CN114268372B - Fast write-read laser pulse sequence device for temporal multimode quantum memory - Google Patents

Abstract

The invention discloses a fast write-read laser pulse sequence device for time multi-mode quantum memory, comprising a write laser pulse device and a read laser pulse device symmetrical to the origin; the write laser pulse device includes at least one set of write laser pulses Equipment, each group of write laser pulse equipment includes the first lens, the first acousto-optic modulator, and two first 45-degree total reflection light guide mirrors distributed up and down, the first acousto-optic modulation The device is located on one side of one of the first 45-degree total reflection light guide mirrors; the read laser pulse device includes at least one set of read laser pulse equipment, the number of read laser pulse equipment and the write laser pulse equipment are equal and the positions are symmetrical to the origin; the origin, The focus of the first lens and the focus of the second lens coincide. The present invention alleviates technical problems such as too low number of patterns generated per unit time, low space utilization rate, and difficult expansion in the prior art, so as to meet the demand for large-scale use in quantum communication.

Description

Fast write-read laser pulse sequence device for temporal multimode quantum memory

technical field

The invention relates to the technical field of quantum communication, in particular to a fast write-read laser pulse sequence device for time multi-mode quantum memory.

Background technique

Quantum multi-mode storage plays an important role in quantum communication and quantum relay. A very important index to measure the quality of multi-mode storage is the number of modes generated per unit time, which is crucial for the realization of quantum communication. The existing DLCZ-type quantum memory with time doubling mostly stores multiple time patterns in a single spatial direction of the atomic cloud, but it faces serious problems such as high noise and short life. The latest scientists proposed a scheme to store multiple different time patterns in different spatial directions of the atomic cloud, that is, to apply a series of write-read laser pulses with different temporal differences and from different spatial directions to act on the atomic cloud to induce the Duan-Lukin -Cirac-Zoller-like Raman process to realize the preparation of multiple time-mode quantum memories.

There are currently two main means of implementing this scheme. The first one uses Acousto Optical Deflectors (AOD) with timing control to generate different time modes (write-read laser pulses), that is, by effectively changing the frequency of AOD After a single pulsed laser beam passes through an acousto-optic deflector, it becomes multiple write-read lasers propagating in different directions, thereby realizing the generation of multiple write-read laser pulse sequences. The device of this scheme is simple, but the generation rate of the write-read pulse is too low, for example, the time required to generate a single time pattern can reach the order of μs, and the realization of the quantum relay scheme in quantum communication requires that the pulse period be as short as possible, and at the same time The program also requires relatively high experimental technology. The second is to construct different time modes (write-read laser pulses) through the Acousto Optic Modulator network. In 2017, we proposed the multiplication technology of single photons through the Acousto Optic Modulator network. In 2019, we demonstrated it experimentally A scheme for generating temporal multi-mode DLCZ-type quantum memory. In this experiment, in order to realize multi-mode memory, we sequentially incident 19 write-read laser pulses on a cold atomic ensemble along different directions in space. This scheme can generate a A series of write-read laser pulses with a time interval of less than 100 ns, but the device for generating write-read laser pulse sequences in different directions is complicated. Different directions in space are incident on the atomic ensemble. Similarly, in the direction of the read pulse, the same number of fiber coupling heads and acousto-optic modulators are required to achieve efficient spatial coupling with the write laser pulse. This scheme has poor stability and low space utilization, which will not be conducive to the further expansion of the temporal pattern.

To sum up, the existing experimental devices for realizing time-multiplied quantum memory have common problems such as low number of patterns generated per unit time and low space utilization, and there is no experimental device that can meet the requirements of large-scale use in quantum communication. Design.

Contents of the invention

The purpose of the present invention is to overcome the problems in the above-mentioned prior art, and provide a fast write-read laser pulse sequence device for time multi-mode quantum memory, so as to alleviate the low number of modes produced per unit time in the prior art , low space utilization, difficult to expand and other technical problems, so as to meet the needs of large-scale use in quantum communication.

To this end, the present invention provides a fast write-read laser pulse sequence device for time multimode quantum memory, including a write laser pulse device and a read laser pulse device symmetrical to the origin; the write laser pulse device includes at least one A group of write laser pulse devices, each group of write laser pulse devices includes a first lens, a first acousto-optic modulator, and two first 45-degree total reflection light guide mirrors distributed up and down in sequence from right to left along a straight line , the first acousto-optic modulator is located on one side of one of the first 45-degree total reflection light guide mirrors; the read laser pulse device includes at least one set of read laser pulse equipment, the read laser pulse equipment and the The number of write laser pulse devices is equal and the positions are symmetrical to the origin. The read laser pulse device includes a second lens, a second acousto-optic modulator, and two second 45-degree angles arranged up and down along a straight line from left to right. A total reflection light guide mirror, the second acousto-optic modulator is located on one side of one of the second 45-degree total reflection light guide mirrors; the origin, the focus of the first lens and the focus of the second lens coincidence; the first AOM and the second AOM are respectively controlled by FPGA to input laser pulses, the adjacent first AOMs are connected in series, and the adjacent second AOMs The light modulators are connected in series.

Further, the left and right sides of the first AOM in the horizontal direction are respectively provided with a third lens, the distances between the two third lenses and the first AOM are equal, and the third lens The diameter of the lens is not greater than half of the diameter of the first lens; the left and right sides of the second acousto-optic modulator are respectively provided with a fourth lens, and the two fourth lenses are respectively connected to the second acousto-optic modulator. The distances between the light modulators are equal, and the diameter of the fourth lens is not larger than half of the diameter of the second lens.

Further, the FPGA emits laser pulses of multiple frequencies, and the frequency difference between two adjacent laser pulses is equal.

Further, the period of the laser pulse emitted by the FPGA is 100 ns, the pulse width is 60 ns, and the pulse interval is 40 ns.

Further, the write laser pulse device includes three groups of the write laser pulse device, the read laser pulse device includes three groups of the read laser pulse device, each group of the write laser pulse device and the read laser pulse device One by one symmetrical.

A fast write-read laser pulse sequence device for temporal multi-mode quantum memory provided by the present invention has the following beneficial effects:

Compared with the first solution mentioned in the background, the present invention uses an acousto-optic deflector, which can set the pulse interval within a hundred ns. Compared with its pulse width of the order of us, it will be greatly shortened in quantum communication. communication time;

Compared with the second scheme, the present invention uses an acousto-optic modulator to construct different time modes, and uses a single acousto-optic modulator to realize the design of six write-read optical paths, which greatly reduces the cost of the scheme and improves the space utilization rate. Herein The storage of more time patterns can be realized on the basis.

Description of drawings

Figure 1 is a time sequence diagram of different time intervals issued by the FPGA control;

Figure 2 is a device diagram of a single acousto-optic modulator to realize six-way writing and reading laser pulses;

Fig. 3 is a timing diagram of realizing six write and read light pulses by a single AOM;

Fig. 4 is the design diagram of the multi-channel time mode experiment realized by the AOM network.

Detailed ways

A number of specific embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, but it should be understood that the protection scope of the present invention is not limited by the specific embodiments.

In this application document, unspecified component models and structures are all prior art known to those skilled in the art, and those skilled in the art can set them according to the needs of the actual situation. In the embodiments of this application document No specific restrictions are made.

In the present invention, at first we design and send a series of continuous time pulses through the Labview program control software (produced by NI Company of the United States) 7966R, because the clock frequency of the board card is set as 100Hz, so we can realize the design of its width, interval, etc. of the pulse sequence (greater than 10ns), in the experiment, when the corresponding hardware output is selected as an acousto-optic modulator, the pulse width can be compressed to within 30ns, and the output laser still has a perfect Gaussian output wave packet. When the pulse width is about 1us, the output laser is no longer a Gaussian wave packet, which affects the transmission characteristics of the laser and cannot meet the experimental requirements. Therefore, the technical solution adopted in the present invention is: we pass the write-read laser beams through the acousto-optic modulator in two directions, and change the diffraction frequency of the acousto-optic modulator in real time through the change of the FPGA output voltage, thereby controllably changing the laser deflection direction , making it incident on the center of an atomic ensemble sequentially along different directions in space. A single acousto-optic modulator generates six write-read laser pulses in different spatial directions, and realizes efficient spatial coupling between corresponding write-read beams. In actual operation, the writing laser is sequentially sent out by two fiber-optic coupling heads, passing through the AOM in two directions while changing the diffraction frequency of the AOM, and with the real-time control of the FPGA, a single AOM can generate six writing laser pulses , and enter the atoms after collimating the beam using a lens. Then, the acousto-optic network is constructed through m acousto-optic modulators to finally realize the time-multiplied quantum memory with 6×m time patterns. This scheme can simplify the experimental device, reduce the cost of the scheme, improve the space utilization rate, and reduce the technical difficulty. Strong scalability. Compared with the prior art, the beneficial effect of the present invention is that compared with the first scheme mentioned in the background, that is, using an acousto-optic deflector, we can set the pulse interval to within a hundred ns, compared to its pulse width us Quantum communication will greatly shorten its communication time. Compared with the second scheme using acousto-optic modulators to construct different time modes, our single acousto-optic modulator realizes the design of six write-read optical paths, which greatly reduces the cost of the solution and improves space utilization. On this basis The storage of more time patterns can be realized.

As shown in Figure 1, the FPGA of the present invention uses the 7966R board card that National Instruments (NI) Co., Ltd. of the United States produces, and the fixed clock frequency of this board card is 100MHz, so it can be designed to produce a time sequence with a time interval of more than 10ns, and can simultaneously Complete operations such as data collection and analysis. The board has 48 input (output) ports. In the present invention, we set two output ports to respectively control the writing and reading of light to send a series of time-series pulses. When the pulse sent is high level in the figure, it means the output pulse , when it is low, it means that the pulse output is turned off. We plan to design and send out a series of time sequences with a period of 100ns, a pulse width of 60ns, and a pulse interval of 40ns.

Example 1

This embodiment provides a fast write-read laser pulse sequence device for temporal multi-mode quantum memory, using a single acousto-optic modulator to realize six write and read pulses.

Specifically, as shown in Figure 2, two acousto-optic modulators AOM _W and AOM _R are used in the figure to represent the acousto-optic modulators in the optical path of writing light and reading light respectively. The acousto-optic modulators are gooch&housego imported from Germany (model 3200 -124), the center frequency is 200MHz. Use a pair of f ₁ =f ₂ =300mm (f' ₁ =f' ₂ =300mm) plano-concave lens group to match the AOM, place the AOM at the focal point of the lens, f ₃ =f' ₃ = 1000mm means converging lens, 45°HR means 45° total reflection light guide mirror. As shown in Figure 2, we divide the writing light emitted by the laser into two parts, the writing light W _α and the writing light W _β (the sequence of generating the writing light is realized by turning off the acousto-optic modulator), and first turn on the writing light W _α ( Turn off the writing light W _β ), and the writing light W _α will be diffracted after passing through the AOM _W , and the diffraction frequency of the AOM (-1 level) will be changed to 180MHz, 200MHz, and 220MHz in turn through the timing board control (as shown in the figure 3), at this time, due to the frequency difference of the acousto-optic modulator, its diffraction angle and azimuth change, we will sequentially obtain three write laser pulses in different spatial directions, and adjust the f ₁ and f ₂ lens positions so that the focus is on the acoustic The central position of the light modulator realizes three writing parallel light beams (corresponding to writing light w ₁ , w ₂ , and w ₃ in the figure). At this time, turn off the writing light W _α , turn on the writing light W _β , after the reverse writing laser beam passes through the acousto-optic modulator and f ₁ , f ₂ lenses, we will get another three writing parallel beams (corresponding to the writing light w ₄ in the figure , w ₅ , w ₆ ), to adjust the orientation of the light guide mirror, we adjust the two groups (6 channels) of writing light pulses to be parallel, focus them through the lens f ₃ and converge on a certain point in space along different directions in space (atomic ensemble), adjust The spot size is about 0.5mm. Similarly, use the FPGA to issue the time sequence shown in Figure 1 to build the reading AOM system. Under the action of the reading light R _α and reading light R _β and the AOM _R , six parallel reading light beams are obtained through the lens system (corresponding to the figure Middle reading light R ₁ , R ₂ , R ₃ , R ₄ , R ₅ , R ₆ ). It is worth noting that the generated write light beam must be efficiently spatially coupled with the corresponding read light beam, so as to ensure that each corresponding write light and read light spatial mode match, that is, the write light emitted from w _i and the read light emitted by R _i Lights are perfectly coincident (required for DLCZ scheme). When the diffraction frequency of the AOM _w in the main optical path changes, the writing frequency acting on the atoms changes, which is not conducive to the development of multi-mode storage. Therefore, we design to change the saturation absorption synchronously when changing the diffraction frequency of the AOM in the main optical path. The frequency of the acousto-optic modulator in the optical path realizes that the writing optical frequency acts on a fixed energy level.

Figure 3 is the timing diagram of this embodiment. When we debug the experimental timing through the FPGA, the operating frequency of the acousto-optic modulator is changed by changing the output voltage, and six write laser pulses with diffraction frequencies of 180MHz, 200MHz, and 220MHz are sequentially issued. Acting on the acousto-optic modulator, corresponding to the w ₁ -w ₆ light beams in the figure, as shown in Figure 2, the light beams act on the acousto-optic modulator from two different directions. We sequentially send out a series of constant frequency (200MHz) R ₁ -R ₆ read light pulses through the AOM, which also correspond to the read light in two different directions, and realize the spatial coupling of the write light and the read light.

Example 2

This embodiment is that the present invention uses an AOM network to realize a multi-channel time mode.

As shown in FIG. 4 , in the embodiment of the present invention, single photons (ie, Stokes photons and anti-Stokes photons) are generated by spontaneous Raman scattering. In the case of spontaneous Raman scattering, a beam of weakly detuned writing light and a beam of strongly resonant reading light are required. Both the writing light and the reading light are two optical paths with opposite optical paths in the pulsed light after laser chopping. When the write light and read light are irradiated on the atomic ensemble, there will be a certain probability of Stokes photons being excited. If the single photon detector detects the Stokes photons, it proves that the formation of Stokes photons and atomic internal Entanglement of spin waves. Correspondingly, a beam of strong resonant reading light is applied in the opposite direction of the writing light, so that the spin wave information in the atom can be released in the form of anti-Stokes photons. As shown in Figure 4, we design the acousto-optic modulator network to realize the design diagram of the multi-channel time mode experiment. Based on the reference in Fig. modulator as an example). Connect three acousto-optic modulators AOM ₁ , AOM ₂ , and AOM ₃ in series in the writing-reading direction. Firstly, write light W _α is controlled by FPGA to pass through the three acousto-optic modulators sequentially from top to bottom. The diffraction frequency of the optical modulator can thus generate write laser pulses in nine different directions (w ₄ -w ₆ , w ₁₀ -w ₁₂ , w ₁₆ -w ₁₈ ) in the figure (three beams of light emitted by the same AOM Simplified as one way), at this moment, turn off the writing light W _α and turn on the writing light W _β , similarly, it can generate another 9 different directions in the figure (w ₁ -w ₃ , w ₇ -w ₉ , w ₁₃ -w ₁₅ ) After the writing laser pulse passes through the corresponding converging lens organization _f3 , a series of 18 writing laser pulses will be able to act on the atomic ensemble along different spatial directions. We collect Stokes photons in the S ₁ direction. Assuming that Stokes photons are detected when the i write light w _i acts on it, the corresponding read pulse R _i is turned on through FPGA feedback control, and the stored self The spin wave information is converted into anti-Stokes photons and released, and anti-Stokes photons are collected in the T ₁ direction. Based on this, we will build a quantum memory with 18 time modes. In real quantum communication, based on the time multi-mode storage scheme we proposed and the space multi-mode storage scheme we have realized in 2017, it is expected to store 200-300 space-time modes.

The above disclosures are only a few specific embodiments of the present invention, however, the embodiments of the present invention are not limited thereto, and any changes conceivable by those skilled in the art shall fall within the protection scope of the present invention.

Claims (4)

1. The rapid writing-reading laser pulse sequence device for the time multimode quantum memory is characterized by comprising a writing laser pulse device and a reading laser pulse device which are symmetrical in origin;

the writing laser pulse device comprises at least one group of writing laser pulse equipment, wherein each group of writing laser pulse equipment comprises a first lens, a first acousto-optic modulator and two first 45-degree total reflection light guide lenses which are sequentially arranged from right to left along a straight line, and the first acousto-optic modulator is positioned on one side of one of the first 45-degree total reflection light guide lenses;

the reading laser pulse device comprises at least one group of reading laser pulse equipment, the number of the reading laser pulse equipment is equal to that of the writing laser pulse equipment, the positions of the reading laser pulse equipment are in origin symmetry, the reading laser pulse equipment comprises a second lens, a second sound light modulator and two second 45-degree total reflection light guide lenses which are distributed up and down in sequence along a straight line from left to right, and the second sound light modulator is positioned on one side of one of the second 45-degree total reflection light guide lenses;

the origin, the first lens focus and the second lens focus coincide;

the first acoustic optical modulators and the second acoustic optical modulators are respectively used for controlling laser pulse input through an FPGA, the adjacent first acoustic optical modulators are connected in series, and the adjacent second acoustic optical modulators are connected in series;

a third lens is respectively arranged on the left side and the right side of the horizontal direction of the first acousto-optic modulator, the distances between the two third lenses and the first acousto-optic modulator are equal, and the diameter of the third lens is not more than half of the diameter of the first lens;

and the left side and the right side of the horizontal direction of the second acoustic optical modulator are respectively provided with a fourth lens, the distances between the two fourth lenses and the second acoustic optical modulator are respectively equal, and the diameter of the fourth lens is not more than half of the diameter of the second lens.

2. The rapid write-read laser pulse train device for time multimode quantum memory of claim 1, wherein the FPGA controls the acousto-optic modulator to emit laser pulses of a plurality of frequencies, the frequency differences of adjacent two of the laser pulses being equal.

3. The rapid write-read laser pulse train device for time multimode quantum memory of claim 1, wherein the period of the laser pulse emitted from the FPGA is 100ns, wherein the pulse width is 60ns and the pulse interval is 40ns.

4. The fast write-read laser pulse train apparatus for time multimode quantum memory of claim 1, wherein the write laser pulse apparatus comprises three sets of the write laser pulse devices, and the read laser pulse apparatus comprises three sets of the read laser pulse devices, each set of the write laser pulse devices and the read laser pulse devices being in one-to-one symmetry.

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