Magneto-optical trap device

Abstract

This magneto-optical trap device comprises: a vacuum container in which atoms to be cooled and captured are enclosed; an optical element which, on the basis of laser supplied from a light source, generates a pair of parallel light beams that travel in mutually opposing directions and are circularly polarized light beams having the same rotational direction of electric field vectors when facing the respective traveling directions; and a diffraction element which has a plurality of dielectric nanostructures arranged in n-fold symmetry (n is an integer of 3 or more) on a plane perpendicular to the traveling directions of the pair of parallel light beams, and emits a diffracted light beam, which is a circularly polarized light beam having a rotational direction opposite to that of the incident parallel light beam, to the side opposite to the incident side at a predetermined diffraction angle for at least one parallel light beam of the pair of parallel light beams, wherein the atoms are cooled and captured in a region in which the pair of parallel light beams and the diffracted light beam overlap inside the vacuum container.

Description

Magneto-optical trap device

[0001] The present disclosure relates to magneto-optical trapping devices used to cool and trap atoms.

[0002] Using atoms cooled to cryogenic temperatures, atomic clocks, atomic interferometers, cooled-atom quantum computers, etc. Magneto-optical traps (MOTs) are known as a method for cooling and trapping atoms to cryogenic temperatures.

[0003] As an example of a magneto-optical trap, a technique is disclosed in Patent Document 1 or Non-Patent Document 1, in which an incident laser beam is diffracted using a diffraction grating, the diffracted beam intersects with the incident laser beam, and atoms are cooled and trapped at the center of the intersecting plane. This technique is called a grating magneto-optical trap (GMOT), and enables the miniaturization of magneto-optical trap devices.

[0004] U.S. Pat. No. 1,027,8275

[0005] "A surface-patterned chip as a strong source of ultracold atoms for quantum technologies", CC Nshii et al., Nature Nanotechnology 8, 321 (2013)

[0006] Alkali metal elements and alkaline earth metal elements are considered to be suitable atoms for use in magneto-optical traps. However, in the invention disclosed in Patent Document 1, the types of alkali metal atoms that can be cooled and trapped are limited ( ７ Li, ８７ Rb, ８５ Rb, etc.) For this reason, there is a demand for highly efficient cooling and capture of a wide range of atomic species.

[0007] An object of the present disclosure is to provide a magneto-optical trapping device that is compact and capable of cooling and trapping a wide range of atomic species with high efficiency.

[0008] A magneto-optical trapping device according to one aspect of the present disclosure comprises a vacuum vessel enclosing atoms to be cooled and captured; an optical element that generates, based on laser light supplied from a light source, a pair of parallel beams of circularly polarized light that travel in opposite directions and have the same rotation direction of their electric field vectors when facing in their respective directions of travel; and a diffraction element that has a plurality of dielectric nanostructures arranged with n-fold symmetry (n is an integer greater than or equal to 3) on a plane perpendicular to the direction of travel of the pair of parallel beams, and that outputs diffracted light that is circularly polarized and has the opposite rotation direction to the incident parallel beam at a predetermined diffraction angle on the side opposite to the incident side, and cools and captures the atoms in a region inside the vacuum vessel where the pair of parallel beams and the diffracted light overlap.

[0009] According to the present disclosure, a magneto-optical trapping device can be miniaturized and a wide range of atomic species can be cooled and trapped with high efficiency.

[0010] FIG. 1 is a block diagram illustrating a functional configuration of a magneto-optical trapping device according to an embodiment of the present disclosure; FIG. 2 is a flowchart illustrating an example of an operation of the magneto-optical trapping device; FIG. 3 is a diagram illustrating a first configuration example of a magneto-optical trapping device according to an embodiment of the present disclosure; FIG. 4 is a diagram illustrating a state of laser light incident on a specific region in a vacuum vessel in a magneto-optical trapping device of a comparative example; FIG. 5 is a diagram illustrating a second configuration example of a magneto-optical trapping device according to an embodiment of the present disclosure; FIG. 6 is a diagram illustrating a third configuration example of a magneto-optical trapping device according to an embodiment of the present disclosure; FIG. 7 is a diagram illustrating a modification of the third configuration example of a magneto-optical trapping device according to an embodiment of the present disclosure; FIG. 8 is a diagram illustrating a fourth configuration example of a magneto-optical trapping device according to an embodiment of the present disclosure; FIG. 9 is a diagram illustrating a fifth configuration example of a magneto-optical trapping device according to an embodiment of the present disclosure; FIG. 10 is a diagram illustrating a structure of a diffraction element; FIG. 11 is a diagram illustrating a first example of periodically arranged regions formed on a surface of a substrate of a diffraction element; FIG. 12 is a diagram illustrating a second example of periodically arranged regions formed on a surface of a substrate of a diffraction element; 1 is a diagram illustrating a diffraction pattern formed on one surface of a diffraction element having a first example of periodic arrangement regions when parallel light is incident perpendicularly from the other surface side. FIG. 2 is a diagram illustrating a diffraction pattern formed on one surface of a diffraction element having a second example of periodic arrangement regions when parallel light is incident perpendicularly from the other surface side. FIG. 3 is a diagram illustrating a third example of periodic arrangement regions formed on the surface of a substrate of a diffraction element. FIG. 4 is a diagram illustrating a diffraction pattern in a diffraction element employing a third example of a two-dimensional periodic arrangement of dielectric nanostructures. FIG. 5 is a diagram for explaining the unit structure of a dielectric nanostructure. FIG. 6 is a diagram for explaining the unit structure of a dielectric nanostructure. FIG. 7 is a diagram illustrating a first example of a two-dimensional periodic arrangement of dielectric nanostructures in a diffraction element. FIG. 8 is a diagram illustrating a second example of a two-dimensional periodic arrangement of dielectric nanostructures in a diffraction element.FIG. 10 is a diagram showing a third example of a two-dimensional periodic array of dielectric nanostructures in a diffraction element.

[0011] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the drawings. However, more detailed explanation than necessary, such as detailed explanation of already well-known matters and redundant explanation of substantially the same configuration, may be omitted.

[0012] 1 is a block diagram illustrating the functional configuration of a magneto-optical trap device 100 according to an embodiment of the present disclosure. As shown in FIG. 1, the magneto-optical trap device 100 includes a vacuum vessel 1, a repumping light source 2, a cooling light source 3, a pump 4, a magnetic field generator 5, a control unit 6, an optical element 7, and a diffraction element 8.

[0013] The vacuum vessel 1 is a vessel in which atoms to be cooled and captured are sealed. The inside of the vacuum vessel 1 can be kept at a vacuum by a pump 4. In this embodiment, the inside of the vacuum vessel 1 is kept at an ultra-high vacuum (10 －５ Pa or less), and more preferably, 10 －６ It has the ability to maintain the temperature at or below 100 Pa.

[0014] At least a part of the vacuum vessel 1 is made of a material that is transparent to the laser light generated by the re-pumping light source 2 and the cooling light source 3. An example of the material of the vacuum vessel 1 is glass.

[0015] In the present embodiment, examples of atoms to be cooled and captured include alkali metal atoms, more specifically, Li, K, Rb, Cs, etc.

[0016] The repump light source 2 emits repump light. The repump light source 2 is a light source capable of adjusting the laser frequency near the resonance frequency of the atoms to be cooled and trapped. The repump light source 2 is composed of, for example, an external cavity semiconductor laser. The repump light emitted from the repump light source 2 is incident on a specific region Rs (see Figure 3B described below) inside the vacuum vessel 1. The specific region Rs is a region where atoms are cooled and trapped. Details of the specific region Rs will be described later. The repump light is light for returning atoms that can no longer absorb the cooling laser light described below due to spontaneous emission to a level where they can be trapped.

[0017] The cooling light source 3 emits a cooling laser beam for cooling and trapping atoms. The cooling light source 3 is a light source capable of adjusting the laser frequency near the resonance frequency of the atoms to be cooled and trapped. The cooling light source 3 is configured, for example, by an external cavity semiconductor laser. The cooling laser beam emitted from the cooling light source 3 is converted into a pair of parallel beams by an optical element 7 and enters a specific region Rs inside the vacuum vessel 1. The wavelength of the laser beam generated by the cooling light source 3 may be set based on the atomic species to be cooled and trapped.

[0018] The pump 4 pumps the inside of the vacuum vessel 1 －６ The chamber is evacuated to a vacuum of not more than Pa. Examples of the pump 4 include an ion pump and a getter pump, but other pumps may also be used.

[0019] The magnetic field generating device 5 generates a quadrupole magnetic field for a specific region Rs inside the vacuum vessel 1. The magnetic field generating device 5 is, for example, a pair of anti-Helmholtz coils arranged symmetrically with respect to the specific region Rs inside the vacuum vessel 1.

[0020] The control unit 6 controls the operations of the repumping light source 2, the cooling light source 3, the pump 4, and the magnetic field generator 5. The control unit 6 controls each component of the magneto-optical trap device 100 according to a pre-created program. The control unit 6 may also control each component based on the operation of the user of the magneto-optical trap device 100.

[0021] The optical element 7 generates a pair of parallel beams of light traveling in opposite directions based on the cooling laser light generated by the cooling light source 3 .

[0022] Diffraction element 8 has a plurality of dielectric nanostructures arranged on a plane perpendicular to the traveling direction of a pair of parallel beams, with n-fold symmetry (n is an integer equal to or greater than 3) with respect to a central optical axis. The central optical axis is the central optical axis of the magneto-optical trap formed by magneto-optical trap device 100, and is an optical axis that passes through specific region Rs and is parallel to the traveling direction of the parallel beams.

[0023] The diffraction element 8, based on the incidence of at least one of a pair of parallel beams of light, emits diffracted light that travels obliquely with respect to the direction of travel of the parallel beams toward a specific region Rs inside the vacuum vessel 1, using a plurality of dielectric nanostructures. The dielectric nanostructures are elements that have a structure with a period smaller than the wavelength of light and that diffract light.

[0024] The diffraction element 8 diffracts at least one of a pair of parallel beams of light toward the opposite side from the incident side and emits diffracted light that is circularly polarized and whose rotation direction is opposite to that of the incident parallel beam at a predetermined diffraction angle. That is, in the present disclosure, the diffraction element 8 is a transmissive diffraction element that emits diffracted light by diffracting incident light toward the opposite side from the incident side. In this specification, when a certain light is circularly polarized, the rotation direction of the electric field vector when facing the propagation direction of the light is referred to as the rotation direction of the circular polarization of the light. The diffracted light emitted from the diffraction element 8 travels in a direction oblique to the propagation direction of the parallel beam and enters a specific region Rs inside the vacuum vessel 1. Note that there is light that enters the diffraction element 8, passes through it, and travels parallel to the central optical axis, and the light that enters the specific region Rs may contribute to magneto-optical trapping.

[0025] Diffraction element 8 emits n-component diffracted light beams (n is an integer of 3 or greater) having the same diffraction angle and diffraction efficiency based on the incidence of at least one of a pair of parallel beams. As a result, the n-component diffracted light beams are incident on specific region Rs from directions that are n-fold symmetric with respect to the central optical axis. Note that the central optical axis is the central optical axis of the magneto-optical trap formed by magneto-optical trap device 100, and is an optical axis that passes through specific region Rs and is parallel to the traveling direction of the parallel beams.

[0026] An example of a transmission type diffraction element is a diffraction element in which a dielectric nanostructure made of a dielectric material with a high refractive index is periodically arranged on a substrate. When the diffraction element 8 is placed inside the vacuum chamber 1, it is desirable that the material (substrate and dielectric nanostructure) of the diffraction element 8 be made of a material that does not react with the metal atoms to be cooled and captured.

[0027] The optical element 7 and the diffraction element 8 will be described in detail in the configuration examples given later.

[0028] 1 , the optical element 7 and the diffraction element 8 are disposed between the vacuum vessel 1 and the cooled-light source 3, but the present disclosure is not limited to this. For example, at least one of the optical element 7 and the diffraction element 8 may be disposed on the opposite side of the vacuum vessel 1 from the cooled-light source 3. Furthermore, at least one of the optical element 7 and the diffraction element 8 may be disposed inside the vacuum vessel 1.

[0029] In the example shown in FIG. 1, the vacuum vessel 1 and the pump 4 are shown as separate components, but for example, a mechanism that functions as the pump 4 may be incorporated into the vacuum vessel 1.

[0030] FIG. 2 is a flowchart for explaining an example of the operation of the magneto-optical trap device 100. In FIG.

[0031] In step S1, the control unit 6 operates the pump 4 to create a vacuum (10 －６ In the following steps, the pump 4 continues to operate.

[0032] In step S2, the control unit 6 supplies the alkali metal atomic gas to be cooled and captured into the vacuum vessel 1 from a predetermined supply source.

[0033] In step S3, the control unit 6 operates the magnetic field generating device 5 to apply a quadrupole magnetic field to the specific region Rs inside the vacuum vessel 1.

[0034] In step S4, the control unit 6 operates the repumping light source 2 and the cooling light source 3 to form a magneto-optical trap in the specific region Rs inside the vacuum vessel 1. As a result, atoms to be cooled and trapped are cooled and trapped in the specific region Rs.

[0035] <Configuration Example of Magneto-Optical Trap Device> A specific configuration example of the magneto-optical trap device 100 according to the embodiment of the present disclosure will be described below.

[0036] 3A and 3B are diagrams illustrating a first configuration example of the magneto-optical trap device 100 according to an embodiment of the present disclosure. FIG. 3A is a block diagram of the optical element 7 in the magneto-optical trap device 100 of the first configuration example. FIG. 3B shows laser light incident on the specific region Rs in the first configuration example. FIG. 3B is a schematic perspective view of the interior of the vacuum vessel 1. Although not shown, a quadrupole magnetic field is applied to the interior of the vacuum vessel 1 by the magnetic field generator 5. Although not shown, repump light is incident on the specific region Rs from the repump light source 2 of FIG. 1.

[0037] 3A , the optical element 7 includes a first collimated light generating unit 71 and a second collimated light generating unit 72. The first collimated light generating unit 71 generates a first collimated light Lp1 based on the laser light generated by the cooling light source 3. The second collimated light generating unit 72 generates a second collimated light Lp2 based on the laser light generated by the cooling light source 3. The first collimated light Lp1 and the second collimated light Lp2 are either of a pair of collimated lights traveling in opposite directions. The first collimated light Lp1 and the second collimated light Lp2 are circularly polarized lights whose electric field vectors rotate in the same direction when facing their respective traveling directions.

[0038] The pair of parallel beams generated by the first parallel beam generating unit 71 and the second parallel beam generating unit 72 are incident on the vacuum chamber 1 so as to face each other. In the following description, the traveling direction of the first parallel beam Lp1 is referred to as the first direction, and the traveling direction of the second parallel beam Lp2 is referred to as the second direction. The first direction and the second direction are opposite to each other. Note that in FIG. 3B , the first parallel beam Lp1 and the second parallel beam Lp2, which are parallel beams, are illustrated as solid arrows pointing toward the specific region Rs. The first parallel beam generating unit 71 and the second parallel beam generating unit 72 are not illustrated in FIG. 3B .

[0039] 3B, the first parallel light Lp1 and the second parallel light Lp2 are incident in mutually opposing directions toward the inside of the vacuum vessel 1. The first direction, which is the traveling direction of the first parallel light Lp1, and the second direction, which is the traveling direction of the second parallel light Lp2, are mutually opposing directions along the central optical axis.

[0040] In the first configuration example, the diffraction element 8 is disposed between the specific region Rs and the first collimated light generating unit 71 (i.e., the optical element 7 that generates the first collimated light Lp1). The diffraction element 8 may be disposed either outside or inside the vacuum vessel 1. The diffraction element 8 is disposed on a plane P perpendicular to the propagation directions (i.e., the first direction and the second direction) of the pair of collimated light generated by the first collimated light generating unit 71 and the second collimated light generating unit 72. The diffraction element 8 is a transmissive diffraction element that emits diffracted light by diffracting the first collimated light Lp1 of the pair of collimated light toward the side opposite to the incident side. Based on the incidence of at least one of the pair of collimated light (here, the first collimated light Lp1), the diffraction element 8 emits diffracted light Ld, which is circularly polarized light with a rotation direction opposite to that of the incident collimated light (first collimated light Lp1) at a predetermined diffraction angle.

[0041] In the example shown in FIG. 3B , the diffraction element 8 is formed in a circular shape with an opening 81 at the center. The circular shape of the diffraction element 8 in the example shown in FIG. 3B is an example of a shape that is n-fold symmetric with respect to the central optical axis. The circular opening 81 provided in the center of the diffraction element 8 is provided to allow the first parallel light Lp1 to pass through. Note that the circular shapes of the diffraction element 8 and the circular shapes of the opening 81 shown in FIG. 3B are examples of the present disclosure, and the shapes of the diffraction element and the opening in the present disclosure are not limited to the example shown in FIG. 3B .

[0042] The diffraction element 8 transmits the first parallel light Lp1, thereby emitting diffracted light Ld at a predetermined diffraction angle α with respect to the central optical axis of the magneto-optical trap. In the example shown in FIG. 3B , the diffraction element 8 emits diffracted light Ld that travels from its entire circumferential direction toward the specific region Rs. In FIG. 3B , four hollow arrows are used to illustrate a portion of the diffracted light Ld traveling from the entire circumferential direction toward the specific region Rs. The predetermined diffraction angle α may be adjusted as appropriate depending on the position of the diffraction element 8 so that the diffracted light Ld travels toward the specific region Rs.

[0043] The specific region Rs is a partial region inside the vacuum vessel 1, where a pair of parallel beams (first parallel beam Lp1 and second parallel beam Lp2 that have passed through the opening 81) and the diffracted beam Ld emitted by the diffraction element 8 overlap. The specific region Rs is also located approximately at the center of the pair of coils that make up the magnetic field generating device 5. Atoms inside the vacuum vessel 1 are cooled and captured in the specific region Rs due to the radiation pressure caused by the pair of parallel beams and diffracted beams, as well as the influence of the quadrupole magnetic field.

[0044] As described above, the diffraction element 8 has a plurality of dielectric nanostructures 83 (see FIG. 9A described later) periodically arranged on a plane perpendicular to the direction of travel of the pair of parallel beams. This allows the diffraction element 8 to emit n-component diffracted beams, each with the same diffraction angle and diffraction efficiency, toward the central optical axis of the magneto-optical trap. Furthermore, the diffraction element 8 rotates the circularly polarized light of the emitted diffracted beam in the opposite direction to the circularly polarized light of the incident beam (here, the first parallel beam Lp1). Details of the diffraction element 8 having such properties will be described later.

[0045] When the specific region Rs is projected onto the plane P on which the diffraction element 8 is disposed, the position of the specific region Rs is the center position of the diffraction element 8. As a result, diffracted light Ld is incident on the specific region Rs from all circumferential directions of the diffraction element 8. Note that even if the diffraction element 8 does not have the circular shape exemplified in FIG. 3B , it is sufficient that the specific region Rs is configured to be the center position of the diffraction element 8 when the specific region Rs is projected onto the plane P on which the diffraction element 8 is disposed.

[0046] With this configuration, in the first configuration example, a pair of parallel light beams, a first parallel light beam Lp1 and a second parallel light beam Lp2, traveling in opposite directions are incident on the specific region Rs inside the vacuum vessel 1. In addition to these, diffracted light beam Ld traveling in an oblique direction with respect to the central optical axis is incident on the specific region Rs. The diffracted light beam Ld is incident on the specific region Rs from all around the circumference of the diffraction element 8. The rotation directions of the circularly polarized light of the first parallel light beam Lp1 and the second parallel light beam Lp2 are the same, and the rotation directions of the circularly polarized light of the first parallel light beam Lp1 and the circularly polarized light of the diffracted light beam Ld are opposite to each other.

[0047] As a result, atoms to be cooled and captured within the vacuum vessel 1 are subjected to radiation pressure from the first parallel light Lp1, the second parallel light Lp2, and the diffracted light Ld that pass through the opening 81. The frequencies of these lights are set slightly lower than the resonant frequency of the atoms. Due to the Doppler effect, the frequency of light seen from the atoms is closer to the resonant frequency of the atoms in the direction opposite to the direction of the atoms' velocity than that of light traveling in the same direction. Therefore, the atoms are subjected to stronger radiation pressure from the light traveling in the opposite direction to the direction of their velocity. This causes the atoms to decelerate. Furthermore, due to the shift in the resonant frequency of the atoms caused by the magnetic field, the frequency of light traveling toward the center of the quadrupole magnetic field is closer to the resonant frequency of the atoms than the frequency of light traveling away from the center. Therefore, the atoms are subjected to stronger radiation pressure toward the center of the quadrupole magnetic field, and are concentrated near the center of the quadrupole magnetic field within the specific region Rs.

[0048] In order for atoms to be suitably trapped within the specific region Rs and at the center of the quadrupole magnetic field, the intensities of the first parallel light Lp1 and the second parallel light Lp2, as well as the optical characteristics of the optical element 7 and the diffraction element 8 (such as the diffraction efficiency and diffraction angle of the diffraction element 8), must be appropriately set so as to maintain a balance between the intensities of the radiation pressures caused by the first parallel light Lp1, the second parallel light Lp2, and the diffracted light Ld incident on the specific region Rs. These parameters may be set through experiments or the like based on the atomic species to be cooled and trapped, the characteristics of the cooling laser light used, and the like. This allows the magneto-optical trap device 100 to efficiently cool and trap atoms in the specific region Rs.

[0049] The diffraction element 8 may be disposed inside the vacuum vessel 1 or outside the vacuum vessel 1 .

[0050] (Comparison between the first configuration example and the comparative example) The effect of the magneto-optical trap device 100 according to the embodiment of the present disclosure will be explained by comparing the first configuration example of the magneto-optical trap device 100 according to the embodiment of the present disclosure shown in FIG. 3 with the comparative example.

[0051] 4 is a diagram showing the cooling laser light incident on a specific region Rs in a vacuum vessel in a comparative magneto-optical trap device 500. In the comparative magneto-optical trap device 500, the diffraction element 507 is a reflective diffraction element that reflects the incident light and emits diffracted light. As a result, in the comparative magneto-optical trap device 500, parallel light Lp, which is parallel light traveling in a first direction, and diffracted light Ld, which is generated by the diffraction element 507 diffracting and reflecting the parallel light Lp, are incident on the specific region Rs. Therefore, the comparative example differs from the first exemplary configuration of the magneto-optical trap device 100 according to the embodiment of the present disclosure shown in FIG. 3B in that the second parallel light Lp2 is not incident. Note that in FIG. 4, the traveling direction of the parallel light Lp is shown as a first direction, and the opposite direction is shown as a second direction.

[0052] As described above, in order to efficiently cool and trap atoms in a magneto-optical trapping device, it is necessary that the radiation pressure of the laser beam applied to the specific region Rs be three-dimensionally symmetric and that the intensity of the radiation pressure be balanced. In the magneto-optical trapping device 500 of the comparative example shown in FIG. 4 , the radiation pressure of the laser beam applied to the specific region Rs includes a first-direction component due to the parallel light Lp, a second-direction component due to the diffracted light Ld, and components in multiple directions perpendicular to the second direction. Because the diffracted light Ld emitted by the diffraction element 507 are symmetrical with respect to the optical axis of the magneto-optical trap, the components in the multiple directions perpendicular to the second direction are balanced in intensity. Therefore, in the magneto-optical trapping device 500 of the comparative example, it is believed that the balance between the first-direction component of the radiation pressure due to the parallel light Lp and the second-direction component of the radiation pressure due to the diffracted light Ld is maintained, thereby enabling atoms to be cooled and trapped in the specific region Rs.

[0053] However, since the intensity of the diffracted light Ld generated by reflection is generally weaker than that of the incident light, when only the parallel light Lp and the diffracted light Ld are incident on the specific region Rs, as in the comparative example of Figure 4, it may be difficult to maintain the balance of the radiation pressure in the specific region Rs.

[0054] 3, the second parallel light Lp2 is further incident on the specific region Rs, which makes it easier to maintain the balance of the radiation pressure in the specific region Rs compared to the comparative example in which the second parallel light Lp2 is not incident, thereby improving the performance of trapping atoms in the specific region Rs.

[0055] In a magneto-optical trapping device that cools and traps atoms by irradiating a specific region Rs with parallel light traveling in one direction and diffracted light traveling obliquely relative to that direction, as shown in Figure 4, alkali metal atoms are used as atoms that are easy to cool and trap, but recent research has shown that the larger the atomic number, the larger the nuclear spin quantum number, making it more difficult to cool and trap. ７ Li, ８７ Rb, ８５Although atoms such as Rb can be cooled and trapped, it is known to be difficult to suitably cool and trap Cs, which has a higher atomic number.

[0056] In a first exemplary configuration of the magneto-optical trap device 100 according to the embodiment of the present disclosure, both a first parallel light beam Lp1 and a second parallel light beam Lp2 traveling in the opposite direction to the first parallel light beam Lp1 are incident on the specific region Rs. This compensates for the radiation pressure in the first direction generated by the first parallel light beam Lp1, thereby increasing the number of atomic species that can be cooled and trapped. Specifically, in the first exemplary configuration of the magneto-optical trap device 100 according to the embodiment of the present disclosure, the intensities of the parallel light beam Lp1 and the second parallel light beam Lp2, as well as the diffraction efficiency of the diffraction element 8, which is a transmissive diffraction element, are adjusted, and then the intensity ratio between these is adjusted. １３３ Experiments have shown that it is possible to cool and capture Cs.

[0057] As described above, according to the first configuration example of the magneto-optical trap device 100 according to the embodiment of the present disclosure, the diffraction element 8, which is a transmissive diffraction element, causes a pair of parallel beams (first parallel beam Lp1 and second parallel beam Lp2) traveling in opposite directions to be incident on the specific region Rs, in addition to the diffracted beam Ld. This makes it easier to maintain the balance of the radiation pressure of the laser beam acting on the specific region Rs than in the comparative example in which only one parallel beam and the diffracted beam are incident on the specific region. This makes it possible to increase the number of atomic species that can be cooled and trapped, and to perform efficient cooling and trapping.

[0058] (Second Configuration Example) The magneto-optical trap device according to the present disclosure is not limited to the first configuration example described above, and may have a number of configurations. Below, a second configuration example of magneto-optical trap device 100 according to an embodiment of the present disclosure will be described.

[0059] 5A and 5B are diagrams illustrating a second configuration example of magneto-optical trap device 100 according to an embodiment of the present disclosure. Fig. 5A is a block diagram of optical element 7 in magneto-optical trap device 100 of the second configuration example. Fig. 5B shows laser light incident on specific region Rs in the second configuration example. Fig. 5B is a schematic diagram of the inside of vacuum vessel 1 as viewed from the side.

[0060] 5A, in the second configuration example of magneto-optical trap device 100, second collimated light generating section 72 of optical element 7 has a mirror 721 and a quarter-wave plate 722. Mirror 721 reflects first collimated light Lp to generate second collimated light Lr.

[0061] 5B , the mirror 721 and the quarter-wave plate 722 are disposed in a position facing the first collimated light generating unit 71 (i.e., the side on which the first collimated light Lp is incident) with respect to the specific region Rs. The mirror 721 is disposed perpendicular to the traveling direction (first direction) of the first collimated light Lp1. The quarter-wave plate 722 is disposed adjacent to the mirror 721 and on the side on which the first collimated light Lp is incident from the mirror 721.

[0062] The quarter-wave plate 722 imparts a phase difference of π / 2 between the two orthogonal polarization components of the first collimated light Lp. Since the first collimated light Lp passes through the quarter-wave plate 722 both before and after reflection by the mirror 721, the rotation direction of the circularly polarized light of the second collimated light Lr becomes the same as the rotation direction of the circularly polarized light of the first collimated light Lp1.

[0063] In the second configuration example, the second parallel light generating unit 72 of the optical element 7 reflects the first parallel light Lp that has passed through the specific region Rs using a mirror 721 to generate the second parallel light Lr of the pair of parallel lights.

[0064] That is, in the second configuration example, the specific region Rs is incident with the first parallel light Lp, the diffracted light Ld emitted from the diffraction element 8 in response to the incidence of the first parallel light Lp, and the second parallel light Lr obtained by reflecting the first parallel light Lp by the mirror 721 and the quarter-wave plate 722. The first parallel light Lp travels along the first direction, and the second parallel light Lr travels along the second direction. As a result, the first parallel light Lp and the second parallel light Lr are incident on the specific region Rs in directions opposing each other.

[0065] The diffraction element 8 is a transmissive diffraction element, similar to the first configuration example. The diffraction element 8 diffracts the first parallel light Lp in the direction opposite to the incident side to emit diffracted light Ld. The diffraction element 8 is disposed on a plane P perpendicular to the first direction and the second direction.

[0066] The diffraction element 8 emits diffracted light Ld, which travels obliquely with respect to the central optical axis of the magneto-optical trap, from all directions. At this time, the diffraction element 8 rotates the circularly polarized light of the incident light in the opposite direction to the circularly polarized light of the outgoing diffracted light.

[0067] The opening 81 of the diffraction element 8 is provided to allow the first parallel light Lp incident on the specific region Rs, the mirror 721 and the quarter-wave plate 722 to pass through.

[0068] The second configuration example can also achieve the same effect as the first configuration example. That is, a pair of parallel light beams, a first parallel light beam Lp and a second parallel light beam Lr, traveling in opposite directions, are incident on the specific region Rs inside the vacuum vessel 1. In addition, diffracted light Ld traveling in a direction oblique to the first direction, which is emitted by the diffraction element 8 after transmitting the first parallel light beam Lp, is incident on the specific region Rs. The first parallel light beam Lp and the second parallel light beam Lr have the same rotation direction of the circularly polarized light, while the rotation direction of the circularly polarized light of the first parallel light beam Lp1 and the rotation direction of the circularly polarized light of the diffracted light Ld are opposite to each other.

[0069] In this way, due to the influence of the first parallel light Lp, the second parallel light Lr, and the diffracted light Ld incident on the specific region Rs and the quadrupole magnetic field, the atoms are subjected to radiation pressure in a direction toward the specific region Rs, and are suitably cooled and captured.

[0070] As in the first configuration example, the intensities of the first parallel light Lp and the second parallel light Lr and the optical characteristics of the optical element 7 and the diffraction element 8 (such as the reflectance of the mirror 721 and the transmittance and diffraction angle of the diffraction element 8) may be appropriately set so as to maintain a balance among the intensities of the radiation pressures caused by the first parallel light Lp, the second parallel light Lr, and the diffracted light Ld incident on the specific region Rs. This allows the magneto-optical trap device 100 to efficiently cool and trap atoms in the specific region Rs.

[0071] (Third Configuration Example) A third configuration example of the magneto-optical trap device 100 according to the embodiment of the present disclosure will be described. In the third configuration example, first and second parallel beams of light traveling in two opposing directions are transmitted through a diffraction element 8, which is a transmissive diffraction element, to emit diffracted beams.

[0072] 6A and 6B are diagrams illustrating a third configuration example of magneto-optical trap device 100 according to an embodiment of the present disclosure. Fig. 6A is a block diagram of optical element 7 in magneto-optical trap device 100 of the third configuration example. Fig. 6B shows laser light incident on specific region Rs in the third configuration example. Fig. 6B is a schematic diagram of the inside of vacuum vessel 1 as viewed from the side.

[0073] 6A , in the third configuration example, similarly to the other configuration examples, the optical element 7 has a first collimated light generating unit 71 and a second collimated light generating unit 72. The first collimated light generating unit 71 generates a first collimated light Lp1 of the pair of collimated lights based on the laser light generated by the cooling light source 3. The second collimated light generating unit 72 generates a second collimated light Lp2 of the pair of collimated lights based on the laser light generated by the cooling light source 3. The first collimated light generating unit 71 and the second collimated light generating unit 72 set the rotation directions of the circular polarization of the first collimated light and the second collimated light to the same direction.

[0074] As a result, the pair of parallel beams of light generated by the optical element 7 enter the vacuum vessel 1 so as to face each other.

[0075] In the third configuration example, the two diffraction elements 8A and 8B are transmissive diffraction elements, as in the other configuration examples. As shown in FIG. 6B , the diffraction element 8A is disposed between the first parallel light generating unit 71, in other words, the side on which the first parallel light Lp1 is incident, and the specific region Rs. The diffraction element 8B is disposed between the second parallel light generating unit 72, in other words, the side on which the second parallel light Lp2 is incident, and the specific region Rs. The diffraction element 8A diffracts the incident first parallel light Lp1 and emits the first diffracted light Ld1 obliquely relative to the central optical axis, which then enters the specific region Rs. The diffraction element 8B diffracts the incident second parallel light Lp2 and emits the second diffracted light Ld2 obliquely relative to the central optical axis, which then enters the specific region Rs. The rotation direction of the circularly polarized light of the first parallel light Lp1 and the rotation direction of the circularly polarized light of the first diffracted light Ld1 are opposite to each other. The rotation direction of the circularly polarized light of the second parallel light Lp2 and the rotation direction of the circularly polarized light of the second diffracted light Ld2 are opposite to each other.

[0076] The diffraction element 8 has openings 81A and 81B which are provided to allow the first parallel light Lp1 and the second parallel light Lp2 to pass through, respectively.

[0077] The third configuration example can achieve the following effects. A pair of parallel light beams, a first parallel light beam Lp1 that has passed through the opening 81A and a second parallel light beam Lp2 that has passed through the opening 81B, traveling in opposite directions, are incident on the specific region Rs inside the vacuum vessel 1. In addition, a first diffracted light beam Ld1 that is emitted by the diffraction element 8A after diffracting the first parallel light beam Lp1 and traveling in a direction oblique to the first direction, and a second diffracted light beam Ld2 that is emitted by the diffraction element 8B after diffracting the second parallel light beam Lp2 and traveling in a direction oblique to the second direction, are incident on the specific region Rs. The first parallel light beam Lp1 and the second parallel light beam Lp2 have the same rotation direction of the circularly polarized light, and the rotation direction of the circularly polarized light of the first parallel light beam Lp1 and the second parallel light beam Lp2 is opposite to that of the first diffracted light beam Ld1 and the second diffracted light beam Ld2.

[0078] In this way, due to the influence of the first parallel light Lp1, the second parallel light Lp2, the first diffracted light Ld1, and the second diffracted light Ld2 incident on the specific region Rs, and the quadrupole magnetic field, the atoms are subjected to radiation pressure in the direction toward the specific region Rs, and are suitably cooled and captured.

[0079] In the third configuration example, the intensities of the first parallel light Lp1 and the second parallel light Lp2, the first diffracted light Ld1, and the second diffracted light Ld2 incident on the specific region Rs, and the optical characteristics of the optical element 7 and the diffracting elements 8A and 8B (e.g., the diffraction efficiency and diffraction angle of the diffracting elements 8A and 8B, and the transmittance of the openings 81A and 81B) may be appropriately set so as to maintain a balance among the intensities of the radiation pressures caused by the first parallel light Lp1, the second parallel light Lp2, the first diffracted light Ld1, and the second diffracted light Ld2. This allows the magneto-optical trap device 100 to efficiently cool and trap atoms in the specific region Rs.

[0080] According to the third configuration example, the number of diffracted light components incident on the specific region Rs is increased compared to the other configuration examples, which makes it easier to maintain the balance of radiation pressure that cools and captures atoms in the specific region Rs. This is thought to enable cooling and capturing of more atomic species.

[0081] (Modification of the Third Configuration Example) A modification of the third configuration example will be described. Fig. 7 is a diagram for explaining a modification of the third configuration example of magneto-optical trap device 100 according to an embodiment of the present disclosure. The modification of the third configuration example of magneto-optical trap device 100 differs from the third configuration example in that each of diffraction elements 8A and 8B does not have an opening.

[0082] 7 shows the laser light incident on the specific region Rs in a modification of the third configuration example. FIG. 7 is a schematic diagram of the inside of the vacuum vessel 1 as viewed from the side.

[0083] 7, in the modification of the third configuration example, similarly to the third configuration example, the diffraction element 8A is disposed between the side on which the first parallel light Lp1 is incident and the specific region Rs, and the diffraction element 8B is disposed between the side on which the second parallel light Lp2 is incident and the specific region Rs.

[0084] The diffraction element 8A transmits the incident first parallel light Lp1, thereby emitting transmitted light Lt1 parallel to the central optical axis, and emitting diffracted light Ld1 obliquely to the first direction on the side opposite to the side on which the first parallel light Lp1 is incident.

[0085] In this case, as in the third configuration example, the diffraction element 8A sets the rotation direction of the circularly polarized light of the incident first parallel light Lp1 and the rotation direction of the circularly polarized light of the outgoing diffracted light Ld1 to be opposite to each other. The diffraction element 8A also sets the rotation direction of the circularly polarized light of the incident first parallel light Lp1 and the rotation direction of the circularly polarized light of the outgoing transmitted light Lt1 to be the same. The diffracted light Ld1 emitted by the diffraction element 8A is incident on the specific region Rs from all directions around its circumference.

[0086] The diffraction element 8B transmits the incident second parallel light Lp2, thereby emitting transmitted light Lt2 parallel to the central optical axis, and emitting diffracted light Ld2 obliquely to the second direction on the side opposite to the side on which the second parallel light Lp2 is incident.

[0087] In this case, as in the third configuration example, the diffraction element 8B sets the rotation direction of the circularly polarized light of the incident second collimated light Lp2 and the rotation direction of the circularly polarized light of the outgoing diffracted light Ld2 to be opposite to each other. The diffraction element 8B also sets the rotation direction of the circularly polarized light of the incident second collimated light Lp2 and the rotation direction of the circularly polarized light of the outgoing transmitted light Lt2 to be the same. The diffracted light Ld2 emitted by the diffraction element 8B is incident on the specific region Rs from all directions around its circumference.

[0088] According to the modified example of the third configuration example, the following effect can be obtained. A pair of parallel light beams, a first transmitted light beam Lt1 and a second transmitted light beam Lt2, traveling in opposite directions, are incident on the specific region Rs inside the vacuum vessel 1. In addition, a first diffracted light beam Ld1 traveling in a direction oblique to the first direction, which is obtained by diffracting the first parallel light beam Lp1 and output by the diffraction element 8A, and a second diffracted light beam Ld2 traveling in a direction oblique to the second direction, which is obtained by diffracting the second parallel light beam Lp2 and output by the diffraction element 8B, are incident on the specific region Rs. The first transmitted light beam Lt1 and the second transmitted light beam Lt2 have the same rotation direction of the circularly polarized light, and the rotation direction of the circularly polarized light of the first transmitted light beam Lt1 and the second transmitted light beam Lt2 is opposite to that of the first diffracted light beam Ld1 and the second diffracted light beam Ld2.

[0089] In this way, due to the influence of the first transmitted light Lt1, the second transmitted light Lt2, the first diffracted light Ld1, and the second diffracted light Ld2 incident on the specific region Rs, and the quadrupole magnetic field, the atoms are subjected to radiation pressure in the direction toward the specific region Rs, and are suitably cooled and captured.

[0090] In a modification of the third configuration example, the intensities of the first transmitted light Lt1 and the second transmitted light Lt2 incident on the diffraction elements 8A and 8B, as well as the optical characteristics of the optical element 7 and the diffraction elements 8A and 8B (e.g., the diffraction efficiency and diffraction angle of the diffraction elements 8A and 8B, and the transmittance of the openings 81A and 81B) may be appropriately set so as to maintain a balance among the intensities of the radiation pressures caused by the first transmitted light Lt1, the second transmitted light Lt2, the first diffracted light Ld1, and the second diffracted light Ld2 incident on the specific region Rs. This allows the magneto-optical trap device 100 to efficiently cool and trap atoms in the specific region Rs.

[0091] (Fourth Configuration Example) A fourth configuration example of magneto-optical trap device 100 according to an embodiment of the present disclosure will be described. Fig. 8 is a diagram for explaining the fourth configuration example of magneto-optical trap device 100 according to an embodiment of the present disclosure. The fourth configuration example of magneto-optical trap device 100 differs from the first and second configuration examples in that no opening is provided in the center of diffraction element 8.

[0092] 8 shows the laser light incident on the specific region Rs in the fourth configuration example. FIG. 8 is a schematic perspective view of the inside of the vacuum vessel 1.

[0093] In the fourth configuration example, similarly to the first configuration example, a pair of parallel beams, a first parallel beam Lp1 and a second parallel beam Lp2, are incident on the vacuum vessel 1 so as to face each other.

[0094] The diffraction element 8, which is a transmissive diffraction element, transmits incident light to emit transmitted light Lt and emits diffracted light Ld on the side opposite to the incident light side. The diffraction element 8 is disposed on a plane P perpendicular to the first direction and the second direction. In the example shown in FIG. 8 , the diffraction element 8 has a circular shape, but as described in the first configuration example, the present disclosure is not limited to this.

[0095] The diffraction element 8 emits diffracted light Ld traveling in a direction oblique to the first direction (the central optical axis of the magneto-optical trap) and transmitted light Lt traveling in a direction parallel to the central optical axis. At this time, the diffraction element 8 sets the rotation direction of the circularly polarized light of the incident first parallel light Lp1 and the rotation direction of the circularly polarized light of the emitted diffracted light Ld to be opposite to each other. Furthermore, the diffraction element 8 sets the rotation direction of the circularly polarized light of the incident first parallel light Lp1 and the rotation direction of the circularly polarized light of the emitted transmitted light Lt to be the same. The diffracted light Ld emitted by the diffraction element 8 is incident on the specific region Rs from all directions around its circumference.

[0096] The fourth configuration example can achieve the following effects. A pair of parallel light beams, a transmitted light beam Lt and a second parallel light beam Lp2, traveling in opposite directions, are incident on a specific region Rs inside the vacuum vessel 1. The transmitted light beam Lt is the first parallel light beam Lp1 transmitted by the diffraction element 8. In addition, diffracted light beam Ld, which is emitted by the diffraction element 8 after diffracting the first parallel light beam Lp1 in the direction opposite to the incident side, is incident on the specific region Rs. The diffracted light beam Ld travels in a direction oblique to the central optical axis of the magneto-optical trap. The first parallel light beam Lp1, the transmitted light beam Lt, which is the first parallel light beam Lp1 transmitted by the diffraction element 8 without diffracting it, and the second parallel light beam Lp2 all have the same circular polarization rotation direction. Meanwhile, the circular polarization rotation directions of the first parallel light beam Lp1, the transmitted light beam Lt, and the second parallel light beam Lp2 are opposite to each other.

[0097] In this way, due to the influence of the first parallel light Lp1, the second parallel light Lp2, the transmitted light Lt, and the diffracted light Ld incident on the specific region Rs, and the quadrupole magnetic field, the atoms are subjected to radiation pressure in the direction toward the specific region Rs, and are suitably cooled and captured.

[0098] In the fourth configuration example, the intensities of the transmitted light Lt and the second parallel light Lp2, as well as the optical characteristics (diffraction angle, diffraction efficiency, transmittance, etc.) of the optical element 7 and the diffraction element 8, may be appropriately set so as to maintain a balance among the intensities of the radiation pressures caused by the transmitted light Lt, the second parallel light Lp2, and the diffracted light Ld incident on the specific region Rs. This allows the magneto-optical trap device 100 to efficiently cool and trap atoms in the specific region Rs.

[0099] In the fourth configuration example, unlike the other configuration examples, the diffraction element 8 does not have an opening, so the area of ​​the diffraction element 8 that receives the first parallel light Lp1 is larger than in the other configuration examples. This makes it possible to increase the volume of the specific region Rs formed by the overlapping of the light beams of each component. This makes it possible to increase the number of atoms that can be cooled and captured, and improve the atom trapping performance, compared to the other configuration examples.

[0100] 9 is a combination of the transmissive diffraction element in the fourth configuration example and the mirror and λ / 4 wave plate in the second configuration example. In the fifth configuration example, the first parallel light Lp is incident on the vacuum chamber 1.

[0101] That is, in the fifth configuration example, the transmitted light Lt that is transmitted through the diffraction element 8 due to the incidence of the parallel light Lp is incident on the specific region Rs, and at least a portion of the transmitted light Lt is incident on the mirror 721 and the quarter-wave plate 722 that are provided in positions facing the diffraction element 8 across the specific region Rs. With this configuration, in addition to the transmitted light Lt, reflected light Lr generated by the mirror 721 and the quarter-wave plate 722 is incident on the specific region Rs that faces the transmitted light Lt.

[0102] 9 is a diagram for explaining a fifth configuration example of the magneto-optical trap device 100 according to the embodiment of the present disclosure. Fig. 9 is a schematic diagram of the inside of the vacuum vessel 1 as viewed from the side, showing the laser light incident on the specific region Rs. Even with this configuration, it is possible to obtain the same effect as the fourth configuration example.

[0103] (Structure of Diffraction Element 8) The structure of the diffraction element 8, which is a transmission type diffraction element, will be described in detail below.

[0104] In the present disclosure, the diffraction element 8, which is a transmissive diffraction element, is configured by periodically arranging a plurality of unit structures of at least one type of dielectric nanostructure 83 on a substrate 82. FIG. 10 is a diagram for explaining the structure of the diffraction element 8. In the following description, it is assumed that the plurality of unit structures of the dielectric nanostructure 83 are arranged on the surface of the substrate 82 along the x and y directions, which are perpendicular to each other. The xy plane is a plane parallel to the surface of the substrate 82, and the direction perpendicular to the xy plane is the z direction. FIG. 10 shows the plurality of unit structures of the dielectric nanostructure 83 arranged along the x direction and extending from the substrate 82 in the z direction. Note that while FIG. 10 shows the plurality of unit structures of the dielectric nanostructure 83 arranged along the x direction, in reality, the plurality of unit structures of the dielectric nanostructure 83 are also arranged along the y direction. Furthermore, FIG. 10 schematically illustrates the structure of the diffraction element 8, and the shapes and sizes of each component are not accurate.

[0105] Fig. 10 is a cross-sectional schematic diagram of a diffraction element 8, showing a state in which a plurality of dielectric nanostructures 83 are periodically arranged in a row along the x direction on a substrate 82. The example shown in Fig. 10 is an example of the structure of the diffraction element 8 of the present disclosure. The reason why the widths in the x direction of the unit structures of the dielectric nanostructure 83 in Fig. 10 are different from each other is because the respective unit structures, each having a rectangular parallelepiped shape, are arranged on the substrate 82 in different orientations, as will be described later.

[0106] However, the present disclosure is not limited to this, and a plurality of periodic arrangement regions Ra in which the arrangement directions of the plurality of unit structures of the dielectric nanostructure 83 differ from each other may be formed on the substrate 82 of the diffraction element 8. The periodic arrangement region Ra refers to a region in which the plurality of unit structures of the dielectric nanostructure 83 are periodically arranged according to a certain arrangement rule. Fig. 11A is a diagram showing a first example of the periodic arrangement region Ra formed on the surface of the substrate 82 of the diffraction element 8, and Fig. 11B is a diagram showing a second example of the periodic arrangement region Ra formed on the surface of the substrate 82 of the diffraction element 8. Figs. 11A and 11B show the surface of the substrate 82 as viewed from the z direction perpendicular to the substrate 82.

[0107] In the first example shown in FIG. 11A and the second example shown in FIG. 11B, four periodically arranged regions Ra1 to Ra4 are arranged on the surface of a substrate 82 of a circular diffraction element 8. FIG. 11A shows an example in which an opening O is provided around a center C, while FIG. 11B shows an example in which no opening is provided. The four periodically arranged regions Ra1 to Ra4 are arranged at positions that are four-fold symmetric with respect to each other with respect to the center C of the circular diffraction element 8. In other words, the four periodically arranged regions Ra1 to Ra4 are arranged at positions rotated 90 degrees from each other around the center C. When the specific region Rs is projected onto the surface of the substrate 82 of the diffraction element 8, the position of the specific region Rs is positioned so that it overlaps with the center C, allowing diffracted light emitted from the diffraction element 8 to be incident on the specific region Rs from all directions around the circular diffraction element 8.

[0108] Furthermore, the periodic arrangement regions Ra1 to Ra4 are arranged so that the x direction (a direction in which the arrangement angle differs depending on the period), which is one of the arrangement directions of the multiple unit structures of the dielectric nanostructure 83 that each of them has, is perpendicular to a line connecting the center C of the diffraction element 8 and the center of each of the periodic arrangement regions Ra1 to Ra4. As a result, for two adjacent periodic arrangement regions, for example, the periodic arrangement region Ra1 and the periodic arrangement region Ra2, the x direction in the periodic arrangement region Ra1 is a direction rotated 90 degrees around the center C from the x direction in the periodic arrangement region Ra2.

[0109] When circularly polarized parallel light is incident perpendicularly to one surface of a diffraction element 8 having the structure illustrated in Figures 11A and 11B, the diffraction pattern shown in Figures 12A and 12B is generated on the other surface. Figures 12A and 12B are diagrams illustrating the diffraction pattern formed on the other surface of a diffraction element 8 having the periodic array regions of Figures 11A and 11B when parallel light is incident perpendicularly from one surface. More specifically, when parallel light is incident perpendicularly from one surface of a diffraction element 8 having the periodic array regions of Figures 11A and 11B, the shapes of the transmitted light and diffracted light projected onto a predetermined surface parallel to the other surface of the diffraction element 8 and spaced apart from the other surface are as shown in Figures 12A and 12B. That is, Figures 12A and 12B schematically show how the transmitted light and diffracted light are emitted from the diffraction element 8 based on the incidence of parallel light.

[0110] 12A and 12B, circularly polarized transmitted and diffracted light is generated in response to the incidence of circularly polarized parallel light. The direction of rotation of the circularly polarized light of the transmitted light is the same as that of the incident light, and the direction of rotation of the circularly polarized light of the diffracted light is opposite to that of the incident light.

[0111] Furthermore, the present disclosure is not limited to this, and only one periodic arrangement region Ra in which the arrangement directions of the unit structures of the dielectric nanostructure 83 differ from each other may be formed on the substrate 82 of the diffraction element 8. Figure 13 is a diagram showing a third example of a periodic arrangement region Ra formed on the surface of the substrate 82 of the diffraction element 8. As shown in Figure 13, the third example shows a diffraction element 8 having only one circular periodic arrangement region. Figure 13 shows the surface of the substrate 82 as viewed from the z direction perpendicular to the substrate 82.

[0112] 14 is a diagram illustrating a diffraction pattern in a diffraction element 8 employing a third example of a two-dimensional periodic arrangement of dielectric nanostructures 83. As shown in Fig. 14, when circularly polarized parallel light is incident on the circular diffraction element 8 employing the third example of the periodic arrangement illustrated in Fig. 13, the cross-sectional beam shapes of the transmitted light and diffracted light are circular, similar to the cross-sectional beam shape of the incident parallel light.

[0113] 14, circularly polarized transmitted light and diffracted light are generated in response to the incidence of circularly polarized parallel light. The direction of rotation of the circularly polarized light of the transmitted light is the same as the direction of rotation of the circularly polarized light of the incident light, and the direction of rotation of the circularly polarized light of the diffracted light is opposite to the direction of rotation of the circularly polarized light of the incident light.

[0114] In the third example shown in Figures 13 and 14, the beam cross-sectional area of ​​the diffracted light is larger than that of the first example shown in Figures 11A and 12A and the second example shown in Figures 11B and 12B, so the volume of the specific region Rs (see Figures 3B, 5B, 6B, 7, 8, and 9), which is the region where the diffracted light overlaps, can be made relatively large. This makes it possible to capture a relatively large number of atoms in the specific region Rs.

[0115] 15A and 15B are diagrams for explaining the unit structure of the dielectric nanostructure 83. Fig. 15A shows a perspective view of the unit structure of the dielectric nanostructure 83 formed on a substrate 82. Fig. 15B shows a top view (viewed from the z direction) of the unit structure of the dielectric nanostructure 83.

[0116] The substrate 82 is made of an amorphous material or a single crystal material that has high transmittance at least for the wavelength of the cooling laser light (the first parallel light Lp1 in the example shown in FIG. 3).

[0117] The dielectric nanostructure 83 is a nanometer-order structure formed of a dielectric material having a wavelength equal to or less than the target wavelength. The dielectric nanostructure 83 is made of a material having a low absorption coefficient at the target wavelength and a refractive index higher than that of the substrate 82, such as Si, GaN, or TiO. ２ , a polymer, or a combination thereof. When the diffraction element 8 is placed inside the vacuum vessel 1, the material of the dielectric nanostructure 83 is preferably a material that does not easily react with the atoms to be cooled and trapped.

[0118] As shown in Figure 15A, the unit structure of the dielectric nanostructure 83 is formed, for example, in the shape of a rectangular parallelepiped. Note that, since the unit structure of the dielectric nanostructure 83 is a structure on the order of nanometers, it may not be formed into an accurate rectangular parallelepiped due to influences such as manufacturing errors. For this reason, the unit structure of the dielectric nanostructure 83 can actually take shapes other than a rectangular parallelepiped, such as an elliptical cylinder, a polygonal cylinder, an elliptical cone, or a polygonal pyramid. The top and bottom surfaces of the unit structure of the dielectric nanostructure 83 have a shape having a major axis and a minor axis (for example, a rectangle, an ellipse, or a polygon similar to these).

[0119] The direction in which the unit structure of the dielectric nanostructure 83 faces with respect to the substrate 82 is represented by the arrangement angle θ. In the example shown in Fig. 15B, the angle formed between the x direction of the substrate 82 and the long axis direction of the unit structure of the dielectric nanostructure 83 is represented as the arrangement angle θ.

[0120] The dielectric nanostructure 83 functions as a half-wave plate because each unit structure has a shape including a long side and a short side. With this shape, as shown in Figure 15A, the dielectric nanostructure 83 outputs two circularly polarized lights: output light 1, which is circularly polarized in the same direction as the incident light, and output light 2, which is circularly polarized in the opposite direction to the incident light.

[0121] Furthermore, due to the arrangement angle θ of the dielectric nanostructure 83, a phase difference occurs between the output light 1 and the output light 2 emitted from the dielectric nanostructure 83 and the incident light. The output light 1 has a phase difference of 0 with respect to the incident light, and the output light 2 has a phase difference of 2θ with respect to the incident light. Therefore, the phase difference between the output light 1 and the output light 2 is 2θ.

[0122] In this way, the dielectric nanostructure 83 functions to spatially change the phase of the incident light, thereby enabling the dielectric nanostructure 83 to generate diffracted light having a desired diffracted wavefront.

[0123] By suitably setting the arrangement angles of the plurality of dielectric nanostructures 83 in the diffraction element 8, the diffraction element 8 can emit diffracted light having a desired diffraction wavefront including a desired diffraction pattern. Specifically, when the arrangement angles of two dielectric nanostructures 83 separated in the x direction are θ1 and θ2, respectively, a phase difference of 2*(θ1-θ2) occurs between the positions of the two dielectric nanostructures 83. By suitably setting the arrangement positions and arrangement angles of the dielectric nanostructures 83 arranged on the substrate 82, this spatial phase difference can be manipulated, making it possible to emit diffracted light having a desired diffraction wavefront.

[0124] Fig. 16 is a diagram showing a first example of a two-dimensional periodic arrangement of dielectric nanostructures 83 in the diffraction element 8. The first example of the periodic arrangement shown in Fig. 16 corresponds to the example of the periodic arrangement used in the first example of the periodic arrangement region shown in Fig. 11A and the second example of the periodic arrangement region shown in Fig. 11B. The arrangement example shown in Fig. 16 is just one example, and the diffraction element of the present disclosure is not limited to the structure shown in Fig. 16. In practice, the arrangement of the dielectric nanostructures 83 may be adjusted as appropriate based on the diffraction angle, diffraction efficiency, etc. of the diffracted light Ld used in the magneto-optical trap device 100.

[0125] Fig. 16 shows the surface as viewed from the z direction perpendicular to the substrate 82. As shown in Fig. 15, in the diffraction element 8, a plurality of unit structures of the dielectric nanostructure 83 are periodically arranged along the x direction and the y direction which are perpendicular to each other.

[0126] 16, the plurality of unit structures of the dielectric nanostructure 83 arranged along the x direction are arranged at different arrangement angles θ with respect to the x direction depending on the period p. In the example shown in FIG. 16, the arrangement angle θ is the angle between the long axis direction of the unit structure of the dielectric nanostructure 83 and the x direction.

[0127] On the other hand, the multiple unit structures of the dielectric nanostructure 83 arranged along the y direction are arranged at approximately the same arrangement angle θ with respect to the y direction by the period p. Note that, although "approximately the same arrangement angle" is used here to allow for some deviation in angle due to the influence of manufacturing errors, etc., it is ideal that the arrangement angle be the same.

[0128] The coordinates of the unit structure of each dielectric nanostructure 83 in the xy plane are (x ａ , y ｂ ), the diffraction angle by the diffraction element 8 is α, and the wavelength of the first parallel light Lp1 (laser light) incident on the diffraction element 8 is λ, the arrangement angle θ(x ａ , y ｂ ) can be expressed by the following formula (1): where a and b are positive integers and indicate the period in which the unit structure of the dielectric nanostructure 83 is arranged. １ is the refractive index of the diffracting medium, but here, because of the vacuum, n １ can be considered as 1.

[0129] In addition, when a plurality of unit structures of the dielectric nanostructure 83 are arranged at an equal interval period p in each of the x direction and the y direction, the coordinates (x ａ , y ｂ ) can be expressed by the following formula (2).

[0130] FIG. 17 is a diagram showing a second example of a two-dimensional periodic array of dielectric nanostructures 83 in a diffraction element 8. The second example of the periodic array shown in FIG. 17 corresponds to the third example of the periodic array region shown in FIG. 13. FIG. 17 is an image of a prototype diffraction element 8, taken using a scanning electron microscope (SEM), showing the surface of the prototype diffraction element 8 viewed from the z direction perpendicular to the substrate 82. In the second example of the periodic array shown in FIG. 17, the arrangement angle θ of the dielectric nanostructures 83 is designed by an inverse problem design process. A diffraction element 8 employable in the present disclosure can also be obtained with such a configuration.

[0131] As described above, the diffraction element 8 has a structure in which a dielectric nanostructure 83 that converts incident circularly polarized light into output light 1 that is circularly polarized in the same direction of rotation and output light 2 that is circularly polarized in the opposite direction of rotation is formed on a substrate 82. The diffraction element 8 may also have a periodic arrangement region Ra on the substrate 82 in which the dielectric nanostructures 83 are periodically arranged so that the arrangement angle varies periodically. This allows the diffraction element 8 to generate a phase difference in the output light depending on the location where the incident light is incident, and to emit diffracted light having a desired diffraction wavefront.

[0132] Furthermore, the diffraction element 8 may be designed so that, for incident circularly polarized light having a Gaussian beam shape, output light 1 having circular polarization in the same rotation direction and output light 2 having circular polarization in the opposite rotation direction are output, and output light 1 and output light 2 have flat-top beam shapes. The diffraction element 8 designed in this manner has a two-dimensional periodic array of dielectric nanostructures 83 as exemplified in Fig. 18. Fig. 18 is a diagram showing a third example of a two-dimensional periodic array of dielectric nanostructures 83 in the diffraction element 8.

[0133] A flat-top beam is a beam that has a uniform light intensity distribution across the laser cross section and a sharp drop in light intensity at the edges. In this case, the emitted light 1 and emitted light 2 can be shaped to have a uniform intensity distribution, making it possible to capture a relatively large number of atoms more stably.

[0134] The above-described arrangement examples of the periodic arrangement regions Ra in the diffraction element 8 (see FIGS. 11A, 11B, and 13) are merely examples, and the present disclosure is not limited thereto. In the present disclosure, for example, the diffraction element 8 may have n (n is an integer of 3 or greater) periodic arrangement regions Ra arranged at positions with n-fold symmetry relative to each other around the center C. While an example with four-fold symmetry is shown in FIGS. 11A and 11B, the present disclosure also includes diffraction elements having periodic arrangement regions arranged at positions with, for example, three-fold symmetry or five-fold or greater rotational symmetry.

[0135] Furthermore, when the n periodic array regions included in the diffraction element 8 are arranged at positions with n-fold symmetry with respect to each other, each periodic array region is arranged so that the x direction, which is one of the two directions in which the dielectric nanostructures are arranged, is perpendicular to a line passing through the center of symmetry and the center of each periodic array region. As a result, the x direction in a first periodic array region among the multiple periodic array regions is a direction obtained by rotating the x direction in a second periodic array region adjacent to the first periodic array region by 360 / n degrees.

[0136] 13 and 14 illustrate an example in which the diffraction element 8 employing the third example of the periodic arrangement emits four diffracted beams, but the present disclosure is not limited to this. By adjusting the arrangement angle of each dielectric nanostructure 83 on the substrate 82, the diffraction element 8 may be configured to emit three or five or more diffracted beams.

[0137] The number of unit structures of the dielectric nanostructure 83 included in the diffraction element 8 is 10 １０ The number is preferably 1 or less because it is easy to design and manufacture the size of the optical elements used.

[0138] Furthermore, when the n periodically arranged regions included in the diffraction element 8 are arranged at positions with n-fold symmetry with respect to each other, n may be infinite. In this case, the arrangement angle θ(x ａ , y ｂ ) can be expressed by the following equation (10). In this case, the diffraction element 8 can be regarded as an axicon lens that focuses the incident laser light at a certain angle (diffraction angle α) around the optical axis of the laser light. The definitions of the parameters are the same as those in equation (1), and n １ can be considered as 1 due to the vacuum.

[0139] The disclosures of the specification, drawings and abstract contained in Japanese Patent Application No. 2024-147577, filed on August 29, 2024, are incorporated herein by reference in their entirety.

[0140] The present disclosure is useful for magneto-optical trapping devices that use non-orthogonal light to cool and trap atoms, and for cooling and trapping a variety of atomic species.

[0141] REFERENCE SIGNS LIST 100 Magneto-optical trap device 1 Vacuum vessel 2 Repumping light source 3 Cooling light source 4 Pump 5 Magnetic field generator 6 Control unit 7 Optical element 71 First parallel light generating unit 72 Second parallel light generating unit 721 Mirror 722 1 / 4 wavelength plate 8, 8A, 8B Diffraction element 81, 81A, 81B Aperture 82 Substrate 83 Dielectric nanostructure Rs Specific region

Claims

1. A magneto-optical trap device comprising: a vacuum vessel that encloses atoms to be cooled and captured; an optical element that generates, based on laser light supplied from a light source, a pair of parallel beams of circularly polarized light that travel in opposite directions and have the same rotation direction of their electric field vectors when facing in their respective directions of travel; and a diffraction element that has a plurality of dielectric nanostructures arranged in n-fold symmetry (n is an integer of 3 or more) on a plane perpendicular to the direction of travel of the pair of parallel beams, and that emits diffracted light of at least one of the pair of parallel beams at a predetermined diffraction angle to the side opposite to the incident side, and that is circularly polarized light whose rotation direction is opposite to that of the incident parallel beam; and 2. A magneto-optical trap device as described in claim 1, wherein the diffraction element, upon incidence of at least one of the pair of parallel beams, emits n-component diffracted beams that pass through the region and enter the region from directions that are n-fold symmetric (n is an integer of 3 or greater) with respect to a central optical axis that is parallel to the direction of propagation.

3. A magneto-optical trap device as described in claim 1 or 2, wherein the diffraction element is arranged between the region and the optical element that generates one of the pair of parallel beams, diffracts the one of the incident parallel beams to the opposite side from the incident side and emits the diffracted beam, and has an opening that passes the one of the parallel beams, and the one of the parallel beams that has passed through the opening, the other of the pair of parallel beams, and the diffracted beam emitted by the diffraction element are incident on the region.

4. A magneto-optical trap device as described in claim 1 or 2, wherein the diffraction element is arranged between the region and the optical element that generates one of the pair of parallel beams, and diffracts the one of the incident parallel beams in a direction opposite to the incident side to emit diffracted beam, and has an opening that passes the one of the parallel beams, and the optical element has a mirror and a quarter-wave plate that reflects the one of the parallel beams that has passed through the opening to generate the other of the pair of parallel beams, and the one of the parallel beams that has passed through the opening, the other of the pair of parallel beams generated by reflection by the optical element, and the diffracted beam emitted by the diffraction element are incident on the region.

5. A magneto-optical trap device as described in claim 1 or 2, comprising two of the diffraction elements, each of which is arranged at an opposing position between the region and the optical element that generates the pair of parallel beams, and which diffracts one and the other of the incident parallel beams to the opposite side from the incident side and emits diffracted beams, and has an opening that passes each of the pair of parallel beams, and the pair of parallel beams that have passed through the opening and the diffracted beams emitted by the two diffraction elements are incident on the region.

6. A magneto-optical trap device as described in claim 1 or 2, comprising two diffraction elements, each of which is arranged at an opposing position between the region and the optical element that generates the pair of parallel beams, diffracting one incident parallel beam and the other incident parallel beam to the side opposite to the incident side and emitting diffracted beams, and transmitting each of the pair of parallel beams, wherein the transmitted pair of parallel beams and the diffracted beams emitted by the two diffraction elements are incident on the region.

7. A magneto-optical trap device as described in claim 1 or 2, wherein the diffraction element is arranged on the side opposite to the side where one of the pair of parallel beams enters the region, diffracts the other incident parallel beam to the side opposite to the incident side and emits diffracted beam, and transmits the other parallel beam, and the one parallel beam, the transmitted beam that has transmitted the other parallel beam, and the diffracted beam emitted by the diffraction element are incident on the region.

8. A magneto-optical trap device as claimed in claim 1 or 2, wherein the diffraction element is arranged between the region and the optical element that generates one of the pair of parallel beams, and transmits a part of the one of the incident parallel beams and diffracts the other part in the direction opposite to the incident side to emit diffracted light, and the optical element has a mirror and a quarter-wave plate that reflects the part of the transmitted one of the parallel beams to generate the other of the pair of parallel beams, and the region is incident with the parallel light of the part of the transmitted one of the parallel beams, the other of the parallel beams generated by reflection by the optical element, and the diffracted light emitted by the diffraction element.

9. The magneto-optical trap device according to claim 1, wherein the diffraction element has a substrate on the surface of which is formed a periodic arrangement region in which the plurality of dielectric nanostructures are periodically arranged along two directions perpendicular to each other.

10. A magneto-optical trap device as described in claim 9, wherein in the periodic arrangement region, when one of the two directions is the x direction, the plurality of dielectric nanostructures arranged along the x direction are arranged at different arrangement angles with respect to the x direction depending on their periodic positions.

11. A magneto-optical trap device as described in claim 10, wherein in the periodic arrangement region, when the other of the two directions is the y direction, the multiple dielectric nanostructures arranged along the y direction are arranged at approximately the same arrangement angle along the y direction.

12. The magneto-optical trap device according to claim 11, wherein the arrangement angle θ is expressed by the following formula (1): However, x ａ is the x-coordinate of the dielectric nanostructure in the xy plane (a is a positive integer), y ｂ is the y coordinate of the dielectric nanostructure in the xy plane (b is a positive integer), α is the diffraction angle by the diffraction element, λ is the wavelength of the laser light, n １ is the refractive index of the diffracting medium, and in vacuum, n １ is 1.

13. A magneto-optical trap device as described in claim 12, wherein when two adjacent periodic array regions are a first periodic array region and a second periodic array region, the x direction in the first periodic array region is a direction obtained by rotating the x direction in the second periodic array region by 360 / n degrees with respect to the center of symmetry.

14. The magneto-optical trap device of claim 1, wherein the diffraction element is designed to receive circularly polarized incident light having a Gaussian beam shape, output a first output light having circular polarization in the same rotational direction and a second output light having circular polarization in the opposite rotational direction, and to have flat-top beam shapes for the first output light and the second output light.

Images