Microwave system for falling type cold atom microwave clock

Abstract

The invention provides a microwave system for a falling type cold atom microwave clock. The microwave system comprises a microwave generator, a first microwave cut-off waveguide, a second microwave cut-off waveguide and a special-shaped cylindrical resonance main cavity, and the special-shaped cylindrical resonance main cavity is divided into a first cylindrical resonance cavity and a second cylindrical resonance cavity; wherein the microwave generator generates a first microwave standing wave field, a second microwave standing wave field and a third microwave standing wave field in the first cylindrical resonant cavity, and generates a fourth microwave standing wave field in the second cylindrical resonant cavity; the height of the second microwave standing wave field area used for separating field oscillation is smaller than the height of the fourth microwave standing wave field area used for separating field oscillation in the second cylindrical resonant cavity. Compared with the prior art that the second microwave standing wave field area and the fourth microwave standing wave field area have the same height, the height of the fourth microwave standing wave field area is greater than that of the second microwave standing wave field area, so that the time difference of falling cold atoms in the two areas is reduced, and the contrast ratio of the frequency discrimination spectrum line can be improved.

Description

Technical Field

[0001] This application relates to atomic frequency standard technology, and particularly to a microwave system for a falling cold atom microwave clock. Background Art

[0002] A falling cold atom microwave clock is a time-frequency metrology instrument that outputs a frequency standard signal. The falling cold atom microwave clock uses a cold atom cloud as a quantum reference system to obtain a discrimination frequency spectrum line, and can easily achieve high reliability, high frequency stability, high frequency accuracy, and low frequency drift. It can be used as a highly stable small holding clock and has very broad application prospects.

[0003] The falling cold atoms undergo magnetic state selection and separation field oscillation, and the atomic transition probability is obtained by measuring the number of atoms in the ground state and the excited state of the clock transition to obtain the discrimination frequency spectrum line. For the existing microwave cavity structure, the heights of the two microwave standing wave fields used to realize the separation field oscillation in the cavity are the same. Thus, since the speeds of the falling cold atoms passing through these two microwave standing wave fields are different, the times for the atoms to pass through these two microwave standing wave fields are also different. Furthermore, the microwave energies felt by the atoms during the two interactions between the cold atoms and the microwave are different, resulting in a lower contrast of the discrimination frequency spectrum line (Ramsey interference fringes), and ultimately limiting the frequency stability of the falling cold atom microwave clock.

[0004] Therefore, how to ensure that the times of the falling cold atoms passing through the two microwave standing wave fields of the separation field oscillation in the microwave cavity structure are the same is an urgent problem to be solved. Summary of the Invention

[0005] This application provides a microwave system for a falling cold atom microwave clock to solve the problem that the different speeds of the falling cold atoms passing through the separation field oscillation region result in different microwave energies felt by the atoms, thereby causing a lower contrast of the discrimination frequency spectrum line.

[0006] In a first aspect, this application provides a microwave system for a falling cold atom microwave clock. The microwave system includes: a microwave generator, a first microwave cutoff waveguide, a second microwave cutoff waveguide, and a resonant main cavity of a special-shaped cylinder;

[0007] The first microwave cutoff waveguide is disposed above the resonant main cavity of the special-shaped cylinder, and the second microwave cutoff waveguide is disposed below the resonant main cavity of the special-shaped cylinder. The resonant main cavity of the special-shaped cylinder is used to generate a microwave standing wave field. The first microwave cutoff waveguide and the second microwave cutoff waveguide and the resonant main cavity of the special-shaped cylinder form a falling channel for cold atoms, and the first microwave cutoff waveguide and the second microwave cutoff waveguide are used to prevent the microwave standing wave field from leaking from the resonant main cavity of the special-shaped cylinder;

[0008] The resonant main cavity of the special-shaped cylinder includes a first cylindrical resonant cavity and a second cylindrical resonant cavity. The first cylindrical resonant cavity is located above the second cylindrical resonant cavity and is connected to it.

[0009] The microwave generator is connected to the resonant main cavity of the special-shaped cylinder. The microwave generator is used to generate a microwave signal with the transition frequency between two hyperfine energy levels of cold atoms. The microwave signal generates a first microwave standing wave field in the upper part of the first cylindrical resonant cavity, a second microwave standing wave field in the middle part of the first cylindrical resonant cavity, and a third microwave standing wave field in the lower part of the first cylindrical resonant cavity. Among them, the magnetic field directions of the first microwave standing wave field and the third microwave standing wave field at the central axis of the resonant main cavity of the special-shaped cylinder are the same, and the magnetic field directions of the first microwave standing wave field and the second microwave standing wave field at the central axis of the resonant main cavity of the special-shaped cylinder are opposite.

[0010] The height of the second cylindrical resonant cavity is greater than the height of the part of the second microwave standing wave field in the first cylindrical resonant cavity. The height of the fourth microwave standing wave field generated by the microwave signal in the second cylindrical resonant cavity is greater than the height of the second microwave standing wave field. The magnetic field directions of the fourth microwave standing wave field and the second microwave standing wave field at the central axis of the resonant main cavity of the special-shaped cylinder are the same.

[0011] The magnetic field directions of the first microwave standing wave field, the second microwave standing wave field, the third microwave standing wave field, and the fourth microwave standing wave field at the central axis of the resonant main cavity of the special-shaped cylinder are parallel to the central axis of the resonant main cavity.

[0012] Optionally,

[0013] The height of the part of the first microwave standing wave field in the first cylindrical resonant cavity is the same as the height of the part of the second microwave standing wave field in the first cylindrical resonant cavity.

[0014] The height of the part of the first microwave standing wave field in the first cylindrical resonant cavity is the same as the height of the part of the third microwave standing wave field in the first cylindrical resonant cavity.

[0015] Optionally,

[0016] The height of the part of the first microwave standing wave field in the first cylindrical resonant cavity, the height of the part of the second microwave standing wave field, the height of the part of the third microwave standing wave field, and the height of the part of the fourth microwave standing wave field in the second cylindrical resonant cavity are determined according to the line width of the discrimination spectral line of cold atoms and the distance from the cold atom emission position to above the first microwave standing wave field.

[0017] Optionally,

[0018] The height of the part where the fourth microwave standing wave field is located is calculated based on the condition that the time for cold atoms to pass through the second microwave standing wave field is the same as that through the fourth microwave standing wave field.

[0019] Optionally, the diameter of the resonant cavity of the first cylinder is greater than that of the second cylinder.

[0020] Optionally, the microwave system for the falling cold atom microwave clock further includes: a cold atom generator and a microwave controller;

[0021] The microwave controller is connected to the microwave generator and the resonant main cavity of the special-shaped cylinder, and the microwave controller is used to adjust the microwave signal generated by the microwave generator.

[0022] Optionally, the microwave controller includes: a microwave power attenuator and a microwave switch;

[0023] The microwave power attenuator is used to attenuate the power of the microwave signal generated by the microwave generator, and the microwave switch is used to turn on or off the microwave signal generated by the microwave generator.

[0024] In a second aspect, the present application further provides a method for falling cold atom magnetic state selection and separation field oscillation, which is applied to the microwave system for the falling cold atom microwave clock according to any one of the first aspect, and the method includes:

[0025] When it is detected that cold atoms pass through the first microwave standing wave field region, control the microwave controller to output a microwave signal with a π-pulse microwave power, and feed the microwave signal with the π-pulse microwave power into the resonant main cavity of the special-shaped cylinder to generate a first microwave standing wave field, a second microwave standing wave field, a third microwave standing wave field, and a fourth microwave standing wave field;

[0026] When it is detected that cold atoms pass through the second microwave standing wave field region, control the microwave controller to output a microwave signal with a π / 2-pulse microwave power, and feed the microwave signal with the π / 2-pulse microwave power into the resonant main cavity of the special-shaped cylinder to generate a new first microwave standing wave field, a new second microwave standing wave field, a new third microwave standing wave field, and a new fourth microwave standing wave field;

[0027] When it is detected that cold atoms pass through the third microwave standing wave field region, control the microwave controller to stop feeding the microwave signal;

[0028] When it is detected that cold atoms pass through the fourth microwave standing wave field region, control the microwave controller to output a microwave signal with a π / 2-pulse microwave power, and feed the microwave signal with the π / 2-pulse microwave power into the resonant main cavity of the special-shaped cylinder to generate a new first microwave standing wave field, a new second microwave standing wave field, a new third microwave standing wave field, and a new fourth microwave standing wave field.

[0029] Optionally, the method further includes:

[0030] The time that the cold atoms experience in the second microwave standing wave field is the same as the time that they experience in the fourth microwave standing wave field.

[0031] Optionally, the cold atoms are rubidium atoms or cesium atoms.

[0032] A microwave system for a falling cold atom microwave clock provided by the present application, the microwave system includes: a microwave generator, a first microwave cutoff waveguide, a second microwave cutoff waveguide, and a resonant main cavity of a special-shaped cylinder, and the resonant main cavity of the special-shaped cylinder is divided into a first cylindrical resonant cavity and a second cylindrical resonant cavity; wherein, the microwave generator generates a first microwave standing wave field, a second microwave standing wave field, and a third microwave standing wave field in the first cylindrical resonant cavity, and generates a fourth microwave standing wave field in the second cylindrical resonant cavity; the height of the second microwave standing wave field region for separating field oscillations is less than the height of the fourth microwave standing wave field region for separating field oscillations in the second cylindrical resonant cavity. Compared with the same height of the second microwave standing wave field region and the fourth microwave standing wave field region in the prior art, the height of the fourth microwave standing wave field region is greater than that of the second microwave standing wave field, reducing the time difference that the cold atoms experience in the two regions, and being able to improve the contrast of the discrimination frequency spectrum line. Description of the Drawings

[0033] The drawings here are incorporated into the specification and form a part of this specification, showing embodiments consistent with the present application, and are used together with the specification to explain the principles of the present application.

[0034] Figure 1 It is a schematic structural diagram of Embodiment 1 of a microwave system for a falling cold atom microwave clock provided by the present application;

[0035] Figure 2 It is a schematic diagram of the sectional distribution and its height dimensions of Embodiment 2 of a microwave system for a falling cold atom microwave clock provided by the present application;

[0036] Figure 3 It is a schematic structural diagram of Embodiment 3 of a microwave system for a falling cold atom microwave clock provided by the present application;

[0037] Figure 4 It is a schematic flowchart of Embodiment 1 of a method for falling cold atom magnetic state selection and separation field oscillation provided by the present application.

[0038] Through the above drawings, the clear embodiments of the present application have been shown, and there will be more detailed descriptions hereinafter. These drawings and textual descriptions are not intended to limit the scope of the concept of the present application in any way, but to illustrate the concept of the present application to those skilled in the art by referring to specific embodiments. Detailed Embodiments

[0039] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application. Instead, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0040] First, the terms involved in this application are explained:

[0041] Falling cold atom microwave clock: It is a time-frequency measuring instrument that outputs atomic frequency standard signals.

[0042] The state selection and separation field oscillation process of the falling cold atom is the core step of the working principle of the falling cold atom microwave clock.

[0043] The process of state selection is to prepare the cold atoms to a single state of clock transition, generally using magnetic selection or optical selection; magnetic selection requires the atoms to be acted upon by a π microwave pulse with a π pulse microwave power to achieve the transition of the atoms from one state to another.

[0044] Separation field oscillation refers to the interaction between atoms and two microwave pulses with a certain time interval, which realizes the transition of atoms from one state to another; separation field oscillation can significantly increase the interaction time between microwaves and atoms, realize the interference of atomic states (i.e. Ramsey interference), and obtain interference fringes with narrow linewidth, i.e., narrow linewidth discrimination spectrum lines, which makes the falling cold atom microwave clock have high frequency stability.

[0045] A stable and uniform microwave standing wave field can be formed in the microwave resonant cavity. The magnetic selection state and separation field oscillation of atoms are all completed by using the microwave resonant cavity. Therefore, the microwave cavity is the core device of the falling cold atom microwave clock. The resonant frequency of the microwave resonant cavity is tuned to the transition frequency close to the two hyperfine energy levels of the cold atom ground state.

[0046] In the microwave cavity structure of the existing falling cold atom microwave clock, the two microwave standing wave fields used to realize the atomic separation field oscillation in the cavity have the same height. Since the falling cold atoms are in a free fall process, the speed is getting faster and faster. Therefore, the speed of the falling cold atoms when passing through the two microwave standing wave fields is different, which makes the time for the atoms to pass through the two microwave standing wave fields different. In turn, the microwave energy felt by the atoms when the cold atoms and microwaves act twice is different, resulting in a low contrast of the discrimination spectrum lines (Ramsey interference fringes), which will eventually limit the frequency stability of the falling cold atom microwave clock.

[0047] Moreover, in the prior art, the magnetic state selection and separation field oscillation process of falling cold atoms are realized through two independent microwave cavities, resulting in a relatively large volume and weight of the falling cold atom microwave clock.

[0048] In view of this, the inventors found through research that when the heights of the two microwave standing wave fields in the atomic separation field oscillation are the same, the time for the cold atoms to pass through the second microwave standing wave field is shorter than that of the first microwave standing wave field, and the microwave energy acting on them is smaller. Therefore, by designing the microwave cavity structure of the falling cold atom microwave clock, the time for the cold atoms to pass through the second microwave standing wave field is increased, and the microwave energy acting on them is greater, making the contrast of the discrimination spectral line more obvious. When the time for the cold atoms in the second microwave standing wave field is the same as that in the first microwave standing wave field, the contrast of the discrimination spectral line is maximized, and the frequency of the falling cold atom microwave clock is more stable. Based on this, the present application proposes a microwave system for a falling cold atom microwave clock.

[0049] The following will specifically describe the technical solutions of the present application and how the technical solutions of the present application solve the above technical problems with specific embodiments. These several specific embodiments below can be combined with each other, and the same or similar concepts or processes may not be repeated in some embodiments. The embodiments of the present application will be described below with reference to the accompanying drawings.

[0050] Figure 1 FIG. is a schematic structural diagram of Embodiment 1 of a microwave system for a falling cold atom microwave clock provided by the present application. As Figure 1 shown, the falling cold atom microwave clock includes: a first microwave cutoff waveguide 11, a second microwave cutoff waveguide 12, a microwave generator 13, and a resonant main cavity 14 of a special-shaped cylinder;

[0051] The first microwave cutoff waveguide 11 is disposed above the resonant main cavity 14 of the special-shaped cylinder, and the second microwave cutoff waveguide 12 is disposed below the resonant main cavity 14 of the special-shaped cylinder. The resonant main cavity 14 of the special-shaped cylinder is used to generate a microwave standing wave field. The first microwave cutoff waveguide 11 and the second microwave cutoff waveguide 12 are used to form a falling channel for cold atoms with the resonant main cavity of the special-shaped cylinder, and the first microwave cutoff waveguide 11 and the second microwave cutoff waveguide 12 are used to prevent the microwave standing wave field from leaking from the resonant main cavity 14 of the special-shaped cylinder.

[0052] Among them, both the first microwave cutoff waveguide 12 and the second microwave cutoff waveguide 12 can adopt a cutoff waveguide or an aperture waveguide structure, which can prevent the microwave standing wave field in the resonant main cavity 14 of the special-shaped cylinder from leaking under the condition of ensuring the passage of cold atoms.

[0053] The resonant main cavity 14 of the special-shaped cylinder includes a first cylindrical resonant cavity 141 and a second cylindrical resonant cavity 142. The first cylindrical resonant cavity 141 is located above the second cylindrical resonant cavity 142 and is in communication with it. The central axis of the resonant main cavity 14 of the special-shaped cylinder is the cold atom falling channel.

[0054] The microwave generator 13 is connected to the resonant main cavity 14 of the special-shaped cylinder. The microwave generator 13 is used to generate a microwave signal with the transition frequency of two hyperfine energy levels of cold atoms. The microwave signal generates a first microwave standing wave field 1411 in the upper part of the first cylindrical resonant cavity 141, a second microwave standing wave field 1412 in the middle part of the first cylindrical resonant cavity 141, and a third microwave standing wave field 1413 in the lower part of the first cylindrical resonant cavity 141. Among them, the magnetic field directions of the first microwave standing wave field 1411 and the third microwave standing wave field 1413 at the central axis of the resonant main cavity 14 of the special-shaped cylinder are the same, and the magnetic field directions of the first microwave standing wave field 1411 and the second microwave standing wave field 1412 at the central axis of the resonant main cavity 14 of the special-shaped cylinder are opposite. Among them, the microwave generator can be a generator with adjustable microwave power, or a generator without adjustable microwave power. If it is a generator without adjustable microwave power, an external adjustment device needs to be added to control the microwave power fed into the resonant main cavity 14 of the special-shaped cylinder.

[0055] The height of the second cylindrical resonant cavity 142 is greater than the height of the part where the second microwave standing wave field 1412 is located in the first cylindrical resonant cavity 141. The height of the fourth microwave standing wave field 1421 generated by the microwave signal in the second cylindrical resonant cavity 142 is greater than the height of the second microwave standing wave field 1412. The magnetic field directions of the fourth microwave standing wave field 1421 and the second microwave standing wave field 1412 at the central axis of the resonant main cavity 14 of the special-shaped cylinder are the same.

[0056] The magnetic field directions of the first microwave standing wave field 1411, the second microwave standing wave field 1412, the third microwave standing wave field 1413, and the fourth microwave standing wave field 1421 at the central axis of the resonant main cavity 14 of the special-shaped cylinder are parallel to the central axis of the resonant main cavity.

[0057] Among them, the microwave signal in the first microwave standing wave field 1411 region acts on the cold atoms to realize the state selection process of the cold atoms. The microwave signals of the second microwave standing wave field 1412 and the fourth microwave standing wave field 1421 act on the cold atoms to realize the separation field oscillation process of the cold atoms. The microwave signal of the third microwave standing wave field 1413 is turned off when the cold atoms pass through the third microwave standing wave field 1413 region, and the cold atoms freely evolve.

[0058] Among them, the microwave generator 13 generates a microwave signal with the transition frequency between two hyperfine energy levels of cold atoms and feeds it into the special-shaped cylindrical resonant cavity. The resonant frequencies of the four microwave standing wave fields generated in the special-shaped cylindrical resonant cavity are close to the transition frequency between the two hyperfine energy levels of the atomic ground state. In a microwave cold atom clock, the injected resonant frequency is determined according to the hyperfine energy levels of the atoms. After the cold atoms are determined, the required resonant frequency is determined. Therefore, the standing wave mode of the microwave standing wave field generated in the resonant cavity of the special-shaped cylinder is determined by the radius and height of the circular cavity. To form the standing wave mode of the above four microwave standing wave fields, the radius and height of the special-shaped cylinder can be determined according to the mode of mathematical derivation or simulation.

[0059] The cold atoms are rubidium atoms or cesium atoms cooled by laser.

[0060] Optionally, after the microwave generator feeds in the microwave signal, it is necessary to ensure that the resonant frequency in the second cylindrical resonant cavity 142 is the same as the resonant frequency in the first cylindrical resonant cavity 141. However, the height of the second cylindrical resonant cavity 142 (i.e., the region of the fourth microwave standing wave field 1421) is greater than the height of the second microwave standing wave field 1412 in the first cylinder. Therefore, the radius of the second cylindrical resonant cavity 142 (i.e., the region of the fourth microwave standing wave field 1421) has to be smaller than the radius of the first cylindrical resonant cavity 141 to generate the same resonant frequency.

[0061] It should be noted that the radius and height involved in this application refer to the inner distance of the cylinder.

[0062] The falling cold atom microwave clock further includes a photoelectric detection device, which can detect the cold atom group passing through the resonant main cavity of the special-shaped cylinder and detect the transition probability in the cold atoms.

[0063] This application provides a microwave system for a falling cold atom microwave clock. The resonant main cavity 14 of the special-shaped cylinder is divided into a first cylindrical resonant cavity 141 and a second cylindrical resonant cavity 142. The height of the region of the second microwave standing wave field 1412 for separating field oscillation in the first cylindrical resonant cavity 141 is less than the height of the region of the fourth microwave standing wave field 1421 for separating field oscillation in the second cylindrical resonant cavity 142. Compared with the prior art, the height of the region of the fourth microwave standing wave field 1421 becomes higher, reducing the time difference experienced by cold atoms in the two regions, which can improve the contrast of the discrimination spectral line (Ramsey interference fringe) and improve the frequency stability of the falling cold atom microwave clock.

[0064] Figure 2 This is a schematic diagram of the cross-sectional distribution and height dimensions of the second embodiment of the microwave system for a falling cold atom microwave clock provided by this application, as Figure 2As shown, based on the first embodiment, the height of the portion of the first cylindrical resonator 141 of the microwave system for a falling cold atom microwave clock where the first microwave standing wave field 1411 is located is the same as the height of the portion of the first cylindrical resonator 141 where the second microwave standing wave field 1412 is located.

[0065] The height of the portion of the first cylindrical resonator 141 where the first microwave standing wave field 1411 is located is the same as the height of the portion of the first cylindrical resonator 141 where the third microwave standing wave field 1413 is located.

[0066] In this embodiment, the heights h1, h2, and h3 of the regions of the first microwave standing wave field 1411, the second microwave standing wave field 1412, and the third microwave standing wave field 1413 generated in the first cylindrical resonator 141 are the same. There is no need to process the first cylinder. By feeding a microwave signal according to the designed radius and height of the first cylinder, three microwave standing wave fields of the same height can be generated.

[0067] Furthermore, based on the second embodiment, the heights of the regions of the first microwave standing wave field 1411, the second microwave standing wave field 1412, and the third microwave standing wave field 1413 generated in the first cylindrical resonator 141 are the same. Then, the height h1 of the portion of the first cylindrical resonator 141 where the first microwave standing wave field 1411 is located, the height h2 of the portion where the second microwave standing wave field 1412 is located, the height h3 of the portion where the third microwave standing wave field 1413 is located, and the height h4 of the portion of the second cylindrical resonator 142 where the fourth microwave standing wave field 1421 is located are determined according to the line width of the spectral line for cold atom discrimination and the distance from the cold atom emission position above the first microwave standing wave field 1411.

[0068] Specifically, the distance from the starting position of the cold atom at rest above the first microwave standing wave field 1411 is L. The heights of the first microwave standing wave field 1411, the second microwave standing wave field 1412, the third microwave standing wave field 1413, and the fourth microwave standing wave field 1421 formed in the resonator of the special-shaped cylinder are h1, h2, h3, and h4 respectively, and h1 = h2 = h3 = d. The cold atom starts to freely fall along the cavity axis from rest. Assuming the times for the cold atom to pass through the first microwave standing wave field 1411, the second microwave standing wave field 1412, the third microwave standing wave field 1413, and the fourth microwave standing wave field 1421 are τ1, τ2, τ3, and τ4 respectively, then τ2, τ3, and τ4 satisfy the following relationship:

[0069]

[0070] Among them, the linewidth of the Ramsey interference fringe, which is the discrimination spectral line of the falling cold atom microwave clock, is equal to 1 / (2*τ3) according to the generation mechanism of the linewidth of the interference fringe. Therefore, when the linewidth of the discrimination spectral line of the required falling cold atom microwave clock is determined, that is, τ3 is a known value; g is the acceleration due to gravity; d is the height of any one of the first microwave standing wave field 1411, the second microwave standing wave field 1412, and the third microwave standing wave field 1413, and L is the distance of the cold atom from above the first microwave standing wave field 1411. Further, the value of d can be solved according to the expression of τ3, and thus the height values of the first microwave standing wave field 1411, the second microwave standing wave field 1412, and the third microwave standing wave field 1413 can be determined as d = h1 = h2 = h3.

[0071] Further, when the action time of the falling cold atom in the second microwave standing wave field 1412 and the fourth microwave standing wave field 1421 is the same, that is, τ2 = τ4, according to the expressions of τ2 and τ4, the value of the height h4 of the fourth microwave standing wave field 1421 can be solved. Finally, the optimal geometric relationship satisfied by the height h1 of the second microwave standing wave field 1412 and the height h4 of the fourth microwave standing wave field 1421 is obtained.

[0072] For the special-shaped cylindrical resonator designed according to the optimal geometric relationship satisfied by the height h1 of the second microwave standing wave field 1412 and the height h4 of the fourth microwave standing wave field 1421, the time of the two separation field oscillations experienced by the cold atom in it is the same, which can further improve the contrast of the discrimination spectral line.

[0073] Optionally, when the action time of the falling cold atom in the second microwave standing wave field 1412 and the fourth microwave standing wave field 1421 satisfies a preset relationship, that is, τ2 = A*τ4, where A is an adjustment coefficient and is a preset constant. According to the expressions of τ2 and τ4, the value of the height h4 of the fourth microwave standing wave field 1421 can be solved. Finally, the geometric relationship satisfied by the height h1 of the second microwave standing wave field 1412 and the height h4 of the fourth microwave standing wave field 1421 is obtained.

[0074] Optionally, considering the influence of the air resistance on the cold atom during the falling process, the above formula can be deformed.

[0075] In one deformation method, the acceleration of the cold atom during falling is deformed into the acceleration considering air resistance.

[0076] Figure 3 This is a schematic structural diagram of Embodiment 3 of a microwave system for a falling cold atom microwave clock provided by the present application. As Figure 3 shown, on the basis of Embodiment 1, the falling cold atom microwave clock further includes: a cold atom generator 15, a microwave controller 16;

[0077] The microwave controller 16 is connected to the microwave generator 13 and the resonant main cavity 14 of the special-shaped cylinder. The microwave controller is used to adjust the microwave signal generated by the microwave generator.

[0078] The microwave controller 16 includes: a microwave power attenuator 161 and a microwave switch 162.

[0079] The microwave generator is used to generate a microwave signal with a frequency of the transition frequency between two hyperfine energy levels of the ground state of rubidium atoms or cesium atoms.

[0080] The microwave power attenuator 161 is used to adjust and control the power of the microwave signal generated by the microwave generator 13.

[0081] The microwave switch 162 is used to turn on or off the microwave signal generated by the microwave generator.

[0082] After being set, the microwave power attenuator can attenuate the microwave signal with π-pulse microwave power into a microwave signal with π / 2-pulse microwave power, and inject the attenuated microwave signal into the resonant main cavity 14 of the special-shaped cylinder.

[0083] This embodiment provides a microwave system for a falling cold atom microwave clock. The falling cold atom microwave clock controls the frequency of the resonant signal injected into the resonant main cavity 14 of the special-shaped cylinder through the microwave controller.

[0084] Figure 4 The following is a schematic flowchart of the first embodiment of a method for falling cold atom magnetic state selection and separation field oscillation provided by this application, which is applied to any of the falling cold atom microwave clocks in the above embodiments, such as Figure 4 As shown, the method includes:

[0085] S401. When it is detected that cold atoms pass through the first microwave standing wave field region, control the microwave controller to output a microwave signal with π-pulse microwave power, and feed the microwave signal with π-pulse microwave power into the resonant main cavity of the special-shaped cylinder to generate the first microwave standing wave field, the second microwave standing wave field, the third microwave standing wave field, and the fourth microwave standing wave field.

[0086] In this step, the cold atom generator emits cold atoms, where the cold atoms can be rubidium atoms or cesium atoms. The cold atoms fall freely. When it is detected that the cold atoms start to enter the first microwave standing wave field 1411 region in the resonant main cavity 14 of the special-shaped cylinder, the microwave signal with π-pulse microwave power is fed into the resonant main cavity 14 of the special-shaped cylinder. The cold atoms complete the magnetic state selection process in the first microwave standing wave field 1411.

[0087] In a possible implementation manner, the required time τ1 is pre-calculated according to the distance between the cold atom generator and the first microwave standing wave field 1411 region, and the microwave signal is injected after the cold atom generator emits cold atoms and after τ1 time.

[0088] In a possible implementation, when cold atoms pass through the first microwave standing wave field 1411 region at the edge of the resonant main cavity 14 of the special-shaped cylinder, a signal is detected by a detection device, and after receiving the signal, a microwave signal is injected.

[0089] S402. When it is detected that cold atoms pass through the second microwave standing wave field region, control the microwave controller to output a microwave signal with a π / 2 pulse microwave power, and feed the microwave signal with the π / 2 pulse microwave power into the resonant main cavity of the special-shaped cylinder to generate a new first microwave standing wave field, a new second microwave standing wave field, a new third microwave standing wave field, and a new fourth microwave standing wave field.

[0090] In this step, when it is detected that cold atoms pass through the first microwave standing wave field 1411 and enter the second microwave standing wave field 1412 region, a microwave signal with a π / 2 pulse microwave power is fed into the resonant main cavity 14 of the special-shaped cylinder. The cold atoms complete the first π / 2 microwave excitation within the second microwave standing wave field 1412.

[0091] In a possible implementation, the required time τ2 is pre-calculated based on the distance between the cold atom generator and the second microwave standing wave field 1412 region, and a microwave signal is injected after the cold atom generator emits cold atoms and after a time τ2 has elapsed.

[0092] In a possible implementation, when cold atoms pass through the second microwave standing wave field 1412 region at the edge of the resonant main cavity 14 of the special-shaped cylinder, a signal is detected by a detection device, and after receiving the signal from the detection device, a microwave signal is injected.

[0093] S403. When it is detected that cold atoms pass through the third microwave standing wave field region, control the microwave controller to stop feeding the microwave signal.

[0094] In this step, during the period from when the cold atoms start to enter the third microwave standing wave field 1413 region to when they just leave this region, no microwave signal is fed into the resonant cavity of the special-shaped cylinder, and at this time, the cold atoms freely evolve.

[0095] In a possible implementation, the required time τ3 is pre-calculated based on the distance between the cold atom generator and the third microwave standing wave field 1413 region, and a microwave signal is injected after the cold atom generator emits cold atoms and after a time τ3 has elapsed.

[0096] In a possible implementation, when cold atoms pass through the third microwave standing wave field 1413 region at the edge of the resonant main cavity 14 of the special-shaped cylinder, a signal is detected by a detection device, and after receiving the signal from the detection device, a microwave signal is injected.

[0097] S404. When it is detected that cold atoms pass through the fourth microwave standing wave field region, control the microwave controller to output a microwave signal with a π / 2 pulse microwave power, and feed the microwave signal with the π / 2 pulse microwave power into the resonant main cavity of the special-shaped cylinder to generate a new first microwave standing wave field, a new second microwave standing wave field, a new third microwave standing wave field, and a new fourth microwave standing wave field.

[0098] During the period from when it is detected that cold atoms start to enter the fourth microwave standing wave field 1421 region to when they just leave this region, output a microwave signal with a π / 2 pulse microwave power. The microwave signal is fed into the resonant cavity of the special-shaped cylinder to form a microwave standing wave field in the cavity. At this time, the cold atoms complete the second π / 2 microwave excitation in the fourth microwave standing wave field 1421. Thus, the cold atoms complete the separated field oscillation process.

[0099] In a possible implementation, the required time τ4 is pre-calculated based on the distance between the cold atom generator and the fourth microwave standing wave field 1421 region, and a microwave signal is injected after the cold atom generator emits cold atoms and after a time of τ4.

[0100] In a possible implementation, when it is detected by the detection device that cold atoms pass through the fourth microwave standing wave field region at the edge of the resonant main cavity 14 of the special-shaped cylinder and a signal is sent, a microwave signal is injected after receiving the signal from the detection device.

[0101] The height of the fourth microwave standing wave field region is greater than the height of the second microwave standing wave field, resulting in a longer time in the fourth microwave standing wave field compared to the time experienced at the same height, which can improve the contrast of the interference fringes.

[0102] In an implementation, when the height of the fourth microwave standing wave field region and the height of the second microwave standing wave field region satisfy the optimal geometric relationship in the above embodiment, the time experienced by the cold atoms in the second microwave standing wave field is the same as the time experienced in the fourth microwave standing wave field.

[0103] In a possible implementation, when the height of the fourth microwave standing wave field region is greater than the height when satisfying the optimal geometric relationship, after the cold atoms experience a time period of τ2 in the region of the fourth microwave standing wave field, the signal of the microwave standing wave field is turned off. This can make the action time of the two excitations the same.

[0104] In an implementation, when the height of the fourth microwave standing wave field region is smaller than the height when satisfying the optimal geometric relationship, the time experienced by the cold atoms in the region of the fourth microwave standing wave field is less than the time experienced in the second microwave standing wave field. However, at this time, the contrast of the interference fringes is also improved compared to the same height in the prior art.

[0105] After the cold atoms pass through the resonant cavity of the special-shaped cylinder, detect the transition probabilities between the ground state and the excited state of the cold atoms to form a discrimination spectral line.

[0106] This embodiment provides a method for falling cold atom magnetic state selection and separation field oscillation. The cold atoms sequentially pass through the first microwave standing wave field, the second microwave standing wave field, the third microwave standing wave field, and the fourth microwave standing wave field. The state selection process is completed in the first microwave standing wave field, the first π / 2 microwave excitation is completed in the second microwave standing wave field, free evolution is completed in the third microwave standing wave field, the second π / 2 microwave excitation is completed in the fourth microwave standing wave field, and the time experienced in the second microwave standing wave field is the same as the time experienced in the fourth microwave standing wave field. The received microwave energy of the cold atom separation field oscillation is the same, avoiding the low contrast of the interference fringes caused by the same height of the two microwave standing wave fields in the prior art, and improving the frequency stability of the falling cold atom microwave clock.

[0107] In the present invention, unless otherwise clearly specified, terms such as "connection" and "feeding" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrally formed. It can be a mechanical connection, an electrical connection, or capable of communicating with each other. It can be directly connected, or indirectly connected through an intermediate medium. It can be the communication inside two components or the interaction relationship between two components, unless otherwise clearly defined. For those of ordinary skill in the art, the specific meanings of the above terms in the present invention can be understood according to specific circumstances.

[0108] It should be understood that the above specific embodiments of the present invention are only used for exemplary illustration or explanation of the principle of the present invention, and do not constitute a limitation to the present invention. Therefore, any modifications, equivalent replacements, improvements, etc. made without departing from the spirit and scope of the present invention shall be included within the protection scope of the present invention. In addition, the appended claims of the present invention are intended to cover all changes and modifications that fall within the scope and boundary of the appended claims, or equivalent forms of such scope and boundary.

[0109] It should be understood that the present application is not limited to the precise structures already described and shown in the drawings, and various modifications and changes can be made without departing from its scope. The scope of the present application is only limited by the appended claims.

Claims

1. A microwave system for a falling cold atom microwave clock, characterized in that, The microwave system includes: a microwave generator, a first microwave cutoff waveguide, a second microwave cutoff waveguide, and a resonant main cavity of a special-shaped cylinder; The first microwave cutoff waveguide is disposed above the resonant main cavity of the special-shaped cylinder, and the second microwave cutoff waveguide is disposed below the resonant main cavity of the special-shaped cylinder. The resonant main cavity of the special-shaped cylinder is used to generate a microwave standing wave field. The first microwave cutoff waveguide and the second microwave cutoff waveguide, together with the resonant main cavity of the special-shaped cylinder, form a falling channel for cold atoms. The first microwave cutoff waveguide and the second microwave cutoff waveguide are used to prevent the leakage of the microwave standing wave field from the resonant main cavity of the special-shaped cylinder; The resonant main cavity of the special-shaped cylinder includes a first cylindrical resonant cavity and a second cylindrical resonant cavity. The first cylindrical resonant cavity is located above the second cylindrical resonant cavity and is in communication with it; The microwave generator is connected to the resonant main cavity of the special-shaped cylinder. The microwave generator is used to generate a microwave signal with the transition frequency between two hyperfine energy levels of cold atoms. The microwave signal generates a first microwave standing wave field in the upper part of the first cylindrical resonant cavity, a second microwave standing wave field in the middle part of the first cylindrical resonant cavity, and a third microwave standing wave field in the lower part of the first cylindrical resonant cavity in the first cylindrical resonant cavity. Among them, the magnetic field directions of the first microwave standing wave field and the third microwave standing wave field at the central axis of the resonant main cavity of the special-shaped cylinder are the same, and the magnetic field directions of the first microwave standing wave field and the second microwave standing wave field at the central axis of the resonant main cavity of the special-shaped cylinder are opposite; The height of the second cylindrical resonant cavity is greater than the height of the part of the second microwave standing wave field in the first cylindrical resonant cavity. The height of the fourth microwave standing wave field generated by the microwave signal in the second cylindrical resonant cavity is greater than the height of the second microwave standing wave field. The magnetic field directions of the fourth microwave standing wave field and the second microwave standing wave field at the central axis of the resonant main cavity of the special-shaped cylinder are the same; The magnetic field directions of the first microwave standing wave field, the second microwave standing wave field, the third microwave standing wave field, and the fourth microwave standing wave field at the central axis of the resonant main cavity of the special-shaped cylinder are parallel to the central axis of the resonant main cavity.

2. The microwave system for a falling cold atom microwave clock according to claim 1, wherein the height of the part of the first microwave standing wave field in the first cylindrical resonant cavity is the same as the height of the part of the second microwave standing wave field in the first cylindrical resonant cavity; the height of the part of the first microwave standing wave field in the first cylindrical resonant cavity is the same as the height of the part of the third microwave standing wave field in the first cylindrical resonant cavity.

3. The microwave system for a falling cold atom microwave clock according to claim 2, wherein The heights of the portions where the first microwave standing wave field, the second microwave standing wave field, the third microwave standing wave field are located in the first cylindrical resonator, and the height of the portion where the fourth microwave standing wave field is located in the second cylindrical resonator are determined according to the linewidth of the spectral line for cold atom discrimination and the distance from the cold atom emission position to above the first microwave standing wave field.

4. The microwave system for a falling cold atom microwave clock according to any one of claims 1 to 3, characterized in that The height of the portion where the fourth microwave standing wave field is located is calculated based on the condition that the time for the cold atom to pass through the second microwave standing wave field is the same as the time for the fourth microwave standing wave field.

5. The microwave system for a falling cold atom microwave clock according to any one of claims 1 to 3, characterized in that, The diameter of the resonator of the first cylinder is greater than the diameter of the resonator of the second cylinder.

6. The microwave system for a falling cold atom microwave clock according to any one of claims 1 to 3, characterized in that, The microwave system further includes: a cold atom generator, a microwave controller; The microwave controller is connected to the microwave generator and the main resonator of the special-shaped cylinder, and the microwave controller is used to adjust the microwave signal generated by the microwave generator.

7. The microwave system for a falling cold atom microwave clock according to claim 6, characterized in that, The microwave controller includes: a microwave power attenuator and a microwave switch; The microwave power attenuator is used to attenuate the power of the microwave signal generated by the microwave generator, and the microwave switch is used to turn on or off the microwave signal generated by the microwave generator.

8. A method for the falling cold atom magnetic state selection and separation field oscillation, characterized in that Applied to the microwave system for a falling cold atom microwave clock according to any one of claims 1 to 7, the method includes: When it is detected that the cold atom passes through the first microwave standing wave field region, controlling the microwave controller to output a microwave signal with a π-pulse microwave power, and feeding the microwave signal with the π-pulse microwave power into the main resonator of the special-shaped cylinder to generate the first microwave standing wave field, the second microwave standing wave field, the third microwave standing wave field and the fourth microwave standing wave field; When it is detected that the cold atom passes through the second microwave standing wave field region, controlling the microwave controller to output a microwave signal with a π / 2-pulse microwave power, and feeding the microwave signal with the π / 2-pulse microwave power into the main resonator of the special-shaped cylinder to generate a new first microwave standing wave field, a new second microwave standing wave field, a new third microwave standing wave field and a new fourth microwave standing wave field; When it is detected that the cold atom passes through the third microwave standing wave field region, controlling the microwave controller to stop feeding the microwave signal; When it is detected that the cold atom passes through the fourth microwave standing wave field region, controlling the microwave controller to output a microwave signal with a π / 2-pulse microwave power, and feeding the microwave signal with the π / 2-pulse microwave power into the main resonator of the special-shaped cylinder to generate a new first microwave standing wave field, a new second microwave standing wave field, a new third microwave standing wave field and a new fourth microwave standing wave field.

9. The method according to claim 8, wherein The method further includes: The time that the cold atom experiences in the second microwave standing wave field is the same as the time that the cold atom experiences in the fourth microwave standing wave field.

10. The method according to claim 8, wherein The cold atom is a rubidium atom or a cesium atom.

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