A small cold atomic clock device and method for timekeeping system

Abstract

A small cold atomic clock device and method for a timekeeping system, wherein a two-dimensional magneto-optical trap is arranged in the direction of the atomic beam emission of an atomic furnace, the atomic beam emitted from the two-dimensional magneto-optical trap enters the three-dimensional magneto-optical trap through a collimating device, a magnetron microwave cavity is placed inside the three-dimensional magneto-optical trap, after the cold atoms are prepared, the atomic group enters the magnetron microwave cavity by gravity, the atomic group enters the annular microwave cavity after passing through the magnetron microwave cavity, the atoms passing through the annular microwave cavity enter the population number detection device, the population number detection device is connected to an ion pump, the ion pump maintains the vacuum environment of the entire system, three layers of magnetic shielding cylinders made of permalloy material are arranged in sequence outside the system, wherein an optical shutter is also arranged between the three-dimensional magneto-optical trap and the annular microwave cavity, allowing the cold atom loading and microwave excitation processes to be implemented in parallel; the invention has the advantages of compact structure, short working cycle, etc., and can significantly reduce the cost and volume of the cold atomic clock.

Description

Technical Field

[0001] The invention belongs to the technical field of atomic clocks, and in particular relates to a small cold atomic clock device and method for a timekeeping system. Background Art

[0002] Time plays an important role in national production. The generation and maintenance of the International Coordinated Time (UTC) requires time-keeping atomic clocks to have low drift rate, high stability and long-term operation capability. Using laser cooling technology, the temperature of particles is cooled to near absolute zero, allowing for more precise measurement of reference frequencies and obtaining more stable and accurate time and frequency signals. The drift rate of small cold atomic clocks is about one order of magnitude smaller than that of active hydrogen clocks, and they are portable and can operate for a long time, which has certain application value in timekeeping systems.

[0003] In 1997, the European Space Agency announced the implementation of the space cold atomic cesium clock project PHARAO (P. Laurent et al., "The ACES / PHARAO space mission," Comptes Rendus Phys., vol. 16, no. 5, pp. 540–552, 2015). The project intends to use the microgravity environment of space to obtain longer coherence time, thereby obtaining more accurate frequency signals to meet the needs of applications such as precision physical measurements and verification of general relativity. In 2016, the space cold atomic rubidium clock developed by the Shanghai Institute of Optics and Fine Mechanics of the Chinese Academy of Sciences successfully achieved in-orbit operation (L. Liu et al., "In-orbit operation of an atomic clock based on laser-cooled 87 Rb atoms,” Nat. Commun., vol. 9, 2760, 2018). The above cold atomic clock has the following shortcomings: 1. The atomic clock has a long working cycle (> 1s), which makes the phase noise of the local oscillator the main factor limiting the short-term stability of the atomic clock; 2. The above cold atomic clock system is large in size, and the physical system length exceeds 1 meter. 3. The two-dimensional magneto-optical trap is not used to generate a slow atomic beam, and the atomic loading rate is low. 4. Designed for the space microgravity environment, it is necessary to use optical methods to eject atoms, which increases the complexity of the optical system and working timing. Summary of the invention

[0004] The technical problem to be solved by the present invention is to overcome the deficiencies of the above-mentioned prior art and provide a small cold atomic clock device and method with high stability and low drift rate.

[0005] The technical solution adopted to solve the above technical problems is: a two-dimensional magneto-optical trap is arranged in the direction of the atomic beam emission of the atomic furnace, the atomic beam emitted by the two-dimensional magneto-optical trap enters the three-dimensional magneto-optical trap through a collimating device, the magnetron microwave cavity is placed inside the three-dimensional magneto-optical trap, after the cold atoms are prepared, the atomic group enters the magnetron microwave cavity with the help of gravity, an optical shutter is arranged between the three-dimensional magneto-optical trap and the annular microwave cavity, after the atomic group passes through the magnetron microwave cavity, the optical shutter is opened, the atoms enter the annular microwave cavity after passing through the optical shutter, and the atoms passing through the annular microwave cavity enter the population number detection device, the population number detection device is connected to the ion pump, and the ion pump maintains the vacuum environment of the entire system.

[0006] The atomic furnace, two-dimensional magneto-optical trap, collimator and three-dimensional magneto-optical trap of the present invention are placed horizontally with their central axes in the same horizontal plane, and the magnetron microwave cavity, optical shutter, annular microwave cavity and population number detection device are placed vertically with their central axes in the same vertical plane.

[0007] The magnetron microwave cavity of the present invention is vertically placed inside the three-dimensional magneto-optical trap and is located 20 mm below the center of the three-dimensional magneto-optical trap.

[0008] The collimating device of the present invention is a cylindrical structure with a through hole processed at the center, and the diameter of the through hole is 0.5-1.5 mm.

[0009] The annular microwave cavity of the present invention consists of four regions: an atomic channel, a rectangular waveguide, an atomic excitation zone and a cutoff waveguide. The atomic channel is arranged in the middle of the annular microwave cavity, is a hollow rectangular structure, has a length L2 of 137 mm and a width W3 of 8 mm; the rectangular waveguide is located at the front and rear sides of the atomic channel, has a length L2 of 137 mm and a width W2 of 26 mm; the atomic excitation zone is located at the left and right sides of the atomic channel, has a width W1 of 62 mm and a length L1 of 29.7 mm; the atomic excitation zone is provided with a cutoff waveguide at an end away from the atomic channel, has a hollow rectangular structure, has a length L3 of 30 mm and a width W3 of 8 mm, and the inner height of the entire annular cavity is 8 mm.

[0010] A method for implementing a small cold atomic clock device for a timekeeping system of the present invention comprises the following steps:

[0011] S1, heating the atomic furnace to produce rubidium atomic beam;

[0012] S2, the rubidium atomic beam enters the two-dimensional magneto-optical trap and the three-dimensional magneto-optical trap for cooling; the working conditions of the two-dimensional magneto-optical trap are a magnetic field intensity of 5G / cm, a laser detuning frequency of -15MHz, and a pumping light intensity of 10mW / cm 2 , the back pump light intensity is 1mW / cm 2 , the push light intensity is 500μW / cm 2The working conditions of the three-dimensional magneto-optical trap are a magnetic field strength of 5G / cm, a laser detuning frequency of -15MHz, and a cooling light intensity of 10mW / cm 2 , the back pump light intensity is 1mW / cm 2 , beam diameter 8~20mm;

[0013] S3: After the three-dimensional magneto-optical trap works for 180 to 500 ms, the magnetic field is turned off, the laser detuning frequency is increased to -80 MHz, and the cooling light intensity is reduced to 1 mw / cm 2 , polarization gradient cooling is performed, after which the cooling laser is turned off and the optical shutter is opened, and the cold atom group flies through the magnetron microwave cavity under the action of gravity;

[0014] S4, after the cooled atomic group passes through the optical shutter, close the optical shutter, restart the cooling laser, and perform the next cycle of atomic cooling;

[0015] S5. The cold atomic group in the magnetron microwave cavity is selected under the action of the state selection cavity and the repulsive light. The resonant frequency of the magnetron microwave cavity as the state selection cavity is 6.83468 GHz. When the atomic group passes through the magnetron microwave cavity, the laser is used to repel the atomic group to the ground state |F=1, F m =0>, so that the rubidium atoms that continue to fall are all in |F=1, F m =0>;

[0016] S6, the atoms after the state selection continue to fall, and successively pass through the atomic excitation zone, atomic channel, and atomic excitation zone of the annular microwave cavity, and then enter the population number detection device;

[0017] S7. Detect the ratio of the number of atoms of the rubidium atoms in the ground state F=1 and F=2 in the population detection device to obtain a clock signal.

[0018] Compared with the prior art, the present invention has the following advantages:

[0019] 1. The present invention adopts a magnetron microwave cavity as a state-selecting cavity and places it inside a three-dimensional magneto-optical trap, which helps to miniaturize the system.

[0020] 2. An optical shutter is used to separate the cold atom loading area and the atomic excitation area, allowing cold atom loading and microwave excitation to be performed simultaneously, shortening the atomic clock's operating cycle and thus reducing the atomic clock's requirements for the local oscillator phase noise.

[0021] 3. There is no need to use optical methods to eject atoms. The atoms fall due to gravity, which simplifies the optical system and working sequence. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic structural diagram of an embodiment of the present invention.

[0023] Figure 2 yes Figure 1 Schematic diagram of the structure of the middle annular microwave cavity 7.

[0024] Figure 3 yes Figure 1 Schematic diagram of the electric field distribution of the annular microwave cavity 7.

[0025] Figure 4 yes Figure 1 Working timing diagram.

[0026] In the figure: 1. Atomic furnace; 2. Two-dimensional magneto-optical trap; 3. Collimation device; 4. Three-dimensional magneto-optical trap; 5. Magnetron microwave cavity; 6. Optical shutter; 7. Ring microwave cavity; 8. Population number detection device; 9. Ion pump; 7-1. Cutoff waveguide; 7-2. Atomic excitation region; 7-3. Rectangular waveguide; 7-4. Atomic channel. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below with reference to the accompanying drawings and embodiments, but the present invention is not limited to these embodiments.

[0028] Example 1

[0029] exist Figure 1 In the present invention, a small cold atomic clock device for a timekeeping system is provided. A two-dimensional magneto-optical trap 2 is arranged in the direction of the atomic beam emission of the atomic furnace 1. The atomic furnace 1 generates a rubidium atomic beam by heating. The rubidium atomic beam enters the two-dimensional magneto-optical trap 2 by diffusion. The atomic beam emitted by the two-dimensional magneto-optical trap 2 enters the three-dimensional magneto-optical trap 4 after being collimated by the collimator 3. The collimator 3 of this embodiment is a cylindrical structure with a through hole processed in the center. The diameter of the through hole is 1 mm. The atomic furnace 1, the two-dimensional magneto-optical trap 2, the collimator 3, and the three-dimensional magneto-optical trap 4 are placed horizontally and the central axes are located in the same horizontal plane.

[0030] The magnetron microwave cavity 5 is vertically placed inside the three-dimensional magneto-optical trap 4, 20 mm below the center of the three-dimensional magneto-optical trap 4. After the cold atoms are prepared, the atomic group enters the magnetron microwave cavity 5 by gravity. The magnetron microwave cavity 5 in this embodiment has the same structure as the magnetron microwave cavity involved in the patent number: ZL2017113893696, the invention name is "A low temperature sensitive pulsed laser pumped rubidium clock physical system", the inner diameter of the support tube is 25 mm, the outer diameter is 33 mm, and the height is 26 mm. The four pole pieces are evenly arranged on the inner wall of the support tube through the spine, and the gap between adjacent pole pieces is 1.6 mm. The pole piece is an arc plate concentric with the support tube, the inner diameter of the pole piece is 20 mm, and the thickness is 1 mm. A cutoff waveguide is arranged at one end of the magnetron microwave cavity 5 close to the annular microwave cavity 7. The cutoff waveguide is 5 mm long and has an inner diameter of 10 mm.

[0031] exist Figure 2 ,3 In the embodiment, an optical shutter 6 is arranged between the three-dimensional magneto-optical trap 4 and the annular microwave cavity 5. After the atomic group passes through the magnetron microwave cavity 5, the optical shutter 6 is opened, and the atoms enter the annular microwave cavity 7 after passing through the optical shutter 6. The annular microwave cavity 7 of this embodiment is composed of four regions: an atomic channel 7-4, a rectangular waveguide 7-3, an atomic excitation region 7-2, and a cutoff waveguide 7-1. The atomic channel 7-4 is arranged in the middle of the annular microwave cavity 7. The atomic channel 7-4 is a hollow rectangular structure with a length L2 of 137 mm and a width W3 of 8 mm. Rectangular waveguide 7-3 is located on the front and back sides of atomic channel 7-4, and the length L2 of rectangular waveguide 7-3 is 137mm, and the width W2 is 26mm; atomic excitation zone 7-2 is located on the left and right sides of atomic channel 7-4, and the width W1 of atomic excitation zone 7-2 is 62mm, and the length L1 is 29.7mm; atomic excitation zone 7-2 is provided with cutoff waveguide 7-1 at the end away from atomic channel 7-4, and cutoff waveguide 7-1 is a hollow rectangular structure, and the length L3 of cutoff waveguide 7-1 is 30mm, and the width W3 is 8mm. The inner height of the entire annular cavity is 8mm. The resonance mode of atomic excitation zone 7-2 of annular microwave cavity 7 is TE 201 mode, so that the magnetic field in the atomic channel 7-4 region is parallel to the quantization axis. The resonance mode of the rectangular waveguide 7-3 is TE 103 mode to ensure that the microwave cavity has a short length.

[0032] The atoms passing through the annular microwave cavity 7 enter the population number detection device 8. The magnetron microwave cavity 5, the optical shutter 6, the annular microwave cavity 7, and the population number detection device 8 are placed vertically with their central axes located in the same vertical plane. The population number detection device 8 is connected to the ion pump 9, which maintains the vacuum environment of the entire system with a vacuum degree better than 1×10 -7 Pa. All components in the system are connected through vacuum flanges, microwave signals are fed in through SMA interfaces, optical signals are fed in through optical windows, and three layers of magnetic shielding tubes made of Permalloy are sequentially arranged outside the system.

[0033] exist Figure 4 In the present device, a small two-dimensional magneto-optical trap 2 and a three-dimensional magneto-optical trap 4 are used. The atoms that have been cooled fall under the action of gravity, and atomic state selection, excitation and detection are completed in sequence. A magnetron microwave cavity is used as a state selection cavity, and a ring microwave cavity is used as an excitation cavity. The error signal is obtained by detecting the atomic population. The atomic clock periodically repeats the atomic cooling-state selection-excitation-detection process according to the set timing, and the atomic cooling process is implemented in parallel with the excitation process.

[0034] The present invention relates to a method for realizing a small cold atomic clock device for a timekeeping system, which comprises the following steps:

[0035] S1, heating the atomic furnace 1 to generate a rubidium atomic beam;

[0036] S2, the rubidium atomic beam enters the two-dimensional magneto-optical trap 2 and the three-dimensional magneto-optical trap 4 for cooling; the working conditions of the two-dimensional magneto-optical trap 2 are a magnetic field intensity of 5G / cm, a laser detuning frequency of -15MHz, and a pumping light intensity of 10mW / cm 2 , the back pump light intensity is 1mW / cm 2 , the push light intensity is 500μW / cm 2 The working conditions of the 3D MOT 4 are a magnetic field strength of 5 G / cm, a laser detuning frequency of -15 MHz, and a cooling light intensity of 10 mW / cm 2 , the back pump light intensity is 1mW / cm 2 , beam diameter 10mm;

[0037] S3, after the three-dimensional magneto-optical trap 4 works for 340ms, the magnetic field is turned off, the laser detuning frequency is increased to -80MHz, and the cooling light intensity is reduced to 1mW / cm 2 , polarization gradient cooling is performed, after which the cooling laser is turned off and the optical shutter 6 is opened, and the cold atom group falls through the magnetron microwave cavity 5 under the action of gravity;

[0038] S4, after the cooled atomic group passes through the optical shutter 6, the optical shutter 6 is closed, the cooling laser is restarted, and the next cycle of atomic cooling is performed;

[0039] S5, the cold atomic group in the magnetron microwave cavity 5 is selected under the action of the state selection cavity and the repulsive light; wherein the resonant frequency of the magnetron microwave cavity 5 as the state selection cavity is 6.83468GHz, when the atomic group passes through the magnetron microwave cavity 5, the laser is used to repel the atomic group to the ground state|F=1, F m ≠0>, so that the rubidium atoms that continue to fall are all in |F=1, F m =0>;

[0040] S6, the atoms after the state selection continue to fall, and successively pass through the atomic excitation zone 7-2 of the annular microwave cavity, the atomic channel 7-4, the atomic excitation zone 7-2, and then enter the population number detection device 8;

[0041] S7. Detect the ratio of the number of atoms of the rubidium atoms in the ground state F=1 and F=2 in the population number detection device 8 to obtain a clock signal.

[0042] Example 2

[0043] In the above-mentioned embodiment 1, the collimating device 3 of this embodiment is a cylindrical structure with a through hole processed in the center, and the diameter of the through hole is 0.5 mm.

[0044] The remaining components and their connection relationships are exactly the same as those in Example 1. The implementation method is exactly the same as that in Example 1.

[0045] Example 3

[0046] In the above-mentioned embodiment 1, the collimating device 3 of this embodiment is a cylindrical structure with a through hole processed in the center, and the diameter of the through hole is 1.5 mm.

[0047] The remaining components and their connection relationships are exactly the same as those in Example 1. The implementation method is exactly the same as that in Example 1.

[0048] Example 4

[0049] In the above embodiment 1, in the implementation method of this embodiment

[0050] In step S2, the beam diameter is 8 mm;

[0051] In step S3, after the three-dimensional magneto-optical trap 4 operates for 180 ms, the magnetic field is turned off.

[0052] The remaining components and their connection relationships are exactly the same as those in Example 1. The implementation method is exactly the same as that in Example 1.

[0053] Example 5

[0054] In the above embodiment 1, in the implementation method of this embodiment

[0055] In step S2, the beam diameter is 20 mm;

[0056] In step S3, after the three-dimensional magneto-optical trap 4 operates for 500 ms, the magnetic field is turned off.

[0057] The remaining components and their connection relationships are exactly the same as those in Example 1. The implementation method is exactly the same as that in Example 1.

Claims

1. A small cold atomic clock device for a timekeeping system, wherein a two-dimensional magneto-optical trap (2) is arranged in the direction of the atomic beam emission of an atomic furnace (1), the atomic beam emitted from the two-dimensional magneto-optical trap (2) enters a three-dimensional magneto-optical trap (4) through a collimating device (3), a magnetron microwave cavity (5) is placed inside the three-dimensional magneto-optical trap (4), after the cold atoms are prepared, the atomic group enters the magnetron microwave cavity (5) by gravity, an optical shutter (6) is arranged between the three-dimensional magneto-optical trap (4) and the annular microwave cavity (7), after the atomic group passes through the magnetron microwave cavity (5), the optical shutter (6) is opened, the atoms enter the annular microwave cavity (7) after passing through the optical shutter (6), the atoms passing through the annular microwave cavity (7) enter a population number detection device (8), the population number detection device (8) is connected to an ion pump (9), and the ion pump (9) maintains a vacuum environment of the entire system, characterized in that: The annular microwave cavity (7) is composed of four regions: an atomic channel (7-4), a rectangular waveguide (7-3), an atomic excitation region (7-2), and a cutoff waveguide (7-1). The atomic channel (7-4) is arranged in the middle of the annular microwave cavity (7). The atomic channel (7-4) is a hollow rectangular structure with a length (L2) of 137 mm and a width (W3) of 8 mm. The rectangular waveguide (7-3) is located at the front and rear sides of the atomic channel (7-4). The rectangular waveguide (7-3) has a length (L2) of 137 mm and a width (W3) of 8 mm. (W2) is 26mm; the atomic excitation zone (7-2) is located on the left and right sides of the atomic channel (7-4), the atomic excitation zone (7-2) has a width (W1) of 62mm and a length (L1) of 29.7mm; a cutoff waveguide (7-1) is provided at the end of the atomic excitation zone (7-2) away from the atomic channel (7-4), the cutoff waveguide (7-1) is a hollow rectangular structure, the length (L3) of the cutoff waveguide (7-1) is 30mm, the width (W3) is 8mm, and the inner height of the entire annular cavity is 8mm; The atomic furnace (1), two-dimensional magneto-optical trap (2), collimator (3), and three-dimensional magneto-optical trap (4) are placed horizontally with their central axes located in the same horizontal plane, and the magnetron microwave cavity (5), optical shutter (6), annular microwave cavity (7), and population number detection device (8) are placed vertically with their central axes located in the same vertical plane.

2. A small cold atomic clock device for a timekeeping system according to claim 1, characterized in that: The magnetron microwave cavity (5) is vertically placed inside the three-dimensional magneto-optical trap (4), and is located 20 mm below the center of the three-dimensional magneto-optical trap (4).

3. The small cold atomic clock device for a timekeeping system according to claim 1, characterized in that: The collimating device (3) is a cylindrical structure with a through hole processed in the center, and the diameter of the through hole is 0.5 to 1.5 mm.

4. A method for implementing a small cold atomic clock device for a timekeeping system as claimed in any one of claims 1 to 3, characterized in that It consists of the following steps: S1, heating the atomic furnace (1) to generate a rubidium atomic beam; S2, the rubidium atomic beam enters the two-dimensional magneto-optical trap (2) and the three-dimensional magneto-optical trap (4) for cooling; wherein the working conditions of the two-dimensional magneto-optical trap (2) are a magnetic field intensity of 5G / cm, a laser detuning frequency of -15 MHz, and a pumping light intensity of 10mW / cm 2 , the back pump light intensity is 1mW / cm 2 , the push light intensity is 500μW / cm 2 The working conditions of the three-dimensional magneto-optical trap (4) are a magnetic field strength of 5 G / cm, a laser detuning frequency of -15 MHz, and a cooling light intensity of 10 mW / cm 2 , the back pump light intensity is 1mW / cm 2 , beam diameter 8~20mm; S3, after the three-dimensional magneto-optical trap (4) works for 180 to 500 ms, the magnetic field is turned off, the laser detuning frequency is increased to -80 MHz, and the cooling light intensity is reduced to 1 mw / cm 2 , polarization gradient cooling is performed, after which the cooling laser is turned off and the optical shutter is opened (6), and the cold atom group flies through the magnetron microwave cavity (5) under the action of gravity; S4, after the cooled atomic group passes through the optical shutter (6), the optical shutter (6) is closed, the cooling laser is restarted, and the next cycle of atomic cooling is performed; S5. The cold atomic group in the magnetron microwave cavity (5) is selected under the action of the state selection cavity and the repulsive light; wherein the resonant frequency of the magnetron microwave cavity (5) as the state selection cavity is 6.83468 GHz. When the atomic group passes through the magnetron microwave cavity (5), the laser is used to repel the rubidium atoms in the ground state, so that the rubidium atoms that continue to fall are all in the ground state; S6, the atoms after the state selection continue to fall, and successively pass through the atomic excitation region (7-2), the atomic channel (7-4), the atomic excitation region (7-2) of the annular microwave cavity, and then enter the population detection device (8); S7. Detecting the ratio of the number of atoms of the rubidium atoms in the ground state F=1 and F=2 in the population detection device (8) to obtain a clock signal.

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