JP7201172B2 - Atomic interferometer diffraction image detection method, atomic interferometer, atomic gyroscope - Google Patents

Description

The present invention relates to an atomic interferometer, and more particularly to diffraction image detection technology.

International Application No. PCT/JP2018/027827 filed prior to this application discloses a Mach-Zehnder atomic interferometer 900 (see FIG. 1) as an invention related to the present invention.

The Mach-Zehnder atomic interferometer 900 utilizes n-th order (where n is a predetermined positive integer equal to or greater than 2) Bragg diffraction. A Mach-Zehnder atomic interferometer 900 includes an atomic beam generator 100 , an interference section 200 , a traveling light standing wave generator 300 and an observation section 400 . The atomic beam generator 100, the interference section 200, and the observation section 400 are housed in a vacuum chamber (not shown).

The atomic beam generator 100 includes an atomic beam source 111 and an atomic beam collimator 113 . The atomic beam generator 100 continuously generates atomic beams 100a (thermal atomic beams or cold atomic beams) in which individual atoms are in the same state. A thermal atomic beam is generated, for example, by passing a high-speed atomic gas obtained by sublimating a high-purity metal mass 115 with an atomic beam source 111 through an atomic beam collimator 113 . The atomic beam collimator 113 is composed of, for example, a plurality of slits spaced apart in the traveling direction of the atomic beam 100a, as is well known. Also, the cooled atomic beam is generated, for example, by passing high-speed atomic gas through a Zeeman Slower (not shown) or a two-dimensional cooling device. International Application No. PCT/JP2018/027825 filed before the present application describes, as an invention related to the present invention, that the atoms of the atomic beam are alkaline earth metal atoms (calcium, strontium, barium, radium), alkali metal atoms (calcium, strontium, barium, radium), Earth-like metal atoms (similar to alkaline-earth metal atoms, atoms with an electronic configuration that does not have a magnetic moment due to electron spin in the ground state, examples include beryllium, magnesium, ytterbium, cadmium, mercury, etc.), alkali It is disclosed to be a stable isotope of an earth metal atom, or a stable isotope of an alkaline earth-like metal atom. In particular, among alkaline-earth metal atoms, alkaline-earth-like metal atoms, stable isotopes of alkaline-earth-like metal atoms, and stable isotopes of alkaline-earth-like metal atoms, atoms that do not have nuclear spins are affected by the environmental magnetic field. Not affected at all.

The traveling light standing wave generator 300 generates three traveling light standing waves (a first traveling light standing wave 200a, a second traveling light standing wave 200b, a third Generating an optical standing wave 200c). The traveling light standing wave that satisfies the n-order Bragg diffraction condition will be explained later.

The atomic beam 100a passes through three traveling light standing waves 200a, 200b, and 200c in the interference section 200. FIG. Since alkaline-earth metal atoms, alkaline-earth-like metal atoms, stable isotopes of alkaline-earth metal atoms, and stable isotopes of alkaline-earth-like metal atoms do not have hyperfine structures, Mach-Zehnder atomic interferometers At 900, a photoirradiated transition between two different momentum states |g, p ₀ > and |g, p ₁ > at the same internal state is utilized. The interference unit 200 obtains an atomic beam (diffraction image) 100b as a result of interaction between the atomic beam 100a and the three traveling light standing waves 200a, 200b, and 200c.

When the atomic beam 100a from the atomic beam generator 100 passes through the first traveling optical standing wave 200a, the states of individual atoms whose initial states are |g, p _{0 >} and |g , p ₁ >. If the interaction between the first traveling light standing wave 200a and atoms is set appropriately, the existence probability of |g, p ₀ > immediately after passing through the first traveling light standing wave 200a and |g, p ₁ The ratio of existence probability of > is 1:1. Through the absorption and emission of 2n photons traveling in opposite directions, an atom acquires the momentum of 2n photons (=p ₁ -p ₀ ) when transitioning from |g, p ₀ > to |g, p ₁ >. obtain. Therefore, the direction of motion of atoms in state |g, p ₁ > deviates greatly from the direction of motion of atoms in state |g, p ₀ >. That is, when the atomic beam 100a passes through the first traveling optical standing wave 200a, the atomic beam 100a consists of atoms in state |g, p ₀ > and state |g, p ₁ in a one-to-one ratio. It splits into atomic lines consisting of > atoms. The first traveling optical standing wave 200a is called a π/2 pulse and functions as an atomic beam splitter. The traveling direction of an atomic beam composed of atoms in the state |g, p ₁ > is based on the n-order Bragg diffraction condition. The angle between the direction of the 0th-order light (that is, the traveling direction of the atomic beam 100a composed of atoms in the state |g, p ₀ > without Bragg diffraction) and the direction based on the n-th order Bragg diffraction condition is the angle of the 0th-order light. It is n times the angle between the direction and the direction based on the first-order Bragg diffraction condition. In other words, it is possible to increase the spread (in other words, divergence) between the traveling direction of the atomic beam composed of the atoms in the state |g, p ₀ > and the traveling direction of the atomic beam composed of the atoms in the state |g, p ₁ >.

After the splitting, the atomic beam composed of atoms in the state |g, p ₀ > and the atomic beam composed of atoms in the state |g, p ₁ > pass through the second traveling optical standing wave 200b. At this time, if the interaction between the second traveling light standing wave 200b and the atoms is appropriately set, the atoms in the state |g, p ₀ > are formed by passing through the second traveling light standing wave 200b. The atomic beam is reversed to an atomic beam composed of atoms in state |g, p ₁ > during the transit process, and an atomic beam composed of atoms in state |g, p ₁ > is reversed from an atom in state |g, p ₀ > during the transit process. Inverts to a new atomic line. At this time, as for the former, the traveling direction of the atoms transitioning from |g, p ₀ > to |g, p ₁ > deviates from the motion direction of the atoms in the state |g, p ₀ > as described above. As a result, the traveling direction of the atomic beam composed of atoms in the state |g, p ₁ > after passing through the second traveling light standing wave 200b is changed to the state |g after passing through the first traveling light standing wave 200a. , p ₁ >. As for the latter, the _{atom acquires} the momentum and Lose the same momentum. That is, the direction of motion of the atoms in the transition from |g, p ₁ > to |g, p ₀ > deviates from the direction of motion of the atoms in the pre-transition state |g, p ₁ >. As a result, the traveling direction of an atomic beam composed of atoms in the state |g, p ₀ > after passing through the second traveling light standing wave 200b is changed to the state |g after passing through the first traveling light standing wave 200a. , p ₀ >. The second traveling optical standing wave 200b is called a π pulse and functions as a mirror of atomic beams.

After the inversion, the atomic beam composed of atoms in state |g, p ₀ > and the atomic beam composed of atoms in state |g, p ₁ > pass through the third traveling optical standing wave 200c. At this passing point, the atomic line composed of the atoms in the post-inversion state |g, p ₀ > and the atomic line composed of the atoms in the post-inversion state |g, p ₁ > intersect each other. At this time, if the interaction between the third traveling light standing wave 200c and atoms is appropriately set, an atomic line composed of atoms in the state |g, p ₀ > and an atom composed of atoms in the state |g, p ₁ > An atomic beam (diffraction image) 100b corresponding to the overlapping state of |g, p ₀ > and |g, p ₁ > of individual atoms included in the intersecting region with the line is obtained. Theoretically, the traveling direction of the atomic beam 100b obtained after passing through the third traveling light standing wave 200c is either the direction parallel to the direction of the 0th order light or the direction based on the nth order Bragg diffraction condition. or both. This atomic beam 100 b is the output of the interference section 200 . The third traveling optical standing wave 200c is called a π/2 pulse and functions as a combiner of atomic beams.

Angular velocities or accelerations in the plane containing the two paths of the atomic beam from the action of the first traveling optical standing wave 200a to the action of the third traveling optical standing wave 200c in the Mach-Zehnder atomic interferometer 900. is applied, a phase difference occurs between the two paths of the atomic beam from the action of the first traveling optical standing wave 200a to the action of the third traveling optical standing wave 200c. This is reflected in the existence probability of the state |g, p ₀ > and the existence probability of the state |g, p ₁ > of each atom that has passed through the optical standing wave 200c. Therefore, the observation unit 400 detects the angular velocity or acceleration by observing the atomic beam 100b from the interference unit 200 (that is, the atomic beam 100b obtained after passing through the third traveling optical standing wave 200c). For example, the observation unit 400 irradiates the atomic beam 100b from the interference unit 200 with the probe light 408, and the photodetector 409 detects the fluorescence from the atoms in the state |g, p ₁ >. Examples of the photodetector 409 include a photomultiplier tube and a fluorescence photodetector. In addition, according to this embodiment, the spatial resolution is improved, that is, two paths after passing through the third traveling light standing wave (an atomic beam composed of atoms of state |g, p ₀ > and a state |g, A CCD image sensor can also be used as the photodetector 409 because the intervals between the atomic lines (atomic lines composed of atoms with p ₁ >) are wide. Alternatively, when a channeltron is used as the photodetector 409, the atomic beam on one of the two paths after passing through the third traveling light standing wave is ionized by laser light or the like instead of the probe light, Ions may be detected with a channeltron.

As described above, the first traveling optical standing wave 200a functions as a splitter, the second traveling optical standing wave 200b functions as a mirror, and the third traveling optical standing wave 200c functions as a combiner. have the function of Each of the three traveling light standing waves (the first traveling light standing wave 200a, the second traveling light standing wave 200b, and the third traveling light standing wave 200c) satisfying these conditions is Gaussian. It is realized by appropriately setting the beam waist, wavelength, light intensity of the beam (Gaussian beam), and the difference frequency between the opposing laser beams. The beam waist of the Gaussian beam can be set optically (for example, laser light is focused by a lens), and the light intensity of the Gaussian beam can be set electrically (for example, the power of the Gaussian beam is adjusted). The optical configuration itself of the traveling light standing wave generator 300 that generates the three traveling light standing waves 200a, 200b, and 200c is well known, so the description is omitted (in FIG. 1, the laser light source, lens, Mirrors, Acousto-Optic Modulators (AOMs), etc. are shown).

The atomic beam 100a usually spreads at a small solid angle and includes atoms having a velocity component in a direction orthogonal to the traveling direction of the atomic beam 100a (hereinafter simply referred to as the orthogonal direction). Therefore, the atomic beam 100a spreads at the position of the observation section 400 due to the atoms that have not interacted with the three traveling light standing waves 200a, 200b, and 200c.

According to the Mach-Zehnder atomic interferometer 900 that utilizes the n-th order (n≧2) Bragg diffraction, the path of the atoms in the atomic beam 100b from the interference section 200 based on the n-th order Bragg diffraction condition depends on the value of n. It diverges from the direction of the 0th order light. Therefore, if the value of n is large, the path of atoms based on the n-order Bragg diffraction condition is formed outside the spread of the atomic beam 100a. In other words, the observation unit 400 can accurately observe the diffraction image because the atomic path based on the nth-order Bragg diffraction condition is not buried in the atomic beam 100a. However, high-power laser light is required to achieve the high-order Bragg diffraction condition. Therefore, from the viewpoint of power saving, it is preferable that the value of n is small.

When the value of n is small, the atomic beam 100a must be sufficiently collimated so that the path of the atoms based on the n-order Bragg diffraction condition is not buried in the atomic beam 100a. However, if the atomic beam 100a is sufficiently collimated using a plurality of slits spaced apart in the traveling direction of the atomic beam 100a, the flux of the atomic beam 100a is reduced and the SN ratio of the atomic interferometer is deteriorated.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a diffraction image detection technique in an atom interferometer that can ensure the flux of atomic beams and can satisfactorily observe diffraction images even under low-order Bragg diffraction conditions.

A diffraction image detection method of the present invention is a diffraction image detection method for an atomic interferometer. The atom interferometer detects that individual atoms that are alkaline earth metal atoms, alkaline earth-like metal atoms, stable isotopes of alkaline earth metal atoms, or stable isotopes of alkaline earth-like metal atoms are in the same state. an atomic beam generator for continuously generating atomic beams; a traveling light standing wave generator for generating three or more traveling light standing waves that satisfy the low-order Bragg diffraction condition; and an atomic beam and three or more traveling light constants. It includes an interference section that obtains an atomic beam resulting from interaction with existing waves, and an observation section that observes the atomic beam from the interference section. In the diffraction image detection method, (1) the atomic beam generator generates an atomic beam having an atomic number density distribution including a range in which the atomic number density of the atomic beam is uniform at the position of the observation unit; (2) a second step in which the observation unit observes the atomic beam from the interference unit under conditions where no standing wave of traveling light exists to obtain an atomic number density distribution in which no diffraction image is formed; , (3) the atomic number density at which the observation unit observes the atomic beam from the interference unit in the presence of all the traveling light standing waves, and the diffraction image under the low-order Bragg diffraction condition is formed within the range (4) a fourth step of obtaining a diffraction image based on the difference between the atomic number density distribution obtained in the second step and the atomic number density distribution obtained in the third step; and a step.

Further, the atom interferometer of the present invention comprises an atomic beam generator that continuously generates atomic beams in which individual atoms are in the same state, and a traveling light standing wave generator that generates three or more traveling light standing waves. , an interference unit for obtaining an atomic beam resulting from interaction between the atomic beam and three or more traveling optical standing waves, and an observation unit for observing the atomic beam from the interference unit. The atoms are alkaline earth metal atoms, alkaline earth-like metal atoms, stable isotopes of alkaline earth metal atoms, or stable isotopes of alkaline earth-like metal atoms. Each traveling optical standing wave satisfies the lower-order Bragg diffraction condition. The atomic beam generator includes an atomic beam source and an atomic beam collimator including two or more slits arranged in the traveling direction of the atomic beam from the atomic beam source. The atomic beam is collimated by the atomic beam collimator to such an extent that the diffraction image under the low-order Bragg diffraction condition is included inside the atomic beam.

Stated from another point of view, the atom interferometer of the present invention comprises an atomic beam generator that continuously generates atomic beams in which individual atoms are in the same state, and a traveling beam generator that generates three or more traveling optical standing waves. An optical standing wave generator, an interference unit for obtaining an atomic beam resulting from interaction between the atomic beam and three or more traveling optical standing waves, and an observation unit for observing the atomic beam from the interference unit. The atoms are alkaline earth metal atoms, alkaline earth-like metal atoms, stable isotopes of alkaline earth metal atoms, or stable isotopes of alkaline earth-like metal atoms. Each traveling optical standing wave satisfies the lower-order Bragg diffraction condition. The atomic beam generator generates an atomic beam having an atomic number density distribution including a range in which the atomic number density of the atomic beam is uniform at the position of the observation unit. A diffraction image under the low-order Bragg diffraction condition is formed within this range.

According to the present invention, in an atom interferometer, it is possible to secure the flux of the atomic beam and to observe the diffraction image satisfactorily even under the conditions of low-order Bragg diffraction.

A related invention Mach-Zehnder atomic interferometer. A Mach-Zehnder atomic interferometer of an embodiment. Atomic number density distribution of the atomic beam generated by the atomic beam generator. Atomic number density distribution of the atomic beam on which the diffraction image was formed. Diffraction image detection processing flow.

Embodiments of the present invention are described by taking a Mach-Zehnder atomic interference scheme as an example. Note that FIG. 2 is for understanding the embodiment, and the dimensions of each component illustrated are different from the actual dimensions.

Since the Mach-Zehnder atomic interferometer of this embodiment is partially the same as the Mach-Zehnder atomic interferometer 900 described above, the differences between the two will be described here. As for the technical matters common to both, the description of the Mach-Zehnder atomic interferometer 900 described above is incorporated here, thereby omitting the redundant description of the common matters.

In this embodiment, the traveling light standing wave generator 300 generates three traveling light standing waves (a first traveling light standing wave 200a and a second traveling light standing wave 200b) that satisfy the n-order Bragg diffraction condition. , to generate a third traveling optical standing wave 200c). Although n=1 is assumed in this embodiment, a small value for n is preferred (eg, n is 1, 2, 3, or 4).

The atomic beam generator 100 generates an atomic beam 100a having a predetermined atomic number density distribution at the position of the observation unit 400 under conditions where no standing wave of traveling light exists (step S1). The "predetermined atomic number density distribution" is an "atomic number density distribution including a range W in which the atomic beam 100a has a uniform atomic number density". The “range W in which the atomic number density of the atomic beam 100a is uniform” is, for example, a range in which the change in the atomic number density is within a minute range regardless of the position. Preferably, as shown in FIG. is a range in which the atomic number density of is constant in the direction perpendicular to the traveling direction of the atomic beam 100a. In FIG. 3, the atomic species is calcium, the heating temperature in the atomic beam source 111 is 513° C., the width of each of the two slits constituting the atomic beam collimator 113 is 0.1 mm, and the interval between the two slits is 280 mm. , the distance from the atomic beam collimator 113 to the first traveling light standing wave 200a is set to 126 mm, the interval between the first traveling light standing wave 200a and the second traveling light standing wave 200b is set to 252 mm, and the second The distance between the traveling light standing wave 200b and the third traveling light standing wave 200c is 252 mm, and the distance from the third traveling light standing wave 200c to the observation unit 400 is 504 mm. is. "Position" on the horizontal axis in FIG. 3 means the distance in the orthogonal direction from the center of the atomic line 100a. The "predetermined atomic number density distribution" more preferably has reproducibility. That is, the atomic beam 100a has substantially the same atomic number density distribution at different times at the position of the observation section 400 under the condition that no traveling optical standing wave exists.

The atomic beam 100a having such a predetermined atomic number density distribution can be produced by, for example, an atomic beam collimator 113 composed of a plurality of slits as in the conventional art, and a traveling light standing wave 200a that satisfies the low-order Bragg diffraction condition. , 200b, and 200c are collimated to such an extent that the diffraction image 100c is included inside the atomic beam 100a (more precisely, within the range W). As a result, a diffraction image 100c, which is the result of interaction between the atomic beam 100a and the traveling light standing waves 200a, 200b, and 200c that satisfy the lower-order Bragg diffraction condition, appears as a change in the atomic number density within the range W (Fig. 4). The peak value of the atomic number density of the diffraction image 100c changes according to the angular velocity or acceleration applied to the atom interferometer. In FIG. 4, as an example, when the peak value of the atomic number density is maximized (this is bright interference, which corresponds to when the input angular velocity is 0 mrad/sec in the above simulation), the diffraction image 100c and the atomic number density shows the diffraction image 100c when the peak value of is minimized (this is dark interference and corresponds to the input angular velocity of 0.48 mrad/sec in the above simulation).

Therefore, in order to obtain an accurate diffraction image 100c, it is sufficient to obtain the atomic number density in the range W under the condition that all the traveling light standing waves do not exist. Therefore, the observation unit 400 observes the atomic beam 100a from the interference unit 200 under the condition that no traveling light standing wave exists, and detects the atomic beam 100c for which no diffraction image 100c is formed by the traveling light standing wave. An atomic number density distribution (see FIG. 3) of 100a is obtained (step S2).

Furthermore, the observation unit 400 observes the atomic beam 100a from the interference unit 200 in the presence of all traveling light standing waves, and the traveling light standing waves 200a, 200b, and 200c that satisfy the low-order Bragg diffraction condition. Obtain the atomic number density distribution (see FIG. 4) of the atomic beam 100a in which the diffraction image 100c is formed within the range W (step S3).

Then, the observation unit 400, based on the difference between the atomic number density distribution obtained in the process of step S2 and the atomic number density distribution obtained in the process of step S3, the standing traveling light that satisfies the low-order Bragg diffraction condition. A diffraction image 100c is obtained from the waves 200a, 200b, and 200c (step S4). Thus, by removing the atomic number density distribution without the diffraction image 100c obtained in the process of step S2 from the atomic number density distribution obtained in the process of step S3, an accurate diffraction image 100c can be obtained. can.

Note that the order of the processing in step S2 and the processing in step S3 may be reversed.

Further, when the Mach-Zehnder atomic interferometer 900 is used as an atomic gyroscope, the observation unit 400 may further perform processing for detecting angular velocity or acceleration from the diffraction image 100c obtained in the processing of step S4. . Since the process of detecting the angular velocity or acceleration from the diffraction image by atomic interference is well known, the description thereof will be omitted.

The atomic interferometer example above uses a Mach-Zehnder atomic interference scheme with one splitting, one flipping and one mixing using three traveling optical standing waves. , but not limited to this type, for example, a multistage Mach-Zehnder atomic interference scheme with multiple splittings, multiple flips, and multiple mixings may be utilized. See reference 1 for such a multistage Mach-Zehnder atomic interference scheme.
(Reference 1) Takatoshi Aoki et al., “High-finesse atomic multiple-beam interferometer comprised of copropagating stimulated Raman-pulse fields,” Phys. Rev. A 63, 063611 (2001) - Published 16 May 2001.

Further, the atomic interferometer of the present invention is not limited to the Mach-Zehnder atomic interferometer, and may be, for example, a Ramsey-Bode atomic interferometer.

In addition, the present invention is not limited to the above-described embodiments, and can be modified as appropriate without departing from the scope of the present invention. For example, the atomic beam 100a is not limited to the thermal atomic beam described above, and may be a cold atomic beam.

100 Atomic beam generator 100a Atomic beam 100b Atomic beam 100c Diffraction image 111 Atomic beam source 113 Atomic beam collimator 115 Metal mass 200 Interference part 200a First traveling light standing wave 200b Second traveling light standing wave 200c Third traveling optical standing wave 300 traveling optical standing wave generator 400 observation unit 408 probe light 409 photodetector 900 Mach-Zehnder atomic interferometer

Claims (5)

Continuous generation of atomic beams in which individual atoms that are alkaline-earth metal atoms, alkaline-earth-like metal atoms, stable isotopes of alkaline-earth metal atoms, or stable isotopes of alkaline-earth-like metal atoms are in the same state. an atomic beam generator;
a traveling light standing wave generator for generating three or more traveling light standing waves that satisfy the low-order Bragg diffraction condition;
an interference unit that obtains an atomic beam as a result of interaction between the atomic beam and the three or more traveling optical standing waves;
A diffraction image detection method for an atom interferometer including an observation unit that observes the atomic beam from the interference unit,
a first step in which the atomic beam generator generates the atomic beam having an atomic number density distribution including a range in which the atomic number density of the atomic beam is uniform at the position of the observation unit;
a second step in which the observation unit observes the atomic beam from the interference unit under a condition in which all of the traveling optical standing waves do not exist to obtain the atomic number density distribution in which no diffraction image is formed;
The number of atoms for which the observation unit observes the atomic beam from the interference unit under the condition that all the traveling light standing waves exist, and the diffraction image under the low-order Bragg diffraction condition is formed within the range. a third step of obtaining a density distribution;
a diffraction image having a fourth step of obtaining the diffraction image based on the difference between the atomic number density distribution obtained in the process of the second step and the atomic number density distribution obtained in the process of the third step; Detection method. In the diffraction image detection method according to claim 1,
The diffraction image, wherein the range is a range in which the atomic number density of the atomic beam is constant in a direction orthogonal to the traveling direction of the atomic beam under a condition where all the traveling light standing waves do not exist. Detection method. an atomic beam generator for continuously generating atomic beams in which individual atoms are in the same state;
a traveling light standing wave generator for generating three or more traveling light standing waves;
an interference unit that obtains an atomic beam as a result of interaction between the atomic beam and the three or more traveling optical standing waves;
an observation unit that observes the atomic beam from the interference unit,
said atom is an alkaline earth metal atom, an alkaline earth-like metal atom, a stable isotope of an alkaline earth metal atom, or a stable isotope of an alkaline earth-like metal atom;
each said traveling optical standing wave satisfies a low-order Bragg diffraction condition,
The atomic beam generating device generates the atomic beam having an atomic number density distribution including a range in which the atomic number density of the atomic beam is uniform at the position of the observation unit;
A diffraction image under the low-order Bragg diffraction condition is formed within the range ,
The observation unit obtains a first atomic number density distribution by performing observation under a condition in which all of the traveling light standing waves do not exist, and performs observation under a condition in which all of the traveling light standing waves exist. to obtain a second atomic number density distribution, and obtain the diffraction image using the difference between the first atomic number density distribution and the second atomic number density distribution
atomic interferometer. In the atomic interferometer according to claim 3 ,
The atomic interference, wherein the range is a range in which the atomic number density of the atomic beam is constant in a direction perpendicular to the traveling direction of the atomic beam under a condition in which all of the traveling optical standing waves do not exist. Total. an atomic gyroscope,
An atom interferometer according to either claim 3 or claim 4 ,
The observation section included in the atomic interferometer is an atomic gyroscope that detects angular velocity or acceleration by observing the atomic beam from the interference section.

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