Quantum state preparation method of continuous cold cesium atom beam

Abstract

The invention provides a quantum state preparation method of a continuous cold cesium atom beam, and relates to the field of cold atom physics and quantum frequency standards. According to the method, an external magnetic field is arranged in a quantum state preparation area, when an atomic beam penetrates through the preparation area, the atomic beam interacts with two beams of orthogonal laser at the same time, and therefore quantum state preparation is completed. The first laser beam is unpolarized, and the frequency of the first laser beam is locked on a cesium atom D2 line F = 4gt; f '= 3gt; on the transition frequency, the frequency of the second laser beam is locked on the cesium atom D2 line F = 3gt; f '= 3gt; in the transition frequency, the polarization direction is parallel to the direction of the external magnetic field. The cesium atoms are pumped to the energy level F = 3 through the first laser beam, the cesium atoms are prepared to the energy level F = 3 through the second laser beam, and m = 0gt; and quantum states. A reflector is arranged in the incident direction of each beam of laser, and incident light returns along the same path to form correlation, so that scattering force in two directions is balanced, a one-dimensional optical cohesive group is formed to cool atoms again, and stability of cold atom beams is guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of cold atom physics and quantum frequency standards, and in particular relates to a method for preparing the quantum state of a continuous cold cesium atomic beam. Background Art

[0002] Historically, there are many methods for preparing quantum states of cesium atoms. Early thermal cesium beam atomic clocks used state-selecting magnets to select atoms in a certain quantum state, but only used 1 / 16 of the atoms, resulting in a large amount of waste of the remaining atoms. Chinese invention patent CN110780585B discloses an optically pumped cesium beam atomic clock, which uses optical pumping technology that can prepare all atoms to the same ground state energy level F=3, but only 1 / 7 of the atoms are in the |F=3,m=0> quantum state required for the clock transition. If dual-optical pumping technology is used, all atoms can be prepared to the same quantum state more precisely. Chinese invention patent CN118377209A discloses a physical system of an optically pumped cold cesium beam atomic clock, which applies dual-light pumping technology to a cold cesium atomic beam. However, due to the slow movement of cold atoms, the interaction time between atoms and lasers is long when dual-light pumping is applied, and the number of transition cycles is too large (on average, one cesium atom transitions more than 10 times). The scattering force caused by atomic spontaneous radiation will change the direction of atomic movement. If the pumping light is incident from one side, the cold atomic beam will be deflected or even cut off, which will reduce the atomic utilization rate. Summary of the invention

[0003] In order to overcome the above technical problems existing in the existing dual-light pumping technology, the present invention provides a method for preparing the quantum state of a continuous cold cesium atomic beam.

[0004] The technical solution adopted by the present invention to solve its technical problem is:

[0005] The first aspect of the present invention discloses a method for preparing a quantum state of a continuous cold cesium atomic beam, which is implemented by a device for preparing a quantum state of a continuous cold cesium atomic beam, and the device for preparing a quantum state of a continuous cold cesium atomic beam comprises a cold cesium atomic beam source, an external magnetic field generation module and a pumping module; wherein the pumping module is arranged in a quantum state preparation area, and comprises a first laser beam and a second laser beam; and the first laser beam is an unpolarized laser with a frequency of |F=4>→|F'=3>, and the second laser beam is a polarized laser with a frequency of |F=3>→|F'=3>, and the polarization direction of the second laser beam is consistent with the direction of the magnetic field generated by the external magnetic field generation module;

[0006] The quantum state preparation method comprises:

[0007] S1, generating a uniform magnetic field in the quantum state preparation area by an external magnetic field generation module;

[0008] S2, using a cold cesium atomic beam source to emit a cold cesium atomic beam to the quantum state preparation area, so that the ground state energy level of the cesium atom undergoes Zeeman splitting in a uniform magnetic field;

[0009] S3, the cesium atom after Zeeman splitting interacts with the first laser beam and the second laser beam at the same time, so that the first laser beam pumps the cesium atom to the F=3 energy level, and the second laser beam prepares the cesium atom to the |F=3,m=0> quantum state.

[0010] In step S1, the strength of the uniform magnetic field is 60 mGs.

[0011] In step S2, the quantum states of the cesium atoms after Zeeman splitting include |F=3,m=0>, |F=3,m=±1>, |F=3,m=±2>, |F=3,m=±3> and |F=4,m=0>, |F=4,m=±1>, |F=4,m=±2>, |F=4,m=±3> and |F=4,m=±4>.

[0012] Step S3 also includes:

[0013] Reflectors are set in the incident directions of the first laser beam and the second laser beam to make the incident light return along the original path to form a counter-reflection, thereby balancing the scattering forces in two directions and forming a one-dimensional optical sticky mass to cool the atoms again, ensuring the stability of the cold atomic beam.

[0014] The second aspect of the present invention discloses a quantum state preparation device for a continuous cold cesium atomic beam, comprising a cold cesium atomic beam source, an external magnetic field generation module and a pumping module; wherein:

[0015] A cold cesium atomic beam source, used for emitting a cold cesium atomic beam to the quantum state preparation area;

[0016] An external magnetic field generation module is used to generate a uniform magnetic field in the quantum state preparation area so that the ground state energy level of the cesium atoms undergoes Zeeman splitting in the uniform magnetic field;

[0017] The pumping module is arranged in the quantum state preparation area, and includes a first laser beam and a second laser beam; the first laser beam is an unpolarized laser with a frequency of |F=4>→|F'=3>, and the second laser beam is a polarized laser with a frequency of |F=3>→|F'=3>, and the polarization direction of the second laser beam is consistent with the direction of the magnetic field generated by the external magnetic field generation module;

[0018] The cold cesium atomic beam, the first laser beam and the second laser beam are orthogonal to the same point, so that the cesium atoms after Zeeman splitting interact with the first laser beam and the second laser beam at the same time, so that the first laser beam pumps the cesium atoms to the F=3 energy level, and the second laser beam prepares the cesium atoms to the |F=3,m=0> quantum state.

[0019] The external magnetic field generation module includes two coils, which generate a uniform magnetic field with an intensity of 60mGs after the two coils are energized.

[0020] The pumping module also includes a reflecting mirror arranged in the incident direction of the first laser beam and the second laser beam; the first laser beam and the second laser beam are reflected by the reflecting mirror and return along the original path to form a counter-reflection, thereby balancing the scattering forces in two directions and forming a one-dimensional optical viscosity to cool the atoms again, thereby ensuring the stability of the cold atomic beam.

[0021] In summary, the scheme proposed in the present invention has the following technical effects: it can concentrate atoms on the quantum state |F=3,m=0> required for the clock transition, which is helpful to improve the signal-to-noise ratio of the atomic clock; by arranging corresponding reflectors in the incident direction of the two laser beams, the incident light can be returned along the original path, so that the atoms are subjected to the same scattering force in two opposite directions, which not only ensures the stability of the cold atomic beam, but also forms a one-dimensional optical sticky mass to cool the atoms again, avoiding the scattering force from cutting off the cold atomic beam, thereby improving the atomic utilization rate; the symmetry of the distribution of cesium atoms in each quantum state is improved, which helps to reduce the Rabi pulling and Ramsey pulling on the transition frequency of the atomic clock, and improve the accuracy of the output frequency of the atomic clock. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific implementation methods of the present invention or the technical solutions in the prior art, the drawings required for use in the specific implementation methods or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some implementation methods of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0023] Figure 1 It is a front view of a quantum state preparation device for a continuous cold cesium atomic beam according to an embodiment of the present invention;

[0024] Figure 2 A top view of a quantum state preparation device for a continuous cold cesium atomic beam according to an embodiment of the present invention;

[0025] Figure 3 It is a side view of a quantum state preparation device of a continuous cold cesium atomic beam according to an embodiment of the present invention.

[0026] Description of Reference Numerals

[0027] 1: cold cesium atomic beam; 2: cold cesium atomic beam source; 3: non-polarized laser; 4: π-polarized laser; 5: reflector A; 6: reflector B; 7: coil A; 8: coil B. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the embodiments of the present invention clearer, the technical solution in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0029] It can be understood that the terms "first", "second", etc. used in the present application can be used in this article to describe various elements, but these elements are not limited by these terms. These terms are only used to distinguish the first element from another element.

[0030] like Figure 1-3 , after the cold cesium atomic beam 1 is emitted from the cold cesium atomic beam source 2, it enters the quantum state preparation area, which is composed of laser 3, laser 4, reflector 5, reflector 6, coil 7, and coil 8. Energize coil 7 and coil 8 to generate a uniform magnetic field with an intensity of 60mGs, and the magnetic field direction is the y direction (optionally, the π polarization direction). The two ground state energy levels F=3 and F=4 of the cesium atom will undergo Zeeman splitting in the magnetic field, respectively generating the required quantum states |F=3,m=0>, |F=3,m=±1>, |F=3,m=±2>, |F=3,m=±3> and |F=4,m=0>, |F=4,m=±1>, |F=4,m=±2>, |F=4,m=±3>, |F=4,m=±4>. Cold cesium atom beam 1, laser 3, and laser 4 are orthogonal at the same point, so cold cesium atom beam 1 will interact with laser 3 and laser 4 at the same time. Laser 3 is unpolarized, and its frequency is locked to the transition frequency of cesium atom D2 line F=4→F'=3. The frequency of laser 4 is locked to the transition frequency of cesium atom D2 line F=3→F'=3. The polarization direction is π polarization, that is, the y direction parallel to the magnetic field direction, and only π transitions between sub-energy levels of F=3→F'=3 are stimulated. Since the transition probability of |F=3,m=0>→|F'=3,m=0> is 0, and the unpolarized laser 3 can continuously pump atoms at the F=4 energy level to various quantum states of the F=3 energy level, the final result is that the atoms will be concentrated in the |F=3,m=0> quantum state. Reflectors 5 and 6 are respectively arranged in the incident direction of each laser beam to make the incident light return along the original path to form a counter-reflection, thereby balancing the scattering forces in two directions and forming a one-dimensional optical cohesive group to cool the atoms again, thus ensuring the stability of the cold atom beam. That is, by arranging corresponding reflectors in the incident direction of the two laser beams, the incident light can be returned along the original path, so that the atoms are subjected to the same scattering forces in two opposite directions, which not only ensures the stability of the cold atom beam, but also forms a one-dimensional optical cohesive group to cool the atoms again.

[0031] It should be noted that the plane of the reflector must be perpendicular to the direction of the incident light to ensure that the incident light returns along the original path and balances the scattering forces in two directions. If the reflector is not parallel to the direction of the incident light, the atomic beam will be deflected in one direction, which will reduce the atomic utilization rate when used in an atomic clock.

[0032] Please note that the technical features of the above embodiments can be combined arbitrarily. In order to make the description concise, all possible combinations of the technical features in the above embodiments are not described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification. The above embodiments only express several implementation methods of the present application, and their descriptions are relatively specific and detailed, but they cannot be understood as limiting the scope of the invention patent. It should be pointed out that for ordinary technicians in this field, without departing from the concept of the present application, several variations and improvements can be made, which all belong to the scope of protection of the present application. Therefore, the scope of protection of the patent in this application shall be based on the attached claims.

Claims

1. A method for preparing the quantum state of a continuous cold cesium atomic beam, characterized in that: The method is implemented by a quantum state preparation device of a continuous cold cesium atomic beam, which comprises a cold cesium atomic beam source, an external magnetic field generation module and a pumping module; wherein the pumping module is arranged in a quantum state preparation area, and comprises a first laser beam and a second laser beam; and the first laser beam is an unpolarized laser with a frequency of |F=4>→|F'=3>, and the second laser beam is a polarized laser with a frequency of |F=3>→|F'=3>, and the polarization direction of the second laser beam is consistent with the direction of the magnetic field generated by the external magnetic field generation module; The quantum state preparation method comprises: S1, generating a uniform magnetic field in the quantum state preparation area by an external magnetic field generation module; S2, using a cold cesium atomic beam source to emit a cold cesium atomic beam to the quantum state preparation area, so that the ground state energy level of the cesium atom undergoes Zeeman splitting in a uniform magnetic field; S3, the cesium atom after Zeeman splitting interacts with the first laser beam and the second laser beam at the same time, so that the first laser beam pumps the cesium atom to the F=3 energy level, and the second laser beam prepares the cesium atom to the |F=3,m=0> quantum state; Step S3 also includes: Reflectors are set in the incident directions of the first laser beam and the second laser beam to make the incident light return along the original path to form a counter-reflection, thereby balancing the scattering forces in two directions and forming a one-dimensional optical sticky mass to cool the atoms again, ensuring the stability of the cold atomic beam.

2. The method for preparing a quantum state according to claim 1, characterized in that: In step S1, the strength of the uniform magnetic field is 60 mGs.

3. The method for preparing a quantum state according to claim 1, characterized in that: In step S2, the quantum states of the cesium atoms after Zeeman splitting include |F=3,m=0>, |F=3,m=±1>, |F=3,m=±2>, |F=3,m=±3> and |F=4,m=0>, |F=4,m=±1>, |F=4,m=±2>, |F=4,m=±3> and |F=4,m=±4>.

4. A quantum state preparation device for a continuous cold cesium atomic beam, characterized in that: It includes a cold cesium atomic beam source, an external magnetic field generation module and a pumping module; wherein, A cold cesium atomic beam source, used for emitting a cold cesium atomic beam to the quantum state preparation area; An external magnetic field generation module is used to generate a uniform magnetic field in the quantum state preparation area so that the ground state energy level of the cesium atoms undergoes Zeeman splitting in the uniform magnetic field; The pumping module is arranged in the quantum state preparation area, and includes a first laser beam and a second laser beam; the first laser beam is an unpolarized laser with a frequency of |F=4>→|F'=3>, and the second laser beam is a polarized laser with a frequency of |F=3>→|F'=3>, and the polarization direction of the second laser beam is consistent with the direction of the magnetic field generated by the external magnetic field generation module; The cold cesium atomic beam, the first laser beam and the second laser beam are orthogonal to the same point, so that the cesium atoms after Zeeman splitting interact with the first laser beam and the second laser beam at the same time, so that the first laser beam pumps the cesium atoms to the F=3 energy level, and the second laser beam prepares the cesium atoms to the |F=3,m=0> quantum state; The pumping module also includes a reflecting mirror arranged in the incident direction of the first laser beam and the second laser beam; the first laser beam and the second laser beam are reflected by the reflecting mirror and return along the original path to form a counter-reflection, thereby balancing the scattering forces in two directions and forming a one-dimensional optical viscosity to cool the atoms again, thereby ensuring the stability of the cold atomic beam.

5. The quantum state preparation device according to claim 4, characterized in that: The external magnetic field generation module includes two coils, which generate a uniform magnetic field with an intensity of 60mGs after the two coils are energized.

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