Device and method for calibrating detection efficiency of single-photon detector based on quantum storage

Abstract

The invention belongs to the technical field of quantum information science, and particularly relates to a device and method for calibrating the detection efficiency of a single-photon detector based on quantum storage. The device comprises a first exciting light generation device, a second exciting light generation device, an atomic medium (9), a first Fabry-Perot cavity (10), a second Fabry-Perot cavity (13), a first polarization selection filter (11), a second polarization selection filter (14), a first single-photon detector (12) and a second single-photon detector (15). The atoms in the atom medium are transited to different storage states under the action of the writing light, the atoms in the different storage states are read by utilizing different polarization states of the reading light in the different storage states, and meanwhile, the final detection efficiency is detected by utilizing the single-photon detector. And measuring the transmission efficiency in a transmission path, and calculating the final efficiency of the single-photon detector by utilizing a formula and combining two experimental results.

Description

Technical Field

[0001] This invention belongs to the field of quantum information science and technology, specifically relating to a device and method for calibrating the detection efficiency of a single-photon detector based on quantum storage. Background Technology

[0002] Single-photon detectors (SPDs) are widely used in research fields such as quantum communication and quantum computing. They can accurately detect the presence of a single photon even under extremely low light intensity. SPDs typically possess extremely high temporal resolution and sensitivity, responding to a single photon on an extremely short timescale. Detection efficiency is a crucial indicator for evaluating the performance of SPDs, and environmental factors have a significant impact on this efficiency. The main environmental factors include temperature, wavelength of the light source, fiber quality, and external electromagnetic interference. These factors can prevent achieving the ideal detection efficiency, making it essential to measure the real-time detection efficiency of the detector under different environmental conditions crucial for quantum experiments.

[0003] The detection efficiency given by a single-photon detector is the overall detection efficiency, which includes the loss efficiency of the photon transmission path, the efficiency of atomic state transitions returning to the ground state from the transition path, and the final detection efficiency of the single-photon detector, thus obtaining the overall complete efficiency.

[0004] A common method for calculating the efficiency of a single-photon detector involves using a light source of known intensity and wavelength. The detector's efficiency is calculated by comparing the number of incident photons detected with the actual number of incident photons. However, this method requires precise calculation of the exact number of incident photons, which is related to light intensity and photon transmission efficiency. It necessitates a thorough understanding of light properties and requires stringent calibration conditions. Furthermore, the transmission efficiency of a single-photon detector cannot be measured experimentally. Therefore, developing a method to experimentally measure the efficiency of a single-photon detector remains a valuable research topic.

[0005] In summary, existing methods require high conditions and specifically require irradiating a particular type of light to measure the detector's efficiency. They cannot determine the detector's efficiency during the experiment. Therefore, a simpler method that can determine the detector's efficiency during the experiment is essential. Summary of the Invention

[0006] The technical problem to be solved by this invention is the unknown retrieval efficiency of single-photon detectors under different environmental factors. Since temperature and noise photons affect the retrieval efficiency of single-photon detectors, it is impossible to know the specific retrieval efficiency of the detector. This invention proposes a method and device for calibrating the efficiency of single-photon detectors based on quantum storage.

[0007] The technical solution adopted in this invention is:

[0008] A device for calibrating the detection efficiency of a single-photon detector based on quantum storage is characterized by comprising a first excitation light generating device, a second excitation light generating device, an atomic medium 9, a first Fabry-Perot cavity 10, a second Fabry-Perot cavity 13, a first polarization-selective filter 11, a second polarization-selective filter 14, a first single-photon detector 12, and a second single-photon detector 15.

[0009] The first excitation light generating device is used to generate right-hand circularly polarized writing light to act on the atomic medium 9, causing the atoms in the atomic medium 9 in the ground state to transition to the storage state. When the atoms transition to the storage state, they will release scattered photons due to spontaneous Raman scattering. When the scattered photons are defined as left-hand circularly polarized light, the atomic state falls into the first storage state. When the scattered photons are right-hand circularly polarized light, the atomic state falls into the second storage state.

[0010] The second excitation light generating device is used to generate left-hand circularly polarized readout light that acts on the atomic medium 9 to read out the atomic state in the storage state. When the readout light acts on the first storage state, the atoms in the storage state will release right-hand circularly polarized readout photons when they transition from the storage state to the ground state. When the readout light acts on the second storage state, the atoms in the storage state will release left-hand circularly polarized readout photons when they transition from the storage state to the ground state.

[0011] The first Fabry-Perot cavity 10, the first polarization-selective filter 11, and the first single-photon detector 12 are connected in sequence, and the second Fabry-Perot cavity 13, the second polarization-selective filter 14, and the second single-photon detector 15 are connected in sequence. Both the first Fabry-Perot cavity 10 and the second Fabry-Perot cavity 13 are used to filter out noise photons with the same frequency as the excitation light generated by Rayleigh scattering. The first polarization-selective filter 11 and the second polarization-selective filter 14 are configured to select either left-handed or right-handed light to pass through. When the first polarization-selective filter 11 is configured to select left-handed light, the second polarization-selective filter 14 is configured to select right-handed light. At this time, the left-handed photon is detected by the first single-photon detector 12 and is in the first... An atom in a stored state transitions to the ground state under the action of read light, releasing a right-handed circularly polarized readout photon. The right-handed readout photon is detected by the second single-photon detector 15. The counts of written and readout photons after N write-read operations are counted and recorded to calculate the first readout efficiency. When the first polarization selection filter 11 is set to select right-handed light to pass through, the second polarization selector 14 is set to select left-handed light to pass through. At this time, the right-handed written photon is detected by the first single-photon detector 12. An atom in the second stored state transitions to the ground state under the action of read light, releasing a left-handed circularly polarized readout photon. The left-handed readout photon is detected by the second single-photon detector 15. The counts of written and readout photons after N write-read operations are counted and recorded to calculate the second readout efficiency.

[0012] The detection efficiency of the single-photon detector is calculated based on the first readout efficiency and the second readout efficiency.

[0013] Furthermore, the specific method for calculating the detection efficiency of a single-photon detector based on the first readout efficiency and the second readout efficiency is as follows: the first readout efficiency is defined as... , , Write down the photon count under the corresponding conditions. , This corresponds to the readout photon count under the written photon condition; the second readout efficiency is defined as... , , The count of photons is obtained by statistical analysis under corresponding conditions. This refers to the readout photon count under the corresponding write-out photon condition; the detection efficiency of a single-photon detector. The calculation formula is:

[0014]

[0015] in, , , It is the CG coefficient of the left-handed transition channel. It is the CG coefficient of the right-handed transition channel. It refers to transmission path efficiency.

[0016] Furthermore, the first excitation light generating device includes a first continuously tunable laser source 1, a first optical attenuator 2, a first acousto-optic modulator 3, and a first polarization controller 4 connected in sequence; the second excitation light generating device includes a second continuously tunable laser source 5, a second optical attenuator 6, a second acousto-optic modulator 7, and a second polarization controller 8 connected in sequence.

[0017] Furthermore, the first continuously tunable laser source 1 and the second continuously tunable laser source 5 are solid-state lasers or semiconductor lasers.

[0018] Furthermore, the first optical attenuator 2 and the second optical attenuator 7 are optical attenuators.

[0019] Furthermore, the operating wavelength range of the first acousto-optic modulator 3 and the second acousto-optic modulator 7 covers the wavelengths of atomic energy level transitions in the atomic medium 9.

[0020] Furthermore, the first polarization controller 4 and the second polarization controller 8 are composed of a quarter-wave plate and a half-wave plate.

[0021] Furthermore, the atomic medium 9 is an atom with multiple energy levels that can be used for quantum storage.

[0022] Furthermore, the first Fabry-Perot cavity 10 and the second Fabry-Perot cavity 13 are formed by parallel mirrors to create an optical cavity; the first polarization selection filter 11 and the first polarization selection filter 14 are composed of a quarter-wave plate, a half-wave plate, and a polarization beam splitter; the first single-photon detector 11 and the first single-photon detector 13 operate using the avalanche diode principle.

[0023] A method for calibrating the detection efficiency of a single-photon detector based on quantum storage includes:

[0024] Atomic medium 9 was prepared in the ground state;

[0025] The first excitation light generating device generates writing light to transition atoms in the atomic medium 9 to the storage state. At the same time, due to spontaneous Raman scattering, the atoms will scatter left-hand circularly polarized writing photons that fall into the first storage state and scatter right-hand circularly polarized writing photons that fall into the second storage state.

[0026] The second excitation device generates readout light, which acts on the atomic medium 9, causing the atoms in the first storage state to transition from the storage state to the ground state, simultaneously releasing right-handed readout photons. The transition path is the first CG coefficient. The transition path it represents;

[0027] The first polarization selector 11 is set to left-handed polarization, and the second polarization selector 14 is set to right-handed polarization. The first single-photon detector 12 is used to detect the first excitation device, and the photon count is recorded. The second single-photon detector 15 detects the readout photon from the second excitation device, obtaining the readout photon detected under the written-out photon condition. The first readout efficiency was calculated. ;

[0028] The second excitation light device generates readout light, which acts on the atomic medium 9, causing the second storage-state atom to transition from the storage state to the ground state, simultaneously releasing a left-handed readout photon. The transition path is the second CG coefficient. The transition path it represents;

[0029] The first polarization selector 11 is set to right-handed polarization, and the second polarization selector 14 is set to left-handed polarization; the first single-photon detector 12 is used to detect the first excitation device, and the photon count is recorded. The second single-photon detector 15 detects the readout photon from the second excitation device, obtaining the readout photon detected under the written-out photon condition. The second readout efficiency was calculated. ;

[0030] The transmission efficiency is obtained by injecting a laser beam in reverse from the writing channel and measuring the ratio of the optical power before detector 15 to that after atomic medium 9. ;

[0031] Based on the obtained data, the retrieval efficiency of the single-photon detector itself was finally calculated. :

[0032]

[0033] in , .

[0034] The beneficial effects of this invention are: it provides a device for calibrating the efficiency of a single-photon detector based on quantum storage. In this invention, atoms in the atomic medium transition to different storage states under the action of writing light. Atoms in different storage states are read using different polarization states of read light, and the final detection efficiency is detected using a single-photon detector. The transmission efficiency in the transmission path is measured by combining two experimental results using a formula, and the final efficiency of the single-photon detector is calculated. Attached Figure Description

[0035] Figure 1 This is a schematic diagram of a device for calibrating the efficiency of a single-photon detector based on quantum storage.

[0036] Figure 2 This is a schematic diagram illustrating the working principle of a method for calibrating the efficiency of a single-photon detector based on quantum storage. (Original attached diagram) Figure 2 (This contains two images; it is recommended to describe them separately.)

[0037] Figure 3 for Detailed Implementation

[0038] The technical solution of the present invention will now be described in detail with reference to the accompanying drawings:

[0039] like Figure 1 As shown, the device of the present invention includes a first excitation light generating device, a second excitation light generating device, an atomic medium 9, a first Fabry-Perot cavity 10, a second Fabry-Perot cavity 13, a first polarization-selective filter 11, a second polarization-selective filter 14, a first single-photon detector 12, and a second single-photon detector 15.

[0040] Atomic medium 9 was prepared in advance using pump light to form atomic states. At the ground state energy level.

[0041] The first continuously tunable laser source 1 is used to generate writing light, with a center wavelength of 795 nm and a linewidth of less than 1 MHz. The detuning is -10 MHz, and the power is set to 2 uW.

[0042] The first optical attenuator 2 has its input end connected to the output end of the continuously tunable laser source 1 via free space propagation. The optical attenuator 2 adjusts the power of the continuously excited light input therein.

[0043] The first acousto-optic modulator 3 has its input end and the output end of the first optical attenuator propagating through free space. It is used to modulate the excitation light output by the optical attenuator 2 into a pulse excitation light with a width of 100 ns. Its operating wavelength is 600nm-1000nm, so that the continuous excitation light is modulated into pulse excitation light.

[0044] The first polarization controller 4 is a polarization controller with an operating wavelength of 795 nm. The input terminal of the polarization controller 4 and the output terminal of the acousto-optic modulator 3 are connected via free space propagation, and it is used to adjust the polarization state of the pulsed excitation light output by the acousto-optic modulator 3 to right-hand circularly polarized light. .

[0045] Atomic medium 9, receiving the write excitation light generated by the first excitation light, will be in a state of... The ground-state atomic medium transforms into an excited state, simultaneously emitting scattered left-handed circularly polarized light, after which the atoms fall into a storage state. .

[0046] The first Fabry-Perot cavity 10 has its input end connected to the atomic medium 9 through free space, and is used to filter out noise photons with the same frequency as the excitation light generated by Rayleigh scattering of the excitation light.

[0047] The first polarization-selective filter 11, whose input is connected to the Fabry-Perot cavity 10 via free space, consists of a quarter-wave plate, a half-wave plate, and a polarization beam splitter. The polarization selector selects left-handed circularly polarized light by adjusting the device.

[0048] The first single-photon detector 12 has its input end connected to the first polarization selector 11 via free space. It is used to detect filtered and polarized photons. After N write-read experiments, the average number of write photons received after N experiments is obtained. .

[0049] The second continuously tunable laser source 5 is used to generate readout light. The detuning is -10 MHz, the linewidth is approximately 100 kHz, and the power is set to 2 mW.

[0050] The second optical attenuator 6 has its input terminal connected to the output terminal of the continuously tunable laser source 5 via free space propagation. The optical attenuator 6 adjusts the power of the continuously excited light input therein.

[0051] The second acousto-optic modulator 7 has its input end and the output end of the first optical attenuator propagating through free space. It is used to modulate the excitation light output by the optical attenuator 6 into pulsed excitation light. Its operating wavelength is 600nm-1000nm, so that continuous excitation light is modulated into pulsed excitation light.

[0052] The second polarization controller 8 is a polarization controller with an operating wavelength of 795 nm. The input terminal of the polarization controller 8 and the output terminal of the acousto-optic modulator 7 are connected via free space propagation, and it is used to adjust the polarization state of the pulsed excitation light output by the acousto-optic modulator 7 to left-handed circularly polarized light. .

[0053] Atomic medium 9, receiving the read excitation light generated by the second excitation light, will be in a state of... The first storage state atom medium transforms into an excited state, simultaneously emitting scattered right-handed circularly polarized light. Afterward, the atom falls back into the ground state. .

[0054] The second Fabry-Perot cavity 13 has its input end connected to the atomic medium 9 through free space, and is used to filter out noise photons with the same frequency as the excitation light generated by Rayleigh scattering of the excitation light.

[0055] The second polarization-selective filter 14, whose input segment is connected to the Fabry-Perot cavity 13 via free space, consists of a quarter-wave plate, a half-wave plate, and a polarization beam splitter. The polarization selector selects right-hand circularly polarized light by adjusting the device.

[0056] The second single-photon detector 15 has its input segment connected to the second polarization selector 14 via free space for detection filtering. The polarized photons are subjected to N readout experiments to obtain the average number of readout photons received after N experiments. .

[0057] Through formula The detection efficiency corresponding to the first transition channel is obtained.

[0058] In the second experiment, the polarizations of the two write and read beams remained unchanged. The first polarization selector was adjusted to select right-hand circularly polarized light, corresponding to the second storage state. The second polarization selector is adjusted to select left-handed circularly polarized light, and the light in the state of... The second storage state atom medium transforms into an excited state, simultaneously emitting scattered left-handed circularly polarized light, after which the atom falls back into the ground state. After N write-read experiments, the following was obtained. , .

[0059] Through formula The detection efficiency corresponding to the second transition channel is obtained.

[0060] The principle of calibrating the detection efficiency of a single-photon detector based on quantum storage is as follows:

[0061] Atoms themselves have energy levels that evolve into Because the motion of atoms leads to the existence of a kinetic phase, it is related to the position of the atoms. Assume the atoms move along... The probability of a photon being emitted in a certain direction is Since the direction of photon radiation from an atom is within a sphere centered on the atom, the probability of detecting a photon in a specific direction for a single atom is...

[0062]

[0063] The formula is the probability of obtaining a readout photon in a specific direction at a new position, given a readout photon, multiplied by the probability that the atom can generate a readout photon. This yields the probability of obtaining a readout photon in a specific direction. Phase change in write state This represents the phase change during readout. It can be seen that if... + =0, which means + = + The probability of reading out a photon from a specific direction is equal to the probability of an atom producing a readout photon. This also means that the maximum probability is obtained when the write light and readout light are collinear, and when the write light and readout light are collinear.

[0064] Since there are N atoms in the atomic pool, the collective effect of these N atoms can further increase the readout probability.

[0065]

[0066] This allows for the following when two lines are collinear: = The probability of generating readout light in a specific direction is increased by N times.

[0067] Next, consider the probability of reading out photons in a real-world scenario. Under phase-matching conditions, the solid angle range of the readout photons that can be collected should be the divergence angle of the readout photons from the atom center. When light is emitted, it is generally Gaussian scattered light. Given this divergence angle, we can calculate the area of ​​photons scattered in a specific direction.

[0068] We are detecting readout photons within this area. As mentioned earlier, the probability amplitude of transitions in different channels (i.e., the corresponding CG coefficients) also affects... By combining all the above factors that influence the readout of photons, we can arrive at the following conclusion.

[0069]

[0070] The photon scattering probability outside the corresponding outgoing divergence angle is .

[0071]

[0072] The area corresponding to the divergence angle can be considered almost zero, so here... It can be considered as

[0073]

[0074] Therefore, we can conclude that...

[0075]

[0076] Here, readout efficiency is the proportion of the readout probability in the desired direction to the total readout probability.

[0077]

[0078] in

[0079]

[0080] because Atomic density can be written in a different way. Where n is the atomic number density and L is the longitudinal dimension of the atomic group. Because

[0081]

[0082] in Let be the atomic absorption cross section, which is a constant for atoms. Therefore, let be...

[0083]

[0084]

[0085] Regarding the overall efficiency measured in this paper

[0086]

[0087] Atomic medium 9 is prepared to the ground state, and then the first excitation device generates read excitation light to prepare the atoms from the ground state to the first and second storage states, as follows: Figure 1A left-handed photon is released to the first storage state, and a right-handed photon is released to the second storage state. A polarization selector selects the corresponding polarization to detect the write-out photon. Then, a second excitation device generates a right-handed readout photon, which returns to the ground state through different transition channels. This is achieved using the formula... Calculate .

[0088] By testing the outgoing photons from the polarization selector and the incident photons from the single-photon detector, two equations are derived.

[0089]

[0090]

[0091] The unknown is ,and It can be solved by equations Detection efficiency. Comparing the two, the solution...

[0092]

[0093]

[0094] in , To obtain the results required by this specification. The detection efficiency, as shown in the final equation, only requires knowing... , , The final detector efficiency can be obtained by calculating the efficiency of these three factors. This demonstrates how to obtain the efficiency of a single-photon detector calibrated based on quantum storage, as described in this specification.

Claims

1. A device for calibrating the detection efficiency of a single-photon detector based on quantum storage, characterized in that, It includes a first excitation light generating device, a second excitation light generating device, an atomic medium (9), a first Fabry-Perot cavity (10), a second Fabry-Perot cavity (13), a first polarization-selective filter (11), a second polarization-selective filter (14), a first single-photon detector (12), and a second single-photon detector (15). The first excitation light generating device is used to generate right-hand circularly polarized writing light to act on the atomic medium (9), causing the atoms in the atomic medium (9) in the ground state to transition to the storage state. When the atoms transition to the storage state, they will release scattered photons due to spontaneous Raman scattering. When the scattered photons are defined as left-hand circularly polarized light, the atomic state falls into the first storage state. When the scattered photons are right-hand circularly polarized light, the atomic state falls into the second storage state. The second excitation light generating device is used to generate left-hand circularly polarized readout light to act on the atomic medium (9) and read out the atomic state in the storage state. When the readout light acts on the first storage state, the atoms in the storage state will release right-hand circularly polarized readout photons when they transition from the storage state to the ground state. When the readout light acts on the second storage state, the atoms in the storage state will release left-hand circularly polarized readout photons when they transition from the storage state to the ground state. The first Fabry-Perot cavity (10), the first polarization-selective filter (11), and the first single-photon detector (12) are connected in sequence, and the second Fabry-Perot cavity (13), the second polarization-selective filter (14), and the second single-photon detector (15) are connected in sequence; wherein the first Fabry-Perot cavity (10) and the second Fabry-Perot cavity (13) are both used to filter out noise photons with the same frequency as the excitation light generated by Rayleigh scattering of the excitation light; the first polarization-selective filter (11) and the second polarization-selective filter (14) are set to select left-handed or right-handed light to pass through; when the first polarization-selective filter (11) is set to select left-handed light to pass through, the second polarization selector (14) is set to select right-handed light to pass through, at which time the left-handed photon is detected by the first single-photon detector (12). It is detected that the atom in the first storage state transitions to the ground state under the action of the read light and releases a right-handed circularly polarized readout photon. The right-handed readout photon is detected by the second single-photon detector (15). The count of the written photon and readout photon after N write-read operations is counted and recorded, thereby calculating the first readout efficiency. When the first polarization selection filter (11) is set to select right-handed light to pass through, the second polarization selector (14) is set to select left-handed light to pass through. At this time, the right-handed written photon is detected by the first single-photon detector (12). The atom in the second storage state transitions to the ground state under the action of the read light and releases a left-handed circularly polarized readout photon. The left-handed readout photon is detected by the second single-photon detector (15). The count of the written photon and readout photon after N write-read operations is counted and recorded, thereby calculating the second readout efficiency. The detection efficiency of the single-photon detector is calculated based on the first readout efficiency and the second readout efficiency.

2. The device for calibrating the detection efficiency of a single-photon detector based on quantum storage according to claim 1, characterized in that, The specific method for calculating the detection efficiency of a single-photon detector based on the first readout efficiency and the second readout efficiency is as follows: the first readout efficiency is defined as... , , Write down the photon count under the corresponding conditions. , This corresponds to the readout photon count under the written photon condition; the second readout efficiency is defined as... , , The count of photons is obtained by statistical analysis under corresponding conditions. This refers to the readout photon count under the corresponding write-out photon condition; the detection efficiency of a single-photon detector. The calculation formula is: ， in, , , It is the CG coefficient of the left-handed transition channel. It is the CG coefficient of the right-handed transition channel. It refers to transmission path efficiency.

3. The device for calibrating the detection efficiency of a single-photon detector based on quantum storage according to claim 1, characterized in that, The first excitation light generating device includes a first continuously tunable laser source (1), a first optical attenuator (2), a first acousto-optic modulator (3), and a first polarization controller (4) connected in sequence; the second excitation light generating device includes a second continuously tunable laser source (5), a second optical attenuator (6), a second acousto-optic modulator (7), and a second polarization controller (8) connected in sequence.

4. The device for calibrating the detection efficiency of a single-photon detector based on quantum storage according to claim 3, characterized in that, The first continuously tunable laser source (1) and the second continuously tunable laser source (5) are solid-state lasers or semiconductor lasers.

5. The device for calibrating the detection efficiency of a single-photon detector based on quantum storage according to claim 3, characterized in that, The first optical attenuator (2) and the second optical attenuator (7) are optical attenuators.

6. The device for calibrating the detection efficiency of a single-photon detector based on quantum storage according to claim 3, characterized in that, The operating wavelength range of the first acousto-optic modulator (3) and the second acousto-optic modulator (7) covers the wavelength of atomic energy level transitions in the atomic medium (9).

7. The device for calibrating the detection efficiency of a single-photon detector based on quantum storage according to claim 3, characterized in that, The first polarization controller (4) and the second polarization controller (8) are composed of a quarter-wave plate and a half-wave plate.

8. The device for calibrating the detection efficiency of a single-photon detector based on quantum storage according to claim 1, characterized in that, The atomic medium (9) is an atom with multiple energy levels that can be used for quantum storage.

9. The device for calibrating the detection efficiency of a single-photon detector based on quantum storage according to claim 1, characterized in that, The first Fabry-Perot cavity (10) and the second Fabry-Perot cavity (13) are formed by parallel mirrors to form an optical cavity; the first polarization selective filter (11) and the first polarization selective filter (14) are composed of a quarter-wave plate, a half-wave plate, and a polarization beam splitter; the first single-photon detector (11) and the first single-photon detector (13) work using the avalanche diode principle.

10. A method for using the apparatus for calibrating the detection efficiency of a single-photon detector based on quantum storage as described in any one of claims 1-9, characterized in that, include: Atomic media (9) are prepared in the ground state; The first excitation light generating device generates writing light to transition the atoms in the atomic medium (9) to the storage state. At the same time, due to spontaneous Raman scattering, the atoms will scatter left-hand circularly polarized writing photons into the first storage state and scatter right-hand circularly polarized writing photons into the second storage state. The second excitation light device generates readout light, which acts on the atomic medium (9) to transition the atom in the first storage state from the storage state to the ground state, while releasing a right-handed readout photon. The transition path is the first CG coefficient. The transition path it represents; The first polarization selector (11) is set to left-handed polarization, and the second polarization selector (14) is set to right-handed polarization. The first single-photon detector (12) is used to detect the first excitation device, and the photon count is recorded. The second single-photon detector (15) detects the readout photon from the second excitation device, and obtains the readout photon detected under the condition of writing out the photon. The first readout efficiency was calculated. ; The second excitation light device generates readout light, which acts on the atomic medium (9), causing the second storage state atom to transition from the storage state to the ground state, while simultaneously releasing a left-handed readout photon. The transition path is the second CG coefficient. The transition path it represents; Set the first polarization selector (11) to right-handed polarization and the second polarization selector (14) to left-handed polarization; use the first single-photon detector (12) to detect the first excitation device and write down the photon count. The second single-photon detector (15) detects the readout photon from the second excitation device, and obtains the readout photon detected under the condition of writing out the photon. The second readout efficiency was calculated. ; The transmission efficiency is obtained by injecting a laser beam in reverse from the writing channel and measuring the ratio of the optical power before the detector (15) to that after the atomic medium (9). ; Based on the obtained data, the retrieval efficiency of the single-photon detector itself was finally calculated. : ， in , .

Images