Pyramid magneto-optical trap based hollow-core fiber cold atom guiding device and working method

Abstract

The present application relates to the technical field of hollow-core optical fiber cold atom guiding, and particularly relates to a hollow-core optical fiber cold atom guiding device based on a pyramid magnetic optical trap and a working method thereof. The guiding device comprises a vacuum cavity, a cold atom group guiding module, a cold atom detection module and a cold atom group preparation module in the vacuum cavity. The cold atom group preparation module comprises a first collimating laser, a reverse Helmholtz coil group and a pyramid reflector. The cold atom group guiding module comprises a second collimating laser, a focusing lens, a first short-wave-pass dichroic mirror, a hollow-core anti-resonant fiber and the cold atom detection module comprises a collimating lens, a second short-wave-pass dichroic mirror and a photodetector. The cold atom group is prepared by the cold atom group preparation module, guided into the optical fiber by the cold atom group guiding module and finally the number of cold atoms is obtained by the cold atom detection module. The present application effectively reduces the spatial optical path complexity of the existing hollow-core optical fiber guiding device and reduces the size of the vacuum system.

Description

Technical Field

[0001] This invention relates to the field of cold atom guidance technology for hollow optical fibers, specifically to a cold atom guidance device and its working method for hollow optical fibers based on a pyramid magneto-optical trap. Background Technology

[0002] In recent years, with breakthroughs in theoretical research on hollow-core photonic crystal fibers and advancements in drawing technology, these fibers have gradually become ideal experimental platforms for quantum sensing, optical storage and retrieval, and superluminescence. The cold atom guidance scheme for hollow-core fibers can confine light and atoms within the hollow core region of the fiber and guide them over long distances, avoiding collisions between atoms and the inner walls of the fiber. This provides a single-mode, diffraction-free light field for the cold atom ensemble, significantly enhancing the intensity of light-atom interactions.

[0003] Transmitting a far-infrared detuned optical field using hollow-core optical fiber can generate a dipole potential well. Applying a dipole force pointing towards the fiber axis to atoms can trap cold atoms near the fiber core, restricting their relative motion in the fiber's radial direction. This principle can be used to fabricate a hollow-core optical fiber-guided cold atom gravimeter, effectively solving the problem of low accuracy in traditional gravimeters during moving measurements, and possessing the potential for multi-vector measurements, making it extremely valuable for development in the field of quantum sensing. In 2018, Xin et al. from Nanyang Technological University first realized an atomic interferometer within a hollow-core optical fiber. However, this hollow-core optical fiber guidance scheme increases the spatial optical path and system complexity of the atomic interferometer, limiting its miniaturization and engineering applications.

[0004] Magneto-optical traps (METs) are a method for cooling and trapping atoms using a gradient magnetic field generated by a pair of Helmholtz coils and three pairs of mutually orthogonal circularly polarized cooling beams. In recent years, a novel pyramid MET has emerged that requires only a single beam of cooling light to prepare cold atoms. Compared to traditional METs, this method saves a significant amount of space and optical components, effectively reducing system size and improving robustness. In 2019, Wu Yufeng et al. from China Jiliang University applied for a Chinese patent (publication number CN 109781088 A) for a miniaturized atomic interferometer gyroscope based on a pyramid MET. In the same year, Holger Müller's group at the University of California, Berkeley, designed a movable pyramid-shaped atomic interferometer by opening a hole at the bottom of a pyramid reflector and adding a reflector below it. This approach eliminates the effects of wavefront phase aberration caused by apex defects and edges of the pyramid reflector and is insensitive to pyramid mirror vibration noise.

[0005] Using a pyramidal magneto-optical trap to prepare cold atom clusters can significantly simplify the spatial optical path of a hollow-core fiber-guided cold atom interferometer and reduce system complexity. However, due to the presence of the hollow fiber, there is always a region of non-reflective light in the vertical direction of the pyramidal magneto-optical trap. In this vertical direction, the atoms experience an imbalance of forces, forming... Figure 3 The beam shown is a cold atom beam, not a stable cold atom cluster. Therefore, existing pyramid magneto-optical trap technology cannot be directly used in hollow fiber guiding devices. Summary of the Invention

[0006] The purpose of this invention is to solve the above-mentioned problems by proposing a cold atom guiding device for hollow-core optical fibers based on a pyramid magneto-optical trap. By tilting the incident angle of the cooling light in a traditional pyramid magneto-optical trap, a stable cold atom cluster is formed. This structure requires only a single cooling beam to complete the cooling and trapping of the cold atom cluster, effectively reducing the spatial optical path complexity of existing hollow-core optical fiber guiding devices and decreasing their vacuum system size.

[0007] The technical solution adopted is as follows:

[0008] A cold atom guiding device for hollow optical fibers based on a pyramid magneto-optical trap, the device comprising:

[0009] The system includes a vacuum cavity, a cold atom cluster guiding module, a cold atom detection module, and a cold atom cluster preparation module located within the vacuum cavity; wherein,

[0010] The cold atom cluster preparation module is a pyramid magneto-optical trap, including a first collimated laser, an anti-Helmholtz coil group, and a pyramid reflector; the first collimated laser provides cooling light and pump light, and the cooling light is irradiated on the pyramid reflector at an inclined angle to form multiple opposing orthogonal circularly polarized beams, and the circularly polarized beams and the anti-Helmholtz coil group form a pyramid magneto-optical trap.

[0011] The cold atom cluster guiding module includes a second collimated laser, a focusing lens, a first short-pass dichroic mirror, and a hollow anti-resonant optical fiber; the second collimated laser includes a far-infrared detuned guiding light and a resonant probe light, and the second collimated laser is reflected by the first short-pass dichroic mirror after passing through the focusing lens, and the reflected second collimated laser is coupled into the hollow anti-resonant optical fiber.

[0012] The cold atom detection module includes a collimating lens, a second short-pass dichroic mirror, and a photodetector. The laser output from the hollow anti-resonant fiber passes through the collimating lens, and the collimated red detuned guiding light is reflected by the second short-pass dichroic mirror. The resonant detection light passes through the second short-pass dichroic mirror and is detected by the photodetector.

[0013] Furthermore, to prepare more stable cold atom clusters, a specific tilt angle can be set. The specific tilt angle is set as follows: the tilt angle, which is the angle between the first collimated laser incident ray and the vertical direction, is θ; h is the distance from the center of the captured cold atom cluster to the upper surface of the hollow anti-resonant fiber; and d is the distance from the upper surface of the hollow anti-resonant fiber to the bottom of the pyramid reflector. The functional relationship between d, h, and the incident angle θ of the beam is obtained through geometric calculation as follows:

[0014]

[0015] Furthermore, the hollow anti-resonant optical fiber includes a hollow optical fiber core, a cladding capillary glass tube, and a hollow optical fiber cladding.

[0016] Furthermore, the pyramid-shaped reflector is composed of a first reflector, a second reflector, a third reflector, and a fourth reflector.

[0017] Furthermore, the bottom of the pyramid reflector has a reserved fiber optic hole with a diameter similar to the outer diameter of the hollow-core anti-resonant fiber; the upper surface of the hollow-core anti-resonant fiber is slightly higher than the reserved fiber optic hole at the bottom of the pyramid reflector.

[0018] Furthermore, by changing the polarization state of the cooling light through the pyramid-shaped reflector, a 180° phase shift is generated between the s-wave and p-wave of the reflected cooling light, thereby forming multiple mutually orthogonal circularly polarized beams.

[0019] Furthermore, the far-infrared detuned guiding light and the resonant probe light are output from the same single-mode polarization-maintaining fiber.

[0020] A method for operating a hollow-core optical fiber cold atom guiding device based on a pyramid magneto-optical trap, the specific steps of which are as follows:

[0021] In the first stage, the preparation of cold atom clusters is as follows: The first collimated laser is turned on and enters the first short-pass dichroic mirror. The transmitted light serves as a cooling beam with an intensity that follows a Gaussian distribution. The cooling beam is then irradiated at a certain angle onto a pyramid-shaped reflector. The pyramid-shaped reflector can change the polarization state of the cooling beam, causing a 180° phase shift between the s-wave and p-wave of the reflected light. This results in multiple mutually orthogonal circularly polarized beams. These circularly polarized beams, together with the anti-Helmholtz coil group, form a pyramid magneto-optical trap, which can cool and trap room-temperature atomic gas in the vacuum cavity, thereby forming cold atom clusters.

[0022] The second stage, the cold atom guidance stage: the cold atom clusters generated in the first stage are released by turning off the first collimating laser, and the far-infrared detuned guiding light is turned on. The far-infrared detuned guiding light is reflected by the first short-pass dichroic mirror after passing through the focusing lens. The far-infrared detuned guiding light is completely reflected by the first short-pass dichroic mirror. The reflected far-infrared detuned guiding light is coupled into the hollow anti-resonant fiber. At the same time, the cold atom clusters are loaded into the hollow anti-resonant fiber under the action of the dipole force of the far-infrared detuned guiding light and form cold atom clusters inside the fiber.

[0023] The third stage, the cold atom detection stage: the far-infrared detuned guiding light is turned off, the resonant detection light is turned on, and the photodetector is used to detect the degree of absorption of the resonant detection light by the cold atoms in the optical fiber, thereby calculating the number of cold atoms guided into the hollow anti-resonant optical fiber.

[0024] Furthermore, in the second stage, the power of the pump light and cooling light is gradually reduced, and the detuning of the cooling light is increased. By cooling with polarization gradient, the temperature of the cold atom cluster is further reduced to the μK level, so as to improve the loading efficiency of the cold atom cluster to the guiding light potential trap.

[0025] The beneficial effects of this invention compared to the prior art are as follows:

[0026] 1. This invention combines a pyramid-shaped magneto-optical trap with a hollow-core fiber atom guidance scheme. By tilting the cooling beam, it avoids the loss of reflected light due to the presence of the fiber, thus realizing a compact atom cooling, confinement, and fiber guidance device. It can effectively reduce the number of spatial optical path elements in the atom guidance system, reduce the system size, and is easy to build and has strong robustness.

[0027] 2. This invention can effectively reduce the complexity of fiber-optic guided interferometer systems and significantly enhance the robustness of the systems; it also solves the problem of low accuracy in mobile measurements of traditional space-type atomic gravimeters, and is of great significance for the miniaturization, integration, engineering application of cold atom interferometers, and mobile inertial measurement. Attached Figure Description

[0028] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained from these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of the hollow fiber cold atom guiding device based on a pyramid magneto-optical trap according to the present invention.

[0030] Figure 2 This is a schematic diagram of the cross-section of the hollow anti-resonant optical fiber of the present invention.

[0031] Figure 3 This is a schematic diagram of the perpendicular incidence of cooling light in this invention.

[0032] Figure 4 This is a schematic diagram showing the oblique incidence of the cooling light in this invention.

[0033] The annotations in the attached figures are explained as follows:

[0034] 1-First collimated laser, 2-Second collimated laser, 3-Focusing lens, 4-First short-pass dichroic mirror, 5-Pyramid reflector, 6-Anti-Helmholtz coil group, 7-Cold atom cluster, 8-Cold atom cluster inside the optical fiber, 9-Hollow-core anti-resonant optical fiber, 10-Collimating lens, 11-Second short-pass dichroic mirror, 12-Photodetector, 13-Russian source, 14-Vacuum pump, 15-Vacuum cavity, 16-First reflector, 17-Second reflector, 18-Third reflector, 19-Fourth reflector, 20-Pre-reserved optical fiber aperture, 21-Hollow-core optical fiber core, 22-Clad capillary glass tube, 23-Hollow-core optical fiber cladding. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0036] The present invention will now be described in further detail with reference to the accompanying drawings:

[0037] A hollow fiber cold atom guiding device based on a pyramid magneto-optical trap, such as Figure 1 As shown, it includes a first collimating laser 1, a second collimating laser 2, a focusing lens 3, a first short-pass dichroic mirror 4, a pyramidal reflector 5, an anti-Helmholtz coil group 6, a hollow anti-resonant fiber 9, a collimating lens 10, a second short-pass dichroic mirror 11, a photodetector 12, a rubidium source 13, a vacuum pump 14, a vacuum chamber 15, a reserved fiber optic hole 20, and the pyramidal reflector 5 includes a first reflector 16, a second reflector 17, a third reflector 18, and a fourth reflector 19.

[0038] The vacuum environment of the vacuum chamber 15 is provided by the vacuum pump 14. The rubidium source 13 provides room temperature atomic gas.

[0039] A cold atom preparation module of the pyramid magneto-optical trap hollow fiber guiding device, consisting of a first collimated laser 1, a focusing lens 3, a pyramidal reflector 5, and an anti-Helmholtz coil group 6, is used to generate cold atom clusters 7. The first collimated laser 1 includes cooling light and pump light. The cooling light cools the atoms, while the pump light re-pumps atoms that have been detuned to outside their closed transition energy levels back to closed transition energy levels, ensuring continuous cooling cycle. The first collimated laser 1 illuminates the pyramidal reflector 5 at a certain tilt angle, forming multiple opposing, mutually orthogonal circularly polarized beams. These circularly polarized beams, together with the anti-Helmholtz coil group 6, form the pyramid magneto-optical trap.

[0040] A cold atom cluster guiding module is composed of a second collimated laser 2, a collimating lens 10, a first short-pass dichroic mirror 4, and a hollow anti-resonant fiber 9, which generates a cold atom cluster 8 inside the fiber. The second collimated laser 2 includes far-infrared detuned guiding light and resonant probe light. After passing through the focusing lens, the second collimated laser 2 is reflected by the first short-pass dichroic mirror 4, and the reflected second collimated laser 2 is coupled into the hollow anti-resonant fiber 9.

[0041] A cold atom detection module is composed of a collimating lens 10, a second short-pass dichroic mirror 11, and a photodetector 12. The laser output from the hollow anti-resonant fiber 9 passes through the collimating lens 10, and the collimated red detuned guiding light is reflected by the second short-pass dichroic mirror 11. The resonant detection light passes through the second short-pass dichroic mirror 11 and is detected by the photodetector 12.

[0042] The high-bandwidth, low-loss, large-core-diameter hollow antiresonant optical fiber used is as follows: Figure 2 As shown, it includes a hollow fiber core 21, a cladding capillary glass tube 22, and a hollow fiber cladding 23. In this device, the upper end face of the fiber is slightly higher than the pre-reserved fiber hole 20 at the bottom of the pyramid reflector 5, and it is fixed using a designed fiber clamp. This hollow anti-resonant fiber 9 can ensure uniform transmission of the laser mode over long distances, providing an almost single-mode, diffraction-free optical field for the guiding light, confining cold atoms in the fiber core and guiding them over long distances. In this embodiment, the fiber extends vertically, as shown... Figure 1 As shown.

[0043] The specific configuration of the pyramid magneto-optical trap is as follows:

[0044] The pyramid magneto-optical trap is the core component of the device of this invention, providing a cold atom cluster. It consists of a first collimated laser 1 incident at an angle (i.e., cooling light and pump light), an anti-Helmholtz coil group 6, and a pyramidal reflector 5. Details are as follows:

[0045] (1) Cooling light, pump light

[0046] The first collimated laser 1 includes cooling light and pump light. Atoms moving in the cooling light experience photon scattering forces opposite to their direction of motion due to the Doppler effect, thus achieving atomic cooling. The pump light re-pumps atoms detuned to levels outside the closed transition, ensuring the cooling cycle continues and enabling the atoms to cool through multiple cycles of stimulated absorption-spontaneous emission.

[0047] (2) Anti-Helmholtz coil assembly

[0048] Cooling light alone cannot trap atoms; a restoring force related to their displacement from the optical center is required. This can be achieved by adding a pair of anti-Helmholtz coils. When the anti-Helmholtz coil group 6 is energized, it generates a four-level gradient magnetic field in space, with zero magnetic field at the center of the coil. This magnetic field is strong around the edges, weak at the center, and coincides with the optical center. Furthermore, the magnetic field strength increases linearly with the distance from the optical center.

[0049] Under the combined influence of cooling light and the non-uniform magnetic field generated by an energized anti-Helmholtz coil, atoms in the cooling region are subjected to a scattering force directed towards the optical center, the magnitude of which is proportional to their distance from the optical center. At this point, the motion of the atom is similar to that of a strongly damped spring oscillator, its velocity continuously decreasing until it is trapped near the zero point of the magnetic field.

[0050] (3) Pyramid reflector

[0051] The pyramid-shaped reflector 5 has a pre-drilled fiber optic hole 20 at its bottom, the diameter of which is approximately equal to the outer diameter of the hollow-core anti-resonant fiber 9. A top view of the pyramid-shaped reflector 5 is shown below. Figure 1 As shown, it consists of a first reflecting mirror 16, a second reflecting mirror 17, a third reflecting mirror 18, and a fourth reflecting mirror 19. These four reflecting mirrors are made of glass or metal, and each mirror is coated with a dielectric film that achieves high reflectivity and creates a 180° phase shift between the S-wave and P-wave of the reflected cooling light. This results in multiple pairs of circularly polarized cooling beams that are perpendicular to each other, propagate in opposite directions, and have orthogonal polarization directions after reflection.

[0052] However, because the bottom of the pyramid reflector 5 has a reserved fiber optic hole 20 and a hollow anti-resonant fiber 9, when the angle between the incident large-size cooling light and the vertical direction is 0°, there is no reflected cooling beam in the area of ​​the reserved fiber optic hole 20. At this time, the cold atom cluster is unbalanced in the vertical direction, and under the action of light scattering force, it forms a structure like... Figure 3 The atomic beam shown is pushed toward the fiber core, making it impossible to achieve stable preparation of cold atomic clusters.

[0053] To prevent the aforementioned phenomena, the cooling light must be incident at a specific angle θ, ensuring that the atoms are in vertical force balance, thus guaranteeing a better cooling effect. This tilt angle θ is determined by the parameters h and d. By selecting the optimal tilt angle, the best balance of cooling light intensity can be achieved, resulting in the best atomic cooling and trapping effect. The specific calculation method is as follows.

[0054] According to such Figure 4 The geometric relationship shown indicates that the incident cooling beam follows a Gaussian distribution, and the angle between its incident angle and the vertical direction is denoted as θ. h is the distance from the center of the captured cold atom cluster to the upper surface of the optical fiber, d is the distance from the upper surface of the optical fiber to the bottom of the pyramid reflector 5, and line segment AF is the line connecting the two reflection points of the cooling beam incident vertically at an angle θ when it passes through the pyramid reflector. AF intersects the upper surface of the hollow anti-resonant optical fiber 9 at point D.

[0055] The functional relationship between d, h and the incident angle θ of the beam, obtained through geometric calculation, is as follows:

[0056]

[0057] Because the intensity of the cooling beam acting on the cold atom cluster is slightly different when the cooling beam is incident at an angle, in order to balance the intensity of the cooling beam pairs in each dimension and provide a more stable cold atom cluster, this can be achieved by translating the first collimated laser. Specifically:

[0058] like Figure 4 As shown, considering that the cooling beam follows a Gaussian distribution, the Gaussian function is: Where x is the distance from a point in the Gaussian beam to the center of the beam, and c is 1 / e of the cooling beam. 2 Radius. The vertically directed cooling beams acting on the cold atom cluster correspond to the Gaussian function positions E and M, respectively. The distances from these two points to the intensity center E are 0 and PM, respectively, where P is the position of the cold atom cluster. The transversely directed cooling beams acting on the cold atom cluster correspond to the Gaussian function positions I and J, respectively. The distances from these two points to the intensity center are IK and JL, respectively. At this point, the forces acting on the cold atom cluster are not balanced. To obtain a stable cold atom cluster, the incident cooling beams need to be translated so that the intensities of all the directed cooling beams acting on the cold atom cluster are equal.

[0059] First, the intensity of the cooling beam perceived vertically by the cold atom cluster is analyzed. This involves calculating the intensity at points E and M. Point E is the center of the intensity, with an intensity of 'a'. To obtain the intensity at point M, the distance L1 from PM must first be calculated. This is derived from geometric relationships.

[0060]

[0061] Similarly, perform an intensity analysis on the cooling beam that the cold atom cloud senses in the transverse direction. From geometric calculations, obtain the distances L2 and L3 between the intensity of the transversely opposed cooling light and the central intensity:

[0062]

[0063]

[0064] In this embodiment, specifically obtain a cold atom cloud by taking typical parameters: the distance h between the cold atom cloud and the end face of the optical fiber is 5 mm, the angle θ between the incident beam and the vertical direction is 5°, and the 1 / e 2 radius c of the cooling light beam is 20 mm. Substitute into equation (1) to obtain the allowable d as 0.48 mm.

[0065] Use the above parameters to calculate L1, L2, and L3, and substitute the calculation results into the Gaussian function F to obtain the ratios of the intensities at points E, M, J, and I to the central intensity as shown in Table 1. The calculation results show that after tilting the beam, the transversely opposed cooling beams at points E and M in the vertical direction almost reach intensity balance. However, for the transversely opposed cooling light at points J and I in the transverse direction, it does not reach complete balance, and the beam needs to be translated to optimize it.

[0066] After translating the beam by a distance f, the distances from the transverse cooling light to the central intensity are JL + f and IK - f respectively. The distances from the vertical cooling light to the central intensity are f and PM - f respectively. Substitute the distances from the translated transverse and longitudinal cooling lights to the central intensity into the Gaussian beam formula for calculation, and perform a parameter scan on the beam translation distance f, with its value range: 0 < f < PM. By calculating the above transverse and longitudinal intensities, it can be seen that when f = 0.44 mm, the intensities of the transversely opposed cooling beams in the transverse and longitudinal directions can both reach the balance state, and the calculation results of the percentage of the intensity of the transversely opposed cooling light are shown in Table 1. It can be considered that at this time, the cooling light reaches intensity balance in all three dimensions and can cool the atoms well.

[0067] Table 1

[0068]

[0069] The method for obtaining a stable cold atom cloud by tilting and translating the cooling beam is summarized as follows:

[0070] a. Incident the cooling light in the vertical direction of the optical fiber, energize the anti-Helmholtz coil group, and observe the generation of an atomic beam in the magneto-optical trap;

[0071] b. Through the above formula (1), calculate the required tilting angle θ from the given h and d. Then adjust the cooling beam to θ and observe the state of the atomic beam until the beam disappears to form a cold atom cloud;

[0072] c. Because the cooling beam follows a Gaussian distribution, when the cooling beam is incident at an angle, the intensity of the cooling beam acting on the cold atom cluster will be slightly different. At this time, through a given 1 / e... 2 The radius c of the cooling light beam is calculated with respect to the horizontal translation distance f of the cooling light beam, and the first collimated laser 1 is translated by the distance f so that the light intensity of the cooling light beam pairs in each dimension reaches a balance, at which point a stable cold atom cluster is formed.

[0073] The basic working method of the hollow-core fiber cold atom guiding device based on the pyramid magneto-optical trap includes three steps: cold atom cluster preparation, cold atom guiding, and cold atom detection, as detailed below:

[0074] (1) Cold atom preparation stage

[0075] The first collimated laser, which follows a Gaussian distribution, is activated and first enters the first short-pass dichroic mirror. The cooling light then illuminates the pyramid-shaped reflector 5 at a certain tilt angle. The pyramid-shaped reflector 5 can change the polarization state of the cooling light, causing a 180° phase shift between the s-wave and p-wave of the reflected light, thereby forming multiple mutually orthogonal circularly polarized beams. The magneto-optical trap can cool and trap atoms, forming cold atom clusters 7. The power of the pump light and cooling light is gradually reduced, and the detuning of the cooling light is increased. That is, through polarization gradient cooling, the temperature of the cold atom clusters is further reduced to the μK level to improve the loading efficiency of the cold atom clusters into the guiding optical potential trap.

[0076] (2) Cold Atom Guiding Stage

[0077] The first collimated laser 1 is turned off, and the far-infrared detuned guiding light in the second collimated laser 2 is turned on. The second collimated laser 2 is output from the same single-mode polarization-maintaining fiber, passes through the focusing lens 3, and is reflected by the first short-pass dichroic mirror 4. Since the dichroic mirror transmits short waves and reflects long waves, the far-infrared detuned guiding light is almost entirely reflected by the first short-pass dichroic mirror 4, while the resonant probe light is reflected only slightly. The reflected light is then coupled into the hollow anti-resonant fiber 9. Since the guiding light approximately follows a Gaussian distribution, the optical dipole force it generates points in the direction of maximum light intensity. Therefore, the cold atom clusters have an optical dipole force pointing into the fiber in the axial direction, and the radial movement of the hollow fiber is always constrained. Under its action, the cold atom clusters 7 are loaded into the hollow anti-resonant fiber 9 and form the cold atom clusters 8 inside the fiber.

[0078] (3) Cold Atom Detection Stage

[0079] After the far-infrared detuned guiding light and resonant probe light are output from the lower end face of the hollow anti-resonant fiber 9, they pass through the collimating lens 10. The collimated guiding light is reflected by the second short-pass dichroic mirror 11, and the resonant probe light passes through the second short-pass dichroic mirror 11 and is detected by the photodetector 12. The guiding light is turned off, and the resonant probe light is turned on. The photodetector 12 is used to detect the degree of absorption of the resonant probe light by the cold atoms in the fiber, thereby calculating the number of cold atoms guided into the hollow anti-resonant fiber 9.

[0080] Obviously, the above embodiments are merely illustrative examples for clear explanation and are not intended to limit the implementation. Those skilled in the art will recognize that other variations or modifications can be made based on the above description. It is neither necessary nor possible to exhaustively list all possible implementations here. However, obvious variations or modifications derived therefrom are still within the scope of protection of this invention.

Claims

1. A hollow-core optical fiber cold atom guiding device based on a pyramid magneto-optical trap, characterized in that, The device includes: The system includes a vacuum cavity, a cold atom cluster guiding module, a cold atom detection module, and a cold atom cluster preparation module located within the vacuum cavity; wherein, The cold atom cluster preparation module is a pyramid magneto-optical trap, including a first collimated laser, an anti-Helmholtz coil group, and a pyramid reflector; the first collimated laser provides cooling light and pump light, and the cooling light is irradiated on the pyramid reflector at an inclined angle to form multiple opposing orthogonal circularly polarized beams, and the circularly polarized beams and the anti-Helmholtz coil group form a pyramid magneto-optical trap. The cold atom cluster guiding module includes a second collimated laser, a focusing lens, a first short-pass dichroic mirror, and a hollow anti-resonant optical fiber; the second collimated laser includes a far-infrared detuned guiding light and a resonant probe light, and the second collimated laser is reflected by the first short-pass dichroic mirror after passing through the focusing lens, and the reflected second collimated laser is coupled into the hollow anti-resonant optical fiber. The cold atom detection module includes a collimating lens, a second short-pass dichroic mirror, and a photodetector. The laser output from the hollow anti-resonant fiber passes through the collimating lens, and the collimated far-infrared detuned guiding light is reflected by the second short-pass dichroic mirror. The resonant detection light passes through the second short-pass dichroic mirror and is detected by the photodetector. The bottom of the pyramid reflector has a reserved fiber optic hole, the diameter of which is comparable to the outer diameter of the hollow anti-resonant fiber; the upper end face of the hollow anti-resonant fiber is slightly higher than the reserved fiber optic hole at the bottom of the pyramid reflector.

2. The hollow-core optical fiber cold atom guiding device based on a pyramid magneto-optical trap according to claim 1, characterized in that, To prepare more stable cold atom clusters, a specific tilt angle is set. This specific tilt angle is defined as follows: the tilt angle, which is the angle between the first collimated laser incident beam and the vertical direction, is θ; the distance from the center of the captured cold atom cluster to the upper surface of the hollow anti-resonant fiber is h; and the distance from the upper surface of the hollow anti-resonant fiber to the bottom of the pyramid reflector is d. The functional relationship between d, h, and the beam incident angle θ is obtained through geometric calculation as follows: 。 3. The hollow-core optical fiber cold atom guiding device based on a pyramid magneto-optical trap according to claim 2, characterized in that, The hollow anti-resonant optical fiber includes a hollow optical fiber core, a cladding capillary glass tube, and a hollow optical fiber cladding.

4. The hollow-core optical fiber cold atom guiding device based on a pyramid magneto-optical trap according to claim 3, characterized in that, The pyramid-shaped reflector consists of a first reflector, a second reflector, a third reflector, and a fourth reflector.

5. A hollow-core optical fiber cold atom guiding device based on a pyramid magneto-optical trap according to claim 4, characterized in that, By altering the polarization state of the cooling light through the pyramid-shaped reflector, a 180° phase shift is generated between the s-wave and p-wave of the reflected cooling light, thereby forming multiple mutually orthogonal circularly polarized beams.

6. The hollow-core optical fiber cold atom guiding device based on a pyramid magneto-optical trap according to claim 5, characterized in that, The far-infrared detuned guiding light and the resonant probe light are output from the same single-mode polarization-maintaining fiber.

7. A method for operating the hollow-core optical fiber cold atom guiding device based on a pyramid magneto-optical trap as described in any one of claims 1-6, characterized in that, The specific steps are as follows: In the first stage, the preparation of cold atom clusters is as follows: The first collimated laser is turned on and enters the first short-pass dichroic mirror. The transmitted light serves as a cooling beam with an intensity that follows a Gaussian distribution. The cooling beam is then irradiated at a certain angle onto a pyramid-shaped reflector. The pyramid-shaped reflector can change the polarization state of the cooling beam, causing a 180° phase shift between the s-wave and p-wave of the reflected light. This results in multiple mutually orthogonal circularly polarized beams. These circularly polarized beams, together with the anti-Helmholtz coil group, form a pyramid magneto-optical trap, which can cool and trap room-temperature atomic gas in the vacuum cavity, thereby forming cold atom clusters. The second stage, the cold atom guidance stage: the first collimating laser is turned off to release the cold atom clusters generated in the first stage, and the far-infrared detuned guiding light is turned on. The far-infrared detuned guiding light is reflected by the first short-wavelength dichroic mirror after passing through the focusing lens. The reflected far-infrared detuned guiding light is coupled into the hollow anti-resonant fiber. At the same time, the cold atom clusters are loaded into the hollow anti-resonant fiber under the action of the dipole force of the far-infrared detuned guiding light and form cold atom clusters inside the fiber. The third stage, the cold atom detection stage: the far-infrared detuned guiding light is turned off, the resonant detection light is turned on, and the photodetector is used to detect the degree of absorption of the resonant detection light by the cold atoms in the optical fiber, thereby calculating the number of cold atoms guided into the hollow anti-resonant optical fiber.

8. The operating method of the hollow-core optical fiber cold atom guiding device based on a pyramid magneto-optical trap according to claim 7, characterized in that, In the second stage, the power of the pump light and cooling light is gradually reduced, and the detuning of the cooling light is increased. By cooling with polarization gradient, the temperature of the cold atom cluster is further reduced to the μK level, so as to improve the loading efficiency of the cold atom cluster to the guiding light potential trap.

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