阅读说明：本技术 自旋布居数锁定的光子存储方法 (Spin population locking photon storage method ) 是由 周宗权 李传锋 于 2019-10-09 设计创作，主要内容包括：一种自旋布居数锁定的光子存储方法,其包括：从掺有Eu～(3+)离子的存储介质中选择出具有目标能级结构的离子系综,并将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,实现对入射信号光子的存储；基于两个π脉冲的自旋布居数锁定,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；以及对光子回波信号的读取过程。本发明的存储方法实现了小时至天量级的超长寿命光子存储器,可用于量子加密U盘、远程量子通信、远程纠缠分发等众多量子信息处理场景中。(A method of spin population locked photon storage, comprising: from doping with Eu 3+ Selecting an ion ensemble with a target energy level structure from an ion storage medium, and preparing an absorption line as 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; storing the incident signal photons based on the photon echo storage of two pi/2 pulses; storing the signal photon as a population structure on a ground state g-s level transition based on spin population locking of the two pi pulses; and a reading process of the photon echo signal. The storage method realizes the ultra-long-life photon storage with the magnitude of hours to days, and can be used in a plurality of quantum information processing scenes such as quantum encryption U disks, remote quantum communication, remote entanglement distribution and the like.)

1. A spin population-locked photon storage method, comprising:

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 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 the photon echo signal, and reading out the signal in the original direction of the incident signal.

2. The spin-population-locked photon storage method of claim 1, said doping being with Eu³⁺The storage medium of ions being isotopically purified¹⁵¹Eu³⁺Or¹⁵³Eu³⁺The transparent single crystal of (1).

3. The method of spin-population-locked photon storage according to claim 1, said secondary doping with Eu³⁺An ion ensemble having a target energy level structure selected from a storage medium of ions, comprising:

applying at least three scanning lasers in optical transition resonance with the sample to obtain Eu doping³⁺Selecting an ion ensemble with a consistent energy level structure from a non-uniformly broadened absorption line of an ion storage medium;

removing one scanning laser beam, and polarizing the spin state of the ion ensemble into an aux energy level of the same initial state;

applying a scanning laser with an aux energy level to excited state transition and simultaneously applying a scanning laser with an s energy level to excited state transition forms an isolated absorption line within the transparent band, the ion population in the absorption line being at the g energy level.

4. The method for storing photons with spin population locking according to claim 1, wherein the preparation of the spatial absorption structure based on Laguerre-Gaussian mode pumping optical field comprises:

applying a Laguerre-Gaussian mode pumping optical field to the storage crystal, wherein the center of the optical field is a black hole with the diameter of about 100um, and energy is concentrated on the outer ring;

one beam of scanning laser is in a transition from a ground state g energy level to an excited state e energy level, and the scanning bandwidth is 10MHz magnitude and is used for eliminating the absorption of the g-e transition;

and the other beam of scanning laser is in a transition from the ground state s energy level to the excited state e energy level, and the scanning bandwidth is 10MHz magnitude, so that the absorption of the s-e transition is eliminated.

5. The spin population locked photon storage method of claim 1, the two pi/2 pulse based photon echo storage, comprising:

a signal photon pulse resonating with a g-e transition;

a first pi/2 pulse resonating with a g-e transition;

the second pi/2 pulse that resonates with the g-e transition.

6. The spin population locked photonic storage method of claim 1, based on two pi-pulse spin population locking, comprising:

a first pi pulse resonating with an s-e transition;

the second pi pulse, which resonates with the s-e transition.

7. The spin-population locked photon storage method of claim 1, reading photon echo signals comprising:

the first pi pulse that resonates with the g-e transition.

8. The method of claim 5, 6 or 7, wherein the pi/2 pulse and the pi pulse satisfy adiabatic fast channel conditions, thereby improving pulse robustness.

9. A spin population locking photon storage method according to claim 5 or 6, wherein said first pi pulse resonant to a g-s transition and said second pi pulse resonant to a g-e transition are interposed between said first pi/2 pulse resonant to a g-e transition and said second pi/2 pulse resonant to a g-e transition.

10. A spin population locked photon storage method as in claim 3, 4, 5, 6 or 7, wherein the pi/2 pulse and the pi pulse in each step of the storage method are not collinear with the propagation direction of the signal photon pulse.

Technical Field

The invention relates to the technical field of quantum information, in particular to a photon storage method with spin population locking.

Background

A photonic memory refers to a memory capable of coherently storing photonic states. The photonic memory is a core device of a quantum network and is a premise for realizing remote quantum communication. The specific physical systems currently used to implement photonic memories include: cold atoms, hot atoms, rare earth doped crystals, and single atoms in the cavity. Various physical systems have respective advantages and disadvantages, but in sum, the technical indexes of the photonic memory cannot meet the specific requirements of practical quantum network construction. One of the key technical requirements is long-lived photon storage, since the storage time determines the channel distance between network points and the maximum quantum state transmission distance that can be achieved.

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. The classical optical storage in the order of minutes is only the storage of classical images observed, and the protection capability of the storage device on the coherence of the optical field is not proved [ reference: heinze, c.hubrich and t.halfmann, phys.rev.lett.111, 033601(2013) ]. The main methods of photon storage include: electromagnetic induction induces transparency, raman scattering, atomic frequency combing, etc. Further improvements in storage life over existing storage schemes have met with significant technical challenges.

Disclosure of Invention

Technical problem to be solved

Accordingly, the present invention is directed to a self-selecting population-locked photon storage method, which at least partially solves the above problems.

(II) technical scheme

To achieve the above object, the present invention provides a spin population locking photon storage method, comprising:

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 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 the photon echo signal, and reading out the signal in the original direction of the incident signal.

In a further embodiment, Eu is doped³⁺The storage medium of ions being isotopically purified¹⁵¹Eu³⁺Or¹⁵³Eu³⁺The transparent single crystal of (1).

In a further embodiment, from the doping with Eu³⁺An ion ensemble having a target energy level structure selected from a storage medium of ions, comprising: applying at least three scanning lasers in optical transition resonance with the sample to obtain Eu doping³⁺Selecting an ion ensemble with a consistent energy level structure from a non-uniformly broadened absorption line of an ion storage medium; removing one scanning laser beam, and polarizing the spin state of the ion ensemble into an aux energy level of the same initial state; applying a scanning laser with an aux energy level to excited state transition and simultaneously applying a scanning laser with an s energy level to excited state transition forms an isolated absorption line within the transparent band, the ion population in the absorption line being at the g energy level.

In a further embodiment, the spatial absorption structure preparation based on the Laguerre-Gaussian mode pump optical field comprises: applying a Laguerre-Gaussian mode pumping optical field to the storage crystal, wherein the center of the optical field is a black hole with the diameter of about 100um, and energy is concentrated on the outer ring; one beam of scanning laser is in a transition from a ground state g energy level to an excited state e energy level, and the scanning bandwidth is 10MHz magnitude and is used for eliminating the absorption of the g-e transition; and the other beam of scanning laser is in a transition from the ground state s energy level to the excited state e energy level, and the scanning bandwidth is 10MHz magnitude, so that the absorption of the s-e transition is eliminated.

In a further embodiment, two pi/2 pulse based photon echo storage comprises: a signal photon pulse resonating with a g-e transition; a first pi/2 pulse resonating with a g-e transition; the second pi/2 pulse that resonates with the g-e transition.

In a further embodiment, spin population locking based on two pi pulses includes:

a first pi pulse resonating with an s-e transition; the second pi pulse, which resonates with the s-e transition.

In a further embodiment, the reading of the photon echo signals comprises: the first pi pulse that resonates with the g-e transition.

In a further embodiment, the pi/2 pulse and the pi pulse satisfy adiabatic fast channel conditions, improving pulse robustness.

In a further embodiment, a first pi pulse that resonates with a g-s transition and a second pi pulse that resonates with a g-e transition are interposed between the first pi/2 pulse that resonates with a g-e transition and the second pi/2 pulse that resonates with a g-e transition.

In a further embodiment, both the pi/2 pulse and the pi pulse in each step of the storage method are not collinear with the direction of propagation of the signal photon pulse.

(III) advantageous effects

The invention provides a photon storage method with spin population number locking, which combines an initial state preparation technology, a stimulated photon echo technology and a Raman spin transfer technology and is based on Eu³⁺The population life of the ground state nuclear spin energy state of the ions realizes the ultra-long life photon memory of hour to day magnitude, and can be used in a plurality of quantum information processing scenes such as quantum encryption U disks, remote quantum communication, remote entanglement distribution and the like. The storage method has the characteristics of long storage life, low noise and easiness in implementation.

Drawings

Fig. 1 schematically illustrates an energy level structure diagram of an ion ensemble 113 prepared by a spin population number-locked long-lifetime photon storage method according to an embodiment of the present disclosure;

FIG. 2 schematically illustrates an optical path diagram in a spin population locked long-lifetime photon storage method of an embodiment of the present disclosure;

FIG. 3 schematically illustrates a spin population locked long-lived photon storage method storage control sequence diagram of an embodiment of the present disclosure;

fig. 4 schematically shows an optical pulse signal output after 3.6 hours of storage achieved by 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 the accompanying drawings in combination with specific embodiments.

The embodiment of the invention provides a spin population number locking photon storage method, which comprises the following steps of doping 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 (namely, an isolated absorption peak under the 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 a photon echo signal reading process, which is used for reading a signal in the original direction of an incident signal and reducing the noise in the storage process.

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, the storage medium is selected to be 10mm long at 0.1% concentration¹⁵¹Eu³⁺The energy level structure of a doped YSO crystal is shown in fig. 1 as an example. Here is selected⁷F₀1/2 nuclear spin energy states at the lower energy level are the g energy level, 3/2 nuclear spin energy states are the s energy level,⁵D₀the 5/2 nuclear spin energy level of the upper energy level is the e energy level,⁷F₀the 5/2 nuclear spin energy state at the lower energy level is the aux energy level. The method specifically comprises the following steps: energy level screening and spin initial state preparation process, and spatial absorption structure system based on Laguerre-Gaussian mode light fieldThe method comprises a standby process, a photon echo storage process based on two pi/2 pulses, a spin population locking process based on two pi pulses and a reading process of a photon echo signal. The respective processes will be described specifically below:

energy level screening and spin-on initial state preparation process for doping Eu³⁺Selecting an ion ensemble with a target energy level structure from a storage medium of ions, and preparing an absorption line of the ions into narrow-band absorption under a transparent background; the preparation process of the spatial absorption structure based on the Laguerre-Gaussian mode light field is used for preparing a transparent circular surface with the diameter of 1mm magnitude on a light transmission section and preparing an absorption circular surface with the diameter of 100um magnitude in the transparent circular surface, and is used for inhibiting noise caused by spatial background absorption. The photon echo storage process based on two pi/2 pulses is used for realizing the short-time storage of the incident signal photon 131 on the transition of the ground state g energy level and the excited state e energy level; the self-spinning population locking process based on two pi pulses is used for storing 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 self-spinning population life; and a photon echo signal reading process, which is used for reading out the signal in the original direction of the incident signal and reducing the noise in the storage process.

Energy level screening and spin-on initial state preparation process for doping Eu³⁺Selecting an ion ensemble with a target energy level structure from a storage medium of ions, and preparing an absorption line of the ions into narrow-band absorption under a transparent background; the preparation process of the spatial absorption structure based on the Laguerre-Gaussian mode light field is used for preparing a transparent circular surface with the diameter of 1mm magnitude on a light transmission section and preparing an absorption circular surface with the diameter of 100um magnitude in the transparent circular surface, and is used for inhibiting noise caused by spatial background absorption.

Energy level screening and initial state preparation are a core technology of the invention. When the storage medium is not subjected to energy level screening and initial state preparation, the incident signal photons will be absorbed by the various resonating ions. The specific energy level structures of these ions vary due to the ubiquitous non-uniform broadening of crystals. This makes the subsequent control pulses impossible to optimize for all ions simultaneously, resulting in low storage efficiency and large noise. After the energy level screening and initial state preparation of the storage medium, only ions with one type of energy level structure participate in interaction. And the absorption line width in the band is narrow, and all applied control pulses can achieve 100% precision theoretically, so that the noise caused by pulse errors is reduced, and the storage efficiency is higher. On the other hand, since ions of other off-ramp frequencies are not absorbed here, noise due to background absorption of other off-ramp frequencies can be suppressed. The key point of the invention for realizing single photon magnitude storage is that.

Specifically, the energy level screening and spin initial state preparation process comprises the following steps: the control light of the storage crystal firstly prepares the absorption band of the storage crystal, and the target absorption band is to prepare a narrow-band absorption line with the line width of 1MHz in a transparent band with the line width of 6 MHz.

Memory crystal as given with reference to fig. 1¹⁵¹Eu³⁺A doped YSO crystal level structure; one representative 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 swept +/-0.5MHz around frequency while applying a beam at f₁Weak pump light with +/-0.5MHz sweep around frequencyField, prepared to the same initial state in the 2MHz bandwidth range, i.e.⁷F₀1/2 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.

The preparation process 12 of the spatial absorption structure based on the Laguerre-Gaussian mode light field aims at preparing an absorption circular surface with a diameter of 100um magnitude in a transparent circular surface with a diameter of 1mm magnitude on a light transmission section, and is used for inhibiting noise caused by spatial background absorption.

The preparation of the spatial absorption structure based on the Laguerre-Gaussian mode light field is a core technology of the invention. When the storage medium does not perform the preparation of the spatially absorbing structure, the control pulses incident at the rear will be absorbed by the spatially extensive ions. Because the control pulse is spatially limited and non-uniform in size, the control pulse energy felt by the ions at the edge of the light spot is low, and high-precision pulse area control cannot be realized. Resulting in erroneous pulse operation and generating large noise. And after the storage medium is prepared by the space absorption structure, only ions in the central area of the space participate in interaction. The spatial dimension of the region is small, all applied control pulses can theoretically achieve 100% precision, and therefore noise caused by pulse errors is small. This is another key to the realization of single photon magnitude storage in the present invention.

Specifically, after the energy level screening and the spin initial state preparation process are completed, a Laguerre-Gaussian mode light field is applied, the center of the light field is a black hole of about 100um, energy is concentrated on an outer ring, and the total size of light spots is about 1 mm.

Wherein one laser beam 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 laser beam is simultaneously on f₁Scanning near the frequency, wherein the scanning bandwidth is 6MHz, and the scanning bandwidth is used for eliminating the absorption of s-e transition;

the photon echo storage process based on two pi/2 pulses is used for realizing the short-time storage of incident signal photons on the transition of a ground state g energy level and an excited state e energy level.

Specifically, the photon echo storage process based on two pi/2 pulses comprises the following steps:

the signal photon pulse, which is resonant with the g-e transition, can be set to a gaussian wave with a pulse width of about 1 us. (ii) a

The first pi/2 pulse resonating with the g-e transition has a pulse area of pi/2 and can set the pulse transfer bandwidth to be 2 MHz; the pulse area should here be determined by the atomic pull ratio oscillation, and all pulse area concepts mentioned below are similar.

The second pi/2 pulse, which resonates with the g-e transition, has a pulse area of pi/2 and can be set to a pulse transfer bandwidth of 2 MHz.

And the spin population locking process based on two pi pulses is used for 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.

Specifically, the spin population locking process based on two pi pulses comprises the following steps:

the first pi pulse resonating with s-e transition has a pulse area of pi, and can set the pulse transfer bandwidth to be 2 MHz;

the second pi pulse, which resonates with the s-e transition, has a pulse area of pi and can set the pulse transfer bandwidth to 2 MHz.

Eu³⁺Population lifetimes of the ground state nuclear spin states of ions are long, on the order of hours short, in various materials, and up to 22 days in YSO crystals [ see literature: konz, et al, Physical Review B68, 085109(2003)]Therefore, the storage life can be prolonged by only prolonging the time interval between the pulses 141.

And the photon echo signal reading process is used for reading a signal in the original direction of an incident signal and reducing the noise in the storage process.

Specifically, a first pi pulse resonating with a g-e transition is applied, the pulse area is pi, and the pulse transfer bandwidth can be set to 2 MHz.

This is a core technology for realizing high signal-to-noise ratio in this embodiment, and two pi/2 pulses are applied in front of the g-e transition, so the population number of the ensemble is in an inverted state where the upper energy level is much larger than the lower energy level; the first pi pulse, applied here, that resonates with the g-e transition, causes the population of the ensemble to be restored back to be predominantly in the lower energy state, so that stimulated fluorescence noise is effectively avoided.

Specifically, all control light pulses satisfy adiabatic fast channel conditions, improving pulse robustness. Here, a Complex Hyperbaric Search (CHS) type control pulse may be used, and may be generated by a conventional arbitrary wave generator. Detailed description of control pulses of the CHS type references: roos and k. molmer, phys. rev. a 69, 022321 (2004).

Specifically, all the pump light/control light and the signal light are overlapped on the storage medium by using a cross optical path method, see fig. 2. The use of inverted, non-collinear control light suppresses the emission of conventional stimulated photon echoes, with signal emission only after the application of the first pi pulse that resonates with a g-e transition. The signal emitting direction is consistent with the incident signal direction, but is not collinear with the pump light/control light, so that the noise suppression is facilitated.

Specifically, the spot diameter of the control light on the storage medium can be set to 200um, and the spot diameter of the signal light on the storage medium can be set to 60um, so that the signal light is ensured to be in a spot central area where the control light is uniform.

The complete memory control pulse sequence is shown in fig. 3. The actual time interval between pulses in the figure is very long, and can be more than an hour magnitude, and the time intervals between other pulses are microsecond magnitude.

FIG. 4 shows the measured optical storage signal, the incident signal pulse containing 10 photons⁷Photon magnitude, the signal collected by the sensitive PMT detector, and the signal light pulse experienced a 3.6 hour storage time. This storage time is far beyond the known lifetime of optical storage (the known longest storage lifetime is 1 minute) and meets the basic requirements of quantum encrypted usb disk applications.

The above embodimentsBased on Eu by combining the initial state preparation technology, the stimulated photon echo technology and the Raman spin transfer technology³⁺Population lifetimes of the ground state nuclear spin states of ions enable long-lived photon storage. The population life of the nuclear spin level can reach one month. Therefore, the storage method supports the ultra-long service life photon memory with the magnitude of hours or more, and can be used in a plurality of quantum information processing scenes such as quantum encryption U disks, remote quantum communication, remote entanglement distribution and the like. The storage method has the characteristics of long storage life, low noise and easiness in implementation.

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.