Device for improving utilization of atoms in energy level transition and CPT atomic clock

Abstract

The application relates to a device for improving the utilization rate of atoms participating in energy level transition and a CPT atomic clock, and relates to the technical field of CPT atomic clocks. The device comprises a radio frequency part, a first Zeeman coil and a second Zeeman coil. The first Zeeman coil is arranged on one side of an atomic gas chamber, the axial direction of the first Zeeman coil is perpendicular to the direction of a background magnetic field, one end of the first Zeeman coil is connected with the radio frequency part, and the other end of the first Zeeman coil has a preset length. The second Zeeman coil is arranged on the other side opposite to the one side of the atomic gas chamber, the axial direction of the second Zeeman coil is perpendicular to the direction of the background magnetic field, one end of the second Zeeman coil is connected with the other end of the first Zeeman coil, the other end of the second Zeeman coil is connected with the other end of the radio frequency part, and the second Zeeman coil and the first Zeeman coil have the same winding direction and the same number of turns. The radio frequency part applies a preset radio frequency field to the first Zeeman coil and the second Zeeman coil. The device can increase the number of atoms participating in CPT and improve the utilization rate of atoms participating in energy level transition.

Description

Technical Field

[0001] This application relates to the field of CPT atomic clock technology, and more specifically, to a device and a CPT atomic clock for improving the utilization rate of atoms participating in energy level transitions. Background Technology

[0002] Two beams of resonant light irradiate a gaseous alkali metal, such as Figure 1 As shown, when the frequency difference (ω1-ω2) between resonance light 1 and resonance light 2 is the same as the frequency corresponding to the energy difference between the ground state 1 and ground state 2 of the alkali metal, energy level transitions from ground state 1 and ground state 2 to excited states cease. At this time, neither resonance light 1 nor resonance light 2 is absorbed by the alkali metal and is transmitted. This phenomenon is called coherent population trapping (CPT), and atomic clocks developed based on this principle are called CPT atomic clocks.

[0003] Currently, the atomic gas chamber of a CPT atomic clock can be filled with a glass bulb containing rubidium-87 and a certain proportion of mixed gas. A 795nm laser source generated by a vertical cavity surface emission laser (VCSEL) is microwave modulated and then converted into left-handed or right-handed polarized light by a glass slide before entering the sealed bubble and interacting with the alkali metal atomic gas inside the glass bulb. By adjusting the laser wavelength and microwave frequency, CPT coherence can be achieved.

[0004] The transmission spectrum is obtained through a photodetector. The laser wavelength and microwave frequency are modulated by a loop. When the microwave frequency is equal to half of the hyperfine energy level of the alkali metal atom's ground state, the CPT coherence intensity is maximized, and the transmitted light intensity also reaches its maximum. The circuitry within the CPT atomic clock contains two frequency-locking loops. The first loop adjusts the laser wavelength to match the atomic transition wavelength. The second loop uses electro-optic modulation of the microwave source to lock the first-order sideband frequency difference of the laser to the atomic resonance frequency. These two first-order sidebands are used to excite the CPT resonance and lock the crystal oscillator frequency at this frequency, thus achieving the frequency output of the atomic clock.

[0005] The strength of the CPT coherent signal is the main factor determining the output frequency of the CPT atomic clock; the stronger the CPT coherent signal, the better the stability of the CPT atomic clock's output frequency. The desired energy levels (F=1, 2, m) among the multiple energy levels after alkali metal atoms undergo Zeeman splitting are... F The strength of the signal is determined by the proportion of alkali metal atoms (=0).

[0006] For example Figure 2 As shown, circularly polarized light (e.g., right-handed circularly polarized light) is typically used. Irradiating alkali metal atoms increases the number of atoms participating in CPT, thereby effectively increasing the signal strength. However, the applicant of this application has discovered the following problems in the actual development of CPT atomic clock products:

[0007] During the actual interaction between circularly polarized light and alkali metal atoms, some atoms will be pumped to F=2, m F At the Zeeman sublevels of ±2, due to the long lifetimes of ground state 1 and ground state 2, it is difficult for atoms to spontaneously relax and transition to other magneton states, resulting in the ground state magnetic quantum number F=2, m F The population in the ±2 energy states continuously increases, requiring the CPT resonance to be achieved. The atomic population at the energy level will decrease accordingly, thereby weakening the CPT signal strength, which will directly lead to a decrease in the stability of the CPT atomic clock output signal.

[0008] The content of the background section is merely technology known to the public and does not necessarily represent existing technology in the field. Summary of the Invention

[0009] This application aims to provide a device and a CPT atomic clock that improve the utilization rate of atoms participating in energy level transitions, in order to solve the above-mentioned technical problems.

[0010] According to one aspect of this application, an apparatus for improving the utilization rate of atoms participating in energy level transitions is provided. The apparatus is used in a CPT atomic clock, which includes at least an atomic gas cell with a background magnetic field. The apparatus includes a radio frequency (RF) unit, a first Zeeman coil, and a second Zeeman coil. The first Zeeman coil is disposed on one side of the atomic gas cell, and its axis is perpendicular to the direction of the background magnetic field. One end of the first Zeeman coil is connected to the RF unit, and the other end has a predetermined length. The second Zeeman coil is disposed on the other side of the atomic gas cell, opposite to one side of the atomic gas cell. Its axis is perpendicular to the direction of the background magnetic field. One end of the second Zeeman coil is connected to the other end of the first Zeeman coil, and the other end is connected to the other end of the RF unit. The second Zeeman coil and the first Zeeman coil have the same winding direction and the same number of turns. The RF unit applies a predetermined RF field to the first and second Zeeman coils.

[0011] According to some embodiments of this application, the number of coil turns ranges from 20 to 100.

[0012] According to one aspect of this application, a CPT atomic clock is provided. The CPT atomic clock includes the aforementioned apparatus and an atomic gas cell. The CPT atomic clock also includes a base coil, a laser source, and a photodetector. The base coil surrounds the atomic gas cell, providing a base magnetic field for the cell. The laser source is disposed on one side of the atomic gas cell, providing laser light to the cell, with the laser direction being the same as the direction of the base magnetic field. The photodetector is disposed on the side of the atomic gas cell opposite to the laser source, converting the laser light after passing through the atomic gas cell into a photocurrent.

[0013] According to some embodiments of this application, the CPT atomic clock further includes a processing unit. The processing unit determines the actual background magnetic field of the atomic gas cell based on a preset radio frequency field.

[0014] According to some embodiments of this application, the CPT atomic clock also includes a magnetic shielding cylinder. The magnetic shielding cylinder has a cavity, in which a first Zeeman coil, a second Zeeman coil, an atomic gas chamber, and a base coil are disposed, and the magnetic shielding cylinder shields external magnetic fields.

[0015] The technical solution of this application involves setting two identical first and second Zeeman coils perpendicular to the background magnetic field of the atomic gas cell. A preset radio frequency field is applied to the first and second Zeeman coils. Based on the Zeeman effect, a field at a specific frequency of F=2,m can be generated. F =±2 Zeeman sublevels are removed to increase the number of atoms participating in CPT. This can increase the atomic population at the energy levels required for CPT resonance, i.e., increase the utilization rate of atoms participating in energy level transitions, thereby increasing the CPT signal strength and improving the stability of the CPT atomic clock output signal. Attached Figure Description

[0016] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 A schematic diagram of atomic energy level transitions is shown;

[0018] Figure 2 This diagram illustrates the light absorption of the Zeeman sublevel of rubidium-87 atoms under circularly polarized light illumination.

[0019] Figure 3 A schematic diagram showing the layout of a first Zeeman coil and a second Zeeman coil according to an embodiment of this application is provided.

[0020] Figure 4 This diagram illustrates the structure of an apparatus according to an embodiment of the present application.

[0021] Figure 5 A schematic diagram of the structure of a CPT atomic clock according to an embodiment of this application is shown.

[0022] Explanation of reference numerals in the attached figures:

[0023] Device 10;

[0024] First Zeeman coil 11; second Zeeman coil 12; radio frequency section 13.

[0025] CPT Atomic Clock 20;

[0026] Atomic gas chamber 21; background coil 22; laser source 23; photodetector 24; magnetic shielding cylinder 25; laser 26.

[0027] Background magnetic field B. Detailed Implementation

[0028] Exemplary embodiments will now be described more fully with reference to the accompanying drawings. However, these exemplary embodiments can be implemented in many forms and should not be construed as limited to the embodiments set forth herein; rather, they are provided so that this application will be thorough and complete, and will fully convey the concept of the exemplary embodiments to those skilled in the art. The same reference numerals in the drawings denote the same or similar parts, and therefore repeated descriptions of them will be omitted.

[0029] The described features, structures, or characteristics can be combined in any suitable manner in one or more embodiments. Numerous specific details are provided in the following description to give a full understanding of embodiments of this disclosure. However, those skilled in the art will recognize that the technical solutions of this disclosure can be practiced without one or more of these specific details, or other methods, components, materials, devices, etc. In these cases, well-known structures, methods, devices, implementations, materials, or operations will not be shown or described in detail.

[0030] Furthermore, the terms “comprising” and “having”, and any variations thereof, are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or apparatus that includes a series of steps or units is not limited to the steps or units listed, but may optionally include steps or units not listed, or may optionally include other steps or units inherent to such process, method, product, or apparatus.

[0031] The terms "first," "second," etc., in the specification, claims, and accompanying drawings of this application are used to distinguish different objects, not to describe a specific order.

[0032] The technical solutions of this application will be clearly and completely described below with reference to the accompanying drawings of the embodiments. Obviously, the described embodiments are only some, not all, of the embodiments of this application. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0033] The English terms used in this application, their full English names, and their corresponding Chinese definitions are as follows:

[0034] CPT, Coherent Population Trapping.

[0035] Total angular momentum quantum number.

[0036] magnetic quantum number.

[0037] EIT, Electromagnetically Induced Transparency, is a direct manifestation of the CPT phenomenon in optical transmission.

[0038] Figure 2 middle, This indicates right-handed circularly polarized light. The ground state of an alkali metal atom (such as rubidium-87) splits into two hyperfine levels: F=1 and F=2.

[0039] This indicates an excited state with a hyperfine level F'=2.

[0040] m F This indicates that each hyperfine level will further split into multiple magneton levels under a magnetic field, determined by the magnetic quantum number m. F The labels (e.g., -2, -1, 0, 1, 2) are used to indicate these energy levels. The vertical lines in the diagram represent these energy levels.

[0041] V hf =6.835 GHz represents the hyperfine level split between the ground states F=1 and F=2, which is the reference frequency of the rubidium-87 atomic clock.

[0042] b-transitions, for example, in right-handed circularly polarized light. Under the influence of the action, alkali metal atoms move from m F =0 Excited to F'=2, m F =1, etc. d-transitions, for example, in right-handed circularly polarized light. Under the influence of the action, alkali metal atoms move from m F=-1 excites to F'=2, m F =0, etc.

[0043] According to one aspect of this application, an apparatus 10 is provided to improve the utilization rate of atoms participating in energy level transitions. The apparatus 10 is used in a CPT atomic clock 20, which includes at least an atomic gas chamber 21, the atomic gas chamber 21 being provided with a background magnetic field B. The atomic gas chamber 21 can be an alkali metal atomic gas chamber.

[0044] See Figure 3 The device 10 may include a radio frequency unit 13 ( Figure 3 (not shown in the image), first Zeeman coil 11 and second Zeeman coil 12.

[0045] A first Zeeman coil 11 is disposed on one side of the atomic gas chamber 21, and the axis of the first Zeeman coil 11 is perpendicular to the direction of the background magnetic field B. One end of the first Zeeman coil 11 is connected to the radio frequency unit 13, and the other end of the first Zeeman coil 11 has a preset length. The preset length can be set according to the length of the atomic gas chamber 21. For example, the other end of the first Zeeman coil 11 can be extended by a wire of the preset length to connect to the second Zeeman coil 12. The preset length can be slightly larger than the length of the atomic gas chamber 21, but should not be too long to avoid bending of the wire.

[0046] The second Zeeman coil 12 is disposed on the opposite side of the atomic gas chamber 21, opposite one side of the atomic gas chamber 21, and the axis of the second Zeeman coil 12 is perpendicular to the direction of the background magnetic field B. For example, the second Zeeman coil 12 can be disposed opposite to the first Zeeman coil 11. The diameters of the first Zeeman coil 11 and the second Zeeman coil 12 can be set according to the width of the atomic gas chamber 21.

[0047] One end of the second Zeeman coil 12 is connected to the other end of the first Zeeman coil 11, and the other end of the second Zeeman coil 12 is connected to the other end of the radio frequency unit 13.

[0048] The second Zeeman coil 12 has the same winding direction and the same number of turns as the first Zeeman coil 11. Both the first Zeeman coil 11 and the second Zeeman coil 12 can be wound clockwise or counterclockwise. The first Zeeman coil 11 and the second Zeeman coil 12 have the same winding direction and the same number of turns.

[0049] For example, the first Zeeman coil 11 and the second Zeeman coil 12 can be wound using the same enameled wire. One end of the enameled wire starts from the first coil (e.g., the first Zeeman coil 11), and after winding a certain number of turns, a predetermined length is left before winding the second coil (e.g., the second Zeeman coil 12). After winding, the other end of the enameled wire exits from the second coil. The first Zeeman coil 11 and the second Zeeman coil 12 can be attached to both sides of the base magnetic field cylinder. The axial direction of the first Zeeman coil 11 and the axial direction of the second Zeeman coil 12 are both perpendicular to the direction of the base magnetic field B. Both ends of the wire are connected to the radio frequency section. The base magnetic field cylinder can be a device that surrounds the alkali metal atom gas cell 21 with base coils 22 to apply a base magnetic field to the alkali metal atom gas cell.

[0050] The radio frequency unit 13 applies a preset radio frequency field to the first Zeeman coil 11 and the second Zeeman coil 12. The sweep range, sweep resolution, and sweep intensity of the preset radio frequency field can be set by a program. Due to the Zeeman effect, Zeeman transitions (F=1, 2, Δm) between hyperfine magnetic energy levels of the ground state of alkali metal atoms can be realized at certain specific frequencies (e.g., frequencies near the theoretical values ​​of atomic Zeeman energy levels). F =±1, where F represents the total angular momentum quantum number, m F (representing the magnetic quantum number), thus allowing the state to be at F=2, m at a certain frequency (e.g., near the theoretical value of the Zeeman level of an atom). F =±2 Zeeman sublevels are removed to increase the number of atoms participating in CPT.

[0051] Through the above embodiments, the technical solution of this application can achieve the following: by setting two identical first Zeeman coils and second Zeeman coils in the direction perpendicular to the local magnetic field of the atomic gas cell, and applying a preset radio frequency field to the first Zeeman coils and second Zeeman coils, a specific frequency can be generated based on the Zeeman effect, where F=2, m F =±2 Zeeman sublevels are removed to increase the number of atoms participating in CPT. This increases the atomic population at the sublevels required for CPT resonance, i.e., increases the utilization rate of atoms participating in sublevel transitions, thereby improving the CPT signal strength and the stability of the CPT atomic clock output signal.

[0052] Optionally, the number of coil turns ranges from 20 to 100. The number of coil turns determines the magnitude of the radio frequency field at a given current. The number of coil turns can be set according to the dimensions of the CPT atomic clock.

[0053] For example, see Figure 4The conductors of the first Zeeman coil 11 and the second Zeeman coil 12 are made of high-conductivity copper enameled wire. The radius of the first Zeeman coil 11 and the second Zeeman coil 12 is 4mm, the number of turns of the first Zeeman coil 11 and the second Zeeman coil 12 is 20 turns, the preset length of the connection between the first Zeeman coil 11 and the second Zeeman coil 12 is 10mm, and the reserved length of the terminal of the first Zeeman coil 11 and the terminal of the second Zeeman coil 12 is 10mm.

[0054] After the winding is completed, the 20 turns of the first Zeeman coil 11 are glued together with optical AB glue, and the 20 turns of the second Zeeman coil 12 are glued together with optical AB glue to prevent them from becoming tangled.

[0055] After the adhesive cures, the first Zeeman coil 11 and the second Zeeman coil 12 are attached to both sides of the base magnetic field cylinder. The axial direction of the first Zeeman coil 11 and the axial direction of the second Zeeman coil 12 are both perpendicular to the direction of the base magnetic field B. The center of the first Zeeman coil 11 and the center of the second Zeeman coil 12 coincide with the center of the side of the base magnetic field cylinder. The two terminals are soldered to the radio frequency section 13 (e.g., radio frequency circuit module). The electrical assembly is completed according to the CPT atomic clock assembly process.

[0056] When the first Zeeman coil 11 and the second Zeeman coil 12 are working, the center frequency of the preset radio frequency field output by the radio frequency unit 13 is set to 7000Hz, the scanning bandwidth is 100Hz, and the frequency resolution is 1Hz. All of the above parameters are adjustable.

[0057] The theoretical value of the background magnetic field is set to 1000nT. During the preset radio frequency field sweep process, the CPT atomic clock output power reaches its minimum value at 7011Hz, and the corresponding EIT signal becomes stronger, that is, the CPT signal strength becomes stronger.

[0058] The technical solution of this application can effectively increase the number of atoms participating in CPT by applying a preset radio frequency field.

[0059] According to one aspect of this application, a CPT atomic clock 20 is provided. See also Figure 5 The CPT atomic clock 20 includes the device 10 and atomic gas chamber 21 as described above. The CPT atomic clock 20 also includes a base coil 22, a laser source 23 and a photodetector 24.

[0060] The base coil 22 surrounds the atomic gas chamber 21, providing a base magnetic field B for the atomic gas chamber 21. A preset current can be applied to the base coil 22 by a constant current source to provide the base magnetic field B for the atomic gas chamber 21. The magnitude of the constant current source can be on the order of hundreds of microamps (μA).

[0061] Laser source 23 is located on one side of atomic gas cell 21 to provide laser 26 to atomic gas cell 21. The direction of laser 26 is the same as the direction of the background magnetic field B.

[0062] The photoelectric detection unit 24 is located on the side of the atomic gas chamber 21 opposite to the laser source 23, and converts the laser 26 after passing through the atomic gas chamber 21 into photocurrent.

[0063] The technical solution of this application can be achieved by setting two identical first Zeeman coils and second Zeeman coils in the direction perpendicular to the local magnetic field of the atomic gas cell, and applying a preset radio frequency field to the first Zeeman coils and second Zeeman coils. Based on the Zeeman effect, a field with F=2,m can be generated at a specific frequency. F Atoms are removed from the ±2 Zeeman sublevels to increase the number of atoms participating in CPT. This increases the atomic population at the sublevels required for CPT resonance, thereby improving the CPT signal strength and the stability of the CPT atomic clock output signal.

[0064] The applicant of this application discovered that, in the actual development of CPT atomic clock products, there is a problem that, due to the compact internal structure and small size of the CPT atomic clock, it is impossible to directly measure the magnitude of the magnetic field inside the atomic gas chamber. Therefore, it is impossible to confirm whether the internal functional modules generate stray magnetic fields during operation, affecting the formation of a stable, single-orientation magnetic field environment inside the atomic gas chamber.

[0065] Optionally, the CPT atomic clock 20 also includes a processing unit (not shown in the figure). The processing unit can determine the actual background magnetic field of the atomic gas cell based on a preset radio frequency field.

[0066] According to the example embodiment, the processing unit can determine the actual background magnetic field of the atomic gas cell based on the specific frequency point (e.g., the frequency point near the theoretical value of the atomic Zeeman energy level) that realizes the Zeeman transition between the hyperfine magnetic energy levels of the ground state of alkali metal atoms, and the quantitative relationship between the Zeeman energy level frequency and the radio frequency field.

[0067] For example, the processing unit can determine the actual background magnetic field of the atomic gas chamber using the following formula:

[0068] ;

[0069] in, The actual background magnetic field (nT); f The specific frequency (Hz) for Zeeman transitions between hyperfine magnetic energy levels in the ground state of alkali metal atoms can be obtained by measurement equipment; It is the gyromagnetic ratio. Hz / nT.

[0070] For example, at a specific frequency of 7011Hz, the control unit calculated the actual background magnetic field to be 1002nT, which is consistent with the theoretical value of 1000nT, thus proving that the internal magnetic field environment of the atomic clock meets the design expectations.

[0071] Through the above embodiments, the technical solution of this application can determine the actual background magnetic field of the atomic gas cell by preset radio frequency field. By comparing the actual background magnetic field with the theoretical value of the background magnetic field, it can be determined whether each functional module inside the CPT atomic clock generates stray magnetic field when working, which can provide a basis for forming a stable and unidirectional magnetic field environment inside the atomic gas cell.

[0072] Optionally, see Figure 5 The CPT atomic clock 20 also includes a magnetic shielding cylinder 25. The magnetic shielding cylinder 25 has a cavity in which a first Zeeman coil 11, a second Zeeman coil 12, an atomic gas chamber 21 and a base coil 22 are disposed. The magnetic shielding cylinder 25 shields the external magnetic field.

[0073] Finally, it should be noted that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions of the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A device for improving the utilization rate of atoms participating in energy level transitions, characterized in that, The device is used in a CPT atomic clock, the CPT atomic clock comprising at least an atomic gas cell, the atomic gas cell being provided with a background magnetic field, the device comprising: Radio frequency section; A first Zeeman coil is disposed on one side of the atomic gas cell, and the axis of the first Zeeman coil is perpendicular to the direction of the background magnetic field. One end of the first Zeeman coil is connected to the radio frequency unit, and the other end of the first Zeeman coil has a preset length. The second Zeeman coil is disposed on the other side of the atomic gas cell, opposite to one side of the atomic gas cell. The axis of the second Zeeman coil is perpendicular to the direction of the background magnetic field. One end of the second Zeeman coil is connected to the other end of the first Zeeman coil, and the other end of the second Zeeman coil is connected to the other end of the radio frequency section. The second Zeeman coil and the first Zeeman coil have the same winding direction and the same number of coil turns. The radio frequency unit applies a preset radio frequency field to the first Zeeman coil and the second Zeeman coil.

2. The apparatus according to claim 1, characterized in that, The number of turns of the coil ranges from 20 to 100.

3. A CPT atomic clock, characterized in that, Including the apparatus and atomic gas chamber as described in any one of claims 1-2, the CPT atomic clock further includes: The base coil surrounds the atomic gas cell to provide the base magnetic field for the atomic gas cell; A laser source is disposed on one side of the atomic gas cell to provide laser light to the atomic gas cell, and the direction of the laser light is the same as the direction of the background magnetic field. The photoelectric detection unit is located on the side of the atomic gas chamber opposite to the laser source, and converts the laser light after passing through the atomic gas chamber into photocurrent.

4. The CPT atomic clock according to claim 3, characterized in that, The CPT atomic clock also includes: The processing unit determines the actual background magnetic field of the atomic gas chamber based on the preset radio frequency field.

5. The CPT atomic clock according to claim 3, characterized in that, The CPT atomic clock also includes: A magnetic shielding cylinder has a cavity in which the first Zeeman coil, the second Zeeman coil, the atomic gas chamber, and the background coil are disposed. The magnetic shielding cylinder shields external magnetic fields.

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