Optical lattice clock and magnetic field correction method for optical lattice clock

Abstract

An optical lattice clock having a new adjustment mechanism for homogenizing a magnetic field using a magnetic field correction coil is realized. The optical lattice clock comprises: a clock transition space (52) in which an atomic group (240) enclosed in an optical lattice is arranged; and a three-axis magnetic field correction coil that corrects the magnetic field of the clock transition space. In addition, an optical receiver (246) as an acquisition unit causes the atomic group (240) enclosed in the optical lattice to perform clock transitions in a correction space (242) that includes the clock transition space and is wider than the clock transition space, and acquires the frequency distribution of the clock transitions in the correction space (242). In addition, the correction unit corrects the magnetic field of the three-axis magnetic field correction coil based on the frequency distribution measured by the acquisition unit.

Description

Technical Field

[0001] The invention relates to an optical lattice clock and a magnetic field correction method for the optical lattice clock. Background Art

[0002] The optical lattice clock is an atomic clock proposed by Hidetoshi Katori, one of the inventors of this application, in 2001. In the optical lattice clock, atomic groups are enclosed in an optical lattice formed by lasers, and the resonant frequency in the visible light region is measured. Therefore, it is possible to measure with an accuracy of 18 bits, which is far higher than the accuracy of the current cesium clock. Optical lattice clocks are being researched and developed not only by the inventor group, but also by various groups at home and abroad, and are being developed into the next generation of atomic clocks.

[0003] Regarding the recent technology of optical lattice clocks, for example, the following patent documents 1 to 3 can be cited. Patent document 1 describes forming a one-dimensional moving optical lattice inside an optical waveguide having a hollow channel. Patent document 2 describes a scheme for setting an effective magic frequency. In addition, patent document 3 describes a radiation shield that reduces the influence of black body radiation emitted from the surrounding walls.

[0004] In an optical lattice clock, time is measured with high precision, so a 1 cm height difference on the earth based on the general relativity effect of gravity can be detected as a deviation in the time process. Therefore, if the optical lattice clock can be made portable and used in the field outside the laboratory, the applicability will be expanded to new geodetic technologies such as underground resource exploration, underground caves, and magma chamber detection. By mass-producing optical lattice clocks and deploying them in various places, it is possible to continuously monitor the time changes of gravitational potential, detect crustal changes, and spatial mapping of gravity fields. In this way, optical lattice clocks are expected to exceed the limits of high-precision time measurement and contribute to society as a new basic technology.

[0005] The following non-patent documents 1 to 5 describe attempts to make optical lattice clocks portable. For example, non-patent document 4 describes a physical package of an optical lattice clock housed in a frame with a length of 99 cm, a width of 60 cm, and a height of 45 cm. In this physical package, an atomic reactor, a Zeeman reducer, and a vacuum chamber are arranged in order in the length direction. In addition, on the outside of the vacuum chamber, a pair of square magnetic field correction coils with a side of about 30 to 40 cm are provided on the three axes of the length direction, the width direction, and the height direction. In order to perform clock transition spectroscopy on atoms under zero magnetic field, the magnetic field correction coil is used to uniformly compensate the magnetic field distribution in the area around the atoms during spectroscopy to zero value.

[0006] To make the magnetic field uniform using the magnetic field correction coil, it is necessary to adjust the current flowing through the magnetic field coil. In the conventional optical lattice clock, the frequency of light emitted by the atomic group in the clock transition space that causes the clock transition is analyzed, and the uniform magnetic field correction is performed to reduce the Zeeman splitting.

[0007] In the field of NMR (Nuclear Magnetic Resonance), the magnetic field in the space where the sample is placed is homogenized. For example, the following patent document 4 describes a gradient shimming method commonly performed in the field of NMR. Specifically, the gradient shimming method detects the magnetic field in the sample when a magnetic field gradient pulse is applied. 2 H nuclear spins are used to grasp the magnetic field distribution in space. Then, the current of the magnetic field correction coil (called the shimming coil) is controlled to make the magnetic field uniform. In addition, in NMR, only the magnetic field of one axis (called the quantization axis) quantized by the strong external magnetic field affects the measurement accuracy, and the magnetic field in the direction perpendicular to the quantization axis can be ignored. Therefore, in the gradient shimming method, only the magnetic field of the quantization axis is corrected.

[0008] Furthermore, in the field of atomic spectroscopy, so-called Helmholtz coils are used to correct uniform components of a magnetic field.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent No. 6206973

[0012] Patent Document 2: Japanese Patent Application No. 2018-510494

[0013] Patent Document 3: Japanese Patent Application Publication No. 2019-129166

[0014] Patent Document 4: U.S. Patent No. 5343151

[0015] Non-patent literature

[0016] Non-patent literature 1: Stefan Vogt et al., "A transportable optical lattice clock", Journal of Physics: Conference Series 723 012020, 2016

[0017] Non-patent literature 2: SB Koller et al., "Transportable Optical Lattice Clock with 7×10-17 Uncertainty", Physical review letters 118073601, 2017

[0018] Non-patent literature 3: William Bowden et al., “A pyramid MOT with integrated optical cavities as a cold atom platform for an optical lattice clock”, Scientific Reports 9 11704, 2019

[0019] Non-patent document 4: S. Origlia et al., "Towards an optical clock for space: Compact, high-performance optical lattice clock based on bosonic atoms", Physical Review A 98, 053443, 2018

[0020] Non-patent literature 5: N. Poli et al., "Prospect for a compact strontium optical lattice clock", Proceedings of SPIE 6673, 2007 Summary of the invention

[0021] Problem that the invention aims to solve

[0022] By further miniaturizing or making the optical lattice clocks described in the above-mentioned Non-Patent Documents 1 to 5 more portable, the transport and installation of the optical lattice clock becomes easier, and the usability is also improved.

[0023] When the magnetic field correction coil is miniaturized and installed close to the space where atoms are trapped, the spatial variation of the generated magnetic field will increase, and it will be difficult to normalize the magnetic field. Therefore, if the number of magnetic field correction coils is increased to increase the precision, the adjustment of the magnetic field correction coil will take time. In addition, when the optical lattice clock is made portable or when it is necessary to measure in an environment where the magnetic field changes, it is required to calibrate the magnetic field quickly and accurately.

[0024] In addition, regarding the homogenization of the magnetic field, if only the magnetic field distribution of the space to be homogenized is grasped for correction, sometimes the accuracy may not necessarily be improved due to magnetic field fluctuations, magnetic field measurement errors, adjustment errors, etc. Therefore, it can be considered that it is desirable to grasp the magnetic field distribution around the space to be homogenized to improve the correction accuracy.

[0025] In addition, in the NMR described in the above-mentioned patent document 4, the NMR device is not intended to be portable, and since the sample is placed in a container, the adjustment of the magnetic field is easy. In addition, in order to measure the relaxation to the magnetic field pulse, the gradient shimming method can be applied. Therefore, the premise of calibrating the magnetic field is very different from that of the optical lattice clock.

[0026] An object of the present invention is to realize an optical lattice clock having a new adjustment mechanism for making a magnetic field uniform using a magnetic field correction coil.

[0027] Solutions for solving problems

[0028] The optical lattice clock of the present invention comprises: a clock transition space, in which an atomic group enclosed in an optical lattice is configured; a three-axis magnetic field correction coil, which corrects the magnetic field of the clock transition space; an acquisition unit, which prompts the atomic group enclosed in the optical lattice to perform clock transition in a correction space that includes the clock transition space and is wider than the clock transition space, and obtains the frequency distribution of the clock transition in the correction space; and a correction unit, which corrects the magnetic field of the three-axis magnetic field correction coil based on the frequency distribution obtained by the acquisition unit.

[0029] In one embodiment of the present invention, a moving unit is provided, which utilizes a moving optical lattice to move the atomic group enclosed in the optical lattice, and the acquisition unit obtains the frequency distribution of clock transitions in the correction space by measuring the frequencies of clock transitions of the atomic group at multiple locations in the correction space moved by the moving unit.

[0030] In one embodiment of the present invention, the three-axis magnetic field correction coil includes: a first coil group, which can only correct the constant term and the first-order spatial differential term in the magnetic field; and a second coil group, which can correct the second-order or higher-order spatial differential terms in the magnetic field. After the correction unit adjusts the current flowing through the second coil group based on the frequency distribution and corrects the higher-order spatial differential terms, it adjusts the current flowing through the first coil group to correct the constant term and the first-order spatial differential term.

[0031] In one aspect of the present invention, the acquisition unit acquires the frequency distribution of the clock transition in the calibration space by spatially detecting the light of the clock transition emitted by the atomic group distributed throughout the calibration space.

[0032] In one embodiment of the present invention, the correction space is extended to both sides of the clock transition space along the axes along which the photons of the optical lattice are arranged.

[0033] In the magnetic field correction method of an optical lattice clock of the present invention, the optical lattice clock comprises: a clock transition space, in which an atomic group enclosed in an optical lattice is configured; and a three-axis magnetic field correction coil, which corrects the magnetic field of the clock transition space. In the optical lattice clock, in a correction space that includes the clock transition space and is wider than the clock transition space, the atomic group enclosed in the optical lattice is prompted to perform clock transition, the frequency distribution of the clock transition in the correction space is obtained, and the magnetic field of the three-axis magnetic field correction coil is corrected based on the obtained frequency distribution.

[0034] Effects of the Invention

[0035] According to the present invention, it is expected that the accuracy of magnetic field correction for the clock transition space of an optical lattice clock can be improved or accelerated. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] Figure 1 It is a schematic diagram showing the overall structure of the optical lattice clock according to the embodiment.

[0037] Figure 2 This is a diagram showing a schematic structure of a physical package of an optical lattice clock.

[0038] Figure 3 This is a diagram schematically showing the appearance of a physical package.

[0039] Figure 4 Yes Figure 3 FIG. 1 is a diagram showing a partial perspective view of the interior of a physical package.

[0040] Figure 5 It is a diagram showing the overall shape of the three-axis magnetic field correction coil.

[0041] Figure 6 FIG. 1 is a diagram showing the shape of the first coil group of the X-axis magnetic field correction coil.

[0042] Figure 7 FIG. 1 is a diagram showing the shape of the second coil group of the X-axis magnetic field correction coil.

[0043] Figure 8 FIG. 1 is a diagram showing the shape of the first coil group of the Y-axis magnetic field correction coil.

[0044] Fig. 9 FIG. 2 is a diagram showing the shape of the second coil group of the Y-axis magnetic field correction coil.

[0045] Fig.10 FIG. 1 is a diagram showing the shape of the first coil group of the Z-axis magnetic field correction coil.

[0046] Fig.11 2 is a diagram showing the shape of the second coil group of the Z-axis magnetic field correction coil.

[0047] Fig.12 It is a diagram showing the shape of a holder of a three-axis magnetic field correction coil.

[0048] Fig.13 This is a diagram showing an example of a correction coil using a flexible printed circuit board.

[0049] Fig.14 This is a diagram showing a cylindrical correction coil using a flexible printed circuit board.

[0050] Fig.15 : is a diagram showing an example of the current flowing through the correction coil.

[0051] Fig.16 is shown with Fig.15 Diagram of the flow of the equivalent current in the correction coil.

[0052] Fig.17 : is a diagram showing another example of the current flowing through the correction coil.

[0053] Fig.18 is shown with Fig.17 Diagram of the flow of the equivalent current in the correction coil.

[0054] Fig.19 FIG. 1 is a diagram showing another example of a correction coil using a flexible printed circuit board.

[0055] Fig. 20 It is a diagram showing a physical package having a spherical vacuum chamber.

[0056] Fig.21 This is a diagram showing another example of the installation of the three-axis magnetic field correction coil.

[0057] Fig. 22 Yes Description Fig.21 Diagram of the support method of the 3-axis magnetic field correction coil.

[0058] Fig.23A Schematic diagram showing a method of correcting a magnetic field.

[0059] Fig. 23B Schematic diagram showing a method of correcting a magnetic field.

[0060] Fig.24 This is a flow chart of the calibration of the 3-axis magnetic field correction coil.

[0061] Fig.25 1 is a flowchart showing the calibration procedure of the three-axis magnetic field correction coil.

[0062] Fig.26 2 is a schematic diagram showing another example of the correction method of the magnetic field.

[0063] Fig. 27 It is a figure which shows the compensation of the leakage magnetic field in a refrigerator.

[0064] Fig.28 It is a cross-sectional view showing the structure of a Zeeman reducer and an MOT device.

[0065] Fig.29 It is a cross-sectional view illustrating the gap of the coil.

[0066] Fig.30 is shown with Fig.28 A diagram of the magnetic field distribution corresponding to the composition.

[0067] Fig.31A It is a cross-sectional view showing the structure of a Zeeman reducer and an MOT device.

[0068] Fig.31B It is a cross-sectional view showing the structure of a Zeeman reducer and an MOT device.

[0069] Fig.32 is shown with Fig.31A , Fig.31B A diagram of the magnetic field distribution corresponding to the composition.

[0070] Fig.33A It is shown Fig.31A , Fig.31B Diagram of the structure of the deformation method.

[0071] Fig.33B It is shown Fig.31A , Fig.31B Diagram of the structure of the deformation method.

[0072] Fig.34 This is a cross-sectional view of a Zeeman coil with a constant outer diameter.

[0073] Fig.35A It is a cross-sectional view showing the encapsulation of the coil for a Zeeman reducer.

[0074] Fig.35B It is a cross-sectional view showing the encapsulation of the coil for a Zeeman reducer. DETAILED DESCRIPTION

[0075] (1) Overview of the physics package

[0076] Figure 1 1 is a schematic diagram showing the overall structure of the optical lattice clock 10. The optical lattice clock is composed of a physical package 12, an optical system device 14, a control device 16, and a PC (Personal computer) 18 in combination.

[0077] The physical package 12 is a device that captures atomic groups, seals them in an optical lattice, and causes clock transitions, as described in detail below. The optical system device 14 is a device that has optical devices such as a laser light emitting device, a laser receiving device, and a laser spectrometer. In addition to emitting laser light and sending it to the physical package 12, the optical system device 14 also receives light emitted by atomic groups due to clock transitions in the physical package 12 and converts it into electrical signals and performs wave separation in the frequency band. The control device 16 is a device that controls the physical package 12 and the optical system device 14. The control device 16 is a computer dedicated to the optical lattice clock 10, and operates by controlling the computer hardware with a processor and a memory using software. In addition to performing, for example, the operation control of the physical package 12 and the operation control of the optical system device 14, the control device 16 also performs analysis processing such as frequency analysis of clock transitions obtained by measurement. The physical package 12, the optical system device 14, and the control device 16 work closely with each other to form the optical lattice clock 10.

[0078] PC18 is a general-purpose computer that operates by controlling computer hardware with a processor and a memory using software. An application for controlling the optical lattice clock 10 is installed in PC18. PC18 is connected to the control device 16, and not only controls the control device 16, but also controls the entire optical lattice clock 10 including the physical package 12 and the optical system device 14. In addition, PC18 becomes the UI (User Interface) of the optical lattice clock 10, and the user can start the optical lattice clock 10, measure the time, confirm the results, etc. through PC18. In this embodiment, the description is centered on the physical package 12. In addition, a system including the physical package 12 and the components required for its control is sometimes referred to as a physical package system. The components required for control are sometimes included in the control device 16 or PC18, but are sometimes built into the physical package 12 itself.

[0079] Figure 2 Schematically shows a physical package 12 of an optical lattice clock according to an embodiment. Figure 3 is a diagram showing an example of the appearance of the physical package 12, Figure 4 Yes Figure 3The internal structure of the physical package 12 is partially shown in perspective. Figure 2 to Figure 4 (and subsequent figures) illustrate an XYZ orthogonal linear coordinate system with the object space (clock transition space 52) in which atoms described later can exist when clock transition spectroscopy is performed as the origin, and the directions are clearly indicated.

[0080] The physical package 12 includes: a vacuum chamber 20, an atomic oven 40, a coil 44 for a Zeeman slower (ZS), an optical resonator 46, a coil 48 for an MOT (Magneto-Optical Trap) device, a low-temperature tank 54, a thermal connection component 56, a refrigerator 58, a vacuum pump body 60 and a vacuum pump cartridge 62.

[0081] The vacuum chamber 20 is a container that keeps the main part of the physical package 12 in a vacuum, and is formed in a roughly cylindrical shape. In detail, the vacuum chamber 20 includes: a main body 22, which is formed in a large roughly cylindrical shape; and a protrusion 30, which is formed in a small roughly cylindrical shape protruding from the main body 22. The main body 22 is a part that accommodates the optical resonator 46 and the like described later. The main body 22 includes: a cylindrical wall 24, which constitutes the side of the cylinder; and a front circular wall 26 and a rear circular wall 28, which constitute the circular surface of the cylinder. The front circular wall 26 is a wall provided with the protrusion 30. The rear circular wall 28 is a wall on the side opposite to the protrusion 30, and is formed in a shape with a larger diameter than the cylindrical wall 24.

[0082] The protrusion 30 includes a cylindrical wall 32 constituting the side of a cylinder and a front circular wall 34. The front circular wall 34 is a circular surface on the side away from the main body 22. The main body 22 side of the protrusion 30 is mostly open, connected to the main body 22, and has no wall.

[0083] The vacuum chamber 20 is arranged so that the central axis of the cylinder of the main body 22 (this axis is called the Z axis) is substantially horizontal. The central axis of the cylinder of the protrusion 30 (this axis is the beam axis) extends vertically above the Z axis and parallel to the Z axis.

[0084] It is assumed that the vacuum chamber 20 is formed to be less than 35 cm in the Z-axis direction, and less than 20 cm in the X-axis direction and the Y-axis direction. It is also conceivable that the length in the Z-axis direction is set to less than 30 cm, less than 25 cm, or less than 20 cm in order to further promote miniaturization. It is also conceivable that it is sufficient to set it to less than 15 cm or less than 10 cm in the X-axis direction and the Y-axis direction. In addition, the distance between the beam axis and the Z-axis is set to, for example, about 10 to 20 mm.

[0085] In the embodiment, four legs 38 are provided near the four corners of the lower part of the main body 22 of the vacuum chamber 20 to support the vacuum chamber 20. The vacuum chamber 20 is made of metal such as SUS (stainless steel) and is made strong enough to withstand the pressure difference when the inside becomes a vacuum. The rear circular wall 28 and the front circular wall 34 of the vacuum chamber 20 are formed in a detachable manner and are disassembled during maintenance and inspection.

[0086] The atomic reactor 40 is a device disposed near the front end of the protrusion 30. The atomic reactor 40 heats the solid metal disposed therein with a heater, and releases atoms that burst out of the metal due to thermal motion from the pores to form an atomic beam 42. The beam axis through which the atomic beam 42 passes is set to be parallel to the Z axis, and is set to intersect the X axis at a position slightly away from the origin. The intersection position corresponds to the capture space 50 described later, which is a tiny space in which atoms are captured. The atomic reactor 40 is basically disposed inside the vacuum chamber 20, but for cooling, the heat dissipation portion extends to the outside of the vacuum chamber 20. In the atomic reactor 40, for example, the metal is heated to a temperature of 750K. As the metal, for example, strontium, mercury, cadmium, ytterbium, etc. are selected, but are not particularly limited to these.

[0087] The Zeeman slowdown coil 44 is arranged on the downstream side of the beam axis of the atomic reactor 40 from the protrusion 30 of the vacuum chamber 20 to the main body 22. The Zeeman slowdown coil 44 is a device that combines a Zeeman slowdown device that slows down atoms in the atomic beam 42 with a MOT device that captures the slowed atoms. Both the Zeeman slowdown device and the MOT device are devices based on atomic laser cooling technology. Figure 2 The Zeeman reducer coil 44 shown is provided with a Zeeman coil used in a Zeeman reducer and one of a pair of MOT coils used in an MOT device as a series of coils. Although it is not possible to clearly distinguish, roughly speaking, the majority from the upstream side to the downstream side corresponds to the Zeeman coil that generates a magnetic field that contributes to the Zeeman reduction method, and the most downstream side corresponds to the MOT coil that generates a gradient magnetic field that contributes to the MOT method.

[0088] In the example shown in the figure, the Zeeman coil is of a decreasing type, with more turns toward the upstream side and fewer turns toward the downstream side. The Zeeman decelerator coil 44 is axially symmetrically arranged around the beam axis so that the atomic beam 42 passes inside the Zeeman coil and the MOT coil. A magnetic field with a spatial gradient is formed inside the Zeeman coil, and the Zeeman deceleration beam 82 is irradiated to decelerate the atoms.

[0089] The optical resonator 46 is a cylindrical component arranged around the Z axis, and an optical lattice is formed inside. A plurality of optical components are provided in the optical resonator 46. By providing a pair of optical mirrors on the X axis and another pair of optical mirrors parallel thereto, the optical lattice light is subjected to multiple reflections between a total of four mirrors to generate a bowtie-type optical lattice resonator. The atomic group captured in the capture space 50 is enclosed inside the optical lattice. In addition, in the optical resonator 46, when the relative frequencies of the two (right-handed and left-handed) optical lattice lights incident on the resonator are shifted, a moving optical lattice is formed in which the standing waves of the optical lattice move. By moving the optical lattice, the atomic group is moved to the clock transition space 52. In the embodiment, it is set to form an optical lattice including a moving optical lattice on the X axis. In addition, as the optical lattice, a two-dimensional or three-dimensional optical lattice in which the lattice is arranged not only on the X axis but also on one or both of the Y axis and the Z axis can also be used. In this way, the optical resonator 46 can be referred to as an optical lattice forming part that forms an optical lattice. The optical resonator 46 is also a device based on the atomic laser cooling technology.

[0090] The MOT device uses coils 48 to generate a gradient magnetic field in the trapping space 50. In the MOT device, MOT light is irradiated along the three axes of X, Y, and Z in the space where the gradient magnetic field is formed. As a result, the MOT device traps atoms in the trapping space 50. The trapping space 50 is set on the X axis. Figure 2 The Zeeman reducer coil 44 shown in the figure is provided with a Zeeman coil used in a Zeeman reducer and one of a pair of MOT coils used in an MOT device as a series of coils. In the figure, a gradient magnetic field that contributes to the MOT method is generated by a portion of the Zeeman reducer coil 44 and the MOT device coil 48.

[0091] The low temperature tank 54 is formed in a manner to surround the clock transition space 52, and the space inside is kept at a low temperature. Therefore, in the space inside, black body radiation is reduced. A thermal connection member 56 serving as a support structure is installed in the low temperature tank 54. The thermal connection member 56 conducts heat from the low temperature tank 54 to the refrigerator 58. The refrigerator 58 is a device that cools the low temperature tank 54 via the thermal connection member 56. The refrigerator 58 has a Peltier element and cools the low temperature tank 54 to, for example, 190K.

[0092] The vacuum pump body 60 and the vacuum pump barrel 62 are devices for evacuating the vacuum chamber 20. The vacuum pump body 60 and the vacuum pump barrel 62 are devices for evacuating the vacuum chamber 20. The vacuum pump body 60 is provided on the outside of the vacuum chamber 20, and the vacuum pump barrel 62 is provided on the inside of the vacuum chamber 20. The vacuum pump barrel 62 is activated by heating by a heater provided on the vacuum pump body 60 at the beginning of the start-up. Thus, the vacuum pump barrel 62 is activated and evacuates by adsorbing atoms.

[0093] The vacuum pump cylinder 62 is provided in the main body 22 in a manner arranged side by side with the Zeeman reducer coil 44. The Zeeman reducer coil 44 is arranged along the beam axis that is eccentric in the X-axis direction relative to the central axis of the cylinder of the main body 22. Therefore, there is a relatively large space on the side opposite to the eccentric direction of the Zeeman reducer coil 44. The vacuum pump cylinder 62 is provided in this space.

[0094] The physical package 12 includes, as optical system components: vacuum-resistant optical windows 64 and 66 for optical lattice light; a vacuum-resistant optical window 68 for MOT light; vacuum-resistant optical windows 70 and 72 for Zeeman slowing light and MOT light; and optical mirrors 74 and 76 .

[0095] The vacuum-resistant optical windows 64 and 66 for optical lattice light are vacuum-resistant optical windows provided in the cylindrical walls 24 facing each other in the main body 22 of the vacuum chamber 20. The vacuum-resistant optical windows 64 and 66 for optical lattice light are provided for incident and emitted optical lattice light.

[0096] The MOT light vacuum-resistant optical window 68 is provided to allow two axes of MOT light among three axes of MOT light used in the MOT device to enter and exit.

[0097] The vacuum-resistant optical windows 70 and 72 for Zeeman slowing light and MOT light are provided to allow the Zeeman slowing light and one-axis MOT light to enter and exit.

[0098] The optical mirrors 74 and 76 are provided to change the directions of the Zeeman deceleration light and the one-axis MOT light.

[0099] In addition, the physical package includes, as cooling components, a cooler 90 for a nuclear reactor, a cooler 92 for a Zeeman speed reducer, and a cooler 94 for an MOT device.

[0100] The reactor cooler 90 is a water cooling device that cools the reactor 40. The reactor cooler 90 is provided outside the vacuum chamber 20, and cools the heat dissipation portion of the reactor 40 that extends to the outside of the vacuum chamber 20. The reactor cooler 90 includes a metal water cooling pipe as a cooling pipe, and cools the vacuum chamber 20 by circulating cooling water as a liquid refrigerant inside.

[0101] The Zeeman reducer cooler 92 is provided on the wall of the vacuum chamber 20 to cool the Zeeman reducer coil 44. The Zeeman reducer cooler 92 includes a metal pipe and allows cooling water to flow inside to remove Joule heat generated in the Zeeman reducer coil 44.

[0102] The MOT device cooler 94 is a heat dissipation part provided in the circular wall part of the vacuum chamber 20. In the MOT device coil 48, the coil generates Joule heat, although the Joule heat is smaller (for example, about 1 / 10) than that in the Zeeman reducer cooler 92. Therefore, the metal of the MOT device cooler 94 extends from the MOT device coil 48 to the outside of the vacuum chamber 20, and releases heat to the atmosphere.

[0103] Furthermore, the physics package 12 includes, as components for correcting the magnetic field, a three-axis magnetic field correction coil 96 , a vacuum-resistant electrical connector 98 , an independent magnetic field compensation coil 102 for a refrigerator, and an independent magnetic field compensation coil 104 for a nuclear reactor.

[0104] The three-axis magnetic field correction coil 96 is a coil for uniformly returning the magnetic field in the clock transition space 52 to zero. The three-axis magnetic field correction coil 96 is formed in a three-dimensional shape to correct the magnetic field in the directions of the three axes X, Y, and Z. Figure 4 In the example shown, the three-axis magnetic field correction coil 96 is formed in a substantially cylindrical shape as a whole. Each coil constituting the three-axis magnetic field correction coil 96 is formed in a point-symmetrical shape with the clock transition space 52 as the center in the direction of each axis.

[0105] The vacuum-proof electric connector 98 is a connector for supplying power into the vacuum chamber 20 and is provided on the circular wall of the vacuum chamber 20. The vacuum-proof electric connector 98 supplies power to the Zeeman reducer coil 44, the MOT device coil 48, and the three-axis magnetic field correction coil 96.

[0106] The independent magnetic field compensation coil 102 for refrigerators is a coil for compensating for the leakage magnetic field from the refrigerator 58 that cools the low temperature tank 54. The Peltier element provided in the refrigerator 58 is a large current device through which a relatively large current flows, and generates a large magnetic field. Although the magnetic field is shielded by a high magnetic permeability material around the Peltier element, it cannot be completely shielded, and a part of the magnetic field leaks. Therefore, the independent magnetic field compensation coil 102 for refrigerators is set to compensate for the leakage magnetic field in the clock transition space 52.

[0107] The independent magnetic field compensation coil 104 for the nuclear reactor is a coil used to compensate for the leakage magnetic field from the heater of the nuclear reactor 40. The heater of the nuclear reactor 40 is also a large current device, and the leakage magnetic field is sometimes not negligible despite the shielding of high magnetic permeability materials. For example, even if the heater circuit is constructed by wiring with non-inductive windings, in the wiring through the wiring terminals or insulating layers, there are actually residual inductive components. In addition, for example, even in the case of covering the nuclear reactor with high magnetic permeability materials to achieve magnetic shielding, there are sometimes parts that cannot be actually covered, such as the atomic beam opening. Therefore, the independent magnetic field compensation coil 104 for the nuclear reactor is set to compensate for the leakage magnetic field in the clock transition space 52.

[0108] (2) Physical packaging actions

[0109] The basic operation of the physics package 12 will be described. In the physics package 12, the vacuum pump cylinder 62 provided inside the vacuum chamber 20 adsorbs atoms, and the inside of the vacuum chamber 20 is evacuated. As a result, the inside of the vacuum chamber 20 becomes, for example, 10 - 8 The vacuum state of the degree of Pa is such that the influence of air components such as nitrogen and oxygen is eliminated. Pretreatment is performed in advance according to the type of vacuum pump to be used. For example, with respect to a non-evaporable getter pump (NEG pump) or an ion pump, it is necessary to roughly evacuate from the atmosphere to a certain degree of vacuum before operating it. In this case, the vacuum chamber is provided with a rough evacuation port in advance, and rough evacuation is performed sufficiently from the port in advance using, for example, a turbomolecular pump. In addition, for example, when a NEG pump is used as the vacuum pump body 60, it is necessary to perform an activation process of heating to a high temperature in a vacuum in advance.

[0110] In the atomic reactor 40, the metal is heated by the heater to a high temperature, and atomic vapor is generated. In this process, the atomic vapor bursting from the metal continuously passes through the fine holes, converges and translates, and forms an atomic beam 42. The atomic reactor 40 is set in a manner so that the atomic beam 42 is formed on a beam axis parallel to the Z axis. In addition, in the atomic reactor 40, the atomic reactor body is heated by the heater, but the atomic reactor body and the joint supporting it are insulated by a thermal insulator, and the joint connected to the physical package is cooled by the atomic reactor cooler 90, so as to prevent or reduce the influence of the high temperature on the physical package 12.

[0111] The coil 44 for the Zeeman decelerator is arranged to be axially symmetrical with respect to the beam axis. The interior of the coil 44 for the Zeeman decelerator is irradiated with a Zeeman deceleration beam 82 and a MOT beam 84 of one axis. The Zeeman deceleration beam 82 is incident from the vacuum-resistant optical window 70 for Zeeman deceleration light and MOT light, and is reflected by the optical mirror 74 arranged downstream of the beam (beam) compared with the coil 48 for the MOT device. Thus, the Zeeman deceleration beam 82 overlaps with the atomic beam 42 and goes upstream of the beam axis approximately parallel to the beam axis. In this process, due to the Zeeman splitting effect and the Doppler shift effect proportional to the intensity of the magnetic field, the atoms in the atomic beam 42 absorb the Zeeman deceleration light, and are given a motion amount in the deceleration direction and decelerated. The Zeeman deceleration light is reflected by the optical mirror 76 placed next to the beam axis upstream of the Zeeman decelerator coil 44, and is emitted from the vacuum-resistant optical window 72 for Zeeman deceleration light and MOT light. Furthermore, although Joule heat is generated in the Zeeman reducer coil 44 , it is cooled by the Zeeman reducer cooler 92 , thereby preventing the coil from being heated to a high temperature.

[0112] The sufficiently decelerated atomic beam 42 reaches the MOT device formed by the MOT coil on the most downstream side of the Zeeman decelerator coil 44 and the MOT device coil 48. In the MOT device, a magnetic field having a linear spatial gradient is formed centered on the capture space 50. In addition, the MOT device is irradiated with MOT light from the positive side and the negative side in the directions of the three axes.

[0113] The MOT light beam 84 in the Z-axis direction is irradiated in the negative direction of the Z-axis, and then is reflected outside the vacuum-resistant optical window 72 for Zeeman deceleration light and MOT light, and is also irradiated in the positive direction of the Z-axis. The remaining two MOT light beams 86a and 86b are irradiated into the MOT device by the vacuum-resistant optical window 68 for MOT light and the optical mirror (not shown). Figure 4 As shown, these two axes are irradiated in two directions that are perpendicular to the Z axis and form 45 degrees with the X axis and the Y axis respectively. By setting the two MOT beams 86a and 86b to be perpendicular to the Z axis, the interval between the Zeeman reducer coil 44 and the MOT device coil 48 can be narrowed, which helps to miniaturize the vacuum chamber 20. When the direction of the irradiated MOT beam is set to form an angle of 45 degrees with the Z axis and the Y axis respectively, it is necessary to ensure a large distance in the beam axis direction so that the MOT beam does not interfere with the Zeeman reducer or the cryogenic tank. In this case, the size of the device will be larger than when the two axes of the MOT light are perpendicular to the Z axis.

[0114] In the MOT device, due to the magnetic field gradient, the atomic beam is decelerated by the restoring force with the capture space 50 as the center. As a result, the atomic group is captured in the capture space 50. In addition, the position of the capture space 50 can be finely adjusted by adjusting the offset value of the generated magnetic field of the three-axis magnetic field correction coil 96. In addition, the Joule heat generated in the MOT device coil 48 is discharged to the outside of the vacuum chamber 20 through the MOT device cooler 94.

[0115] The optical lattice beam 80 is incident on the X-axis from the vacuum-resistant optical window 64 for optical lattice light toward the vacuum-resistant optical window 66 for optical lattice light. An optical resonator 46 having two optical mirrors is provided on the X-axis to cause reflection. Therefore, on the X-axis, an optical lattice potential is formed inside the optical resonator 46 in which a standing wave extends in the X-axis direction. The atomic group is captured by the optical lattice potential.

[0116] By slightly changing the wavelength, the optical lattice can be moved along the X-axis. The atomic group is moved to the clock transition space 52 through the moving unit formed by the moving optical lattice. As a result, the clock transition space 52 deviates from the beam axis of the atomic beam 42, so that the influence of the black body radiation emitted by the high-temperature atomic furnace 40 can be eliminated. In addition, the clock transition space 52 is surrounded by a low-temperature tank 54, shielding it from the black body radiation emitted by the surrounding normal temperature material. In general, since black body radiation is proportional to the fourth power of the absolute temperature of the material, the low temperature brought by the low-temperature tank 54 has a great effect on eliminating the influence of black body radiation.

[0117] In the clock transition space 52, the atoms are irradiated with a laser controlled by optical frequency, and the clock transition (i.e., the resonant transition of the atoms that serve as the reference of the clock) is highly accurately spectroscopically measured to measure the intrinsic and unchanging frequency of the atoms. Thus, an accurate atomic clock is realized. In order to improve the accuracy of the atomic clock, it is necessary to eliminate the disturbances surrounding the atoms and accurately read the frequency. It is particularly important to remove the frequency shift caused by the Doppler effect caused by the thermal motion of the atoms. In an optical lattice clock, the motion of the atoms is frozen by enclosing the atoms in a space much smaller than the wavelength of the clock laser using an optical lattice generated by the interference of lasers. On the other hand, in the optical lattice, the frequency of the atoms will deviate due to the laser that forms the optical lattice. Therefore, as an optical lattice beam 80, by selecting a specific wavelength and frequency called a "magic wavelength" or "magic frequency", the influence of the optical lattice on the resonant frequency is eliminated.

[0118] Clock transitions are also affected by magnetic fields. Since atoms in a magnetic field cause Zeeman splitting corresponding to the strength of the magnetic field, clock transitions cannot be accurately measured. Therefore, in the clock transition space 52, the magnetic field is corrected to make the magnetic field uniform and zero. First, the leakage magnetic field caused by the Peltier element of the refrigerator 58 is dynamically compensated by the refrigerator independent magnetic field compensation coil 102 that generates a compensation magnetic field corresponding to the magnitude of the leakage magnetic field. Similarly, the leakage magnetic field caused by the heater of the nuclear reactor 40 is set to be dynamically compensated by the nuclear reactor independent magnetic field compensation coil 104. In addition, with respect to the Zeeman reducer coil 44 and the MOT device coil 48, at the timing of measuring the frequency of the clock transition, the current signal is turned off and no power is supplied, so as to be free from the influence of the magnetic field. The magnetic field of the clock transition space 52 is further corrected by the three-axis magnetic field correction coil 96. The three-axis magnetic field correction coil 96 is provided in multiple numbers in the direction of each axis, and can not only remove the same components of the magnetic field, but also remove the components that change in space.

[0119] In this way, the laser light causes the atomic group to make a clock transition in a state where the interference is removed. The light emitted as a result of the clock transition is received by the optical system device and the control device performs a spectroscopic process to obtain the frequency. The following is a detailed description of the implementation of the physical package 12.

[0120] (3) Shape and installation method of magnetic field correction coil

[0121] Reference Figure 5 to Figure 11 The three-axis magnetic field correction coil 96 in the physical package 12 will be described. Here, it is assumed that the three-axis magnetic field correction coil 96 is formed into a predetermined shape by winding a coated conductor insulated with polyimide resin or the like around a conductor such as copper.

[0122] Figure 5 : is a perspective view showing all the coils of the three-axis magnetic field correction coil 96. Figure 6 to Figure 11 3A is a perspective view showing each coil constituting the three-axis magnetic field correction coil. The three-axis magnetic field correction coil 96 is mounted near the inner wall of the main body 22 of the vacuum chamber 20. Therefore, the three-axis magnetic field correction coil 96 is formed into a substantially cylindrical shape centered on the clock transition space 52. The three-axis magnetic field correction coil 96 is formed by a first coil group and a second coil group in the direction of each axis of the X-axis, the Y-axis, and the Z-axis.

[0123] Figure 6 1 is a diagram showing the first coil group 120 in the X-axis direction (the direction of the optical lattice forming one axis, the moving direction of the optical lattice). The first coil group 120 includes two coils 122 and 124 that are separated by a distance c in the X-axis direction with the clock transition space 52 as the center. The coils 122 and 124 are both formed into a rectangle with the length of the side in the Y-axis direction set to a and the length of the side in the Z-axis direction set to b. In addition, the coils 122 and 124 are formed into a shape that is point-symmetrical with respect to the clock transition space 52.

[0124] The first coil group 120 forms coils 122 and 124 into square Helmholtz coils so that a magnetic field in the X-axis direction of the center portion can be generated approximately uniformly. The square Helmholtz coil refers to a Helmholtz coil in which coils 122 and 124 are formed into a square of a=b and c / 2a=0.5445. Coils 122 and 124 are a pair of Helmholtz coils that form a highly uniform magnetic field in the X-axis direction when currents of the same magnitude flow in the same direction. However, in an embodiment, currents of different magnitudes and directions can flow through coils 122 and 124. In addition, the uniformity of the magnetic field can be fully improved when coils 122 and 124 are set to a≠b. In the case of a>b, the deviation of the magnetic field distribution in the Y-axis direction tends to be smaller than the deviation of the magnetic field distribution in the Z-axis direction, and in the case of a<b, the deviation of the magnetic field distribution in the Z-axis direction tends to be smaller than the deviation of the magnetic field distribution in the Y-axis direction. When a≠b, the Helmholtz coil optimized for c is referred to as a rectangular Helmholtz coil. The first coil group 120 may be a rectangular Helmholtz coil.

[0125] The first coil group 120 is used to adjust the value of the magnetic field component in the X-axis direction and the spatial first-order differential term in the X-axis direction. First, 1) when the same magnitude of current flows in the same direction through the coils 122 and 124, a uniform magnetic field with almost no gradient in the X-axis direction is generated for the clock transition space 52. On the other hand, 2) when the same magnitude of current flows in the opposite directions through the coils 122 and 124, a magnetic field with substantially the same gradient in the X-axis direction is formed for the clock transition space 52. And, when the magnitude and direction of the current flowing through the coils 122 and 124 are appropriately changed, a magnetic field consisting of the linear sum of 1) and 2) is formed. Therefore, the first coil group 120 can correct the constant term component and the spatial first-order differential term in the X-axis direction for the magnetic field component Bx in the X-axis direction in the clock transition space 52.

[0126] Figure 7 1 is a diagram showing the second coil group 130 in the X-axis direction. The second coil group 130 includes two coils 132 and 134 that are separated and arranged in the X-axis direction with the clock transition space 52 as the center. The coils 132 and 134 are formed so that the square coils are deformed with curvature in the same cylindrical surface with a radius of e, and the center angle is set to f and the height in the Z-axis direction is set to g. The cylindrical surface is formed to be fixed to the fixed surface. Figure 6 The radius of the cylindrical surface of the first coil group 120 is substantially the same as that of e 2 ≈(a / 2) 2 +(c / 2) 2In addition, the coils 132 and 134 are formed into a shape that is point-symmetrical with respect to the clock transition space 52.

[0127] The second coil group 130 is a non-Helmholtz coil having a different shape from the Helmholtz coil. In addition, the coils 132 and 134 of the second coil group are electrically connected, and currents of the same magnitude are passed through them in the same direction. That is, in the coils 132 and 134, currents are passed through them in the direction of arrow 136, or currents are passed through them in the direction of arrow 138. Since the second coil group 130 is a non-Helmholtz coil, in the clock transition space 52 as the center, in addition to generating the same components that follow the Helmholtz coil, different components are also generated. However, since the magnitude and direction of the current are the same, the different components are mainly components of the spatial second-order differential term. That is, the second coil group 130 can correct the constant term component and the spatial second-order differential term in the X-axis direction for the magnetic field component Bx in the X-axis direction in the clock transition space 52.

[0128] The first coil group 120 and the second coil group 130 in the X-axis direction are basically used to control the magnetic field component Bx in the X-axis direction of the three-axis magnetic field correction coil 96. Therefore, they are collectively referred to as the X-axis magnetic field correction coil. When performing correction, first, the value of the spatial second-order differential term in the X-axis direction is reset to zero by the second coil group 130. Then, the value of the spatial first-order differential term in the X-axis direction is reset to zero by the first coil group 120, and the value of the constant term in the X-axis direction is adjusted to zero.

[0129] Figure 8 : is a diagram showing the first coil group 140 in the Y-axis direction. The first coil group 140 is formed by deforming a square coil in a curvature manner and being located on a cylindrical surface of a radius h with the clock transition space 52 as the center. In the first coil group, the composite coil 142 and the composite coil 145 are separately arranged in the Y-axis direction, the composite coil 142 includes a coil 143 and a coil 144, and the composite coil 145 includes a coil 146 and a coil 147. The center angle of the coils 143, 144, 146, and 147 is set to i, and the height in the Z-axis direction is set to j. The coils 143 and 144 are formed so that the end edges overlap or are adjacent to each other. Similarly, the coils 146 and 147 are formed so that the end edges overlap or are adjacent to each other. The composite coil 142 and the composite coil 145 are formed to be point symmetrical with the clock transition space 52 as the center. In addition, the coil 143 and the coil 146 , and the coil 144 and the coil 147 are also formed to be point-symmetrical with the clock transition space 52 as the center.

[0130] First, 3) consider the case where the same current flows in the same direction through the coils 143 and 144. In this case, the currents of the overlapping or adjacent parts cancel each other out, and the composite coil 142 as a whole acts like a large coil. Similarly, when the same current flows in the same direction through the coils 146 and 147, the composite coil 145 as a whole acts like a large coil. The first coil group 140 is set so that the composite coil 142 and the composite coil 145 are a pair of Helmholtz coils. Figure 8 The Helmholtz coil on the cylindrical surface shown (i.e., a Helmholtz coil formed by bending two square coils and arranging them on the same cylindrical surface) refers to a Helmholtz coil with a center angle set to about 120 degrees. The length in the Z-axis direction is not particularly limited, but it is known that the longer the length in the Z-axis direction is compared to the radius of the cylinder, the higher the uniformity of the magnetic field in the center. The first coil group 140 can make the Y-axis component of the magnetic field uniform near the center by adjusting the direction and magnitude of the current flowing.

[0131] Next, 4) the current in the case of forming the Helmholtz coil is slightly changed. Specifically, the current of the coil 143 and the coil 147 is only slightly increased in the same direction. In this case, the component of the Y-axis direction of the magnetic field will have the value of the spatial first-order differential term in the X-axis direction. In addition, strictly speaking, the magnetic field generated by the coil 143 and the coil 147 also has a component in the X-axis direction. When adjusting the first coil group 140, it is also necessary to adjust the X-axis magnetic field correction coil.

[0132] Fig. 9 1 is a diagram showing the second coil group 150 in the Y-axis direction. Fig. 9 The second coil group 150 shown includes a pair of coils 152 and 154 facing each other in the Y-axis direction. Coils 152 and 154 are non-Helmholtz coils formed in a shape in which a circular coil with a radius of k has a curvature and is located on a cylindrical surface with a radius of l centered on the clock transition space 52. In the non-Helmholtz coil, a component of the spatial second-order differential term of the magnetic field is also formed. Therefore, the second coil group 150 is used to control the spatial second-order differential term in the X-axis direction of the magnetic field component By in the Y-axis direction.

[0133] Figure 8 The first coil group 140 and the Fig. 9 The second coil group 150 in the Y-axis direction shown basically forms a Y-axis magnetic field correction coil for correcting the magnetic field component By in the Y-axis direction. The Y-axis magnetic field correction coil can correct the constant term of the magnetic field component By in the Y-axis direction, the spatial first-order differential term in the X-axis direction, and the spatial second-order differential term in the X-axis direction.

[0134] Fig.10 : is a diagram showing the first coil group 160 in the Z-axis direction. The first coil group 160 is configured so that circular composite coils 162 and 165 with a radius of m are opposite to each other at a distance n. The composite coils 162 and 165 are in a point-symmetrical relationship with respect to the center. In addition, the composite coil 162 is formed by overlapping or adjacent chords of semicircular coils 163 and 164. The semicircular coil 163 is configured on the positive side of the X-axis, and the semicircular coil 164 is configured on the negative side of the X-axis. Similarly, the composite coil 165 is formed by combining a semicircular coil 166 located on the positive side of the X-axis with a semicircular coil 167 located on the negative side of the X-axis.

[0135] The dimensions of the composite coils 162 and 165 are set so as to form a Helmholtz coil. The circular Helmholtz coil is in the relationship of m=n. The composite coils 162 and 165 are set in the following range: when the same current of the same magnitude flows in the same direction to both, the uniformity of the magnetic field in the Z direction near the center is substantially equivalent to that of the Helmholtz coil. However, in the coils 163 and 164 constituting the composite coil 162, the direction and magnitude of the current can be freely changed. Therefore, Figure 8 Similar to the first coil group 140 in the Y direction shown, the first coil group 160 can correct the constant term of the magnetic field component Bz in the Z direction and the spatial first-order differential term in the X-axis direction.

[0136] Fig.11 1 is a diagram showing the second coil group 170 in the Z-axis direction. In the second coil group 170, circular coils 172 and 174 with a radius of p are arranged relative to each other at a distance q in the Z-axis direction. The second coil group 170 is a non-Helmholtz coil. In a non-Helmholtz coil, there are different components. Therefore, the spatial second-order differential term in the X-axis direction of the magnetic field component Bz in the Z-axis direction can be corrected.

[0137] Fig.10 The first coil group 160 and the Fig.11 The second coil group 170 in the Z-axis direction shown basically forms a Z-axis magnetic field correction coil for correcting the magnetic field component Bz in the Z-axis direction. The Z-axis magnetic field correction coil can correct the constant term of the magnetic field component Bz in the Z-axis direction, the spatial first-order differential term in the X-axis direction, and the spatial second-order differential term in the X-axis direction.

[0138] Figure 5The three-axis magnetic field correction coil 96 shown is formed by combining and controlling the X-axis magnetic field correction coil, the Y-axis magnetic field correction coil, and the Z-axis magnetic field correction coil. The three-axis magnetic field correction coil 96 can correct the constant term, the spatial first-order differential term in the X-axis direction, and the spatial second-order differential term in the X-axis direction for the magnetic field component Bx in the X-axis direction. For the magnetic field component By in the Y-axis direction, the constant term, the spatial first-order differential term in the X-axis direction, and the spatial second-order differential term in the X-axis direction can be corrected. In addition, for the magnetic field component Bz in the Z-axis direction, the constant term, the spatial first-order differential term in the X-axis direction, and the spatial second-order differential term in the X-axis direction can be corrected.

[0139] In the three-axis magnetic field correction coil 96, correction is performed to uniformly change the value of the magnetic field in the clock transition space 52 to zero. In the one-dimensional optical lattice, the clock transition space 52 is set to a size of, for example, 10 mm in the X-axis direction (the direction of the lattice) and 1 to 2 mm in the Y-axis and Z-axis directions. The magnetic field is controlled for this space so that, for example, the error of the magnetic field is within 3 μG, within 1 μG, or within 0.3 μG. The accuracy of the Helmholtz coil and the non-Helmholtz coil used in the three-axis magnetic field correction coil 96 is set so that the magnetic field can be formed.

[0140] like Figure 4 As shown, the three-axis magnetic field correction coil 96 is formed into a shape having point symmetry with the clock transition space 52 as the center, and can perform magnetic field correction of the clock transition space 52 with good accuracy. However, from a macroscopic point of view, the capture space 50 also exists near the center of the three-axis magnetic field correction coil. Therefore, it can also be used to correct the magnetic field of the capture space 50 generated by the MOT device. That is, during the period when the MOT device is started to capture atoms from the atomic beam 42, the current is controlled to perform magnetic field correction of the capture space 50. And, after the capture is completed, it is only necessary to stop supplying power to the Zeeman reducer coil 44 and the MOT device coil 48 and perform magnetic field correction of the clock transition space 52. In this way, the position of the capture space 50 can be adjusted with high accuracy, and the atomic group can be efficiently enclosed in the optical lattice.

[0141] Fig.12 1 is a diagram showing a cylindrical holder 180 on which a three-axis magnetic field correction coil 96 is mounted. The holder 180 is formed by connecting annular frames 182 and 184 with eight linear frames 186. The three-axis magnetic field correction coil 96 is mounted on the inner wall and the outer wall of the holder 180. The holder 180 is fixed to the rear circular wall 28 of the main body 22 of the vacuum chamber 20. By mounting the three-axis magnetic field correction coil 96 on the holder 180, the assembly and maintenance inspection work of the physical package 12 becomes efficient.

[0142] The holder 180 is formed of a resin, aluminum or the like which is a low magnetic permeability material so as not to affect the magnetic field generated by the three-axis magnetic field correction coil 96. In addition, the holder 180 is provided inside the main body 22 coaxially with the central axis of the cylinder of the main body 22. The holder 180 is formed to a size close to the inner diameter of the main body 22. Therefore, the three-axis magnetic field correction coil 96 and the holder 180 occupy almost no space inside the main body 22. However, the coils 122 and 124 of the first coil group 120 in the X-axis direction are assembled in a manner that they cross the inner side of the main body 22 in a straight line.

[0143] The holder 180 is formed into a sparse structure using a frame. A sparse structure refers to a structure with many gaps on each surface. By setting the holder 180 as a sparse structure, in addition to being lightweight, it is also easy to prevent interference with lasers incident on or emitted from the vacuum chamber 20.

[0144] The three-axis magnetic field correction coil 96 may be entirely mounted on the inner wall of the holder 180, or entirely mounted on the outer wall of the holder 180, instead of being dispersedly mounted on the inner wall and the outer wall of the holder 180. In this case, for example, the three-axis magnetic field correction coil 96 can be simply fixed using a circular ring-shaped fastener that presses the three-axis magnetic field correction coil 96 against the outer wall or a circular ring-shaped fastener that presses the three-axis magnetic field correction coil 96 against the inner wall. In addition, the three-axis magnetic field correction coil 96 can also be fixed to the inner wall of the main body 22 without using the holder 180.

[0145] The three-axis magnetic field correction coil 96 described above is assumed to be formed by winding the coated conductive wire once or a plurality of times. However, a part or all of the three-axis magnetic field correction coil 96 may be formed by a flexible printed circuit board.

[0146] Fig.13 1 is a diagram showing a flexible printed substrate unfolded on a plane. A correction coil 190 is formed on the flexible printed substrate. The correction coil 190 includes: a current path 192, which is composed of a printed electrical conductor such as copper and participates in the formation of a magnetic field; and an insulating portion 194, which is formed of a sheet of flexible resin, etc., so that the correction coil 190 can be flexibly bent. Each current path 192 is connected to a wiring path 196 concentrated at one end. The wiring path 196 is also formed by printing an electrical conductor. The wiring path is a pair of adjacent configurations for supplying current back and forth, which cancels out the magnetic field formed in the surroundings. The wiring path 196 is connected to a terminal connector 198.

[0147] Fig.14 1 is a diagram showing a correction coil 190 bent into a cylindrical shape to match the main body 22 of the vacuum chamber 20. The correction coil 190 includes a boundary portion 199 in which two edges are connected or arranged adjacent to each other. Fig.14, the wiring pathway 196 and the terminal connector 198 are omitted.

[0148] It is assumed that the three-axis magnetic field correction coil composed of a flexible printed circuit board is also mounted on the cylindrical inner wall of the main body 22 or the cylindrical holder 180, similarly to the three-axis magnetic field correction coil 96 formed by winding the coated wire described above. However, in the three-axis magnetic field correction coil 96, in addition to the current path arranged on the cylindrical surface, there is also a current path separated from the cylindrical surface. Specifically, Figure 6 The side of the first coil group 120 with a length a in the X-axis direction shown in FIG. Fig.10 The straight line portion of the first coil group 160 in the Z-axis direction is separated from the cylindrical surface. Therefore, the following describes an example in which the current path arranged on the cylindrical surface among the current paths constituting the three-axis magnetic field correction coil 96 is formed by a flexible printed circuit board.

[0149] Fig.15 and Fig.16 It is shown Fig.10 FIG. 1 is a diagram showing an example in which the circular coil of the first coil group 160 in the Z-axis direction is formed by a flexible printed circuit board. Fig.15 As shown, a counterclockwise current flows in the black line current path 202, and no current flows in the gray line current path 200. At this time, if we consider that the adjacent currents flowing in opposite directions cancel each other out, it can be considered that this is similar to Fig.16 The case where current flows through the virtual current path 203 shown is equivalent.

[0150] Fig.17 and Fig.18 It is shown Figure 8 FIG. 1 is a diagram showing an example in which the outermost coil in the first coil group 140 in the Y-axis direction is formed by a flexible printed circuit board. Fig.17 In the figure, the current in the counterclockwise direction flows in the current path 206 of the black line, and the current does not flow in the current path 204 of the gray line. At this time, if we consider that the adjacent currents flowing in opposite directions cancel each other out, it can be considered that this is similar to Fig.18 The case where current flows through the imaginary current path 208 shown is equivalent.

[0151] In this way, various current paths can be formed in the flexible printed circuit board, such as a current path that flows back along the outer circumference of the cylindrical surface around the cylindrical central axis and a current path that flows back within the cylindrical surface without flowing around the cylindrical central axis.

[0152] In flexible printed substrates, such as Fig.13 In this way, in the development view, a pattern consisting of rectangular current paths can be printed. Fig.19As shown in FIG. 2 , a composite pattern including a rectangular current path 212 and a circular current path 214 is printed. In the physical package 12, since a laser path, a vacuum-resistant optical window, etc. are provided near the wall surface of the vacuum chamber 20, it is effective to provide a circular current path 214 to prevent interference. In addition, in the flexible printed substrate, a composite pattern including a rectangular current path 212 and a circular current path 214 can also be formed. Fig.16 , Fig.18 In addition, a plurality of flexible printed circuit boards can be stacked and used, and a plurality of flexible printed circuit boards can be used to form a part or all of the three-axis magnetic field correction coil.

[0153] In the flexible printed circuit board, a small amount of gas may be released from the resin of the insulating portion 194. Therefore, a material with a small amount of gas release, such as a polyimide resin, is selected for the insulating portion 194. In addition, in the manufacturing process, in addition to performing a degassing process, a defoaming process, a cleaning process, etc., a drying process at an appropriate temperature may be considered.

[0154] The three-axis magnetic field correction coil formed by the flexible printed substrate can be set in the vacuum chamber 20 in various forms. For example, it is conceivable to set the three-axis magnetic field correction coil in the state of being bent into a cylindrical shape near the inner wall surface in the main body 22, and fix it by pressing the three-axis magnetic field correction coil against the fastener of the main body 22. Alternatively, it can also be set to be assembled on the holder 180. Instead of using the holder 180 with a sparse structure, a holder with a dense structure with few holes on the surface can be used to support the surface of the flexible printed substrate.

[0155] On the other hand, the current path away from the cylindrical surface can be formed separately using a covered conductor wire. Alternatively, by changing the structure of the holder, the current path away from the cylindrical surface can also be formed using a flexible printed circuit board.

[0156] Compared with the three-axis magnetic field correction coil 96 formed by winding a coated conductive wire, the three-axis magnetic field correction coil using a flexible printed circuit board is easier to install in the vacuum chamber 20 and has advantages such as high manufacturing reproducibility and improved product yield.

[0157] In addition, the coil shape of the three-axis magnetic field correction coil can be set in various other ways. For example, by arranging a large circular coil between two circular coils on each of the three axes, a Maxwell type three-axis magnetic field correction coil can be formed. The Maxwell type three-axis magnetic field correction coil can correct the constant term, the spatial first-order differential term, and the spatial second-order differential term components of the magnetic field.

[0158] Furthermore, by arranging small circular coils with a predetermined size and interval outside a pair of large circular coils with a predetermined size and interval on each of the three axes, a tetrah type 3-axis magnetic field correction coil can be formed. In the tetrah type 3-axis magnetic field correction coil, correction of the components of the constant term, the spatial first-order differential term, the spatial second-order differential term, and the spatial third-order differential term can be performed.

[0159] The three-axis magnetic field correction coil described above has a spherical shape or a slightly deformed spherical shape as a whole, so that the internal space of the vacuum chamber can be effectively utilized, especially by being mounted on the inner wall or the vicinity of the inner wall of the substantially spherical vacuum chamber.

[0160] Fig. 20 is with Figure 4 The corresponding figure is a diagram schematically showing the appearance and interior of the physical package 218. Figure 4 The same reference numerals are used to designate the same or corresponding components. The vacuum chamber 220 of the physical package 218 is formed by a substantially spherical body portion 222 and a protrusion 30 .

[0161] Inside the main body 222, a three-axis magnetic field correction coil 224 formed of a circular coil is provided with the clock transition space 52 as the center. Fig. 20 In the figure, only one pair of Helmholtz coils is shown in the direction of each axis, but in reality, it is assumed that one or more pairs of non-Helmholtz coils are further provided on each axis. The outer edge of the three-axis magnetic field correction coil 224 can be set to a substantially spherical surface. Therefore, by being provided near the inner wall of the substantially spherical main body 222, interference with other components provided in the internal space of the main body 222 can be prevented, and the degree of design freedom is also increased.

[0162] Similarly, the 3-axis magnetic field correction coil can also be constructed using a square coil. Similar to the circular coil, a Helmholtz-type 3-axis magnetic field correction coil using a pair of square coils, a Maxwell-type 3-axis magnetic field correction coil using three square coils, a 4-group 3-axis magnetic field correction coil using two pairs of square coils, etc. can be used. These 3-axis magnetic field correction coils have a cube shape as a whole or a shape that slightly deforms the cube. Therefore, by assembling it on the inner wall or inner wall surface of a vacuum chamber that is roughly cube-shaped or roughly rectangular, the internal space of the vacuum chamber can be effectively utilized.

[0163] The three-axis magnetic field correction coil can also be mounted at a position closer to the clock transition space 52 than the inner wall of the main body 22 . Fig.21 It is briefly shown Figure 1 FIG. 4 is a diagram of the vicinity of the inner side of the optical resonator 46 shown in FIG. Fig.21In the embodiment, a cubic three-axis magnetic field correction coil 230 is provided in the space between the Zeeman reducer coil 44 and the MOT device coil 48 to replace the Figure 1 The 3-axis magnetic field correction coil 96. The 3-axis magnetic field correction coil 230 is configured with the clock transition space 52 inside the cryogenic tank 54 as the center. The 3-axis magnetic field correction coil 230 is formed by 2 pairs of coil groups including square coils in the directions of the three axes. One pair of the 2 pairs of coil groups is a Helmholtz type coil, and the other pair is a non-Helmholtz type coil. The 3-axis magnetic field correction coil 230 can compensate for the magnetic field components up to the third-order spatial differential term without particularly limiting the size and direction of the current. Or, in the case of Figure 5 to Figure 11 When currents of the same magnitude flow in the same direction as in the non-Helmholtz type coils of the three-axis magnetic field correction coils 96 shown, it is possible to easily compensate for magnetic field components up to the spatial second-order differential term.

[0164] The 3-axis magnetic field correction coil 230 and Figure 5 to Figure 11 The three-axis magnetic field correction coil 96 shown is very small in comparison and is close to the clock transition space 52. Therefore, the magnetic field formed in the clock transition space 52 will change at a relatively small spatial scale. However, the three-axis magnetic field correction coil 230 can compensate for the constant term component and the spatial first-order differential term component in a relatively wide range through the Helmholtz type coil. In addition, through the non-Helmholtz type coil, at least the magnetic field component of the spatial second-order differential term can also be compensated. Therefore, the magnetic field in the clock transition space 52 is uniformly reset to zero with sufficiently high accuracy. In addition, the three-axis magnetic field correction coil 230 is located close to the clock transition space 52, so the current flowing to form the magnetic field can be made very small, and the power saving is excellent.

[0165] Fig. 22 is from Fig.21 The side view from the direction of A. Fig. 22 As shown, the capture space 50 is irradiated with two MOT beams 86a and 86b that are perpendicular to the Z axis and form an angle of 45 degrees with the X axis and the Y axis respectively. In addition, a MOT beam 84 is also irradiated in a direction perpendicular to the paper surface. In order to adjust the gradient magnetic field formed in and around the capture space 50, a bias coil (biascoil) 234 is arranged with the capture space 50 as the center. The bias coil 234 includes: a pair of Helmholtz-type circular coils 234a facing each other along the beam axis, a pair of Helmholtz-type square coils 234b facing each other along the X axis, and a pair of Helmholtz-type square coils 234c facing each other along the Y axis. The bias coil 234 corrects the gradient magnetic field to the desired distribution by adjusting the constant term component or the spatial first-order differential term component using the coils of each axis.

[0166] An optical lattice beam 80 is irradiated on the X axis passing through the capture space 50. A low temperature tank 54 including a clock transition space 52 is set on the optical lattice beam 80. In addition, a three-axis magnetic field correction coil 230 is set around the low temperature tank 54 with the clock transition space 52 as the center. The three-axis magnetic field correction coil 230 is composed of a coil group 230b and two coil groups 230a and 230c, wherein the normal line of the surface of the coil group 230b is parallel to the Z axis, and the normal lines of the surfaces of the two coil groups 230a and 230c are perpendicular to the Z axis and form an angle of 45 degrees with the X axis and the Y axis. That is, the three-axis magnetic field correction coil 230 is configured so that the cubic shape along the X axis, the Y axis, and the Z axis is rotated 45 degrees around the Z axis.

[0167] The 3-axis magnetic field correction coil 230 is supported by flanges 44a and 48a as a supporting member for supporting the MOT device. Therefore, the 3-axis magnetic field correction coil 230 needs to be arranged close to the capture space 50 as the center of the MOT device. On the other hand, the 3-axis magnetic field correction coil 230 needs to be arranged to avoid interference with the MOT beams 86a and 86b passing through the capture space 50. Therefore, the 3-axis magnetic field correction coil 230 is arranged in a shape along the Z axis and the MOT beams 86a and 86b.

[0168] The three-axis magnetic field correction coil 230 includes Helmholtz coils and non-Helmholtz coils in the directions of each axis, and can achieve uniform magnetic field in a wide space including correction of spatial high-order differential terms. Therefore, the magnetic field can be corrected with high accuracy in the X-axis direction, which is the direction of the optical lattice beam 80.

[0169] However, since the three-axis magnetic field correction coil 230 does not surround the capture space 50, it is not possible to correct the magnetic field of the capture space 50. Therefore, as described above, the bias coil 234 for correcting the gradient magnetic field is provided in the capture space 50.

[0170] exist Fig. 20 and Fig.21 In the embodiment, a three-axis magnetic field correction coil 230 composed of a square coil is cited as an example. However, for example, a coil of another shape such as a circular coil may be used instead of a square coil. Figure 5 to Figure 11 The cylindrical three-axis magnetic field correction coil 96 is shown.

[0171] The three-axis magnetic field correction coil can also be set at two positions, one near the clock transition space 52 and the other near the inner wall of the main body 22. For example, it is conceivable to set a Helmholtz type coil near the inner wall of the main body 22 and a non-Helmholtz type coil near the clock transition space 52. By setting the non-Helmholtz type coil near the clock transition space 52, it is possible to easily perform correction of a magnetic field having a large curvature.

[0172] (4) Adjustment of magnetic field correction coil

[0173] The adjustment of the magnetic field of the three-axis magnetic field correction coil is described. Regarding the correction of the magnetic field, the regular magnetic field distribution around the clock transition space 52 is observed. When the magnetic field distribution is uneven, the current of the three-axis magnetic field correction coil 96 is operated to offset it. The observation of the magnetic field distribution is performed by moving the atomic group enclosed in the optical lattice using the moving optical lattice. Through these operations, the state in which each atom contained in the atomic group is always under the same zero magnetic field is reflected.

[0174] Fig.23A and Fig. 23B FIG. 1 is a diagram schematically showing the adjustment process of the three-axis magnetic field correction coil. Fig.23A FIG. 2 shows a state where the atomic group 240 enclosed in the moving optical lattice is moved along the X-axis. Fig. 23B The relationship between the fluorescence transition and the clock transition is shown.

[0175] like Fig.23A As shown, the atomic group 240 is enclosed in a lattice extending in the X-axis direction in a manner having a certain degree of spatial expansion. In the figure, the representative X-coordinate positions to which the atomic group 240 moves are represented as position X1, position X2, position X3, position X4, position X5, and so on. They are positions set in a correction space 242 set for correction of the magnetic field. The correction space 242 is set to a wide range that includes the clock transition space 52 for actual measurement. In an embodiment, since a one-dimensional lattice extending in the X-axis direction of the optical lattice is used, the atomic group 240 is distributed in an extended manner in the X-axis direction, and therefore, in particular, the goal is to return the magnetic field in the X-axis direction to zero with high precision. Therefore, the correction space 242 is set to have an extension in the X-axis direction. Furthermore, when the optical lattice is formed two-dimensionally, it is desirable to set a correction space that expands the clock transition space 52 in the two-dimensional direction, and when the optical lattice is formed three-dimensionally, it is desirable to set a correction space that expands the clock transition space 52 in the three-dimensional direction.

[0176] At each position in the calibration space 242 after the movement, a laser that excites the clock transition is irradiated to the atomic group 240 to excite the clock transition. The frequency of the laser is scanned to measure the frequency of the clock transition at each position. The excitation rate of the clock transition is observed using the electron shelving method. In the electron shelving method, after the clock transition is excited, the atoms are moved to the fluorescence observation space 243. Fig. 23BAs shown, by irradiating the fluorescence transition light, the atom emits fluorescence 244 according to the excitation rate, and the fluorescence is observed by the light receiver 246. The clock transition is Zeeman split according to the magnitude of the magnetic field at each position. Therefore, the magnetic field distribution at each position can be obtained based on the information of Zeeman splitting. Fig.23A The lower part of shows the frequency distribution on the X-axis obtained in this way. This method can measure the magnetic field even in a place where fluorescence cannot be observed (such as in a cryo head). In addition, in addition to the electron shelving method, the non-destructive measurement method using atomic phase shift measurement can also be used to measure the excitation rate of clock transitions.

[0177] Fig.24 and Fig.25 3-axis magnetic field correction coil is a flowchart for explaining the steps of correcting the magnetic field. Fig.24 The steps shown are used for calibration. During calibration, the currents of all coils constituting the 3-axis magnetic field correction coil are stopped (set to 0A), and the distribution of the magnetic field in the directions of the 3 axes is measured (S10). In the measurement of the magnetic field, magnetic sensors such as small coils and Hall elements are used to measure the magnetic field in the directions of the 3 axes. The measured magnetic field represents the background value when the 3-axis magnetic field correction coil is not used. Next, the same current is passed through all coils (set to n) one by one (in Fig.24 The magnetic field distribution in the directions of the three axes is measured by a magnetic field sensor (S12 to S18). By subtracting the background magnetic field from the obtained magnetic field distribution, the basic magnetic field formed by each coil with a current of 1A can be obtained.

[0178] In this calibration, the magnetic field of the calibration space 242 can also be measured. However, the calibration space 242 is located in the low temperature tank 54, and the installation of the magnetic sensor is not necessarily easy. Therefore, the magnetic field can also be measured near the calibration space 242, and it can be combined with the results of the electromagnetic field simulation to estimate the magnetic field. The measurement of the magnetic field can also be carried out in the atmosphere instead of in a vacuum. Thus, the basic magnetic field distribution formed by each coil of the 3-axis magnetic field correction coil with a current of 1A can be grasped. In principle, this calibration only needs to be performed once at the stage of creating the physical package 12.

[0179] Next, according to Fig.25 The magnetic field is corrected by the steps shown. First, as described above, the atomic group 240 is moved by using a moving optical lattice, and the frequency of the clock transition at each position in the correction space 242 is measured (S20). Then, by estimating the effect of Zeeman splitting, the magnetic field distribution in the correction space 242 is obtained (S22). The magnetic field distribution is obtained as the absolute value of the magnetic field.

[0180] Next, an optimization method such as the least square method is used to determine the current corresponding to the magnetic field corrected by each coil (S24). That is, a superposition coefficient is obtained so that the magnetic field formed in the correction space 242 becomes zero uniformly when the basic magnetic fields formed by each coil are superimposed. In addition, as described above, when using two types of coils, the Helmholtz coil and the non-Helmholtz coil, first, for the spatial high-order differential terms generated by the non-Helmholtz coil, the optimal superposition coefficient is obtained by the least square method. Next, for the constant term and the spatial first-order differential term generated by the Helmholtz coil, the optimal superposition coefficient is obtained by the least square method. Thus, the calculation is simplified, and the calculation accuracy is also improved. The obtained superposition coefficient becomes the direction and magnitude of the current flowing through each coil. By passing the obtained current through the three-axis magnetic field correction coil, the magnetic field of the three axes can be corrected (S26).

[0181] Fig.25 The calibration shown does not necessarily need to be performed frequently under normal conditions where the magnetic field does not fluctuate much. For example, when the clock transitions in the clock transition space 52 are repeatedly measured, the calibration can be performed every predetermined number of times. Fig.25 In addition, it is also possible to consider always checking the size of the Zeeman splitting when the clock transition in the clock transition space 52 is measured, and implementing Fig.25 Correction shown.

[0182] When the magnetic field correction by the three-axis magnetic field correction coil is performed in the range of the correction space 242, it can be expected that the magnetic field of the clock transition space 52 can be stably reset to zero in the same manner as when the magnetic field correction by the three-axis magnetic field correction coil is performed in the range of the clock transition space 52. It is considered that this is because, for example, when only a narrow space such as the clock transition space 52 is used as the object, it is affected by various fine-scale disturbances such as slight fluctuations in the magnetic field, errors in magnetic field measurement, and errors in the basic magnetic field of each coil. In fact, in experiments, it has been obtained that the accuracy is improved by performing correction on the correction space 242.

[0183] exist Fig.23A and Fig.25 In the example shown, a moving optical lattice is used to move the atomic group 240 to various positions in the calibration space 242. Fig.26 1 is a diagram schematically showing an example of a magnetic field distribution in the calibration space 242 measured at one time.

[0184] exist Fig.26In the embodiment, the atomic group 250 is enclosed in the optical lattice in the entire area of ​​the calibration space 242. The fluorescence 252a, 252b, 252c, 252d, and 252e of the atomic group 250 are received at once by the CCD camera 254 while retaining the spatial position information, and the frequency is obtained. In this way, the magnetic field distribution of the calibration space 242 can be immediately obtained.

[0185] (5) Independent magnetic field compensation coil

[0186] As described in (1) above, for the Peltier element (refrigerator 58) which is a large current device, an independent magnetic field compensation coil 102 for the refrigerator is provided to compensate for the magnetic field of the clock transition space 52. In addition, for the heater of the nuclear reactor 40, an independent magnetic field compensation coil 104 for the nuclear reactor is provided to compensate for the magnetic field of the clock transition space 52. In the case where the large leakage magnetic field from the large current device is completely compensated by the three-axis magnetic field correction coil, it is necessary to increase the order of the three-axis magnetic field correction coil, increase the current, etc. Therefore, it is effective to provide an independent magnetic field compensation coil to compensate for the magnetic field. Here, the independent magnetic field compensation coil 102 for the refrigerator is taken as an example to explain in detail.

[0187] Fig. 27 1 is a diagram schematically showing a configuration example of a low temperature tank 54, a thermal coupling member 56, a refrigerator 58, and an independent magnetic field compensation coil 102 for the refrigerator. The low temperature tank 54 is a hollow member surrounding the clock transition space 52. Although not shown in the figure, an opening for allowing the optical lattice light to pass into the interior is provided along the X-axis in the wall of the low temperature tank 54. The low temperature tank 54 is made of oxygen-free copper or the like having high thermal conductivity.

[0188] A thermal connection member 56 is mounted on the low temperature tank 54. The thermal connection member 56 is a member that serves as a support structure for supporting the low temperature tank 54 and a path for taking heat away from the low temperature tank 54. The thermal connection member 56 is also made of oxygen-free copper or the like having high thermal conductivity.

[0189] The refrigerator 58 includes a Peltier element 58a, a heat sink 58b, a heat insulating member 58c, and permalloy magnetic field shields 58d and 58e. The Peltier element 58a is connected to the thermal connection member 56, and heat is removed from the thermal connection member 56 by passing current. The heat sink 58b is a member made of oxygen-free copper with high thermal conductivity. The heat sink 58b is provided on the outer wall of the vacuum chamber 20, and releases the heat transferred from the Peltier element 58a to the outside of the vacuum chamber 20.

[0190] The heat insulating member 58c ensures the heat insulation between the permalloy magnetic field shield 58d and the thermal coupling member 56. The heat insulating member 58c is made of a member such as silicon dioxide having low thermal conductivity, and is formed into a spherical shape in order to reduce the number of contact points between the permalloy magnetic field shield 58d and the thermal coupling member 56. The permalloy magnetic field shield 58e is a magnetic field shielding body, and is made of permalloy having high thermal conductivity and high magnetic permeability. The permalloy magnetic field shield 58e is disposed between the Peltier element 58a and the heat sink 58b, and conducts heat from the Peltier element 58a to the heat sink 58b.

[0191] The low temperature tank 54 is provided with a temperature sensor 260 using a thermocouple, thermistor or the like, and the measured temperature T1 is input to the control device 262. In addition, a temperature sensor 264 is provided on the heat sink 58b or its periphery, and the measured temperature T2 is input to the control device 262.

[0192] The control device 262 controls the current so that the temperature T1 of the low temperature tank 54 is always kept at a constant low temperature (e.g., 190 K). The control is performed, for example, by PID (Proportional Integral Differential) control taking into account the temperature T2 on the heat sink 58 b side. The determined current flows to the Peltier element 58 a through the current path 266.

[0193] The Peltier element 58a is a thermoelectric element that moves heat according to the current flowing therethrough. When the current flows therethrough, the Peltier element 58a removes heat from the thermal coupling member 56 on the low temperature side (and the low temperature tank 54 connected to the thermal coupling member 56), and releases the heat to the permalloy magnetic field shield 58e on the high temperature side (and the heat sink 58b connected to the permalloy magnetic field shield 58e).

[0194] A large current of, for example, several amperes flows through the Peltier element 58a. Therefore, a large magnetic field is generated. Most of the Peltier element 58a is covered by the permalloy magnetic field shield 58d and the permalloy magnetic field shield 58e, which are high magnetic permeability materials. Therefore, most of the generated magnetic field flows inside these components and does not leak to the outside. However, from the perspective of heat conduction efficiency, it is impossible to set a magnetic field shield between the thermal coupling component 56 and the Peltier element 58a. Therefore, a leakage magnetic field 270 is generated. The leakage magnetic field 270 will cause the magnetic field in the clock transition space 52 inside the low temperature tank 54 to become disordered.

[0195] Therefore, in the embodiment, the refrigerator independent magnetic field compensation coil 102 is provided around the thermal coupling member 56 which is an opening portion that cannot shield the magnetic field. The refrigerator independent magnetic field compensation coil 102 generates a compensation magnetic field 272 when current flows therethrough.

[0196] In the independent magnetic field compensation coil 102 for refrigerators, current flows through the current path 268 branched from the current path 266. That is, the Peltier element 58a and the independent magnetic field compensation coil 102 for refrigerators are in a relationship of being connected in parallel to the same current path. The resistance of the Peltier element 58a and the resistance of the independent magnetic field compensation coil 102 for refrigerators will slightly change depending on the temperature, but both can be regarded as approximately constant values ​​under the temperature environment in which the measurement is performed. Therefore, the current flowing from the control device 262 to the current path 266 is distributed to the Peltier element 58a and the independent magnetic field compensation coil 102 for refrigerators at a constant ratio.

[0197] When the current flowing through the Peltier element 58a increases, the current flowing through the independent magnetic field compensation coil 102 for refrigerators also increases in proportion to the increase in the current. Therefore, when the leakage magnetic field 270 from the Peltier element 58a increases, the compensation magnetic field 272 generated by the independent magnetic field compensation coil 102 for refrigerators also increases by the same amount. The independent magnetic field compensation coil 102 for refrigerators is formed so that when a current of a certain magnitude flows through the current path 266, the leakage magnetic field 270 in the clock transition space 52 inside the low temperature tank 54 is compensated (a magnetic field of the same magnitude is generated in the opposite direction). Therefore, the magnetic field can be compensated even when the current changes. In addition, although current also flows through the current paths 266 and 268, the current flows back and forth in the current paths 266 and 268 close to each other, so the magnetic field generated is small and does not become a problem.

[0198] The arrangement of the current paths 266 and 268 can be referred to as a compensation current control unit that dynamically changes the current flowing through the independent magnetic field compensation coil 102 for the refrigerator according to the leakage magnetic field 270. The compensation current control unit can also be constructed in other ways, for example, the control device 262 causes the required current obtained by calculation to flow through the independent magnetic field compensation coil 102 for the refrigerator.

[0199] exist Fig. 27 In the example shown, the independent magnetic field compensation coil 102 for refrigerators is formed by a single coil wound around the thermal coupling member 56. In this configuration, since the independent magnetic field compensation coil 102 for refrigerators is disposed near the wall of the vacuum chamber 20, it is possible to prevent the configuration near the low-temperature tank 54 from becoming complicated. However, the location where the independent magnetic field compensation coil 102 for refrigerators is disposed is not particularly limited, and for example, it may be disposed near the low-temperature tank 54. When the independent magnetic field compensation coil 102 for refrigerators is disposed near the low-temperature tank 54, the independent magnetic field compensation coil 102 for refrigerators can be miniaturized and power-saving can be achieved.

[0200] The refrigerator independent magnetic field compensation coil 102 may be formed of a plurality of coils instead of a single coil. When the distribution of the leakage magnetic field in the clock transition space 52 is complicated, it may be possible to perform compensation relatively simply by using a plurality of coils.

[0201] The current device, the independent magnetic field compensation coil and the compensation current control unit constitute a magnetic field compensation module. Since the magnetic field compensation module can perform precise magnetic field compensation, it can be applied to various devices represented by the optical lattice clock 10.

[0202] (6) Zeeman reducer

[0203] Fig.28 4 is a cross-sectional view of the Zeeman reducer coil 44 and the MOT device coil 48. In the illustrated Zeeman reducer coil 44, a coil 282 is wound around a long cylindrical bobbin 280 coaxially arranged with the beam axis. The hollow portion near the center of the bobbin is a space through which the atomic beam 42 flows along the beam axis.

[0204] From a functional point of view, most of the coil 282 is a decreasing type Zeeman coil section 284 in which the number of turns decreases gradually from the upstream side to the downstream side of the beam axis. In addition, near the most downstream side of the coil 282 in the beam axis direction is a MOT coil section 286 with a large number of turns. The coated conductors of the Zeeman coil section 284 and the MOT coil section 286 are continuous, and the magnetic field generated by the Zeeman coil section 284 extends to the vicinity of the MOT coil section 286, and the magnetic field generated by the MOT coil section 286 extends to the downstream side of the Zeeman coil section 284. Therefore, it should be noted that the boundary between the Zeeman coil section 284 and the MOT coil section 286 cannot be clearly defined.

[0205] An upstream flange 288 having a disk shape and a radius larger than the maximum radius of the Zeeman coil section 284 is provided on the upstream side of the beam axis of the bobbin 280. The upstream flange 288 is mounted on the cylindrical wall 32 at the protrusion 30 of the vacuum chamber 20. In addition, a mirror support section (not shown) is mounted in front of the upstream flange 288. An optical mirror 76 is mounted at the front end of the mirror support section.

[0206] Two downstream flanges 290 and 292 formed in the shape of annular rings having the same radius as the MOT coil unit 286 are provided on the downstream side of the beam axis of the bobbin 280. The downstream flange 290 is formed in the shape of annular rings that are relatively thick in the beam axis direction and is provided near the boundary between the Zeeman coil unit 284 and the MOT coil unit 286. The downstream flange 292 is formed in the shape of annular rings that are relatively thin in the beam axis direction and is provided on the downstream side of the MOT coil unit 286. The upper parts of the downstream flanges 290 and 292 are mounted on the upper support member 312, and the lower parts are mounted on the lower support member 314. The upper support member 312 and the lower support member 314 are respectively mounted on the rear circular wall 28 in the main body 22 of the vacuum chamber 20.

[0207] The MOT device coil 48 is arranged at a predetermined distance from the downstream side of the Zeeman reducer coil 44. The MOT device coil 48 is wound around a short cylindrical bobbin 300 coaxially arranged with the beam axis, and the MOT coil 302 is wound. A thin annular flange 304 having the same radius as the MOT coil 302 is provided on the upstream side of the bobbin 300 in the beam axis. In addition, a relatively thick annular flange 306 having the same radius as the MOT coil 302 is provided on the downstream side of the bobbin 300 in the beam axis direction. The upper parts of the flanges 304 and 306 are assembled and fixed to the upper support member 312.

[0208] The bobbin 280, upstream flange 288, and downstream flanges 290, 292 of the Zeeman reducer coil 44 are formed using copper with high thermal conductivity and low magnetic permeability. The bobbin 280, upstream flange 288, and downstream flanges 290, 292 are welded to be tightly bonded with high strength.

[0209] In the Zeeman reducer coil 44, more coils are wound on the upstream side of the beam axis, and the weight of the upstream side is heavier than that of the downstream side. Therefore, by coupling the upstream flange 288 with the cylindrical wall 32 of the protrusion 30 of the vacuum chamber 20, the Zeeman reducer coil 44 is stably arranged inside the vacuum chamber 20.

[0210] In addition, in the coil 44 for the Zeeman reducer, heat is generated due to the current flowing through the coil 282. Since the vacuum chamber 20 is in a vacuum, unlike in the atmosphere, heat conduction through the gas does not occur. Therefore, in the coil 44 for the Zeeman reducer, although a slight cooling effect due to blackbody radiation is also generated, the heat of the coil 282 needs to be removed mainly through heat conduction through the solid. The bobbin 280 is in contact with the coil 282, and heat is effectively conducted from the coil 282. In addition, the upstream flange 288 and the downstream flanges 290 and 292 have a large contact area with the coil 282, and take away the heat from the coil 282. As Figure 2As shown, the upstream flange 288 is connected to the Zeeman reducer cooler 92 at the cylindrical wall 32 of the protrusion 30. The Zeeman reducer cooler 92 cools the upstream flange 288 by circulating cooling water in a water cooling pipe made of copper or the like. In this way, the Zeeman reducer coil 44 is prevented from being overheated.

[0211] The bobbin 300, flanges 304, 306 of the MOT device coil 48 are also formed using copper with high thermal conductivity and low magnetic permeability. In addition, the bobbin 300, flanges 304, 306 are tightly joined by welding with high strength. The MOT coil 302 of the MOT device coil 48 is small and light compared to the coil 282 of the Zeeman reducer coil 44, and the MOT device coil 48 is also light as a whole. Therefore, the MOT device coil 48 is stably assembled to the rear circular wall 28 via the upper support member 312 to which the flanges 304, 306 are fixed.

[0212] In addition, in the MOT coil 302 of the MOT device coil 48, the current flowing is small and the heat generation is small compared with the coil 282 of the Zeeman reducer coil 44. In addition, in the MOT device coil 48, the MOT coil 302 is surrounded by the bobbin 300, flanges 304, and 306 in three directions. Therefore, the heat generated in the MOT coil 302 is transferred to the MOT device cooler 94 via the upper support member 312. It is assumed that the MOT device cooler 94 adopts a water cooling method. However, in the case where the heat to be removed is small, it can also be set to an air cooling method.

[0213] exist Fig.28 In the example, the number of turns of the coil 282 decreases approximately monotonically, but in detail, projections and depressions are formed in the direction of the beam axis. One of the reasons for making it have projections and depressions is to obtain the desired magnetic field strength at a specific position on the beam axis. For example, in the capture space 50 for capturing atoms, the magnetic field needs to be zero. In addition, as another reason, from the perspective of power saving, a configuration in which no magnetic field is generated at a position where a magnetic field is not required can be cited. In the coil 44 for the Zeeman reducer, it is sufficient to generate the magnetic field required to decelerate or constrain atoms. Moreover, as reasons for making it have projections and depressions, mechanical support requirements or thermal heat dissipation requirements can be cited. When the number of turns increases, the weight of the coil increases, and therefore it becomes difficult to support. In addition, the amount of heat dissipated from the coil increases. Therefore, it is possible to consider increasing the number of turns of the coil in a position that is conducive to support or a position with high heat dissipation efficiency. In Fig.28In the example shown, the coil 282 of the Zeeman reducer coil 44 is formed into a relatively convex shape with a large number of turns at the portion in contact with the upstream flange 288, and is formed into a relatively concave shape with a relatively small number of turns on the downstream side. Therefore, the center of gravity of the Zeeman reducer coil 44 is moved to the upstream flange 288 side, and the fixation by the upstream flange 288 is stabilized. In addition, since the contact area between the coil 282 and the upstream flange 288 is also increased, heat conduction can be efficiently performed from the coil 282 to the upstream flange 288.

[0214] Here, refer to Fig.29 To illustrate the void in the coil. Fig.29 It is a cross-sectional view of the upper part of two Zeeman coils 320 and 330. In the Zeeman coil 320, including the portion 322, the number of coil turns decreases monotonically in the beam axis direction. On the other hand, in the Zeeman coil 330, the number of turns is locally small in the portion 332 called the gap. However, in the Zeeman coil 330, the number of turns is locally large before and after the portion 332 in the beam axis direction. Therefore, the distribution of the magnetic field generated by the entire Zeeman coil 330 is substantially equal to the distribution of the magnetic field generated by the Zeeman coil 320.

[0215] It is theoretically possible to determine how to form the gap and the shape of the coil around it. The magnetic field distribution generated by the unit current component follows the Biot-Savart law. In addition, the conversion from magnetic field distribution to current distribution can be treated as a deconvolution method or an inverse problem in a general sense. The method of solving the minimum current path through an inverse problem is recorded in, for example, Mansfield P, Grannell PK. "NMR diffraction in solids." JPhys C: Solid State Phys 6: L422-L427 1973. However, if we do not stick to the minimum current, there are obviously multiple solutions. Fig.29 In the embodiment, assuming that the solution of the minimum current path satisfying the desired magnetic field distribution is the Zeeman coil 320, the Zeeman coil 330 which increases the current density around the gap can also form the desired magnetic field distribution.

[0216] exist Fig.28 In the coil 282 shown, a downstream flange 290 is provided in the middle of the coil 282. This is equivalent to providing the downstream flange 290 at a position with a large gap. In addition, the number of turns before and after the beam direction of the downstream flange 290 is set to be greater than the number of turns when the downstream flange 290 is not provided, thereby eliminating or reducing the influence of the downstream flange 290.

[0217] Fig.30: is a diagram showing the magnetic field distribution in the Zeeman slowdown coil 44 and the MOT device coil 48. The horizontal axis represents the position on the beam axis, and the origin corresponds to the capture space 50. The vertical axis represents the magnitude of the magnetic field on the beam axis. Since the Zeeman slowdown coil 44 and the MOT device coil 48 are formed symmetrically with respect to the beam axis, the magnetic field on the beam axis has only a component in the beam axis direction. The configuration position of the coil 282 of the Zeeman slowdown coil 44 and the configuration position of the MOT coil 302 of the MOT device coil 48 are also shown on the beam axis. The points in the coordinate graph represent the values ​​of the magnetic field obtained by calculation, and the thin lines in the coordinate graph represent the values ​​of the ideal magnetic field in terms of decelerating atoms toward the capture space 50 by Zeeman deceleration.

[0218] The magnetic field reaches its maximum value slightly downstream of the end of the upstream side of the coil 282. The value of the magnetic field decreases sharply slightly upstream of the position where the maximum value is taken, and approaches zero gently further upstream. The ideal magnetic field is a distribution in which the magnetic field is zero outside the coil 282 and the magnetic field does not leak to the outside. However, since the magnetic field generated by the current has an extension in space, for example, without providing a coil in the opposite direction to compensate (cancel) the external magnetic field, it is impossible to make the magnetic field outside the coil 282 completely zero.

[0219] The magnetic field decreases monotonically on the downstream side of the position where the magnetic field takes the maximum value. The number of turns of the coil has some unevenness as described above, but the influence of the surrounding coils creates an ideal monotonically decreasing magnetic field for Zeeman deceleration. The magnetic field with this gradient is roughly consistent with the ideal magnetic field distribution for Zeeman deceleration, indicating that the atoms can be steadily decelerated toward the capture space 50.

[0220] The magnetic field decreases rapidly from just before the downstream end of the coil 282. Although the number of turns of the MOT coil unit 286 located near this position is large, since there is no coil further downstream, the value of the magnetic field decreases rapidly.

[0221] The magnetic field decreases at a substantially constant slope and becomes zero in the capture space 50. Furthermore, the magnetic field decreases at the same slope and becomes the minimum value (negative value becomes maximum) near the MOT coil 302 of the MOT device coil 48. This is because a current flows through the MOT coil 302 in the opposite direction to the coil 282. A Helmholtz-type coil is approximately formed from the vicinity of the MOT coil portion 286 of the coil 282 to the vicinity of the MOT coil 302. Therefore, by flowing a current in the opposite direction through the MOT coil 302, a magnetic field with a constant slope can be formed. In addition, although the illustration is omitted, a magnetic field with a constant slope is also formed in a direction perpendicular to the beam axis. The MOT beam is irradiated from each of the three axes into the gradient magnetic field formed by the MOT device. Thus, atoms can be captured in the capture space 50 as the origin. On the downstream side of the MOT coil 302, the magnetic field gradually approaches zero.

[0222] In this way, by combining the Zeeman reducer coil 44 and the MOT device coil 48, the length in the beam axis direction can be shortened compared to the case where the Zeeman reducer and the MOT device are separately provided. In addition, the overall coil length can be shortened, thereby achieving power saving and heat generation reduction.

[0223] In addition, in the presence of a background magnetic field, the position where the magnetic field becomes zero deviates from the capture space 50. Therefore, during the process of capturing atoms, by adjusting the three-axis magnetic field correction coil 96 or the bias coil of the correction gradient magnetic field, a compensation magnetic field that cancels the background magnetic field near the capture space 50 can be generated.

[0224] Next, refer to Fig.31A and Fig.32 B shows an example of an incremental type Zeeman reducer coil 340 . Fig.31A 2 is a cross-sectional view showing a state before the Zeeman reducer coil 340 is installed inside the vacuum chamber 20. Fig.31B It is a cross-sectional view showing the assembled state. Fig.31A Most of the upstream side of the beam axis in the coil 342 of the Zeeman reducer coil 340 shown is a Zeeman coil section 344 having the function of a Zeeman coil. In addition, the most downstream side of the coil 342 is an MOT coil section 346 in which the functions of a Zeeman coil and a MOT coil are mixed. In the Zeeman coil section 344, the number of turns of the coil increases monotonically from the end on the upstream side toward the downstream side. And, near the end on the downstream side, after repeated bumps and depressions, the number of turns becomes the largest on the most downstream side. For convenience, the vicinity of the largest number of turns is referred to as the MOT coil section 346, but as described above, it also functions as a Zeeman coil.

[0225] The Zeeman reducer coil 340 has a bobbin inside. In addition, a flange 350 is provided at the upstream end, a flange 352 is provided in the middle of the coil 342 near the downstream end, and a flange 354 is provided at the downstream end. The flanges 350, 352, and 354 are welded to the bobbin.

[0226] A mirror support portion (not shown) is mounted on the most upstream flange 350 , and the optical mirror 76 is fixed to the mirror support portion.

[0227] The flanges 352 and 354 on the downstream side are also connected to each other at the part other than the bobbin, which improves the strength. The flange 352 is a thin disk with a large radius. The flange 352 is mounted on the annular support part 370 formed in a ring shape. The ring of the annular support part 370 is equipped with a water cooling pipe 372 in which cooling water flows, and the coil 342 is cooled by the flange 352. In the annular support part 370, two left and right beams 374 are mounted on the upper part, and two left and right beams 376 that also serve as water cooling pipes are mounted on the lower part. The beams 374 and 376 are mounted on the rear circular wall 28 in the main body 22 of the vacuum chamber 20 to support the entirety including the coil 340 for the Zeeman reducer. In addition, the beams 374 and 376 serve as a heat dissipation path for transferring the heat of the coil 342 to the rear circular wall 28. In addition, the cooling water flowing through the beam 376 can also circulate to the heat sink 58b in the refrigerator 58.

[0228] In this configuration, it is assumed that the MOT device coil 380 is attached to the rear circular wall 28 via a separately provided support member. In addition, it is assumed that the Zeeman reducer coil 340 is positioned with the MOT device coil 380 by a positioning mechanism.

[0229] Fig.32 is with Fig.30 The corresponding figure shows the magnetic distribution when using an incremental type Zeeman reducer coil 340 and a MOT device coil 380. The magnetism gradually increases from the downstream side of the coil 342 of the Zeeman reducer coil 340, and reaches a maximum value near the front of the MOT coil part 346. This increase in magnetism is very consistent with the target curve required to achieve Zeeman deceleration. On the downstream side of the position where the maximum value is taken, the magnetism decreases rapidly. Moreover, it decreases from positive to negative at a substantially constant slope before and after the capture space 50 serving as the origin, and becomes zero in the capture space 50. The magnetic field becomes minimum near the MOT device coil 380, and then gradually approaches zero.

[0230] The MOT device portions constituting the front and rear of the capture space 50 are Fig.30Compared with the case of the reduction type, the slope of the magnetic field becomes steeper. This is because the number of turns of the MOT coil unit 346 in the coil 342 is large, and the number of turns of the coil 380 for the MOT device facing each other is also large. By making the slope of the magnetic field steeper, atoms can be captured at a short distance in the beam axis direction.

[0231] in addition, Fig.32 The Zeeman reducer with coil 340 and Fig.30 Compared with the reducing type Zeeman decelerator coil 44, the length in the beam axis direction can be shortened. This is because the atoms can be decelerated efficiently in the increasing type. In the increasing type, the magnetic field required for atomic deceleration can be suppressed compared with the reducing type, so there is an advantage of being able to save electricity.

[0232] On the other hand, in the increased type Zeeman reducer coil 340, since the capture space 50 side is heavy, it is difficult to support it inside the vacuum chamber 20. In addition, in the increased type, since the number of coil turns on the capture space 50 side is large, there is a problem that the heat generation near the center of the vacuum chamber 20 increases and it is difficult to cool. However, as described above, the Zeeman reducer coil 340 is supported near the center of the vacuum chamber 20 by the annular support portion 370 with a cooling function, so these problems do not occur.

[0233] Fig.31A and Fig.31B The mounting method of the added Zeeman reducer coil 340 shown is only an example, and other methods may be adopted. Fig.33A and Fig.33B A modification example will be described.

[0234] Fig.33A 2 is a perspective view showing a state before the Zeeman reducer coil 390 is installed inside the vacuum chamber 20. Fig.33B 3 is a perspective view showing the assembled state. The coil 392 of the Zeeman reducer coil 390 is wound in the same manner as the Zeeman reducer coil 340, and has a bobbin and a plurality of flanges 394, 396, and 398 in roughly the same configuration. However, in the Zeeman reducer coil 390, the shape of the flange 396 disposed near the lower end in the beam direction is a semicircular shape of the lower half. Furthermore, the portion supporting the flange 396 also becomes a semicircular support portion 400 that is roughly U-shaped and is formed by dividing the circular ring into two halves. A water cooling pipe 402 is provided on the semicircular support portion 400.

[0235] exist Fig.33A and Fig.33BIn the manner shown, by making the flange 396 semicircular, the cooling performance is slightly reduced when the circulation of cooling water is the same. On the other hand, in the coil 390 for the Zeeman reducer, since there is a space on the upper part of the flange 396, it is easy to approach the nuclear reactor 40 side from the optical resonator 46 side inside the vacuum chamber 20. In addition, since there is a space on the upper part of the semicircular ring support portion 400, it is also easy to disassemble the optical resonator 46. Moreover, since the distance of the water-cooling pipe in the up-down direction is shortened, it is easy to prevent the flow turbulence caused by convection in the water-cooling pipe. In addition, in Fig.33A , 33B The flange 396 shown in the figure can be provided with holes in the surface as appropriate. When holes are provided, although the efficiency of heat conduction decreases, it can achieve weight reduction. Fig.31A , 31B The flange 352 shown can also be provided with a hole portion in the surface.

[0236] Fig.34 This is a cross-sectional view of another type of Zeeman reducer coil 410. In the Zeeman reducer coil 410, a bobbin 412 having different thicknesses in the beam direction is used. The inner diameter of the cylindrical bobbin 412 is constant, but the outer diameter gradually decreases in a step-like manner from the upstream to the downstream in the beam direction. In addition, the coil 414 wound around the bobbin 412 is wound more toward the downstream side in the beam axis direction. Therefore, the outer diameter of the coil 414 is approximately constant in the beam axis direction.

[0237] exist Fig.34 In the structure shown, by increasing the outer diameter of the bobbin 412, the contact area between the bobbin 412 and the coil 414 becomes larger, thereby improving the efficiency of heat conduction from the coil 414 to the bobbin 412. In addition, since the step of the bobbin 412 can be used to wind the coated conductor, the installation of the coil 414 becomes easy.

[0238] In addition, not limited to the present embodiment, if the coated conductor constituting the coil 414 is not a round wire with a circular cross section, but a rectangular wire with a square cross section, the heat conduction efficiency with the bobbin 412 etc. is further improved. In addition, when the periphery of the coil 414 is covered with a heat conductive cover as shown below, since the outer diameter of the coil 414 is constant, it is easy to make the cover and the coil 414 fit closely and remove heat through the cover.

[0239] The above describes an example in which the Zeeman reducer is disposed inside the vacuum chamber 20. By providing a cooling mechanism for removing the Joule heat generated in the coil, the Zeeman reducer can be disposed in a thermally stable manner inside the vacuum chamber 20. Hereinafter, as another example, an example in which a part or all of the coil is sealed (i.e., encapsulated) with a cover will be described.

[0240] Fig.35A and Fig.35B 1 is a side cross-sectional view showing the Zeeman reducer coil 420 and the cover 440 . Fig.35A 4 is a diagram showing a state before the cover 440 is mounted on the Zeeman reducer coil 420. Fig.35B 2 is a diagram showing a state after assembly. The Zeeman reducer coil 420 is a decreasing type in which the number of turns of the coil gradually decreases in the direction of the beam axis.

[0241] A flange 424 is provided at the end on the upstream side of the beam axis of the bobbin 422 of the coil 420 for the Zeeman reducer, and a flange 426 is also provided at a midway position on the downstream side. The bobbin 422 and the flanges 424 and 426 are formed of copper or the like as in the above-mentioned example, ensuring high thermal conductivity. Sealing members 428 and 430 made of indium are provided on the outer periphery of the flanges 424 and 426. The sealing members 428 and 430 are formed into a relatively thin sheet in the shape of an annular ring (also called a ring shape) or a relatively thick wall in the shape of an annular ring. Indium has the following characteristics: it can stably perform vacuum sealing even when a large temperature change occurs. In addition, a hermetic connector 432 as a vacuum-resistant connector is provided on the flange 426.

[0242] Coil 434 is wound between flange 424 and flange 426 on bobbin 422 , and coil 436 is wound downstream of flange 426 . Coils 434 and 436 are both formed of coated wires insulated with resin copper. Coil 434 and coil 436 are electrically connected via airtight connector 432 .

[0243] The cover 440 is formed in a cylindrical shape and is formed of the same copper as the bobbin 422, the flanges 424, 426, and the coils 434, 436, thereby suppressing deformation due to thermal expansion.

[0244] The cover 440 is provided so as to cover from the flange 424 to the flange 426. That is, a part of the inner peripheral portion of the upstream end portion of the cover 440 surrounds a part of the outer peripheral portion of the flange 424 and is sealed by the sealing member 428. In addition, a part of the inner peripheral portion of the downstream end portion of the cover 440 surrounds a part of the outer peripheral portion of the flange 426 and is sealed by the sealing member 430. The cover 440 is made to have a positive tolerance with respect to the length from the flange 424 to the flange 426, and can reliably surround both.

[0245] The air pressure inside the cover 440 can be freely set as long as the sealing members 428 and 430 can reliably seal. For example, air at atmospheric pressure can be sealed in, and a rough vacuum can also be set. Rough vacuum refers to a state of rarefaction using a turbo pump or the like, for example, set to a level of 1Pa to 0.1Pa. When the inside of the cover 440 is set to a rough vacuum, since the pressure difference between the inside and outside of the cover 440 becomes smaller when the vacuum chamber 20 is set to a vacuum, the separation of the sealing surfaces formed by the sealing members 428 and 430 can be strongly prevented.

[0246] Inert gas such as nitrogen and helium can also be sealed inside the cover 440. The inert gas is selected to be a gas with low reactivity with the resin used in the coil when the coil 434 is heated to a high temperature. The pressure of the inert gas is not particularly limited, for example, it can be 1 atmosphere or a roughly evacuated vacuum state. In addition, the inside of the cover 440 can also be filled with a lightweight resin such as foamed urethane. In this case, the strength of the cover 440 can be improved.

[0247] The Zeeman reducer coil 420 heats up due to Joule heat when energized. The coil 434 with a large number of turns generates more Joule heat than the coil 436 with a small number of turns. Therefore, the coil 434 tends to heat up. In the case of gradually heating up, a trace amount of gas (the gas is called degassing) contained in the resin of the coated wire constituting the coil 434 will be released from the resin. However, in the Zeeman reducer coil 420, the coil 434 is sealed by the bobbin 422, flanges 424, 426 and cover 440, and the degassing will not leak into the interior of the vacuum chamber 20. Therefore, the occurrence of clock transition errors caused by degassing will be prevented. Therefore, the Zeeman reducer coil 420 sealed by the cover 440 functions as a vacuum setting coil with high convenience when set in a vacuum.

[0248] The cover 440 also serves as a heat transfer medium between the flange 424 and the flange 426. That is, heat is transferred between the flange 424 and the flange 426 not only through the bobbin 422 but also through the cover 440, thereby promoting the cooling of the coils 434 and 436.

[0249] In the above description, it is assumed that the cover 440 covers the outer periphery of the flanges 424 and 426 and does not contact the coil 434. However, the cover 440 may contact a part or all of the outer surface of the coil 434. In this case, the heat from the coil 434 is directly transferred to the cover 440, so that the heat dissipation efficiency is improved. In particular, if Fig.34As shown in the coil 414, when the outer diameter of the coil 414 is constant, it is easy to fit closely with the inner circumference of the cover 440. In addition, when it is difficult to form a shape that makes the cover 440 contact the outer surface of the coil 434, a member with thermal conductivity can be inserted between the cover 440 and the coil 434.

[0250] exist Fig.35A and Fig.35B In the embodiment shown, the cover 440 does not cover the coil 436. This is because the number of turns of the coil 436 is small, and the need to take countermeasures against the release of degassing is low. In addition, the coil 436 is a part including the MOT coil portion constituting the MOT device, and the optical resonator 46 and the like are arranged nearby, so that the coil 436 is covered with a cover to avoid enlarging the diameter. However, as long as interference with surrounding devices and components can be avoided, the entirety including the coil 436 can be covered with a cover to perform packaging.

[0251] In addition, Fig.35A and Fig.35B In the example of the embodiment, the reduced type Zeeman reducer coil 420 is taken as an example. However, in the case of the increased type, part or all of the portion including the large number of turns can also be enclosed.

[0252] In addition, in the above description, the cover 440 uses the sealing components 428 and 430 of indium to fit closely with the flanges 424 and 426, and the interior is airtight. However, a sealing component formed of other materials instead of indium may also be used. When a sealing component is used, for example, the cover 440 can be mounted to the flanges 424 and 426 or removed from the flanges 424 and 426 using a fixing screw. However, for example, a semi-permanent sealing method such as welding or vacuum brazing may also be used to make the cover 440 fit closely with the flanges 424 and 426, and the interior is airtight.

[0253] In the above description, an optical lattice clock is cited as an example. However, those skilled in the art can also apply the various technologies of this embodiment to other than optical lattice clocks. Specifically, it can also be applied to atomic clocks other than optical lattice clocks or atom interferometers (atom interferometers) as interferometers using atoms. Moreover, this embodiment can also be applied to various quantum information processing devices for atoms (including ionized atoms). Here, quantum information processing equipment refers to a device that uses the quantum state of atoms or light for measurement, sensing, and information processing. In addition to atomic clocks and atom interferometers, magnetic field meters, electric field meters, quantum computers, quantum simulators, quantum repeaters, etc. can also be exemplified. In the physical packaging of quantum information processing equipment, by using the technology of this embodiment, miniaturization or portability can be achieved in the same way as the physical packaging of optical lattice clocks. In addition, it should be noted that in such equipment, the clock transition space is sometimes not regarded as a space for the purpose of clock measurement, but only as a space that causes clock transition spectroscopy.

[0254] In these devices, for example, by providing the 3-axis magnetic field correction coil of the present embodiment, it is possible to achieve an improvement in the accuracy of the device. In addition, by providing the 3 axes of the present embodiment in a vacuum chamber, it is possible to achieve miniaturization, portability, or high precision of the physical package. Moreover, by introducing a magnetic field compensation module, the magnetic field distribution can be controlled with high precision. In addition, in a physical package using a vacuum chamber, it is effective to provide a vacuum setting coil.

[0255] In the above description, specific aspects are shown for easy understanding, but these are merely examples of implementation, and various other implementations are possible.

[0256] The following are supplementary notes of this embodiment.

[0257] (Note 1)

[0258] A magnetic field compensation module, characterized by comprising:

[0259] A current device is arranged inside a vacuum chamber surrounding a clock transition space in which atoms are arranged, wherein a current used by the device flows to generate a leakage magnetic field;

[0260] a compensating coil arranged in the vicinity of said current device, in which a current for the coil is circulated; and

[0261] A control unit dynamically changes the coil current flowing through the compensation coil to compensate for the leakage magnetic field with respect to the clock transition space.

[0262] (Note 2)

[0263] The magnetic field compensation module according to Supplement 1 is characterized in that:

[0264] The current device is a Peltier element that cools a low-temperature thermostatic bath that maintains the clock transition space at a predetermined low temperature.

[0265] The control unit changes the current for the coil according to the temperature of the cryostat or the device current flowing through the Peltier element.

[0266] (Note 3)

[0267] The magnetic field compensation module according to Supplement 1 is characterized in that:

[0268] A magnetic field shielding body formed of a high magnetic permeability material is arranged around the current device.

[0269] The compensation coil compensates for the leakage magnetic field leaking from the magnetic field shielding body.

[0270] (Note 4)

[0271] The magnetic field compensation module according to Supplement 1 is characterized in that:

[0272] The control unit includes a distribution line for distributing the current for the coil from the current for the device, and distributes the current for the coil according to the current for the device.

[0273] (Note 5)

[0274] A physical packaging system for an optical lattice clock, characterized in that:

[0275] Equipped with the magnetic field compensation module described in Supplementary Note 1.

[0276] (Note 6)

[0277] A physical packaging system for an atomic clock, characterized in that:

[0278] Equipped with the magnetic field compensation module described in Supplementary Note 1.

[0279] (Note 7)

[0280] A physical packaging system for an atomic interferometer, characterized in that:

[0281] Equipped with the magnetic field compensation module described in Supplementary Note 1.

[0282] (Note 8)

[0283] A physical packaging system for a quantum information processing device for atoms or ionized atoms, characterized in that:

[0284] Equipped with the magnetic field compensation module described in Supplementary Note 1.

[0285] (Note 9)

[0286] A physical packaging system, characterized by comprising:

[0287] The magnetic field compensation module described in Note 1; and

[0288] At least one atomic laser cooling technology device in a Zeeman slowdown device, a magneto-optical trap and an optical lattice trap is used to guide the atoms to the clock transition space.

[0289] (Note 10)

[0290] A physical package, characterized in that

[0291] have:

[0292] a vacuum chamber; and

[0293] A Zeeman slowdown device comprises: a bobbin formed in a cylindrical shape, in which an atomic beam flows along a beam axis; and a series of coils wound around the bobbin, wherein the Zeeman slowdown device forms a magnetic field with a spatial gradient in the cylinder.

[0294] The bobbin is provided with a flange formed by expanding the diameter of the outer surface of the tube at a midway position in the beam axis direction.

[0295] The series of coils are wound around the bobbin across the flange,

[0296] The Zeeman reducer is disposed in the vacuum chamber by directly or indirectly assembling the flange to the vacuum chamber.

[0297] (Note 11)

[0298] The physical package according to Supplementary Note 10 is characterized in that:

[0299] The series of coils are of an increased type with more turns on the downstream side than on the upstream side of the atomic beam,

[0300] The flange is disposed on a downstream side of the spool.

[0301] (Note 12)

[0302] The physical package according to Supplementary Note 11 is characterized in that:

[0303] The vacuum chamber is formed into a substantially cylindrical shape with a central axis arranged parallel to the beam axis.

[0304] The flange is indirectly mounted to a cylindrical wall on a downstream side of the atomic beam in the vacuum chamber using a supporting member.

[0305] (Note 13)

[0306] The physical package according to Supplementary Note 12 is characterized in that:

[0307] The flange is formed in a substantially circular shape,

[0308] The support member includes a substantially annular support portion that supports the outer edge of the flange.

[0309] The substantially annular support portion is provided with a cooling mechanism for cooling the flange by circulating a liquid refrigerant through a tube.

[0310] (Note 14)

[0311] The physical package according to Supplementary Note 12 is characterized in that:

[0312] The flange is formed into a substantially fan-shaped shape with a diameter expanding in a direction including vertical downward,

[0313] The support member includes a substantially U-shaped support portion that supports the outer edge of the flange.

[0314] The substantially U-shaped support portion is provided with a cooling mechanism for cooling the flange by circulating a liquid refrigerant through a tube.

[0315] (Note 15)

[0316] The physical package according to Supplementary Note 10 is characterized in that:

[0317] The bobbin and the flange are formed of metal,

[0318] The physical package is provided with a cooling mechanism for directly or indirectly cooling the flange.

[0319] (Note 16)

[0320] The physical package according to Supplementary Note 10 is characterized in that:

[0321] A counterpart coil wound around the beam axis is further provided at a position separated from the Zeeman slowdown device toward the downstream side of the atomic beam.

[0322] The series of coils and the counterpart coil form an MOT magnetic field between the series of coils and the counterpart coil.

[0323] (Note 17)

[0324] A physical package for an optical lattice clock, characterized in that:

[0325] A physical package as described in Supplementary Note 10 is provided.

[0326] (Note 18)

[0327] A physical package for an atomic clock, characterized in that:

[0328] A physical package as described in Supplementary Note 10 is provided.

[0329] (Note 19)

[0330] A physical package for an atomic interferometer, characterized in that:

[0331] A physical package as described in Supplementary Note 10 is provided.

[0332] (Note 20)

[0333] A physical package for a quantum information processing device for atoms or ionized atoms, characterized in that:

[0334] A physical package as described in Supplementary Note 10 is provided.

[0335] (Note 21)

[0336] A vacuum setting coil, characterized by comprising:

[0337] A coil is disposed in the vacuum chamber and is wound around a beam axis through which the atomic beam flows, so as to form a magnetic field with a gradient in space; and

[0338] A sealing member airtightly surrounds a part or the whole of the coil.

[0339] (Note 22)

[0340] The vacuum installation coil according to Supplementary Note 21 is characterized in that

[0341] The sealing member is formed of metal.

[0342] (Note 23)

[0343] The vacuum installation coil according to Supplementary Note 21 is characterized in that

[0344] The sealing member comprises:

[0345] a cylindrical bobbin disposed on the inner circumference of the coil and on which the coil is wound;

[0346] two flanges formed by enlarging the diameter of the outer surface of the cylinder of the bobbin and surrounding the side surfaces of the coil in the direction of the beam axis; and

[0347] A cover surrounds the outer peripheral side of the coil between the two flanges.

[0348] (Note 24)

[0349] The vacuum installation coil according to Supplementary Note 23 is characterized in that

[0350] The cover surrounds at least a portion of the outer circumference of the two flanges.

[0351] (Note 25)

[0352] The vacuum installation coil according to Supplementary Note 23 is characterized in that

[0353] The cover is in direct contact with a part or the entirety of the outer peripheral side of the coil, or is in indirect contact with the coil via a thermally conductive member inserted into a space surrounded by the sealing member.

[0354] (Note 26)

[0355] The vacuum installation coil according to Supplementary Note 21 is characterized in that

[0356] The coil has different numbers of turns in the direction of the beam axis.

[0357] The area surrounded by the sealing member includes a portion having the largest number of turns in the coil.

[0358] (Note 27)

[0359] The vacuum installation coil according to Supplementary Note 21 is characterized in that

[0360] The space surrounded by the sealing member is maintained to be thinner than the atmosphere.

[0361] (Note 28)

[0362] The vacuum installation coil according to Supplementary Note 21 is characterized in that

[0363] An inert gas is sealed in the space surrounded by the sealing member.

[0364] (Note 29)

[0365] The vacuum installation coil according to Supplementary Note 21 is characterized in that

[0366] The space surrounded by the sealing member is filled with a foamable resin.

[0367] (Note 30)

[0368] The vacuum installation coil according to Supplementary Note 21 is characterized in that

[0369] The sealing member has a vacuum-resistant connector,

[0370] A portion of the coil that is airtightly surrounded by the sealing member and a portion that is not airtightly surrounded are electrically connected via the vacuum-resistant connector.

[0371] (Note 31)

[0372] A physical package, characterized by comprising:

[0373] The vacuum setting coil as described in Supplementary Note 21; and

[0374] The vacuum chamber.

[0375] (Note 32)

[0376] The physical package according to Supplementary Note 31 is characterized in that

[0377] The coil is a reduced type coil having a relatively small number of turns on the downstream side of the atomic beam,

[0378] The physical package includes a counterpart coil wound around the beam axis at a position separated from the reduction type coil toward the downstream side of the atomic beam.

[0379] The reducing coil and the opposing coil form a gradient magnetic field for the MOT device between the reducing coil and the opposing coil.

[0380] The sealing member airtightly surrounds a portion of the coil including the beam axis on the most upstream side, but does not surround a portion of the coil including the most downstream side.

[0381] (Note 33)

[0382] The physical package according to Supplementary Note 31 is characterized in that

[0383] The coil is an increased type coil having a relatively large number of turns on the downstream side of the atomic beam,

[0384] The physical package includes a counterpart coil wound around the beam axis at a position separated from the boosting coil toward the downstream side of the atomic beam.

[0385] The adding coil and the other coil form a gradient magnetic field for the MOT device between the adding coil and the other coil.

[0386] The sealing member airtightly surrounds a portion of the coil that includes the most downstream side of the beam axis.

[0387] (Note 34)

[0388] A physical package for an optical lattice clock, characterized in that:

[0389] A physical package as described in Supplementary Note 31 is provided.

[0390] (Note 35)

[0391] A physical package for an atomic clock, characterized in that:

[0392] A physical package as described in Supplementary Note 31 is provided.

[0393] (Note 36)

[0394] A physical package for an atomic interferometer, characterized in that:

[0395] A physical package as described in Supplementary Note 31 is provided.

[0396] (Note 37)

[0397] A physical package for a quantum information processing device for atoms or ionized atoms, characterized in that:

[0398] A physical package as described in Supplementary Note 31 is provided.

[0399] (Note 38)

[0400] A sealing member seals a coil which is arranged in a vacuum chamber and is wound around a beam axis through which an atomic beam flows to form a magnetic field with a gradient in space.

[0401] The sealing member is characterized in that

[0402] The sealing member and the coil side are sealed with indium formed into a ring-shaped sheet or thick-walled shape, thereby airtightly surrounding a part or the entirety of the coil.

[0403] Description of Reference Numerals

[0404] 10 optical lattice clock, 12 physical package, 14 optical system device, 16 control device, 18 PC, 20 vacuum chamber, 22 main body, 24 cylindrical wall, 26 front circular wall, 28 rear circular wall, 30 protrusion, 32 cylindrical wall, 34 front circular wall, 38 leg, 40 atomic furnace, 42 atomic beam, 44 coil for Zeeman reducer, 44a flange, 46 optical resonator, 48 coil for MOT device, 48a flange, 50 capture space, 52 clock transition space, 54 low temperature tank, 56 thermal connection component, 58 refrigerator, 58a Peltier element, 58b heat sink, 58c heat insulation component, 58d, 58e Permalloy magnetic field shield, 60 vacuum pump body, 62 vacuum pump cylinder, 64, 66 optical lattice light resistance vacuum optical window, 68 vacuum-resistant optical window for MOT light, 70, 72 vacuum-resistant optical window for MOT light, 74, 76 optical mirror, 80 optical lattice beam, 82 Zeeman deceleration beam, 84, 86a, 86b MOT beam, 90 cooler for atomic reactor, 92 cooler for Zeeman decelerator, 94 cooler for MOT device, 96 3-axis magnetic field correction coil, 98 vacuum-resistant electrical connector, 102 independent magnetic field compensation coil for refrigerator, 104 independent magnetic field compensation coil for atomic reactor, 120 first coil group, 122, 124 coils, 130 second coil group, 132, 134 coils, 136, 138 arrows, 140 first coil group, 142 composite coil, 143, 144 coils, 145 composite wire coil, 146, 147 coil, 150 second coil group, 152, 154 coil, 160 first coil group, 162 composite coil, 163, 164 coil, 165 composite coil, 166, 167 coil, 170 second coil group, 172, 174 coil, 180 holder, 182, 184, 186 frame, 190 correction coil, 192 current path, 194 insulating portion, 196 wiring path, 198 terminal connector, 199 boundary portion, 200, 202, 203, 204, 206, 208 current path, 210 correction coil, 212, 214 current path, 218 physical package, 220 vacuum chamber, 222 main body, 224, 230 3-axis magnetic field correction coil, 2 40 atomic group, 242 calibration space, 243 fluorescence observation space, 244 fluorescence, 246 optical receiver, 250 atomic group, 252a, 252b, 252c, 252d, 252e fluorescence, 254 CCD camera, 260 temperature sensor, 262 control device, 264 temperature sensor, 266 current path, 268 current path, 270 leakage magnetic field, 272 compensation magnetic field, 280 bobbin, 282 coil, 284 Zeeman coil part, 286 MOT coil part, 288 upstream flange, 290, 292 downstream flange, 300 bobbin, 302 MOT coil, 304, 306 flange, 312 upper support member, 314 lower support member, 320 Zeeman coil, 322 part,330 Zeeman coil, 332 part, 340 Zeeman reducer coil, 342 coil, 344 Zeeman coil part, 346 MOT coil part, 350, 352, 354 flange, 370 annular support part, 372 water cooling pipe, 374, 376 beam, 380 MOT device coil, 390 Zeeman reducer coil, 392 coil, 394, 396, 398 flange, 400 semi-circular support part, 402 water cooling pipe, 410 Zeeman reducer coil, 412 bobbin, 414 coil, 420 Zeeman reducer coil, 422 bobbin, 424, 426 flange, 428, 430 sealing member, 432 airtight connector, 434, 436 coil, 440 cover. ,

Claims

1. An optical lattice clock, characterized in that: have: Clock transition space, where groups of atoms enclosed in optical lattices are configured; A 3-axis magnetic field correction coil, which corrects the magnetic field of the clock transition space; an acquisition unit that causes a group of atoms enclosed in an optical lattice to perform clock transitions in a calibration space that includes the clock transition space and is wider than the clock transition space, and acquires a frequency distribution of the clock transitions in the calibration space; and A correction unit is configured to correct the magnetic field of the three-axis magnetic field correction coil based on the frequency distribution acquired by the acquisition unit.

2. The optical lattice clock according to claim 1, characterized in that: A moving unit is provided, wherein the moving unit moves the atomic group enclosed in the optical lattice by moving the optical lattice, The acquisition unit acquires a frequency distribution of clock transitions in the calibration space by measuring frequencies of clock transitions of the atomic group at a plurality of locations in the calibration space moved by the movement unit.

3. The optical lattice clock according to claim 1, characterized in that: The three-axis magnetic field correction coil comprises: a first coil group, which can only correct the constant term and the first-order spatial differential term in the magnetic field; and a second coil group, which can correct the second-order or higher-order spatial differential terms in the magnetic field. The correction unit adjusts the current flowing through the second coil group based on the frequency distribution to correct the spatial higher-order differential term, and then adjusts the current flowing through the first coil group to correct the constant term and the spatial first-order differential term.

4. The optical lattice clock according to claim 1, characterized in that: The acquisition unit acquires the frequency distribution of the clock transition in the calibration space by spatially detecting the light of the clock transition emitted by the atomic group distributed throughout the calibration space.

5. The optical lattice clock according to claim 1, characterized in that: The correction space is extended to both sides of the clock transition space along the axes along which the photons of the optical lattice are arranged.

6. A method for calibrating a magnetic field of an optical lattice clock, characterized in that: The optical lattice clock has: A clock transition space in which a group of atoms enclosed in an optical lattice is configured; and 3-axis magnetic field correction coils, which correct the magnetic field of the clock transition space, In the optical lattice clock, In a correction space that includes the clock transition space and is wider than the clock transition space, the atomic group enclosed in the optical lattice is prompted to perform clock transition, and a frequency distribution of the clock transition in the correction space is obtained. The magnetic field of the three-axis magnetic field correction coil is corrected based on the acquired frequency distribution.

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