JP2012019261A - Atomic oscillator - Google Patents

Abstract

An atomic oscillator capable of improving frequency accuracy over an EIT type atomic oscillator is provided.
An atomic group generation unit 30 includes a plurality of gaseous alkali metal atoms 2 having a substantially uniform velocity.
An alkali metal atom group 20 containing 1 is generated. The light source 10 has coherence, generates first light and second light having different frequencies and irradiates the alkali metal atom group 20. The light detection unit 40 generates a detection signal 42 corresponding to the intensity of light transmitted through the alkali metal atom group 20. Based on the detection signal 42, the frequency control unit 50 sets the frequency of the first light and the second light so that the first light and the second light form a resonant light pair that causes the alkali metal atom 21 to absorb two-photons. Control at least one of the two light frequencies.
[Selection] Figure 6

Description

  The present invention relates to an atomic oscillator.

Electromagnetically Induced Transparency (EIT) method (CPT (
Coherent Population Trapping (sometimes referred to as Coherent Population Trapping)) is an atomic oscillator that has coherence (coherence) with alkali metal atoms and has different specific wavelengths (
This is an oscillator that utilizes the phenomenon that absorption of resonance light stops when two types of resonance light having a frequency are simultaneously irradiated.

As shown in FIG. 11, the interaction mechanism between the alkali metal atom and the two types of resonance light is a Λ-type 3
It is known that it can be explained by a level system model. The alkali metal atom has two ground levels, and corresponds to the resonance light 1 having a frequency corresponding to the energy difference between the ground level 1 and the excitation level, or the energy difference between the ground level 2 and the excitation level. As is well known, light absorption occurs when the resonance light 2 having the frequency to be irradiated is irradiated to alkali metal atoms alone. However, when this alkali metal atom is simultaneously irradiated with the resonance light 1 and the resonance light 2, the two ground levels are superposed, that is, a quantum interference state, and the excitation to the excitation level is stopped and the resonance light 1 and A transparency phenomenon (EIT phenomenon) in which the resonant light 2 passes through the alkali metal atoms occurs. For example, the ground level and the excited level for the D2 line (wavelength is 852.1 nm) of the cesium atom are 6 ²
S _1/2 and 6 ² P _3/2 , but the ground level 6 ² S _1/2 is the hyperfine quantum number F = 3, 4
The level of F = 3 (corresponds to the ground level 1) and the level of F = 4 (corresponds to the ground level 2). The frequency corresponding to the energy difference is 9.1
92631770 GHz. Therefore, when cesium atoms are simultaneously irradiated with two types of laser light having a wavelength of about 852.1 nm and a frequency difference of 9.192613770 GHz,
An EIT signal phenomenon occurs.

Therefore, when two types of light having different frequencies are irradiated onto an alkali metal atom, the light absorption behavior changes sharply depending on whether the two types of light become a resonance light pair and the alkali metal atom causes the EIT phenomenon. . A signal indicating this steeply changing light absorption behavior is called an EIT signal, and the frequency difference between the resonant light pair is equivalent to the energy difference ΔE ₁₂ between the two ground levels (for example, 9.192613770 GHz for a cesium atom). ) And the level of the EIT signal show a peak value. Therefore, to detect the peak top of the EIT signal, as two kinds of light to be irradiated to the alkali metal atom is resonant light pair, i.e., exactly the frequency that the frequency difference between the two types of light corresponds to Delta] E ₁₂ By controlling the frequency so as to match, a highly accurate oscillator can be realized.

US Pat. No. 6,265,945

However, since the EIT type atomic oscillator detects the peak top of the EIT signal and controls the frequency, if the Q value of the EIT signal (especially the curvature of the peak top) is small, it may cause frequency fluctuations. In some cases, there was a problem with frequency accuracy.

The present invention has been made in view of the above problems, and according to some aspects of the present invention, there is provided an atomic oscillator capable of improving frequency accuracy as compared with an EIT-type atomic oscillator. can do.

(1) The present invention is an atomic oscillator using a quantum interference phenomenon generated by irradiating an alkali metal atom with a resonant light pair, and includes an alkali metal atom including a plurality of gaseous alkali metal atoms having a substantially uniform velocity. An atomic group generation unit that generates a group, a light source that generates coherent first light and second light having different frequencies and irradiates the alkali metal atom group; and the alkali metal atom group A light detection unit that generates a detection signal according to the intensity of the transmitted light, and resonance light that causes the first light and the second light to cause two-photon absorption in the alkali metal atom based on the detection signal A frequency control unit that controls at least one of the frequency of the first light and the frequency of the second light so as to form a pair.

“Two-photon absorption” is a phenomenon in which an alkali metal atom simultaneously absorbs two photons and transitions to an excited state.

“Alkali metal” means an element belonging to Group 1 in the first column of the periodic table (Na, K,
Rb, Cs,.

From the simulation results described later, it is generally considered that the curvature of the peak top of the two-photon absorption signal is larger than the curvature of the peak top of the EIT signal. Therefore, according to the atomic oscillator of the present invention, the frequency accuracy can be improved as compared with the conventional EIT-type atomic oscillator by generating a resonant light pair that causes two-photon absorption in an alkali metal atom.

(2) In this atomic oscillator, the frequency control unit sets the frequency corresponding to the energy difference between the excited state of the alkali metal atom and the first ground state to ω ₁₃ , and the excited state of the alkali metal atom and the second state. The frequency of the first light is ω ₁₃ + Δ (Δ ≠ 0) and the frequency of the second light is ω _2, where the frequency is ω ₂₃ corresponding to the energy difference from the ground state.
_At least one of the frequency of the first light and the frequency of the second light may be controlled so as to be ₃ + Δ.

In this way, control is performed so that the frequency difference between the first light and the second light is equal to the frequency corresponding to the energy difference between the first ground state and the second ground state of the alkali metal atom. Therefore, two-photon absorption can be caused in the alkali metal atom.

(3) This atomic oscillator sets the center frequency of the light generated by the light source to (ω ₁₃ + ω ₂₃ ) /
A center frequency setting unit that sets 2 + Δ, wherein the frequency control unit generates an oscillation signal that oscillates at a frequency corresponding to the detection signal, and the oscillation signal has a frequency at a given frequency conversion rate. A frequency conversion unit for converting, and the light source performs frequency modulation on the light of the center frequency set by the center frequency setting unit by a signal frequency-converted by the frequency conversion unit, and the first light and the The second light may be generated.

In this way, a resonant light pair that causes two-photon absorption in an alkali metal atom can be efficiently generated with one light source.

(4) In this atomic oscillator, the atomic group generation unit may generate the alkali metal atom group by cooling the alkali metal atoms to near zero.

In this way, if the alkali metal atoms are cooled to near absolute zero, an alkali metal atom group having a substantially zero velocity can be generated.

The figure for demonstrating the simulation which generates an EIT signal. The figure which shows the simulation result of an EIT signal. The figure for demonstrating the simulation which generates a two-photon absorption signal. The figure which shows the simulation result of a two-photon absorption signal. The figure which shows the comparison result of the 2nd-order differential value (curvature) of the peak top of an EIT signal and a two-photon absorption signal. The functional block diagram of the atomic oscillator of this embodiment. The figure which shows the specific structural example of the atomic oscillator of this embodiment. The figure for demonstrating the principle of laser cooling. The figure for demonstrating the capture principle of the alkali metal atom group by a magneto-optical trap (MOT). Schematic which shows the frequency spectrum of the emitted light of a semiconductor laser. The figure which shows typically the energy level of an alkali metal atom.

DESCRIPTION OF EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the drawings. The embodiments described below do not unduly limit the contents of the present invention described in the claims. Also, not all of the configurations described below are essential constituent requirements of the present invention.

1. Comparison between EIT signal and two-photon absorption signal Perform simulation to generate EIT signal by approximating alkali metal atom with Λ-type three-level system model and simulation to generate two-photon absorption signal. The characteristics were compared. In these simulations, the type of alkali metal atom is not limited.

1-1. EIT Signal Simulation FIG. 1A and FIG. 1B are diagrams for explaining a simulation for generating an EIT signal. In this simulation, FIG. 1 for an alkali metal atom group containing a number of alkali metal atoms approximated by Λ type three-level system model (A), the frequency coupling light and frequency omega _c is omega _p The probe light is simultaneously irradiated while ω _c is fixed and ω _p is swept. And the light (transmitted light) which permeate | transmitted the alkali atom group is detected by the model of a photo detector (PD: Photo Detector), and the output level of PD is calculated. In addition,
Since the two-photon absorption signal is not clearly generated unless the velocity of the alkali metal group is uniform,
In the simulation of the two-photon absorption signal, which will be described later, all alkali metal atoms are modeled in a state cooled to absolute zero (speed 0). Therefore, in order to make the simulation conditions the same, all the alkali metal atoms are also modeled in a state cooled to absolute zero (speed 0) in the simulation of the EIT signal.

As shown in FIGS. 1A and 1B, the frequency ω _{c of the} coupling light is a frequency ω ₂₃ (corresponding to the energy difference ΔE ₂₃ between the ground level 2 and the excitation level of the alkali metal atom). = Δ
E ₂₃ / h: h is fixed to Planck's constant). On the other hand, the frequency ω _{p of the} probe light is a frequency ω ₁₃ (corresponding to the energy difference ΔE ₁₃ between the ground level 1 and the excitation level of the alkali metal atom.
= ΔE ₁₃ / h). Detuning δ (= (ω _p −ω _c ) −ω ₁₂ )
It can also be considered that the sweep is centered on zero. When δ = 0, the frequency ω ₁₂ (= ΔE ₁₂₎ where the frequency difference between ω _p and ω _c corresponds to the energy difference ΔE ₁₂ between the ground level 1 and the ground level 2.
/ H).

FIG. 2A shows the simulation result. In FIG. 2A, the horizontal axis is δ, and the vertical axis is P.
D indicates the output level, both of which are arbitrary units. As shown in FIG. 2A, an EIT signal is generated in the vicinity of δ = 0 and peaks when δ = 0, that is, ω _p −ω _c = ω ₁₂ . FIG. 2B shows a result of calculating a value (curvature) obtained by second-order differentiation of the PD output level of the simulation result of FIG. In FIG. 2B, the horizontal axis indicates detuning δ, and the vertical axis indicates the second-order differential value (curvature) of the PD output, both of which are arbitrary units. As shown in FIG. 2B, the curvature of the peak top of the EIT signal is about −20. The “curvature” is originally defined as the reciprocal of the “curvature radius”, but reflects the second-order (order) derivative value of the target curve, and therefore, in this specification, “curvature” and “second-order”. "Differential value" is treated as a synonym.

1-2. Simulation of Two-Photon Absorption Signal FIGS. 3A and 3B are diagrams for explaining a simulation for generating a two-photon absorption signal. In this simulation, for an alkali metal atom group containing many alkali metal atoms approximated by the Λ-type three-level system model shown in FIG. 3A (the same alkali metal atom group as in the EIT signal simulation), the probe light frequency is coupled light and the frequency of ω _c ω _p, simultaneously irradiated while sweeping the omega _p securing the omega _c. Then, light (transmitted light) transmitted through the alkali atom group is converted into a photodetector (PD:
Detect with the Photo Detector model and calculate the PD output level. Note that all alkali metal atoms are modeled in a state of being cooled to absolute zero (speed 0).

As shown in FIGS. 3A and 3B, the frequency ω _{c of the} coupling light is ΔE ₂₃ +
The frequency is fixed to ω ₂₃ + Δ (= (ΔE ₂₃ + ΔE) / h) corresponding to ΔE. On the other hand, the frequency ω _{p of the} probe light sweeps around ω ₁₃ . Detuning δ (= (ω _p −ω _c ) −
If ω ₁₂ ) is used, it can be considered that δ + Δ sweeps around 0. δ +
Delta = delta time (i.e. [delta] = 0), the frequency difference between the omega _p and omega _c matches the omega _12.

FIG. 4A shows the simulation result. In FIG. 4A, the horizontal axis indicates δ + Δ and the vertical axis indicates the output level of PD, both of which are arbitrary units. As shown in FIG. 4A, δ + Δ =
A two-photon absorption signal is generated in the vicinity of Δ (δ = 0), and δ + Δ = Δ (δ = 0), that is, ω _p −ω.
It reaches a peak when the _c = _{ω 12.} Further, in the vicinity of δ + Δ = 0 to Δ (δ = −Δ to 0), E
An IT signal is generated and peaks when δ + Δ is a value slightly smaller than Δ (δ is slightly smaller than 0). FIG. 4B shows a result of calculating a value (curvature) obtained by second-order differentiation of the PD output level of the simulation result of FIG. 4A. In FIG. 4B, the horizontal axis indicates detuning δ + Δ, and the vertical axis indicates the second-order differential value (curvature) of the PD output, both of which are arbitrary units. FIG. 4 (B
), The peak top curvature of the EIT signal is about −30, and the peak top curvature of the two-photon absorption signal is about 40.

1-3. Comparison of Simulation Results FIG. 5A shows the EI when the two-photon absorption signal simulation is performed by sweeping Δ.
It is a figure which shows the calculation result of the curvature of each peak top of T signal and a two-photon absorption signal. FIG.
, The horizontal axis indicates Δ, and the vertical axis indicates the absolute value of the curvature of the peak top, both of which are arbitrary units. The curvature of each peak top of the two-photon absorption signal and the EIT signal is indicated by a solid line and a broken line, respectively. FIG. 5B shows the ratio R of the peak top curvature of the two-photon absorption signal and the peak top curvature of the EIT signal shown in FIG. 5A (R = the curvature of the peak top of the two-photon absorption signal / EIT). It is a figure which shows the calculation result of the curvature of the peak top of a signal. In FIG. 5B, the horizontal axis indicates Δ and the vertical axis indicates R. When Δ = 0, the same EIT signal as the EIT signal in FIG. 2A can be obtained. Therefore, in FIG. 5A, the curvature of the peak top of the EIT signal when Δ = 0 in FIG. B
).

From FIG. 5A and FIG. 5B, the curvature of the EIT signal is larger than the curvature of the two-photon absorption signal when Δ is near 0 (approximately in the range of −1 <Δ <1). In the range, it can be seen that the curvature of the two-photon absorption signal is larger than the curvature of the EIT signal. In this simulation, since a general Λ-type three-level system model is used, it can be assumed that a simulation result having the same tendency can be obtained even if the types of alkali metal atoms are limited.

Since it can be said that a signal having a larger peak top curvature is steeper, this simulation result means that if the absolute value of Δ is increased to some extent, a two-photon absorption signal steeper than the EIT signal can be obtained. In other words, if an atomic oscillator is configured to increase the absolute value of Δ to some extent and lock it to the peak top of the two-photon absorption signal, the frequency fluctuation is reduced, and E
The frequency accuracy can be improved as compared with the IT type atomic oscillator.

Further, according to the result of FIG. 5A, the curvature of the peak top of the two-photon absorption signal becomes maximum at Δ = ± 6. If Δ is set so that the curvature of the peak top of the two-photon absorption signal is maximized, the frequency accuracy of the atomic oscillator can be further improved.

Based on the simulation results described above, the atomic oscillator of this embodiment improves the frequency accuracy by using a two-photon absorption signal. Hereinafter, the configuration of the atomic oscillator of this embodiment will be described.

2. Functional Configuration of Atomic Oscillator of this Embodiment FIG. 6 is a functional block diagram of the atomic oscillator of this embodiment. Atomic oscillator 1 of this embodiment
Includes a light source 10, an atomic group generation unit 30, a light detection unit 40, and a frequency control unit 50.

The atomic group generation unit 30 generates an alkali metal atom group 20 including a plurality of gaseous alkali metal atoms 21 having a substantially uniform velocity. For example, the atomic group generation unit 30 may generate the alkali metal atom group 30 by cooling the alkali metal atoms 21 to near absolute zero.

The light source 10 has coherence (coherence), generates first light and second light having different frequencies, and irradiates the alkali metal atom group 20. For example, laser light is light having coherence.

The light detection unit 40 generates a detection signal 42 according to the intensity of the light (transmitted light) 22 that has passed through the alkali metal atom group 20.

Based on the detection signal 42 of the light detection unit 40, the frequency control unit 50 forms a resonance light pair in which the first light and the second light generated by the light source 10 cause the alkali metal atom 21 to absorb two-photons. As described above, frequency control of at least one of the first light and the second light is performed. Specifically, the frequency control unit 50 sets the frequency of the first light to ω ₁₃ + Δ (Δ ≠ 0) and the second light.
At least one of the frequency of the first light and the frequency of the second light may be controlled so that the frequency of the light becomes ω ₂₃ + Δ. By doing so, the frequency difference between the first light and the second light becomes ω ₁₂ (= ω ₁₃ −ω ₂₃ ), and two-photon absorption can be caused in the alkali metal atom 21.

The atomic oscillator 1 of the present embodiment may further be configured to include a center frequency setting unit 60. The center frequency setting unit 60 sets the center frequency of light generated by the light source 10 to (ω ₁₃ + ω
₂₃ ) / 2 + Δ.

In this case, the frequency control unit 50 generates an oscillation signal generation unit 52 that generates an oscillation signal that oscillates at a frequency according to the detection signal 42, and the oscillation signal generated by the oscillation signal generation unit 52 has a frequency at a given frequency conversion rate. The light source 10 is frequency-modulated with the light having the center frequency set by the center frequency setting unit 60 by the frequency-converted signal by the frequency conversion unit 54. The light and the second light may be generated.

  Hereinafter, a more specific configuration of the atomic oscillator of this embodiment will be described.

3. Specific Configuration of the Present Embodiment FIG. 7 is a diagram illustrating a specific configuration example of the atomic oscillator of the present embodiment. As shown in FIG. 7, the atomic oscillator 100 of this embodiment includes a semiconductor laser 110, an alkali metal atom group 12 and the like.
0, laser cooling unit 130, photodetector 140, amplification circuit 150, detection circuit 160, voltage controlled crystal oscillator (VCXO) 170, modulation circuit 180, low frequency oscillator 190, frequency conversion circuit 200, current drive circuit 210. It is configured.

The alkali metal atom group 120 is a collection of gaseous alkali metal atoms having a substantially uniform velocity (hereinafter referred to as “homogeneous system”). In the present embodiment, a uniform alkali metal atom group 120 is created by the laser cooling unit 130.

The laser cooling unit 130 emits gaseous alkali metal atoms generated by the alkali metal atom generation source 131 toward the glass cell 133, and opposes the traveling direction of the alkali metal atoms so that laser light near the resonance frequency is emitted. By irradiating 135, alkali metal atoms are decelerated. The coil 132 is smaller as it is closer to the glass cell 133 along the flight path (deceleration path) of the alkali metal atoms so that the resonance frequency of the alkali metal atoms is close to the frequency of the laser beam 135 in accordance with the deceleration of the alkali metal atoms. A magnetic field with a gradient like that is generated. While passing through this magnetic field, the alkali metal atom repeatedly collides with the photons of the laser beam 135 and gradually decelerates, and is cooled to near absolute zero (laser cooling).

8A, 8B, and 8C are diagrams for explaining the principle of laser cooling. When the photon (resonant light) of the laser beam 135 collides from the traveling direction of the alkali metal atom, the alkali metal atom is decelerated according to the momentum conservation law (FIG. 8A). At this time,
One photon is absorbed and disappears, and at the same time, due to the conservation of energy, the electrons of the alkali metal atom transition to the excited level (FIG. 8B). When returning from the excited level to the ground level, one photon is emitted and generated, but since the directional momentum of the emitted photon is random, on average, the velocity of the atom in the photon emission process does not change (FIG. 8C). . When the next photon collides from the traveling direction of the alkali metal atom, the alkali metal atom further decelerates through the same process. By repeating this, the velocity of the alkali metal atom converges to 0, and the alkali metal atom is cooled to near absolute zero. As the alkali metal atoms are decelerated, a transition energy Doppler shift occurs. In order to correct this, the coil 13 for generating a magnetic field with a magnetic field gradient along the deceleration path.
2 (so-called “Zeeman decelerator”) is added.

The alkali metal atoms sufficiently decelerated in this way are a pair of anti-helmholtz coils 134 arranged so as to face each other with the glass cell 133 interposed therebetween (because FIG. 7 shows the two coils 134 from the overlapping direction). Magneto-optical trap (MOT) using one visible)
: Magneto-Optical Trap) and trapped inside the glass cell 133 to generate a homogeneous alkali metal atom group 120.

FIGS. 9A and 9B are diagrams for explaining the principle of trapping the alkali metal atom group 120 by the magneto-optical trap (MOT). 1 arranged facing the z-axis direction
When currents in opposite directions are passed through the pair of anti-helmholtz coils 134, a magnetic field that changes linearly in proportion to the distance (shift) from the origin is obtained near the origin O (FIG. 9A). Specifically, the magnetic field B at coordinates (x, y, z) is represented by B = (bx, by, −2bz) (b: constant). With this magnetic field generated, it was sufficiently cooled by laser cooling or the like (the speed was almost 0
A) a set of laser beams 136a and 13 from the x-axis direction for the alkali metal atom group 120.
6b is opposed to each other, a pair of laser beams 137a and 137b are irradiated from the y-axis direction, and a pair of laser beams 138a and 138b are irradiated from the z-axis direction to face each other.
An atomic group can be captured near the center (origin O) of the anti-helmholtz coil 134 (FIG. 9B). FIG. 7 is a view as seen from the z-axis direction. The laser beam 1 in the z-axis direction is shown in FIG.
Illustration of 38a and 138b is omitted.

Returning to FIG. 7, the semiconductor laser 110 has a center wavelength λ ₀ (center frequency f ₀ = v / λ _{0, where} v is the speed of light) controlled by the drive current output from the current drive circuit 210. modulation is multiplied by the output signal of the conversion circuit 200 (modulation signal of the modulation frequency f _m) are superimposed, to generate a plurality of lights having different frequencies. The emitted light of the semiconductor laser 110 is applied to the alkali metal atom group 120. Such a semiconductor laser 110 includes:
For example, edge emitting lasers or vertical cavity surface emitting lasers (V
It can be realized by a surface emitting laser such as CSEL (Vertical Cavity Surface Emitting Laser).

FIG. 10 is a schematic diagram showing the frequency spectrum of the emitted light from the semiconductor laser 110. In FIG. 10, the horizontal axis represents the light frequency, and the vertical axis represents the light intensity. As shown in FIG.
The light emitted from the semiconductor laser 110 includes light having a center frequency f ₀ and a plurality of types of light having frequencies of _fm intervals on both sides thereof. In the present embodiment, the two lights in the primary sideband become a resonant light pair that generates a two-photon absorption state in the alkali metal atom.
The center frequency f ₀ and the modulation frequency f _m are adjusted. Specifically, the drive current of the current drive circuit 210 is set to a predetermined amount, and the center frequency f ₀ is matched with (ω ₁₃ + ω ₂₃ ) / 2 + Δ. The modulation frequency _{f m} is the feedback control described later (ω ₁₃ -ω ₂₃₎ / 2 and the match. Thus, the frequency f ₂ of the first-order upper sideband of the optical light frequency f ₁ and the first-order lower sideband (resonant light 1) (resonant light 2) are respectively omega _{13 +} delta and omega _{23 +} delta These two resonance lights 1 and 2 can generate a two-photon absorption state for each atom of the alkali metal atom group 120. In this way, a resonant light pair that causes two-photon absorption in an alkali metal atom can be efficiently generated with one semiconductor laser.

The photodetector 140 detects light (transmitted light) transmitted through the alkali metal atom group 120 and outputs a detection signal corresponding to the intensity of the light. As the number of alkali metal atoms causing two-photon absorption increases, the intensity of transmitted light decreases, and the voltage level of the output signal (detection signal) of the photodetector 140 decreases.

The output signal of the photodetector 140 is amplified by the amplification circuit 150 and input to the detection circuit 160. The detection circuit 160 includes a low frequency oscillator 170 that oscillates at a low frequency of about several Hz to several hundred Hz.
The output signal of the amplifier circuit 150 is synchronously detected using the oscillation signal. Then, the detection circuit 160
The oscillation frequency of the voltage controlled crystal oscillator (VCXO) 170 is finely adjusted according to the magnitude of the output signal. The voltage controlled crystal oscillator (VCXO) 170 oscillates at about several MHz, for example.

In order to enable synchronous detection by the detection circuit 160, the modulation circuit 180 uses the oscillation signal of the low-frequency oscillator 190 (same as the oscillation signal supplied to the detection circuit 160) as a modulation signal, and a voltage controlled crystal oscillator (VCXO) 170. Modulate the output signal. The modulation circuit 180 includes a frequency mixer (mixer), a frequency modulation (FM) circuit, and an amplitude modulation (AM:
(Amplitude Modulation) circuit or the like.

The frequency conversion circuit 200 frequency converts the output signal of the modulation circuit 180 according to the set frequency conversion rate. The frequency conversion circuit 200 is, for example, a modulation circuit 1 with a set multiplication rate.
This can be realized by a PLL (Phase Locked Loop) circuit that multiplies the frequency of 80 output signals.

As described above, the semiconductor laser 110 modulates the output signal of the frequency conversion circuit 200 as a modulation signal (modulation frequency f _m ) by superimposing the output signal of the frequency conversion circuit 200 on the drive current from the current drive circuit 210. Is applied to generate outgoing light having a frequency spectrum as shown in FIG.

Semiconductor laser 110, alkali metal atom group 120, photodetector 140, amplifier circuit 15
0, the detection circuit 160, the voltage control crystal oscillator (VCXO) 170, the modulation circuit 180, and the feedback loop passing through the frequency conversion circuit 200, so that the intensity of the detection signal of the photodetector 140 is minimized, that is, the resonance light 1 The feedback control is applied so that the frequency f ₁ = ω ₁₃ + Δ and the frequency f ₂ of the resonant light ₂ = ω ₂₃ + Δ. Considering the resonance light 1 as the probe light and the resonance light 2 as the coupling light and applying them to FIGS. 3 (A) and 3 (B), δ + Δ
= Δ (δ = 0) is satisfied, and therefore the level of the detection signal of the photodetector 140 matches the level of the peak top of the two-photon absorption signal from the results of FIGS. 4 (A) and 4 (B). To do. That is, according to the atomic oscillator of the present embodiment, the peak top of the two-photon absorption signal can be locked, so that the frequency accuracy can be improved as compared with the conventional EIT type atomic oscillator.

In addition, the semiconductor laser 110, the alkali metal atom group 120, and the current driving circuit 210 in FIG. 7 are the light source 10, the alkali metal atom group 20, and the center frequency setting unit 6 in FIG.
Corresponds to 0. Further, the configuration of the photodetector 140 and the amplifier circuit 150 is the same as that of the photodetector 4 in FIG.
Corresponds to 0. The configuration of the detection circuit 160, the voltage controlled crystal oscillator (VCXO) 170, the modulation circuit 180, the low frequency oscillator 190, and the frequency conversion circuit 200 corresponds to the frequency control unit 50 in FIG. Further, the configuration of the detection circuit 160, the voltage controlled crystal oscillator (VCXO) 170, the modulation circuit 180, and the low frequency oscillator 190 corresponds to the oscillation signal generation unit 52 of FIG. The frequency conversion circuit 200 corresponds to the frequency conversion unit 54 in FIG.

In addition, this invention is not limited to this embodiment, A various deformation | transformation implementation is possible within the range of the summary of this invention.

For example, in the present embodiment, control is performed so that two types of light (frequency f ₀ ± f _m ) in the primary sideband of the light emitted from the semiconductor laser 110 form a resonant light pair. Absent. For example, with light and frequency is light resonant light pair of f _{0 +} f _m of the center frequency f _0, the control such that the light is resonant light pair of light and frequency f ₀ -f _m center frequency f ₀ May be.

Further, for example, in this embodiment, a resonant light pair is efficiently generated by modulating one semiconductor laser, but more simply, two semiconductor lasers are driven by separate drive currents to resonate. A light pair may be generated.

Further, for example, in the present embodiment, feedback control is performed on the frequencies of two types of light serving as a resonant light pair, but the frequency of one light may be fixed and the other frequency may be feedback controlled.

Further, for example, in the present embodiment but is generating two resonant light by applying a modulation to the semiconductor laser 110 generates a single laser beam of frequency f ₀ without applying modulation to the semiconductor laser 110, A single laser beam with frequency f ₀ is converted into an electro-optic modulator (EOM: Electro-Op).
It is also possible to generate two resonance lights by modulating the light incident on a tic modulator. In place of the electro-optic modulator (EOM), an acousto-optic modulator (AOM: Acousto-
Optic Modulator) may be used.

The present invention includes configurations that are substantially the same as the configurations described in the embodiments (for example, configurations that have the same functions, methods, and results, or configurations that have the same objects and effects). In addition, the invention includes a configuration in which a non-essential part of the configuration described in the embodiment is replaced. In addition, the present invention includes a configuration that exhibits the same operational effects as the configuration described in the embodiment or a configuration that can achieve the same object. Further, the invention includes a configuration in which a known technique is added to the configuration described in the embodiment.

1 atomic oscillator, 10 light source, 20 alkali metal atom group, 21 alkali metal atom,
22 transmitted light, 30 atomic group generation unit, 40 light detection unit, 42 detection signal, 50 frequency control unit, 52 oscillation signal generation unit, 54 frequency conversion unit, 60 center frequency setting unit, 100
Atomic oscillator, 110 semiconductor laser, 120 alkali metal atom group, 130 laser cooling unit, 131 alkali metal atom source, 132 coil (Zeeman decelerator), 1
33 glass cell, 134 anti-helmholtz coil, 135, 136a, 136b,
137a, 137b, 138a, 138b, laser beam, 140 photodetector, 150
Amplification circuit, 160 detection circuit, 170 voltage controlled crystal oscillator (VCXO), 180 modulation circuit, 190 low frequency oscillator, 200 frequency conversion circuit

Claims (4)

An atomic oscillator using a quantum interference phenomenon caused by irradiating an alkali metal atom with a resonant light pair,
An atomic group generation unit for generating an alkali metal atom group including a plurality of gaseous alkali metal atoms having a substantially uniform velocity;
A light source that has coherence and generates first light and second light having different frequencies to irradiate the alkali metal atom group;
A light detection unit that generates a detection signal according to the intensity of light transmitted through the alkali metal atom group;
Based on the detection signal, the frequency of the first light and the second light are such that the first light and the second light form a resonant light pair that causes the alkali metal atom to absorb two-photons. An atomic oscillator comprising: a frequency control unit that controls at least one of light frequencies. In claim 1,
The frequency control unit
The frequency corresponding to the energy difference between the excited state of the alkali metal atom and the first ground state is ω ₁₃ , and the frequency ω ₂₃ is equivalent to the energy difference between the excited state of the alkali metal atom and the second ground state. The frequency of the first light and the second light so that the frequency of the first light is ω ₁₃ + Δ (Δ ≠ 0) and the frequency of the second light is ω ₂₃ + Δ. An atomic oscillator that controls at least one of the frequencies of light. In claim 2,
A center frequency setting unit for setting a center frequency of light generated by the light source to (ω ₁₃ + ω ₂₃ ) / 2 + Δ;
The frequency control unit
An oscillation signal generator that generates an oscillation signal that oscillates at a frequency corresponding to the detection signal;
A frequency converter that converts the frequency of the oscillation signal at a given frequency conversion rate,
The light source is
An atomic oscillator that generates the first light and the second light by frequency-modulating light having the center frequency set by a center frequency setting unit with a signal frequency-converted by the frequency conversion unit. In any one of Claims 1 thru | or 3,
The atomic group generation unit
An atomic oscillator that generates the alkali metal atom group by cooling the alkali metal atom to near absolute zero.

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