A method for measuring second-order zeeman shift of an atomic fountain

Abstract

The application discloses a method for measuring second-order Zeeman frequency shift of an atomic fountain, and the method comprises the following steps: acquiring an external axial magnetic field variation through a measuring device installed on a cesium atomic fountain clock; when the external axial magnetic field variation does not exceed a variation threshold, the cesium atomic fountain clock does not need to be interrupted, a coarse measurement of a center frequency of a current magnetic-sensitive Ramsey transition fringe is realized according to the magnetic field variation and a shielding factor, and a corresponding second-order Zeeman frequency shift is obtained; when the external axial magnetic field variation exceeds the variation threshold, the cesium atomic fountain clock is interrupted, and an accurate measurement of the center frequency of the current magnetic-sensitive Ramsey transition fringe is realized by using a magnetic-sensitive Ramsey transition method, and a corresponding second-order Zeeman frequency shift is obtained. The application can realize real-time, rapid and accurate measurement of the second-order Zeeman frequency shift, and is helpful for reducing a deviation between the cesium atomic fountain clock and an international atomic time, improving a monthly operation rate of the cesium atomic fountain clock, and improving a position of the cesium atomic fountain clock in international atomic time calibration.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of atomic fountain clocks, and particularly relates to a method for measuring second-order Zeeman frequency shift of an atomic fountain. BACKGROUND

[0002] International atomic time is an integral time scale with the time unit of international system of units "second", and is adjusted by "leap second" to form international standard time-coordinated universal time. The time unit "second" is defined as "second", and the symbol is s, which is the unit of time in the international system of units. Its definition is to take the frequency of the transition between the hyperfine energy levels of cesium-133 atoms in the absence of interference, that is, the cesium frequency , which is a fixed value of 9192631770 Hz, and its unit Hz is equal to s -1 . The cesium atomic fountain clock is a time-frequency reference device that directly reproduces this definition, has the highest accuracy performance at present, and is used to calibrate other types of time-keeping atomic clocks. In the process of calibrating the free atomic time to generate international atomic time, the frequency deviation, frequency stability, frequency uncertainty and monthly running rate of the cesium atomic fountain clock and the reference hydrogen clock are the main performance indicators. In order to accurately calculate the frequency deviation of the cesium atomic fountain clock and the reference hydrogen clock, it is necessary to deduct various frequency shifts of the cesium atoms due to the influence of environmental physical effects and the motion state of the cesium atoms, mainly including cold atom collision frequency shift, second-order Zeeman frequency shift, blackbody radiation frequency shift, gravitational redshift and the like.

[0003] Among them, the cold atom collision frequency shift and the blackbody radiation frequency shift are obtained by real-time measurement during the operation of the cesium atomic fountain clock, the gravitational redshift is a fixed value related to the altitude of the cesium atomic fountain clock, and the second-order Zeeman frequency shift will change due to the influence of the geomagnetic field. Generally, the second-order Zeeman frequency shift needs to be evaluated by using the traditional measurement method at the end of each operation cycle (one month) of the cesium atomic fountain clock. The traditional method mainly includes: magnetic sensitive Ramsey transition method, low frequency transition method and Rabi transition method. The atomic |3, 1>→|4, 1> Ramsey transition fringe center frequency is obtained by gradually increasing the atomic upward height from the upper end of the excitation cavity to the conventional operation height, so as to calculate the second-order Zeeman frequency shift.

[0004] The measurement process of the above traditional method is relatively complicated, and a complicated experimental device needs to be built, and too many system parameters need to be adjusted. The measurement is time-consuming, the average monthly running rate of the cesium atomic fountain clock is about 90%, and the measurement of the second-order Zeeman frequency shift occupies 1.7%, which will occupy about half a day of operation time of the cesium atomic fountain clock, and will affect the monthly running rate of the cesium atomic fountain clock. In addition, the second-order Zeeman frequency shift cannot be deducted in real time in the measurement of the frequency deviation of the cesium atomic fountain clock and the reference hydrogen clock, which will bring certain error to the subsequent measurement. SUMMARY

[0005] In order to solve the above problems in the prior art, the application provides a method for measuring second-order Zeeman frequency shift of an atomic fountain.

[0006] The application provides a method for measuring second-order Zeeman frequency shift of an atomic fountain, comprising the following steps:

[0007] A measuring device is installed on a cesium atomic fountain clock, and the measuring device is used to measure the external axial magnetic field data of a magnetic shielding device of the cesium atomic fountain clock.

[0008] During the operation of the cesium atomic fountain clock, at a preset sampling time, the external axial magnetic field variation of the magnetic shielding device is determined according to the obtained external axial magnetic field data, and it is judged whether the external axial magnetic field variation exceeds a variation threshold.

[0009] If the external axial magnetic field variation does not exceed the variation threshold, the center frequency shift of a magnetic-sensitive Ramsey transition fringe and the current center frequency of the magnetic-sensitive Ramsey transition fringe are obtained according to the external axial magnetic field variation, and the corresponding second-order Zeeman frequency shift is calculated according to the current center frequency of the magnetic-sensitive Ramsey transition fringe.

[0010] If the external axial magnetic field variation exceeds the variation threshold, the operation of the cesium atomic fountain clock is interrupted, the current magnetic-sensitive Ramsey transition fringe is measured by using a magnetic-sensitive Ramsey transition method, the current magnetic-sensitive Ramsey transition fringe is compared with the previous magnetic-sensitive Ramsey transition fringe, the center frequency of the current magnetic-sensitive Ramsey transition fringe is determined, and the corresponding second-order Zeeman frequency shift is calculated according to the center frequency of the current magnetic-sensitive Ramsey transition fringe.

[0011] In an embodiment of the application, the cesium atomic fountain clock comprises a magneto-optical trap, a state selection cavity, a detector and a fluorescence collection system, the magnetic shielding device and an excitation cavity.

[0012] The magneto-optical trap is used to vertically upwardly project a cold atom group according to a set initial speed and time interval.

[0013] The state selection cavity, the detector and the fluorescence collection system, the magnetic shielding device and the excitation cavity are sequentially arranged from bottom to top along the running path of the cold atom group.

[0014] In an embodiment of the application, the measuring device comprises a single-axis magnetometer probe and a single-axis magnetometer connected thereto, the single-axis magnetometer probe is installed at the outer top of the magnetic shielding device and close to the central axis of the magnetic shielding device, and the installation direction of the single-axis magnetometer probe is parallel to the central axis of the magnetic shielding device.

[0015] In one embodiment of the present application, the sampling time is consistent with the operation period of the cesium fountain clock.

[0016] In one embodiment of the present application, the variation threshold is 1400 nT.

[0017] In one embodiment of the present application, the center frequency shift of the magnetic sensitive Ramsey transition stripe and the current center frequency of the magnetic sensitive Ramsey transition stripe are obtained according to the variation of the external axial magnetic field, comprising:

[0018] The variation of the internal axial magnetic field of the magnetic shielding device is calculated according to the variation of the external axial magnetic field, and the calculation formula is as follows:

[0019] ;

[0020] In the formula, is the variation of the internal axial magnetic field, is the variation of the external axial magnetic field, is the axial shielding factor of the magnetic shielding device;

[0021] The center frequency shift of the magnetic sensitive Ramsey transition stripe is calculated according to the variation of the internal axial magnetic field, and the calculation formula is as follows:

[0022] ;

[0023] In the formula, is the center frequency shift of the magnetic sensitive Ramsey transition stripe;

[0024] The current center frequency of the magnetic sensitive Ramsey transition stripe is obtained according to the center frequency shift and the center frequency of the previous magnetic sensitive Ramsey transition stripe.

[0025] In one embodiment of the present application, the current magnetic sensitive Ramsey transition stripe is measured by the magnetic sensitive Ramsey transition method, comprising:

[0026] The magnetic optical trap is adjusted to have an initial velocity of The cold atom group is vertically upward projected every 2 seconds;

[0027] The microwave of the state selection cavity is adjusted to have a pulse of transition frequency, so that the cold atom group is in a magnetic sensitive state after passing through the state selection cavity; ;

[0028] The excitation microwave frequency of the excitation cavity is scanned according to the preset scanning condition;

[0029] The time-of-flight signal intensity of the falling cold atom clusters at each excitation microwave frequency is measured and recorded using the detector and fluorescence collection system to obtain the current magnetically sensitive Ramsey transition fringes.

[0030] In one embodiment of the present invention, the scanning conditions include: the scanning range is , The center frequency of the previous magnetic Ramsey transition fringe is 0.2 Hz, and the frequency scan step is 0.2 Hz.

[0031] In one embodiment of the present invention, the formula for calculating the second-order Zeeman frequency shift is as follows:

[0032] ;

[0033] In the formula, This represents the relative value of the second-order Zeeman frequency shift. This indicates that there is no interference with Zhong Yueqian. frequency, Represents the absolute value of the second-order Zeeman shift. This represents the center frequency of the magnetically sensitive Ramsey transition fringe.

[0034] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0035] The present invention provides a method for measuring the second-order Zeeman shift of an atomic fountain clock. This method uses a measuring device installed on a cesium atomic fountain clock to acquire the change in the external axial magnetic field. When the change in the external axial magnetic field does not exceed a threshold, the operation of the cesium atomic fountain clock does not need to be interrupted. Based on the magnetic field change and the shielding factor, a coarse measurement of the center frequency of the current magnetically sensitive Ramsey transition fringes is achieved, thus obtaining the corresponding second-order Zeeman shift. When the change in the external axial magnetic field exceeds the threshold, the operation of the cesium atomic fountain clock is interrupted. The current magnetically sensitive Ramsey transition fringes are measured using the magnetically sensitive Ramsey transition method, and compared with the previous magnetically sensitive Ramsey transition fringes to achieve a precise measurement of the center frequency of the current magnetically sensitive Ramsey transition fringes, thus obtaining the corresponding second-order Zeeman shift. Compared with traditional measurement methods, this invention uses a simpler measuring device, is easier to operate, and has a shorter measurement time. It can measure the second-order Zeeman shift in real-time, quickly, and accurately, which greatly helps to reduce the deviation between the cesium atomic fountain clock and International Atomic Time, improve the monthly operating rate of the cesium atomic fountain clock, and enhance the status of the cesium atomic fountain clock in International Atomic Time calibration.

[0036] The above description is merely an overview of the technical solution of the present invention. In order to better understand the technical means of the present invention and to implement it in accordance with the contents of the specification, and to make the above and other objects, features and advantages of the present invention more apparent and understandable, preferred embodiments are described in detail below with reference to the accompanying drawings. Attached Figure Description

[0037] Figure 1 This is a flowchart illustrating a method for measuring the second-order Zeeman shift of an atomic fountain according to an embodiment of the present invention;

[0038] Figure 2 This is a schematic diagram of the structure of the cesium atomic fountain clock with the installation and measuring device provided in an embodiment of the present invention;

[0039] Figure 3 This is a schematic diagram of the external axial magnetic field data of the magnetic shielding device during the sampling time provided in the embodiment of the present invention;

[0040] Figure 4 This is a schematic diagram of the magnetic Ramsey transition fringes corresponding to the change in the external axial magnetic field not exceeding the change threshold provided in the embodiments of the present invention;

[0041] Figure 5 This is a schematic diagram of magnetic Ramsey transition fringes obtained using the magnetic Ramsey transition method according to an embodiment of the present invention.

[0042] Icons: 1-Magneto-optical trap; 2-Cold atom cluster; 3-Selective cavity; 4-Detector and fluorescence collection system; 5-Magnetic shielding device; 6-Excitation cavity; 7-Single-axis magnetometer probe; 8-Single-axis magnetometer; 9-Computer. Detailed Implementation

[0043] To further illustrate the technical means and effects adopted by the present invention to achieve the intended purpose, the following describes in detail a method for measuring the second-order Zeeman shift of an atomic fountain according to the present invention, in conjunction with the accompanying drawings and specific embodiments.

[0044] The foregoing and other technical contents, features, and effects of the present invention will be clearly presented in the following detailed description of specific embodiments in conjunction with the accompanying drawings. Through the description of the specific embodiments, a more in-depth and concrete understanding can be gained of the technical means and effects adopted by the present invention to achieve its intended purpose. However, the accompanying drawings are for reference and illustration only and are not intended to limit the technical solutions of the present invention.

[0045] This invention provides a method for measuring the second-order Zeeman shift of an atomic fountain. Please refer to [link to relevant documentation]. Figure 1 , Figure 1 This is a flowchart illustrating a method for measuring the second-order Zeeman shift of an atomic fountain according to an embodiment of the present invention, as shown below. Figure 1 As shown, the method for measuring the second-order Zeeman shift of an atomic fountain in this embodiment may include the following steps:

[0046] Step 1: Install a measuring device on the cesium atomic fountain clock. The measuring device is used to measure the external axial magnetic field data of the magnetic shielding device of the cesium atomic fountain clock.

[0047] Please see Figure 2 , Figure 2 This is a schematic diagram of the cesium atomic fountain clock with the installation and measuring device provided in an embodiment of the present invention. Figure 2 As shown, in this embodiment, the cesium atom fountain clock includes: a magneto-optical trap 1, a state selection cavity 3, a detector and fluorescence collection system 4, a magnetic shielding device 5, and an excitation cavity 6; wherein, the magneto-optical trap 1 is used to vertically and upwardly project cold atom clusters 2 according to a set initial velocity and time interval; the state selection cavity 3, the detector and fluorescence collection system 4, the magnetic shielding device 5, and the excitation cavity 6 are arranged sequentially from bottom to top along the running path of the cold atom clusters 2.

[0048] During normal operation, the cesium atomic fountain clock generates excitation atoms within the selected cavity 3. Leap Microwave, the excitation cavity 6 is for excitation of atomic generation Leap microwave.

[0049] In this embodiment, the measuring device includes a connected single-axis magnetometer probe 7 and a single-axis magnetometer 8. The single-axis magnetometer probe 7 is installed on the top outer side of the magnetic shielding device 5 near the central axis of the magnetic shielding device 5, and the installation direction of the single-axis magnetometer probe 7 is parallel to the central axis of the magnetic shielding device 5.

[0050] Understandably, the external axial magnetic field data measured by the single-axis magnetometer 8 can be transmitted and recorded in real time by the computer 9 connected to it.

[0051] Step 2: During the operation of the cesium atomic fountain clock, at the preset sampling time, the change in the external axial magnetic field of the magnetic shielding device is determined based on the acquired external axial magnetic field data, and it is determined whether the change in the external axial magnetic field exceeds the change threshold.

[0052] In this embodiment, the sampling time is consistent with the operating cycle of the cesium atomic fountain clock, which is 4 seconds. A schematic diagram of the external axial magnetic field data of the magnetic shielding device during the sampling time is shown below. Figure 3 As shown.

[0053] The full width at half maximum (FWHM) of the Ramsey transition spectral line at the normal operating height of the cesium atomic fountain clock is 1 Hz. When the center frequency of the magnetically sensitive Ramsey transition fringe shifts by more than 1 Hz, it becomes difficult to discern the direction of the shift.

[0054] The relationship between the change in center frequency and the change in the inner axial magnetic field of the magnetic shielding device is shown in the following formula:

[0055] ,

[0056] In the formula, The shift in the center frequency of the magnetically sensitive Ramsey transition fringes. This represents the change in the axial magnetic field.

[0057] Therefore, based on the relationship between the change in center frequency and the change in the inner axial magnetic field of the magnetic shielding device, it can be obtained that when the center frequency shift is 1Hz, the change in the inner axial magnetic field is 0.14nT.

[0058] Axial shielding factor of magnetic shielding device Approximately 10 4 Therefore, according to the relationship between the axial shielding factor of the magnetic shielding device and the inner and outer axial magnetic fields... , This represents the change in the inner axial magnetic field. The change in the outer axial magnetic field is given by the value of 1 Hz. It can be calculated that when the center frequency shift is 1 Hz, the change in the outer axial magnetic field is 1400 nT.

[0059] Therefore, in this embodiment, the change threshold is 1400nT.

[0060] Understandably, since the radial shielding factor of the magnetic shielding device is at least one order of magnitude higher than the axial shielding factor, the variation of the radial magnetic field is not considered here.

[0061] Step 3: If the change in the outer axial magnetic field does not exceed the change threshold, then obtain the center frequency shift of the magnetic Ramsey transition fringe and the current center frequency of the magnetic Ramsey transition fringe based on the change in the outer axial magnetic field. Calculate the corresponding second-order Zeeman frequency shift based on the current center frequency of the magnetic Ramsey transition fringe.

[0062] When the change in the outer axial magnetic field is less than 1400 nT, the magnetically sensitive Ramsey transition fringes are as follows: Figure 4 As shown in the figure, when the center frequency change of the magnetically sensitive Ramsey transition fringes is less than 1 Hz, it is easy to determine the direction and magnitude of the center frequency shift. Therefore, in this embodiment, without interrupting the operation of the cesium atomic fountain clock, the center frequency of the magnetically sensitive Ramsey transition fringes can be roughly measured based on the magnetic field change and the shielding factor, thereby obtaining the second-order Zeeman frequency shift.

[0063] Specifically, obtaining the shift in the center frequency of the magnetically sensitive Ramsey transition fringes and the current center frequency of the magnetically sensitive Ramsey transition fringes based on the change in the external axial magnetic field can include the following steps:

[0064] Step 3.1: Calculate the change in the inner axial magnetic field of the magnetic shielding device based on the change in the outer axial magnetic field. The calculation formula is as follows:

[0065] ;

[0066] In the formula, This represents the change in the inner axial magnetic field. This represents the change in the axial magnetic field. The axial shielding factor of the magnetic shielding device;

[0067] Step 3.2: Calculate the shift in the center frequency of the magnetically sensitive Ramsey transition fringes based on the change in the inner axial magnetic field. The calculation formula is as follows:

[0068] ;

[0069] In the formula, The shift in the center frequency of the magnetically sensitive Ramsey transition fringes;

[0070] Step 3.3: Based on the center frequency shift and the center frequency of the previous magnetic Ramsey transition fringe, obtain the current center frequency of the magnetic Ramsey transition fringe.

[0071] In this embodiment, after obtaining the center frequency of the current magnetically sensitive Ramsey transition fringes, the corresponding second-order Zeeman frequency shift can be calculated using the formula for calculating the second-order Zeeman frequency shift, wherein...

[0072] The formula for calculating the second-order Zeeman frequency shift is as follows:

[0073] ;

[0074] In the formula, This represents the relative value of the second-order Zeeman frequency shift. This indicates that there is no interference with Zhong Yueqian. frequency, Represents the absolute value of the second-order Zeeman shift. This represents the center frequency of the magnetically sensitive Ramsey transition fringe.

[0075] Step 4: If the change in the axial magnetic field exceeds the change threshold, the operation of the cesium atomic fountain clock is interrupted. The current magnetic Ramsey transition fringe is measured using the magnetic Ramsey transition method. The current magnetic Ramsey transition fringe is compared with the previous magnetic Ramsey transition fringe to determine the center frequency of the current magnetic Ramsey transition fringe. The corresponding second-order Zeeman frequency shift is calculated based on the center frequency of the current magnetic Ramsey transition fringe.

[0076] When measuring the second-order Zeeman frequency shift using the magnetic Ramsey transition method, the microwave parameters in the selected cavity 3 are adjusted to excite atom generation. Leap The microwave parameters within the excitation cavity 6 are adjusted to excite atomic generation. Leap pulse.

[0077] Specifically, the current magnetic Ramsey transition fringes are measured using the magnetic Ramsey transition method, including the following steps:

[0078] S1: The magneto-optical trap, with an initial velocity of... Cold atomic clusters are launched vertically upwards every 2 seconds;

[0079] S2: Adjust the microwave in the selected cavity to excite atom generation. Leap A pulse is applied so that the cold atom cluster is in a magnetically sensitive state after passing through the selected cavity. ;

[0080] S3: Scan the excitation microwave frequency of the excitation cavity according to the preset scanning conditions;

[0081] In this embodiment, the scanning conditions include: the scanning range is Typically, the center frequency variation range of magnetically sensitive Ramsey transition fringes is less than ±2 Hz. The frequency is the center frequency of the previous magnetic Ramsey transition fringe, with a frequency scan step of 0.2 Hz. The probability of magnetic Ramsey transitions in cold atom clusters changes with the change of the excitation microwave frequency.

[0082] S4: The flight time signal intensity of the falling cold atom clusters at each excitation microwave frequency is measured and recorded using a detector and fluorescence collection system to obtain the current magnetically sensitive Ramsey transition fringes.

[0083] A schematic diagram of magnetic Ramsey transition fringes obtained using the magnetic Ramsey transition method is shown below. Figure 5 As shown. In this embodiment, the shift in the center frequency of the magnetic Ramsey transition fringe can be obtained by comparing the current magnetic Ramsey transition fringe with the previous one. Then, the center frequency of the current magnetic Ramsey transition fringe can be obtained based on the center frequency of the previous fringe. Finally, the corresponding second-order Zeeman frequency shift can be calculated using the formula for calculating the second-order Zeeman frequency shift. The formula for calculating the second-order Zeeman frequency shift is as follows:

[0084] ;

[0085] In the formula, This represents the relative value of the second-order Zeeman frequency shift. This indicates that there is no interference with Zhong Yueqian. frequency, Represents the absolute value of the second-order Zeeman shift. This represents the center frequency of the magnetically sensitive Ramsey transition fringe.

[0086] In this embodiment, the measurement time for the second-order Zeeman frequency shift using the magnetic Ramsey transition method is 40 seconds, which is negligible in the monthly measurement cycle. After the magnetic Ramsey transition method measurement is completed, the cesium atomic fountain clock resumes normal operation, and the measuring device continues to monitor changes in the magnetic field.

[0087] It should be noted that the second-order Zeeman frequency shift can be measured in real time using the method of this invention. Therefore, when calculating the frequency deviation between the cesium atomic fountain clock and the reference hydrogen clock for the current month, the second-order Zeeman frequency shift for the corresponding time period can be deducted in real time.

[0088] The method for measuring the second-order Zeeman frequency shift of the cesium atomic fountain clock of the present invention is simpler in terms of measuring device, operation process, and measurement time compared with traditional measurement methods. It can measure the second-order Zeeman frequency shift in real time, quickly and accurately, which is of great help to reduce the deviation between the cesium atomic fountain clock and international atomic time, improve the monthly operating rate of the cesium atomic fountain clock, and enhance the status of the cesium atomic fountain clock in international atomic time calibration.

[0089] It should be noted that, in this document, relational terms such as "first" and "second" are used merely to distinguish one entity or operation from another, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Furthermore, the terms "comprising," "including," or any other variations are intended to cover non-exclusive inclusion, such that an article or device comprising a list of elements includes not only those elements but also other elements not expressly listed. Without further limitations, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the article or device comprising said element. Terms such as "connected" or "linked" are not limited to physical or mechanical connections but can include electrical connections, whether direct or indirect. The orientations or positional relationships indicated by terms such as "upper," "lower," "left," and "right" are based on the orientations or positional relationships shown in the accompanying drawings and are used only for the convenience of describing the invention and for simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as limiting the invention.

[0090] In the description of this specification, the references to terms such as "one embodiment," "some embodiments," "example," "specific example," or "some examples," etc., indicate that a specific feature or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the present invention. In this specification, the illustrative expressions of the above terms do not necessarily refer to the same embodiment or example. Furthermore, the specific features or characteristics described may be combined in any suitable manner in one or more embodiments or examples. In addition, those skilled in the art can combine and integrate the different embodiments or examples described in this specification.

[0091] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A method for measuring the second-order Zeeman shift of an atomic fountain, characterized in that, include: A measuring device is installed on the cesium atomic fountain clock, the measuring device being used to measure the external axial magnetic field data of the magnetic shielding device of the cesium atomic fountain clock; During the operation of the cesium atomic fountain clock, at a preset sampling time, the change in the external axial magnetic field of the magnetic shielding device is determined based on the acquired external axial magnetic field data, and it is determined whether the change in the external axial magnetic field exceeds the change threshold. If the change in the outer axial magnetic field does not exceed the change threshold, then the center frequency shift of the magnetically sensitive Ramsey transition fringe and the current center frequency of the magnetically sensitive Ramsey transition fringe are obtained based on the change in the outer axial magnetic field, and the corresponding second-order Zeeman frequency shift is calculated based on the current center frequency of the magnetically sensitive Ramsey transition fringe; wherein, obtaining the center frequency shift of the magnetically sensitive Ramsey transition fringe and the current center frequency of the magnetically sensitive Ramsey transition fringe based on the change in the outer axial magnetic field includes: The change in the inner axial magnetic field of the magnetic shielding device is calculated based on the change in the outer axial magnetic field, using the following formula: ； In the formula, This represents the change in the inner axial magnetic field. This represents the change in the axial magnetic field. The axial shielding factor of the magnetic shielding device; The shift in the center frequency of the magnetically sensitive Ramsey transition fringe is calculated based on the change in the inner axial magnetic field, using the following formula: ； In the formula, The shift in the center frequency of the magnetically sensitive Ramsey transition fringes; The current center frequency of the magnetic Ramsey transition fringe is obtained based on the center frequency shift and the center frequency of the previous magnetic Ramsey transition fringe. If the change in the external axial magnetic field exceeds the change threshold, the operation of the cesium atomic fountain clock is interrupted. The current magnetic Ramsey transition fringe is measured using the magnetic Ramsey transition method. The current magnetic Ramsey transition fringe is compared with the previous magnetic Ramsey transition fringe to determine the center frequency of the current magnetic Ramsey transition fringe. The corresponding second-order Zeeman frequency shift is calculated based on the center frequency of the current magnetic Ramsey transition fringe.

2. The method for measuring the second-order Zeeman shift of an atomic fountain according to claim 1, characterized in that, The cesium atom fountain clock includes: a magneto-optical trap, a state-selection cavity, a detector and a fluorescence collection system, the magnetic shielding device, and an excitation cavity; The magneto-optical trap is used to vertically and upward eject cold atomic clusters according to a set initial velocity and time interval; The state selection cavity, the detector and fluorescence collection system, the magnetic shielding device, and the excitation cavity are arranged sequentially from bottom to top along the running path of the cold atom cluster.

3. The method for measuring the second-order Zeeman shift of an atomic fountain according to claim 1, characterized in that, The measuring device includes a connected single-axis magnetometer probe and a single-axis magnetometer. The single-axis magnetometer probe is installed on the top outer side of the magnetic shielding device near the central axis of the magnetic shielding device, and the installation direction of the single-axis magnetometer probe is parallel to the central axis of the magnetic shielding device.

4. The method for measuring the second-order Zeeman shift of an atomic fountain according to claim 1, characterized in that, The sampling time is consistent with the operating cycle of the cesium atomic fountain clock.

5. The method for measuring the second-order Zeeman shift of an atomic fountain according to claim 1, characterized in that, The change threshold is 1400nT.

6. The method for measuring the second-order Zeeman shift of an atomic fountain according to claim 2, characterized in that, The current magnetically sensitive Ramsey transition fringes were measured using the magnetically sensitive Ramsey transition method, including: The magneto-optical trap is based on an initial velocity of Cold atomic clusters are launched vertically upwards every 2 seconds; The microwave in the selected cavity is adjusted to excite atom generation. Leap A pulse is applied so that the cold atom cluster is in a magnetically sensitive state after passing through the selected cavity. ; The excitation microwave frequency of the excitation cavity is scanned according to the preset scanning conditions; The time-of-flight signal intensity of the falling cold atom clusters at each excitation microwave frequency is measured and recorded using the detector and fluorescence collection system to obtain the current magnetically sensitive Ramsey transition fringes.

7. The method for measuring the second-order Zeeman shift of an atomic fountain according to claim 6, characterized in that, The scanning conditions include: the scanning range is... , The center frequency of the previous magnetic Ramsey transition fringe is 0.2 Hz, and the frequency scan step is 0.2 Hz.

8. The method for measuring the second-order Zeeman shift of an atomic fountain according to claim 1, characterized in that, The formula for calculating the second-order Zeeman frequency shift is as follows: ； In the formula, This represents the relative value of the second-order Zeeman frequency shift. This indicates that there is no interference with Zhong Yueqian. frequency, Represents the absolute value of the second-order Zeeman shift. This represents the center frequency of the magnetically sensitive Ramsey transition fringe.

Images