阅读说明：本技术 量子加密存储装置 (Quantum encryption storage device ) 是由 周宗权 李传锋 于 2019-10-09 设计创作，主要内容包括：一种量子加密存储装置,包括：样品腔(11),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(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。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。(A quantum cryptography storage apparatus comprising: the sample cavity (11) is used for loading the storage crystal and the filtering crystal and cooling the storage crystal and the filtering crystal to a preset temperature; the laser control system (12) is used for generating control light and signal light to realize the quantum storage based on spin population locking of the signal light; a quantum state encoding and analysis system (13) for quantum state encoding and analysis of the signal photons; and the filtering system (14) is used for suppressing noise introduced by the control light and extracting signal photons. The storage device has the advantages of long storage life, high signal-to-noise ratio, strong anti-interference capability and the like, and equipment is simple and easy to operate.)

1. A quantum cryptography storage apparatus comprising:

a sample chamber (11) for loading the storage crystal (111) and the filter crystal (144) and for cooling the storage crystal (111) and the filter crystal (144) to a predetermined temperature;

the laser control system (12) is used for generating control light and signal light to realize the quantum storage based on spin population locking of the signal light;

a quantum state encoding and analysis system (13) for quantum state encoding and analysis of the signal photons;

and the filtering system (14) is used for suppressing noise introduced by the control light and extracting signal photons.

2. The quantum encrypted storage device according to claim 1, the sample cavity (11) comprising:

a low temperature chamber (112) for cooling the storage crystal (111) to a preset temperature;

and the vibration synchronization device (113) is used for synchronously monitoring the vibration signal of the low-temperature cavity (112).

3. The quantum cryptography storage apparatus of claim 1, the laser control system (12) comprising:

a frequency stabilized laser (121) for generating a plurality of beams of laser light;

a first acousto-optic modulator (122) for modulating a beam of the laser light into a control light for a storage crystal;

a second acousto-optic modulator (123) for modulating a beam of the laser light into signal light of a single photon level;

a third acousto-optic modulator (124) for modulating a beam of the laser light into a control light of a filter crystal;

a fourth acousto-optic modulator (125) and a spiral phase plate (126) for modulating a beam of the laser light as a Laguerre-Gaussian mode control light of the storage crystal.

4. The quantum cryptography storage of claim 1, the quantum state encoding and analysis system (13) comprising:

quantum state encoding means (131) for loading the signal light into a specific quantum state;

a quantum state analysis device (132) for analyzing a quantum state of the signal light.

5. The quantum encrypted storage device of claim 1, the filtering system (14) comprising:

a single mode optical fiber (141) for spatially filtering noise;

a narrow-band filter (142) for filtering spectral noise at 1nm level of accuracy;

a high speed optical switch (143) for filtering noise over time;

a filtering crystal (144) for filtering spectral noise at an accuracy on the order of 1 MHz.

6. The quantum cryptography memory device of claim 1, wherein the storage scheme is a spin population locked long-life storage method, and the control light is configured to simultaneously accomplish the absorption band preparation targets of the storage crystal (111) and the filter crystal (114).

7. A quantum cryptography memory device according to claim 1, wherein the storage mode employed is a spin population locked storage method and the control light is configured to simultaneously complete the preparation of the absorption bands of the memory crystal (111) and the filter crystal (114).

8. The quantum cryptography storage apparatus of claim 1, the storage crystal (111) being¹⁵¹Eu³⁺Or¹⁵³Eu³⁺Doped rare earth doped crystals.

9. The quantum cryptography storage apparatus of claim 1, wherein the polarization states of the signal light and the control light are mutually orthogonal polarization states and are axially aligned with the polarization of the storage crystal (111) for suppressing noise caused by the control light.

10. The quantum cryptography storage apparatus of claim 1, further comprising a vibration-isolated platform (15), the sample chamber (11), the laser control system (12), the quantum state encoding and analyzing system (13), and the filtering system (14) being integrally encapsulated on the vibration-isolated platform (15).

Technical Field

The invention relates to the technical field of quantum information, in particular to a quantum encryption storage device capable of storing single photons for a long time.

Background

The ultimate goal of quantum communication development is to construct a nationwide, and even intercontinental, large-scale quantum communication network. Currently, the main challenge facing quantum communication is to realize long-distance quantum communication. Photons are natural carriers for quantum information transfer, however, since the transmission loss of photons in an optical fiber increases exponentially with the transmission distance, even with an ultra-low loss optical fiber in a communication band, the transmission distance is currently limited to less than five hundred kilometers. Due to the quantum state unclonable law, the method of directly amplifying signals by using an amplifier in classical communication is not suitable for quantum communication.

A feasible remote quantum communication scheme is a quantum encryption storage scheme, and the quantum encryption storage scheme is characterized in that photons are stored into a quantum memory (or called quantum encryption U disk) with an ultra-long service life firstly, and then the quantum encryption storage device is transported by using a classical transportation means to realize the remote transmission of the photons. Considering a transmission distance of kilo-kilometer order and a transportation speed of 300 kilometers/hour, the quantum encryption storage device at least needs to support a storage life of an hour order and support photon storage with a high signal-to-noise ratio.

The longest storage life of a single photon realized by the current photon memory is in the order of hundreds of milliseconds, and the longest storage life of classical strong light is in the order of minutes [ reference: heinze, c.hubrich and t.halfmann, phys.rev.lett.111, 033601(2013) ]. Such a memory lifetime is far from reaching the memory time required for quantum cryptography memory devices, and the physical implementation of quantum cryptography memory devices presents significant technical challenges.

Disclosure of Invention

Technical problem to be solved

Based on the technical problem, the invention provides a quantum encryption storage device to realize long-life storage at a single photon level.

(II) technical scheme

The invention provides a quantum encryption storage device, comprising:

the sample cavity is used for loading the storage crystal and the filtering crystal and cooling the storage crystal and the filtering crystal to a preset temperature;

the laser control system is used for generating control light and signal light to realize quantum storage of the signal light based on spin population locking;

the quantum state coding and analyzing system is used for realizing quantum state coding and analysis on the signal photons;

and the filtering system is used for suppressing noise introduced by the control light and extracting signal photons.

In a further embodiment, the sample chamber comprises: the low-temperature cavity is used for cooling the storage crystal to a preset temperature; and the vibration synchronizer is used for synchronously monitoring the vibration signal of the low-temperature cavity.

In a further embodiment, a laser control system comprises: the frequency stabilized laser is used for generating a plurality of beams of laser light; the first acousto-optic modulator is used for modulating a beam of laser into control light of the storage crystal; the second acousto-optic modulator is used for modulating a beam of laser into signal light at a single photon level; the third acousto-optic modulator is used for modulating a beam of laser into control light of the filter crystal; and the fourth acousto-optic modulator and the spiral phase plate are used for modulating a beam of laser into Laguerre-Gaussian mode control light of the storage crystal.

In a further embodiment, a quantum state encoding and analysis system comprises: quantum state encoding means for loading the signal light into a specific quantum state; and a quantum state analysis device for analyzing the quantum state of the signal light.

In a further embodiment, a filtering system comprises: a single mode optical fiber for spatially filtering noise; the narrow-band filter is used for filtering spectral noise on the level of 1nm precision; a high speed optical switch for filtering noise in time; and the filtering crystal is used for filtering the spectrum noise on the accuracy of 1MHz level.

In a further embodiment, the storage scheme employed is a spin population locked long-life storage approach, and the control light is configured to accomplish the absorption band preparation goals of both the storage crystal and the filter crystal.

In a further embodiment, the storage mode employed is a spin population locked storage method, and the control light is configured to simultaneously complete the preparation of the absorption bands of the storage crystal and the filter crystal.

In a further embodiment, the storage crystal is¹⁵¹Eu³⁺Or¹⁵³Eu³⁺Doped rare earth doped crystals.

In a further embodiment, the polarization states of the signal light and the control light are mutually orthogonal polarization states and are axially aligned with the polarization of the memory crystal for suppressing noise caused by the control light.

In a further embodiment, the quantum encryption storage device further comprises a vibration isolation platform, and the sample cavity, the laser control system, the quantum state encoding and analyzing system and the filtering system are integrally packaged on the vibration isolation platform.

(III) advantageous effects

The invention provides a quantum encryption storage device, which realizes the ultra-long-life photon quantum state storage by combining a long-life quantum memory and a multi-degree-of-freedom filtering technology and can be used in a plurality of quantum information processing scenes such as remote quantum communication, remote entanglement distribution and the like. The storage device has the advantages of long storage life, high signal-to-noise ratio, strong anti-interference capability and the like, and equipment is simple and easy to operate.

Drawings

Fig. 1 schematically illustrates a block diagram of a quantum cryptography storage apparatus of an embodiment of the present disclosure;

FIG. 2 schematically illustrates an operational schematic diagram of a quantum cryptography storage device of an embodiment of the present disclosure;

FIG. 3 schematically illustrates an energy level structure and a fabrication method of a memory crystal according to an embodiment of the disclosure;

fig. 4 schematically illustrates a time spectrum of a quantum cryptography storage practical long-life single photon storage of an embodiment of the present disclosure.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to specific embodiments and the accompanying drawings.

The embodiment of the invention provides a quantum encryption storage device, which comprises: a sample chamber 11 for loading the storage crystal 111 and the filter crystal 144 and for cooling the storage crystal 111 and the filter crystal 144 to a predetermined temperature; the laser control system 12 is used for generating control light and signal light to realize quantum storage of the signal light based on spin population locking; a quantum state encoding and analyzing system 13 for implementing quantum state encoding and analysis on the signal photons; and the filtering system 14 is used for suppressing noise introduced by the control optical field and extracting signal photons. The device combines the long-life quantum memory with the multi-degree-of-freedom filtering technology to realize the photon quantum state storage with ultra-long service life. The preset temperature is used for cooling electron-phonon interaction in the crystal and prolonging the coherence time, and the temperature range is lower than 4K, such as 3.5K.

The quantum storage based on spin population locking can comprise: from doping with Eu³⁺Selecting an ion ensemble with a target energy level structure from the ion storage crystal, and preparing an absorption line of ions in the ion ensemble into an isolated absorption peak under a transparent background; preparing a spatial absorption structure based on a Laguerre-Gaussian mode optical field to prepare an absorption structure with central absorption and transparent periphery on the space in the ion system; based on photon echo storage of two pi/2 pulses, the storage of incident signal photons is realized on transition of a ground state g energy level and an excited state e energy level; based on the spin population locking of the two pi pulses, storing the signal photons into a population structure on ground state g energy level-ground state s energy level transition, and prolonging the storage life to the magnitude of the spin population life; and reading photon echo, and reading out signals in the original direction of the incident signals.

Exemplary embodiments of the present invention will be described in more detail below with reference to the accompanying drawings. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these exemplary embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the concept of the invention to those skilled in the art. Like reference symbols in the various drawings indicate like elements. Various elements and regions are schematically illustrated for convenience of explanation, and thus, the inventive concept is not limited thereto.

In an exemplary embodiment, referring to FIG. 1, a quantum cryptography storage apparatus includes a sample chamber 11 for holding a storage crystal 111 and providing a low temperature environment; the laser control system 12 is used for generating control light and signal light to realize a long-life storage scheme of spin population locking; a quantum state encoding and analyzing system 13 for implementing quantum state encoding and analysis on the signal photons; a filtering system 14 for suppressing noise introduced by the control light field and extracting signal photons; and the vibration isolation platform 15 is used for isolating environmental vibration. This will be described in more detail below with reference to a specific embodiment, which is illustrated in fig. 2.

The sample cavity 11 is used for loading the storage crystal 111 to be tested and the filter crystal 144;

specifically, the low temperature chamber 112 is configured to cool the storage crystal 111 to a preset temperature, where the working temperature is set to 3K, and a liquid-helium-free compressor is used for refrigeration; the storage crystal adopts a concentration of 0.1%¹⁵¹Eu³⁺Doped YSO crystals with a thickness of 10 mm.

And a vibration synchronization device 113 for synchronously monitoring the vibration signal of the low temperature cavity 112.

The quantum encryption storage device includes a laser control system 12 for generating control light and signal light;

specifically, the frequency stabilized laser 121 selects a 580nm laser with the parameter of PDH frequency stabilization, the power is 1W, and the line width is 0.2 kHz;

the first acousto-optic modulator 122 selects an acousto-optic modulator with a parameter of 200MHz center frequency, and is used for modulating the laser into control light of a storage crystal; the control sequence of the long-life quantum storage method for controlling the light with reference to spin population locking specifically comprises the following steps: firstly, selecting ions of an energy level type and initializing ion states, and then generating two pi/2 pulses, two spin transfer pi pulses and a pi pulse for population inversion according to sequence requirements.

The second acousto-optic modulator 123 selects an acousto-optic modulator with a parameter of 200MHz center frequency, and is used for modulating the laser into signal light at a single photon level; typical parameters are chosen for pulses of the order of a single photon with a pulse width of 1 us.

A third acousto-optic modulator 124, which selects an acousto-optic modulator with a parameter of 200MHz center frequency, for modulating the laser into control light of the filter crystal; typical parameters are chosen to sweep the laser frequency around the target frequency by 1 MHz.

And the fourth acousto-optic modulator 125 selects an acousto-optic modulator with the parameter of 200MHz center frequency, and a spiral phase plate 126, selects a first-order spiral phase plate of 580nm, and is used for modulating the laser into first-order Laguerre-Gaussian mode control light of the storage crystal.

The quantum encryption storage device comprises a quantum state coding and analyzing system 13 for realizing quantum state coding and analysis on signal photons;

specifically, the quantum state encoding device 131 is configured to load the signal photon into a specific quantum state; a quantum state analysis device 132 for analyzing the quantum state of the signal photon. In this embodiment, the orbital angular momentum freedom of light is selected to load quantum states, and the quantum state encoding device 131 and the quantum state analyzing device 132 are two spatial light modulators, respectively, with a resolution of 512 × 512 and a pixel size of 8 um.

The quantum encryption storage device comprises a filtering system 14, a storage system and a control system, wherein the filtering system is used for suppressing noise introduced by a control optical field and extracting signal photons;

specifically, the single mode fiber 141 is used for spatially filtering noise; selecting 460nm single-mode polarization maintaining fiber;

a narrow band filter 142 for filtering out spectral noise at 1nm level accuracy; selecting an interference filter with the bandwidth of 1nm and the transmittance of more than 99 percent;

a high speed optical switch 143 for filtering noise over time; selecting a high-speed electro-optic modulation crystal, wherein the switching speed is 3ns, and the extinction ratio is 10000: 1;

a filter crystal 144 for filtering out the spectrum noise with a precision of 1MHz level, the filter crystal being 0.1% in concentration¹⁵¹Eu³⁺Doped YSO crystal with thickness of 15mm

In this embodiment, the polarization state of the signal light is aligned with the D1 axis of the YSO crystal to enhance sample absorption. While all the control light polarization states are 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 for suppressing noise caused by the control light.

The quantum cryptography storage apparatus may further comprise a vibration isolation platform 15 for isolating environmental vibrations.

Specifically, an active feedback platform based on piezoelectric ceramic control is selected.

In the embodiment of the invention, the storage process is strictly synchronous with the vibration signal detected by the low-temperature cavity vibration synchronization device 113, and a low-vibration time window is selected to execute photon storage operation.

In the embodiment of the invention, the adopted specific storage scheme is a spin population number locking long-life storage method, and the control light simultaneously fulfills the preparation targets of the absorption bands of the storage crystal 111 and the filter crystal 114.

Referring to the energy level structure shown in fig. 3, the operation of controlling light mainly includes the following four steps:

firstly, energy level selection and initial state preparation of a storage crystal:

the goal of the absorption band preparation for the memory crystal is to prepare a 1MHz wide narrow band absorption line within a 6MHz wide transparent band, with all ions in the absorption line at the g level. The specific preparation method comprises the following steps: from doping with Eu³⁺Selecting an ion ensemble with a target energy level structure from an ion storage medium, and preparing an absorption line of ions under the ion ensemble into narrow-band absorption under a transparent background;

referring to the storage crystal energy level structure given in fig. 3, one exemplary implementation is as follows:

the first step is as follows: first of all f is applied simultaneously₀、f₁、f₂Swept optical field of three frequencies, where f₀The light beam resonates with the g-e transition, f₁The light beam resonates with the g-s transition, f₂Beam and aux energy level to⁵D₀3/2 nuclear spin state transition resonance at the upper level. The optical field is swept around the center frequency by +/-3MHz for each frequency. The first step realizes the selection of ion ensemble with the same energy level structure. Where f is set₀、f₁、f₂Are respectively 400MHz, 434.54MHz and 379.08MHz, corresponding to¹⁵¹Eu³⁺Fine energy level structure of ions in YSO crystal

The second step is that: removing f₂Scanning the laser and continuing to perform f₁And f₀The swept laser is used for polarizing the spin state of the ion ensemble 113 into the same initial state, namely an aux energy level;

the third step: removing all the scanning laser, and applying a beam at f₂A weak pump field sweeping +/-0.5MHz around frequency, while applying a beam of weak pump field sweeping +/-0.5MHz around f1 frequency,the population is prepared to be the same initial state in the bandwidth range of 2MHz, namely⁷F₀1/2 nuclear spin states at the lower energy level.

Through the three steps of operation, at f₀The absorption spectrum of the storage crystal is observed near the frequency, a transparent band of 6MHz is presented, and an absorption line with the line width of 1MHz is isolated. The requirements of the invention on initial state preparation are met, and the noise of the storage device is reduced.

A first acousto-optic modulator 122 is used and is done with an optical path that passes through the modulator twice.

Secondly, preparing a space absorption structure for storing crystals:

the aim of producing a spatial domain absorption structure for a storage crystal is to produce a 1mm diameter transparent region, the central 100um diameter forming the effective absorption, as seen in the cross-section of the storage crystal. The specific preparation method comprises the following steps: preparing a spatial absorption structure based on Laguerre-Gaussian mode optical field to prepare an absorption structure with central absorption and periphery transparency in the space on the ion system.

After the energy level selection and the initial state preparation of the storage crystal are completed, a Laguerre-Gaussian mode light field is applied, the center of the light field is a black hole with the diameter of about 100um, the energy is concentrated on the outer ring, and the total size of light spots is about 1 mm.

Wherein part of the laser light is at f₀Scanning near the frequency, wherein the scanning bandwidth is 6MHz, and the scanning bandwidth is used for eliminating the absorption of g-e transition;

another part of the laser is simultaneously at f₁Scanning near the frequency, wherein the scanning bandwidth is 6MHz, and the scanning bandwidth is used for eliminating the absorption of s-e transition;

through the operation, the crystal presents a transparent area with a diameter of 1mm for signal light and control light control pulses observed on the light transmission section of the storage crystal, and an absorption band with a diameter of 100um is isolated at the center, so that light noise caused by space non-ideality of the control pulses is effectively inhibited.

Using a fourth acousto-optic modulator 125 and using an optical path that passes through the modulator twice. To load the Laguerre-Gaussian mode, the optical field is phase modulated by a first order Laguerre-Gaussian mode helical phase plate 126 to form a ring beam with a central black hole.

Thirdly, preparing an absorption band of the filtering crystal:

the aim of the preparation of the absorption band of the filter crystal is to prepare a transmission band with a line width of 1MHz, while the background is a strong absorption band above 2 GHz. Using a third acousto-optic modulator 124 and using the optical path of a double pass modulator.

Fourthly, storage control process of the storage crystal:

specifically, according to the control sequence requirement of the spin population locked long-life storage method, a signal light pulse with a pulse width of about 1us is modulated by using the second acousto-optic modulator 123, and the light field frequency is f₀(ii) a After 1us, a first acousto-optic modulator 122 is used to generate f₀Pi/2 pulse of frequency, 1us later, applying f₁Pi-pulse of frequency, after controlled over-long storage time, applying f₁Pi pulse of frequency, after 9us, applying a further f₀Pi/2 pulses of frequency; finally, applying an f₀Pi pulses of frequency. Subsequently, the signal light is emitted.

Fig. 4 shows the output measurement result after the storage of the quantum superposition state of the weak light field carrying orbital angular momentum. In this embodiment, the signal pulse contains 10 photons⁷And (4) detecting by using a photomultiplier. Signal pulse carries quantum superposition state | LG_0，-1＞+|LG_0，+1Where | LG_0，-1And LG_0，+1The quantum states of Laguerre-Gaussian mode carrying-h/2 pi and + h/2 pi respectively. The storage time was set to 7.2 hours in this example. The solid line in the figure corresponds to the use of | LG_0，-1＞+|LG_0，+1As a result of measuring the output photons, a significant stored readout signal can be seen. While the dotted line in the figure corresponds to the use of the orthogonal basis vector | LG_0，-1＞-|LG_0，+1The output photon state can be seen to be orthogonal to the result of measuring the output photon. The interference visibility of the read-out quantum state exceeds 99%, and the quantum state carried by the incident pulse is well protected. Storage of the device in comparison with previously known storage devicesThe service life is greatly prolonged, and the storage of photon quantum states is supported.

The embodiment of the invention combines the long-life quantum memory with the multi-degree-of-freedom filtering technology to realize the photon quantum state storage with the ultra-long service life, and can be used in a plurality of quantum information processing scenes such as remote quantum communication, remote entanglement distribution and the like. The storage device has the advantages of long storage life, high signal-to-noise ratio, strong anti-interference capability and the like, and equipment is simple and easy to operate.

The above-mentioned embodiments are intended to illustrate the objects, technical solutions and advantages of the present invention in further detail, and it should be understood that the above-mentioned embodiments are only exemplary embodiments of the present invention, and are not intended to limit the present invention, and any modifications, equivalents, improvements and the like made within the spirit and principle of the present invention should be included in the protection scope of the present invention.