchronization device for synchronously monitoring the vibration signal of the cryogenic chamber.
  • the laser control system includes: a frequency-stabilized laser for generating multiple laser beams; a first acousto-optic modulator for modulating a beam of the laser light into control light of the storage crystal; and a second acousto-optic modulator , Used to modulate a beam of the laser light into single photon level signal light; the third acousto-optic modulator, used to modulate a beam of the laser light into the control light of the filter crystal; the fourth acousto-optic modulator and the spiral phase The sheet is used to modulate a beam of the laser into the Laguerre-Gaussian mode control light of the storage crystal.
  • the quantum state encoding and analysis system includes: a quantum state encoding device for loading the signal light with a specific quantum state; and a quantum state analysis device for analyzing the quantum state of the signal light.
  • the filtering system includes: a single-mode optical fiber to filter out noise in space; a narrow-band filter to filter out spectral noise on the order of 1 nm; and a high-speed optical switch to filter out noise in time. ;
  • the filter crystal is used to filter out the spectral noise on the order of 1MHz accuracy.
  • the storage crystal is 151 Eu 3+ or 153 Eu 3+ doped YSO crystal.
  • the realization of the quantum storage of the signal light based on the spin population lock in the laser control system includes: selecting an ion ensemble with a target energy level structure from a storage crystal doped with Eu 3+ ions , And prepare the absorption lines of the ions of the ion ensemble as isolated absorption peaks under a transparent background; prepare the spatial absorption structure based on the Laguerre-Gaussian mode light field to prepare the spatial absorption of the center and the periphery on the ion ensemble.
  • Transparent absorption structure based on the storage process of two ⁇ /2 pulses of photon echoes, the short-term storage of incident signal photons is realized on the transition between the ground state g energy level and the excited state e energy level; based on two ⁇ pulses Spin population locking process, storing signal photons as a population structure on the ground state g energy level-ground state s energy level transition, extending the storage life to the order of the spin population life; and the effect of the photon echo signal Read, read the echo signal in the original direction of the incident signal, reduce the noise of the storage process.
  • selecting an ion ensemble with a target energy level structure from a storage crystal doped with Eu 3+ ions includes: applying at least three scanning lasers that resonate with the optical transition of the sample, from the Eu 3+ ion doped An ion ensemble with the same energy level structure is selected from the non-uniformly broadened absorption line of the storage medium; one of the scanning laser beams is removed to polarize the spin state of the ion ensemble to the aux energy level of the same initial state; A narrow-band scanning laser with aux energy level to excited state transition is applied, and a scanning laser with s energy level to excited state transition is applied at the same time to form an isolated absorption line in the transparent band, and the ion population in the absorption line is at g energy Level up.
  • the preparation of the spatial absorption structure based on the Laguerre-Gaussian mode light field includes: applying the Laguerre-Gaussian mode light field to the storage crystal, the center of the light field is a black hole of the order of 100um, and the energy is concentrated in the outer circle; one of the beams Scanning laser and ground state g energy level and excited state e energy level jump, scanning bandwidth is on the order of 10MHz, used to eliminate the absorption of ge transition; another scanning laser and ground state s energy level and excited state e energy level jump, scanning bandwidth 10MHz Magnitude, used to eliminate the absorption of se transitions.
  • the storage of photon echoes based on two ⁇ /2 pulses includes: a signal photon pulse that resonates with a ge transition; a first ⁇ /2 pulse that resonates with a ge transition; a first ⁇ pulse that resonates with a se transition ; A second ⁇ pulse resonating with the se transition;
  • the spin population lock based on two ⁇ pulses includes: a second ⁇ /2 pulse resonating with a ge transition; a first ⁇ pulse resonating with a ge transition.
  • the polarization states of the generated signal light and the control light are polarization states orthogonal to each other, and are aligned with the polarization axis of the storage crystal.
  • the present disclosure provides a quantum storage device that can be transported remotely.
  • a quantum storage device that can be transported remotely.
  • ultra-long-life photon quantum state storage is realized, which can be used for remote quantum communication, remote entanglement distribution, etc.
  • the storage device has the advantages of long storage life, high signal-to-noise ratio, strong anti-interference ability, etc., and the equipment is simple and easy to operate.
  • Fig. 1 schematically shows a structural diagram of a transportable quantum storage device according to an embodiment of the present disclosure
  • Fig. 2 schematically shows a working schematic diagram of a transportable quantum storage device according to an embodiment of the present disclosure
  • FIG. 3 schematically shows a schematic diagram of an energy level structure and a preparation method of a memory crystal according to an embodiment of the present disclosure
  • FIG. 4 schematically shows a schematic diagram of a storage control sequence of the disclosed embodiment
  • FIG. 5 schematically shows the time spectrum of the long-lived superposition state photon storage according to the embodiment of the present disclosure.
  • the embodiment of the present disclosure provides a transportable quantum storage device. See FIG. 1, including: a sample cavity 11 for loading a storage crystal 111 and providing a low temperature environment with a preset temperature; a laser control system 12 for generating Control light and signal light, realize the long-life storage solution of spin population lock; Quantum state coding and analysis system 13, used to realize quantum state coding and analysis of signal photons; Filter system 14, used to suppress the introduction of control light field The signal photons are extracted from the noise; the seismic isolation platform 15 is used to isolate environmental vibration.
  • the preset temperature here is to cool the electron-phonon interaction in the crystal and prolong the coherence time.
  • the temperature range is lower than 4K, such as 3.5K.
  • the sample cavity 11 is used to load the storage crystal 111 and the filter crystal 144 to be tested; specifically, the low temperature cavity 112 is used to cool the storage crystal 111 to a preset temperature.
  • the working temperature is set to 3K here, and no liquid helium compression is used.
  • Mechanical refrigeration; the storage crystal adopts 151 Eu 3+ doped YSO crystal with a concentration of 0.1%, and the thickness is 10mm.
  • the vibration synchronization device 113 is used to synchronously monitor the vibration signal of the cryogenic chamber 112.
  • the laser control system 12 is used to generate control light and signal light;
  • the frequency-stabilized laser 121 may be a 580nm laser with PDH frequency-stabilized frequency, with a power of 1W and a line width of 0.2kHz; the first acousto-optic modulator 122 may select an acousto-optic modulator with a center frequency of 200MHz.
  • the laser is modulated into the control light of the storage crystal; the control light is used to realize the control sequence of the long-life quantum storage method of spin population locking, which specifically includes: selecting an ion of an energy level type and initializing the ion ensemble According to the sequence requirements, two ⁇ /2 pulses, two spin shift ⁇ pulses, and one ⁇ pulse for reading the photon echo signal are then generated according to the sequence requirements.
  • the second acousto-optic modulator 123 selects an acousto-optic modulator whose parameter is a 200MHz center frequency for modulating the laser light into a single-photon-level signal light; the typical parameter is a single-photon-level pulse with a pulse width of 1 us.
  • the third acousto-optic modulator 124 selects an acousto-optic modulator whose parameter is a 200MHz center frequency, and is used to modulate the laser as the control light of the filter crystal; the typical parameter is selected to scan the laser frequency at 1MHz near the target frequency.
  • the fourth acousto-optic modulator 125 selects an acousto-optic modulator with a 200MHz center frequency and a spiral phase plate 126, which is selected as a first-order spiral phase plate of 580nm, which is used to modulate the laser into a first-order Laguerre of a storage crystal. -Gaussian mode controls the light.
  • the quantum state encoding and analysis system 13 is used to implement quantum state encoding and analysis of signal photons; specifically, it may include a quantum state encoding device 131 and a quantum state analysis device 132, wherein the quantum state encoding device 131 is used to The signal photon loads a specific quantum state; the quantum state analysis device 132 is used to analyze the quantum state of the signal photon.
  • the degree of freedom of the orbital angular momentum of the light is selected to load the quantum state
  • the quantum state encoding device 131 and the quantum state analysis device 132 are respectively two spatial light modulators with a resolution of 512*512 and a pixel element size of 8um.
  • the filter system 14 is used to suppress noise introduced by the control light field and extract signal photons; specifically, it may include a single-mode fiber 141, a narrowband filter 142, a high-speed optical switch 143, and a filter crystal.
  • single-mode fiber 141 is used to filter out noise in space; 460nm single-mode polarization-maintaining fiber is selected; narrowband filter 142 is used to filter out spectral noise with an accuracy of 1nm; 1nm bandwidth is selected, and the transmittance is greater than 99 % Interference filter; high-speed optical switch 143, used to filter out noise in time; select high-speed electro-optic modulation crystal, switching speed of 3ns, extinction ratio 10000:1; filter crystal 144, used to filter on the order of 1MHz accuracy In addition to the spectral noise, the filter crystal adopts a 0.1% 151 Eu 3+ doped YSO crystal with a thickness of 15mm
  • the polarization state of the signal light is aligned with the D1 axis of the YSO crystal to enhance sample absorption.
  • the polarization state of all control light is aligned with the D1 axis of the YSO crystal.
  • the polarization states of the signal light and the control light are orthogonal to each other to suppress noise caused by the control light.
  • a seismic isolation platform 15 may also be included for isolating environmental vibrations. Specifically, an active feedback platform based on piezoelectric ceramic control is selected.
  • the storage process is strictly synchronized with the vibration signal detected by the cryo-cavity vibration synchronization device 113, and a low vibration time window is selected to perform the photon storage operation.
  • the specific storage scheme adopted is a long-life storage method with spin population locking, and the control light should simultaneously complete the absorption band preparation target of the storage crystal 111 and the filter crystal 114.
  • the operation of controlling light can include the following four steps:
  • the goal of preparing the absorption band of the storage crystal is to prepare a narrow band absorption line with a line width of 1 MHz in a transparent band with a line width of 6 MHz, and all ions in the absorption line are at the g energy level.
  • the first step firstly apply the sweeping light field with three frequencies of f 0 , f 1 , f 2 at the same time, in which the f 0 beam resonates with the ge transition, the f 1 beam resonates with the gs transition, and the f 2 beam and the aux energy level reach 5 The 3/2 nuclear spin energy state transition resonance of the upper energy level of D 0.
  • the light field of each frequency scans +/-3MHz around the center frequency.
  • the first step is to realize the selection of the ion ensemble of the same energy level structure.
  • f 0 , f 1 , and f 2 are set to 400MHz, 434.54MHz, and 379.08MHz respectively, corresponding to the fine energy level structure of 151 Eu 3+ ions in YSO crystals
  • Step 2 Remove the f 2 scanning laser and continue to perform the f 1 and f 0 frequency scanning lasers, which are used to polarize the spin state of the ion ensemble 113 to the same initial state, that is, the aux energy level;
  • Step 3 Remove all the above scanning lasers, apply a weak pump light field that scans +/-0.5MHz around the f 2 frequency, and apply a weak pump that scans +/-0.5MHz around the f 1 frequency at the same time
  • the population is prepared to the same initial state in the 2MHz bandwidth range, that is, the 1/2 nuclear spin energy state of the energy level at 7 F 0.
  • the first acousto-optic modulator 122 is used, and the optical path of the double-pass modulator is used for completion.
  • the preparation goal of the spatial domain absorption structure of the storage crystal is to prepare a transparent area with a diameter of 1mm from the cross-section of the storage crystal when light is transmitted, with a 100um diameter in the center to form effective absorption.
  • a Laguerre-Gaussian mode light field is applied, the center of the light field is a black hole of about 100um, the energy is concentrated in the outer ring, and the total size of the light spot is about 1mm.
  • Some of the lasers scan around the f 0 frequency with a scan bandwidth of 6MHz to eliminate the absorption of ge transitions;
  • the other part of the laser is simultaneously scanned near the frequency f 1 with a scanning bandwidth of 6 MHz to eliminate the absorption of se transitions;
  • the crystal presents a transparent area with a 1mm diameter circle, and an absorption band with a 100um diameter circle is isolated in the center, effectively The optical noise caused by the spatial imperfection of the manipulation pulse is suppressed.
  • the fourth acousto-optic modulator 125 is used, and the optical path of the double-pass modulator is used to complete.
  • the light field is phase-modulated by a first-order Laguerre-Gaussian mode spiral phase plate 126 to form a ring beam with a central black hole.
  • the goal of preparing the absorption band of the filter crystal is to prepare a transmission band with a line width of 1 MHz, and the background is a strong absorption band above 2 GHz.
  • the third acousto-optic modulator 124 is used, and the optical path of the double-pass modulator is used to complete.
  • the second acousto-optic modulator 123 first use the second acousto-optic modulator 123 to modulate a signal light pulse with a pulse width of about 1 us, and the light field frequency is f 0 ; wait for 1 us Then, the first acousto-optic modulator 122 is used to generate a ⁇ /2 pulse of f 0 frequency. After 1 us, a ⁇ pulse of f 1 frequency is applied. After a controllable long storage time, a ⁇ pulse of f 1 frequency is applied. pulse, is applied after the ⁇ 9us a frequency f 0/2 pulse; Finally, ⁇ pulse applied to a frequency f 0. Subsequently, the signal light is emitted.
  • Figure 4 shows a schematic diagram of the complete timing control of this embodiment, including the above four steps.
  • Figure 5 shows the output measurement results of the quantum superposition state carrying the orbital angular momentum of the weak light field after storage.
  • the number of photons contained in the signal pulse is on the order of 10 7 and is detected by a photomultiplier tube.
  • the signal pulse carries the quantum superposition state
  • the storage time is set to 7.2 hours.
  • the solid line in the figure corresponds to the result of measuring the output photon using
  • the dotted line in the figure corresponds to the orthogonal basis vector
  • the interference visibility of the readout quantum state exceeds 99%, which well protects the quantum state carried by the incident pulse. Compared with previously known storage devices, the storage life of the device is greatly improved, and it supports the storage of photon quantum states.
  • the embodiments of the present disclosure realize ultra-long-life photon quantum state storage by combining long-life quantum memory with multi-degree-of-freedom filtering technology, which can be used in many quantum information processing scenarios such as remote quantum communication and remote entanglement distribution.
  • the storage device has the advantages of long storage life, high signal-to-noise ratio, strong anti-interference ability, etc., and the equipment is simple and easy to operate.

Abstract

一种量子存储装置，包括：样品腔，用于装载存储晶体及滤波晶体并用于冷却存储晶体及滤波晶体至预设温度；激光控制系统，用于产生控制光和信号光，实现所述信号光的基于自旋布居数锁定的量子存储；量子态编码及分析系统，用于对信号光子实现量子态编码及分析；滤波系统，用于抑制控制光引入的噪声，提取信号光子。该存储装置具有存储寿命长、信噪比高、抗干扰能力强等优点，设备简单且易于操作。

Description

量子存储装置 技术领域
本公开涉及量子信息技术领域，尤其涉及一种量子存储装置。
背景技术
量子通信发展的最终目标是构建全国乃至洲际的大尺度量子通信网络。目前，量子通信所面临的主要挑战是实现远距离量子通信。光子是量子信息传递的天然载体，然而由于光子在光纤中的传输损耗随着传输距离呈指数级递增，即使利用通讯波段超低损耗光纤，目前传输距离也被限制在五百公里以下。由于量子态不可克隆定律，经典通讯中利用放大器对信号进行直接放大的方法对于量子通信也并不适用。
一种可行的远程量子通信方案是量子加密U盘方案，它首先把光子存入超长寿命的可运输的量子存储器(或称为量子加密U盘)，接着利用经典运输手段运输量子加密U盘实现光子的远距离传输。考虑千公里级的传输距离和300公里/小时的运输速度，量子加密U盘至少需要支持小时量级的存储寿命且支持高信噪比的光子存储。
当前光子存储器实现单光子的最长存储寿命为百毫秒量级，经典强光的最长存储寿命为分钟量级[参考文献：G.Heinze,C.Hubrich and T.Halfmann,Phys.Rev.Lett.111,033601(2013).]。这样的存储寿命远没有达到量子加密U盘所需的存储时间，量子加密U盘的物理实现存在重大技术挑战。
发明内容
本公开一种量子存储装置，包括：样品腔，用于装载存储晶体及滤波晶体并用于冷却存储晶体及滤波晶体至预设温度；激光控制系统，用 于产生控制光和信号光，实现所述信号光的基于自旋布居数锁定的量子存储；量子态编码及分析系统，用于对信号光子实现量子态编码及分析；滤波系统，用于抑制控制光引入的噪声，提取信号光子。
一些实施例中，样品腔包括：低温腔，用于冷却存储晶体至预设温度；振动同步装置，用于同步监测低温腔的振动信号。
一些实施例中，激光控制系统包括：稳频激光器，用于产生多束激光；第一声光调制器，用于将一束所述激光调制为存储晶体的控制光；第二声光调制器，用于将一束所述激光调制为单光子级别的信号光；第三声光调制器，用于将一束所述激光调制为滤波晶体的控制光；第四声光调制器以及螺旋相位片，用于将一束所述激光调制为存储晶体的Laguerre-Gaussian模式控制光。
一些实施例中，量子态编码及分析系统包括：量子态编码装置，用于将所述信号光加载特定的量子态；量子态分析装置，用于分析所述信号光的量子态。
一些实施例中，滤波系统包括：单模光纤，用于在空间上滤除噪声；窄带滤波片，用于滤除1nm量级精度上频谱噪声；高速光开关，用于在时间上滤除噪声；滤波晶体用于在1MHz量级精度上滤除频谱噪声。
一些实施例中，存储晶体为 151Eu 3+或 153Eu 3+掺杂的YSO晶体。
一些实施例中，激光控制系统中实现所述信号光的基于自旋布居数锁定的量子存储，包括：从掺有Eu 3+离子的存储晶体中选择出具有目标能级结构的离子系综，并将离子系综的离子的吸收线制备为透明背景下的孤立吸收峰；基于Laguerre-Gaussian模式光场的空间吸收结构制备，以在所述离子系综上制备出空间上中心吸收而外围透明的吸收结构；基于两个π/2脉冲的光子回波存储过程，在基态g能级与激发态e能级跃迁上，实现对入射信号光子的短时间存储；基于两个π脉冲的自旋布居数锁定过程，把信号光子存储为基态g能级-基态s能级跃迁上的布居数结构，延长存储寿命至自旋布居数寿命的量级；以及对光子回波信号的读取，在入射信号的原方向上读取出回波信号，降低存储过程的噪声。
一些实施例中，从掺有Eu 3+离子的存储晶体中选择出具有目标能级 结构的离子系综，包括：施加至少三束与样品光学跃迁共振的扫描激光，从掺有Eu 3+离子的存储介质非均匀展宽的吸收线中选择出一个能级结构一致的离子系综；撤除其中一束扫描激光，用于将离子系综的自旋状态极化为同一初态的aux能级；施加与aux能级至激发态跃迁的窄带扫描激光，同时施加与s能级至激发态跃迁的扫描激光，形成在透明带内的一个孤立的吸收线，吸收线内离子布居数处于g能级上。
一些实施例中，基于Laguerre-Gaussian模式光场的空间吸收结构制备，包括：对存储晶体施加Laguerre-Gaussian模式光场，其光场中心为100um量级的黑洞，能量集中在外圈；其中一束扫描激光与基态g能级与激发态e能级跃，扫描带宽10MHz量级，用于消除g-e跃迁的吸收；另一束扫描激光与基态s能级与激发态e能级跃，扫描带宽10MHz量级，用于消除s-e跃迁的吸收。
一些实施例中，基于两个π/2脉冲的光子回波存储，包括：与g-e跃迁共振的信号光子脉冲；与g-e跃迁共振的第一π/2脉冲；与s-e跃迁共振的第一π脉冲；与s-e跃迁共振的第二π脉冲；所述基于两个π脉冲的自旋布居数锁定，包括：与g-e跃迁共振的第二π/2脉冲；与g-e跃迁共振的第一π脉冲。
一些实施例中，产生的所述信号光及控制光的偏振态为相互正交的偏振态，并且与存储晶体的偏振轴向对齐。
(三)有益效果
本公开提供了一种量子存储装置，可以进行远程运输，通过将长寿命量子存储器与多自由度滤波技术结合起来，实现超长寿命的光子量子态存储，可用于远程量子通信、远程纠缠分发等众多量子信息处理场景中。该存储装置具有存储寿命长、信噪比高、抗干扰能力强等优点，设备简单且易于操作。
为让本公开的上述特征和优点能更明显易懂，下文特举实施例，并配合所附图式作详细说明如下。
附图说明
图1示意性示出了本公开实施例的可运输的量子存储装置的结构图；
图2示意性示出了本公开实施例的可运输的量子存储装置的工作示意图；
图3示意性示出了本公开实施例的存储晶体的能级结构及制备方式示意图；
图4示意性示出了公开实施例的存储控制序列示意图；
图5示意性示出了本公开实施例实现长寿命叠加态光子存储的时间谱图。
具体实施方式
为使本公开的目的、技术方案和优点更加清楚明白，以下结合具体实施例，并参照附图，对本公开进一步详细说明。
本公开实施例提供了一种可运输的量子存储装置，参见图1，包括：包括：样品腔11，用于装载存储晶体111并提供预设温度的低温环境；激光控制系统12，用于产生控制光和信号光，实现自旋布居数锁定的长寿命存储方案；量子态编码及分析系统13，用于对信号光子实现量子态编码及分析；滤波系统14，用于抑制控制光场引入的噪声，提取信号光子；隔震平台15，用于隔离环境振动。其中，这里的预设温度是为了冷却晶体内的电子-声子相互作用，延长相干时间，温度取值范围低于4K，可选的如3.5K。
以下将以具体的实施例对其进行详细的介绍，参见图2。其中，样品腔11用于装载待测存储晶体111以及滤波晶体144；具体的，低温腔112，用于冷却存储晶体111至预设温度，此处设定工作温度为3K，采用无液氦压缩机制冷；存储晶体采用浓度为0.1％的 151Eu 3+掺杂的YSO晶体，厚度10mm。振动同步装置113用于同步监测低温腔112的振动信号。激光控制系统12，用于产生控制光和信号光；
一些实施例中，稳频激光器121可选取参数为PDH稳频的580nm 激光器，功率1W，线宽0.2kHz；第一声光调制器122可选取参数为200MHz中心频率的声光调制器，用于将所述激光调制为存储晶体的控制光；控制光用于实现自旋布居数锁定的长寿命量子存储方法的控制序列，具体包括：选择一种能级类型的离子并初始化离子系综的状态，然后依据序列要求，产生两个π/2脉冲、两个自旋转移π脉冲以及一个用于读取光子回波信号的π脉冲。
第二声光调制器123，选取参数为200MHz中心频率的声光调制器，用于将所述激光调制为单光子级别的信号光；典型参数选取为1us脉宽的单光子量级的脉冲。
第三声光调制器124，选取参数为200MHz中心频率的声光调制器，用于将所述激光调制为滤波晶体的控制光；典型参数选取为在目标频率附近1MHz扫描激光频率。
第四声光调制器125，选取参数为200MHz中心频率的声光调制器，以及螺旋相位片126，选取为580nm的一阶螺旋相位片，用于将所述激光调制为存储晶体的一阶Laguerre-Gaussian模式控制光。
其中，量子态编码及分析系统13，用于对信号光子实现量子态编码及分析；具体的可以包括量子态编码装置131及量子态分析装置132，其中，量子态编码装置131用于将所述信号光子加载特定的量子态；量子态分析装置132用于分析所述信号光子的量子态。一些实施例中，选择光的轨道角动量自由度加载量子态，量子态编码装置131以及量子态分析装置132分别为两个空间光调制器，分辨率512*512，像素元8um大小。
其中，滤波系统14用于抑制控制光场引入的噪声，提取信号光子；具体的可以包括单模光纤141、窄带滤波片142、高速光开关143和滤波晶体。其中，单模光纤141，用于在空间上滤除噪声；选取460nm单模保偏光纤；窄带滤波片142，用于在1nm量级精度滤除频谱噪声；选取1nm带宽，透过率大于99％的干涉滤波片；高速光开关143，用于在时间上滤除噪声；选取高速电光调制晶体，开关速度为3ns，消光比10000:1；滤波晶体144，用于在1MHz量级精度上滤除频谱噪声，滤波 晶体采用浓度为0.1％的 151Eu 3+掺杂的YSO晶体，厚度15mm
一些实施例中，信号光的偏振态对齐YSO晶体的D1轴向，以增强样品吸收。而所有控制光的偏振态对齐YSO晶体的D1轴向。信号光与控制光的偏振态相互正交用于抑制控制光导致的噪声。
一些实施例中，还可以包括隔震平台15，用于隔离环境振动。具体的，选取基于压电陶瓷控制的主动反馈平台。
本公开实施例中，存储过程与低温腔振动同步装置113探测到的振动信号严格同步，选取低振动时间窗口执行光子存储操作。
本公开实施例中，采用的具体存储方案为自旋布居数锁定的长寿命存储方法，且控制光应同时完成存储晶体111及滤波晶体114的吸收带制备目标。
参考图3所示的能级结构，控制光的操作可以包括以下四个步骤：
一、存储晶体的能级选择及初态制备：
对存储晶体的吸收带制备目标是在一个6MHz线宽的透明带内制备一个1MHz线宽的窄带吸收线，且吸收线内所有离子都处于g能级上。具体制备方法参考：
根据图3给出的存储晶体能级结构，一种代表性的实现方法如下：
第一步：首先同时施加f 0、f 1、f 2三种频率的扫频光场，其中f 0光束与g-e跃迁共振，f 1光束与g-s跃迁共振，f 2光束与aux能级至 5D 0上能级的3/2核自旋能态跃迁共振。每种频率光场在中心频率附近+/-3MHz扫描。第一步实现了同种能级结构离子系综的选择。此处设置f 0、f 1、f 2分别为400MHz，434.54MHz，379.08MHz，对应了 151Eu 3+离子在YSO晶体中的精细能级结构
第二步：撤除f 2扫描激光，继续执行f 1及f 0扫频激光，用于将离子系综113的自旋状态极化为同一初态，即aux能级；
第三步：撤除所有上述扫描激光，施加一束在f 2频率附近+/-0.5MHz扫描的弱泵浦光场，同时施加一束在f 1频率附近+/-0.5MHz扫描的弱泵浦光场，在2MHz带宽范围内把布居数制备到为同一初态，即 7F 0下能级的1/2核自旋能态。
经过以上三步操作，在f 0频率附近观察存储晶体的吸收谱，将呈现出一个6MHz的透明带内，孤立出一个1MHz线宽的吸收线。满足本公开对初态制备的需求，降低存储装置噪声。
使用第一声光调制器122，并采用双次通过调制器的光路完成。
二、存储晶体的空间吸收结构制备：
对存储晶体的空间域吸收结构的制备目标为，从光传输在存储晶体的截面上看，制备一个1mm直径的透明区域，中心100um直径形成有效有效吸收。具体制备方法参考：
在上述存储晶体的能级选择及初态制备完成后，施加Laguerre-Gaussian模式光场，其光场中心为100um左右的黑洞，能量集中在外圈，光斑总大小为1mm左右。
其中部分激光在f 0频率附近扫描，扫描带宽6MHz，用于消除g-e跃迁的吸收；
另一部分激光同时在f 1频率附近扫描，扫描带宽6MHz，用于消除s-e跃迁的吸收；
经过以上操作上，在存储晶体的光传输截面上观察，对信号光以及控制光操控脉冲而言，晶体呈现出一个1mm直径圆的透明区域，中心孤立出一个100um直径圆的吸收带，有效地抑制了操控脉冲的空间不理想性导致的光噪声。
使用第四声光调制器125，并采用双次通过调制器的光路完成。为了加载Laguerre-Gaussian模式，该光场再经过一个一阶Laguerre-Gaussian模式的螺旋相位片126的相位调制，形成一个具有中心黑洞的环状光束。
三、滤波晶体的吸收带制备：
对滤波晶体的吸收带制备目标是制备一个1MHz线宽的透过带，而背景是一个2GHz以上的强吸收带。使用第三声光调制器124，并采用双次通过调制器的光路完成。
四、存储晶体的存储控制过程：
具体的，按照自旋布居数锁定的长寿命存储方法的控制序列要求， 首先使用第二声光调制器123调制出一个1us左右脉宽的信号光脉冲，光场频率为f 0；等待1us后，使用第一声光调制器122先后产生一个f 0频率的π/2脉冲，1us后施加一个f 1频率的π脉冲，经历可控的超长存储时间后，施加一个f 1频率的π脉冲，9us后再施加一个f 0频率的π/2脉冲；最后，施加一个f 0频率的π脉冲。随后，信号光发射。图4给出了本实施例完整时序控制示意图，包括以上四个步骤。
图5给出了弱光场携带轨道角动量的量子叠加态存储后的输出测量结果。本实施例中，信号脉冲含有的光子数为10 7量级，采用光电倍增管探测。信号脉冲携带了量子叠加态|LG 0,-1>+|LG 0,+1>，其中|LG 0,-1>以及|LG 0,+1>分别对应携带-h/2π及+h/2π的Laguerre-Gaussian模式量子态。本实施例设定存储时间为7.2小时。图中实线对应使用|LG 0,-1>+|LG 0,+1>测量输出光子的结果，可以看到显著的存储读出信号。而图中虚线对应使用正交基矢|LG 0,-1>-|LG 0,+1>测量输出光子的结果，可以看到输出光子态与之正交。读出量子态的干涉可见度超过99％，很好地保护了入射脉冲携带的量子态。相比此前已知的存储装置，该装置的存储寿命获得极大提升，且支持光子量子态的存储。
本公开实施例通过将长寿命量子存储器与多自由度滤波技术结合起来，实现超长寿命的光子量子态存储，可用于远程量子通信、远程纠缠分发等众多量子信息处理场景中。该存储装置具有存储寿命长、信噪比高、抗干扰能力强等优点，设备简单且易于操作。
以上所述，仅是本公开的较佳实施例而已，并非对本公开作任何形式上的限制。任何熟悉本领域的技术人员，在不脱离本公开技术方案范围情况下，都可利用上述揭示的方法和技术内容对本公开技术方案做出许多可能的变动和修饰，或修改为等同变化的等效实施例。因此，凡是未脱离本公开技术方案的内容，依据本公开的技术实质对以上实施例所做的任何简单修改、等同变化及修饰，均仍属于本公开技术方案保护的范围内。

Claims (11)

  1. 一种量子存储装置，包括：
    样品腔(11)，用于装载存储晶体(111)及滤波晶体(144)并用于冷却存储晶体(111)及滤波晶体(144)至预设温度；
    激光控制系统(12)，用于产生控制光和信号光，实现所述信号光的基于自旋布居数锁定的量子存储；
    量子态编码及分析系统(13)，用于对信号光子实现量子态编码及分析；
    滤波系统(14)，用于抑制控制光引入的噪声，提取信号光子。
  2. 根据权利要求1所述的量子存储装置，所述样品腔(11)包括：
    低温腔(112)，用于冷却存储晶体(111)至预设温度；
    振动同步装置(113)，用于同步监测低温腔(112)的振动信号。
  3. 根据权利要求1所述的量子存储装置，所述激光控制系统(12)包括：
    稳频激光器(121)，用于产生多束激光；
    第一声光调制器(122)，用于将一束所述激光调制为存储晶体的控制光；
    第二声光调制器(123)，用于将一束所述激光调制为单光子级别的信号光；
    第三声光调制器(124)，用于将一束所述激光调制为滤波晶体的控制光；
    第四声光调制器(125)以及螺旋相位片(126)，用于将一束所述激光调制为存储晶体的Laguerre-Gaussian模式控制光。
  4. 根据权利要求1所述的量子存储装置，所述量子态编码及分析系统(13)包括：
    量子态编码装置(131)，用于将所述信号光加载特定的量子态；
    量子态分析装置(132)，用于分析所述信号光的量子态。
  5. 根据权利要求1所述的量子存储装置，所述滤波系统(14)包括：
    单模光纤(141)，用于在空间上滤除噪声；
    窄带滤波片(142)，用于滤除1nm量级精度上频谱噪声；
    高速光开关(143)，用于在时间上滤除噪声；
    滤波晶体(144)，用于在1MHz量级精度上滤除频谱噪声。
  6. 根据权利要求1所述的量子存储装置，所述存储晶体(111)为 151Eu 3+或 153Eu 3+掺杂的YSO晶体。
  7. 根据权利要求1所述的量子存储装置，所述激光控制系统(12)中实现所述信号光的基于自旋布居数锁定的量子存储，包括：
    从掺有Eu 3+离子的存储晶体(111)中选择出具有目标能级结构的离子系综(1511)，并将离子系综的离子的吸收线制备为透明背景下的孤立吸收峰；
    基于Laguerre-Gaussian模式光场的空间吸收结构制备，以在所述离子系综(1511)上制备出空间上中心吸收而外围透明的吸收结构；
    基于两个π/2脉冲的光子回波存储过程，在基态g能级与激发态e能级跃迁上，实现对入射信号光子的短时间存储；
    基于两个π脉冲的自旋布居数锁定过程，把信号光子存储为基态g能级-基态s能级跃迁上的布居数结构，延长存储寿命至自旋布居数寿命的量级；
    以及对光子回波信号的读取，用于在入射信号的原方向上读取出信号，降低存储过程的噪声。
  8. 根据权利要求7所述的量子存储装置，所述从掺有Eu 3+离子的存储晶体(111)中选择出具有目标能级结构的离子系综(1511)，包括：
    施加至少三束与样品光学跃迁共振的扫描激光，从掺有Eu 3+离子的存储介质(111)非均匀展宽的吸收线中选择出一个能级结构一致的离子系综(1511)；
    撤除其中一束扫描激光，用于将离子系综(1511)的自旋状态极化为同一初态的aux能级；施加与aux能级至激发态跃迁的窄带扫描激光，同时施加与s能级至激发态跃迁的扫描激光，形成在透明带内的一个孤立的吸收线，吸收线内离子布居数处于g能级上。
  9. 根据权利要求7所述的量子存储装置，所述基于 Laguerre-Gaussian模式光场的空间吸收结构制备，包括：
    对存储晶体施加Laguerre-Gaussian模式光场，其光场中心为100um量级的黑洞，能量集中在外圈；
    其中一束扫描激光与基态g能级与激发态e能级跃，扫描带宽10MHz量级，用于消除g-e跃迁的吸收；
    另一束扫描激光与基态s能级与激发态e能级跃，扫描带宽10MHz量级，用于消除s-e跃迁的吸收。
  10. 根据权利要求7所述的量子存储装置，所述基于两个π/2脉冲的光子回波存储，包括：
    与g-e跃迁共振的信号光子脉冲(1531)；
    与g-e跃迁共振的第一π/2脉冲(1532)；
    与g-e跃迁共振的第二π/2脉冲(1535)；
    所述基于两个π脉冲的自旋布居数锁定以及读取过程，包括：
    与s-e跃迁共振的第一π脉冲(1533)；
    与s-e跃迁共振的第二π脉冲(1534)；
    以及与g-e跃迁共振的第一π脉冲(1536)。
  11. 根据权利要求1所述的量子存储装置，产生的所述信号光及控制光的偏振态为相互正交的偏振态，并且与存储晶体(111)的偏振轴向对齐。
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