JP5796454B2 - Atomic oscillator - Google Patents

Description

  The present invention relates to an atomic oscillator, and more particularly to an atomic oscillator having an improved S / N ratio of a Zeeman split EIT spectrum.

  In order to cause the alkali metal atom to exhibit the electromagnetically induced transmission phenomenon, it is necessary to irradiate the alkali metal atom with two resonance lights (frequency ω1, ω2) having different frequencies. As shown in FIG. 6, since the first ground level 33 and the second ground level 34 have a slightly different level energy (ΔE12), the EIT-type atomic oscillator has the resonance light of the first resonance level 31 and the first resonance level 31, respectively. The wavelengths f1 and f2 of the second resonance light 32 are slightly different. The frequency difference f1-f2 (wavelength difference: ω1-ω2) between the first resonance light 31 and the second resonance light 32 irradiated simultaneously is accurately the energy difference ΔE12 between the first ground level 33 and the second ground level 34. 6, the system of FIG. 6 enters a superposition state of two ground levels, and excitation to the excitation level 30 stops (referred to as an EIT phenomenon). The EIT uses this principle to absorb light in the gas cell when the wavelength of one or both of the first resonant light 31 and the second resonant light 32 is changed (that is, conversion to the excitation level 30). This is a method of detecting and using a state where the computer stops. Using this phenomenon, when the frequency difference between the first resonant light 31 and the second resonant light 32 deviates from the frequency corresponding to the energy difference (ΔE12) between the first ground level 33 and the second ground level 34. By detecting and controlling a steep change in light absorption behavior, a highly accurate oscillator can be produced.

In addition, since the energy difference between the first ground level 33 and the second ground level 34 changes sensitively due to the strength and fluctuation of external magnetism, a highly sensitive magnetic sensor can be made using the EIT phenomenon.
FIG. 5 of FIG. 7 (FIG. 7B) discloses a technique for applying a weak magnetic field (magnetic field parallel to resonance light) of about 100 milligauss to the gas cell (alkali metal atom) 115 by the solenoid coil 114. Has been. When a weak magnetic field is applied to an alkali metal atom, the two ground levels constituting the Λ-type three levels and the excited level split into multiple energy levels with different energies (called Zeeman splitting. It is known that the energy level is called the Zeeman level). In addition, the two ground levels (first ground level 33 and second ground level 34) are Zeeman split into a plurality of energy levels, so that the first ground level 33, the second ground level 34, It is known that the output frequency of the atomic oscillator changes in accordance with the change in the energy difference (frequency difference).

Here, among the Zeeman levels split into a plurality, the first ground level 33 and the second ground level 34 that are hardly affected by the magnetic field, and the excitation level 30 (having the magnetic quantum number m _F = 0). It is known that a first ground level 33, a second ground level 34, and an excited level 30) having a magnetic quantum number m _F = 0 exist.
Therefore, if a weak magnetic field having a predetermined intensity is applied to the alkali metal atom in the gas cell in advance, the first ground level 33 and the second ground level 34 having the magnetic quantum number m _F = 0, and the magnetic quantum number m. The output frequency of the atomic oscillator can be controlled such that only a specific Λ-type three level composed of excitation levels 30 having _F = 0 exhibits an electromagnetically induced transmission phenomenon. Thereby, it is said that the influence of the magnetic field on the output frequency of the atomic oscillator can be reduced.

On the other hand, FIG. 3 of FIG. 1 (FIG. 7A) discloses a configuration in which output light (linearly polarized light) of a semiconductor laser is converted into circularly polarized light by a λ / 4 wavelength plate and irradiated to alkali metal atoms. Yes. The reason why the output light (linearly polarized light) of the semiconductor laser is converted to circularly polarized light is related to the splitting of the first ground level 33 and the second ground level 34 into a plurality of Zeeman levels.
For example, when the output light (linearly polarized light) of a semiconductor laser is directly irradiated to an alkali metal atom, the linearly polarized light and the alkali metal atom interact with each other, and the alkali metal atom has all Zeeman quasi including the magnetic quantum number m _F = 0. It becomes evenly distributed in the level (base level). This means that the number of alkali metal atoms present at the ground level of the magnetic quantum number m _F = 0 in the atomic cell is reduced, and that the number of atoms that develop the EIT phenomenon is reduced.

Therefore, in order to increase the probability that an alkali metal atom exists in the ground level of the magnetic quantum number m _F = 0, circularly polarized light is irradiated so that an interaction occurs between the alkali metal atom and the circularly polarized light. ing. For example, as shown in FIG. 8, when the right-handed circularly polarized light is irradiated to the cesium atom, the alkali metal atom that has been irradiated with the right-handed circularly polarized light has an F = 4 ground level (second ground level 34). For five magnetic quantum numbers (m _F = 0, m _F = -4, -3, -2, -1, 0, 1, 2, 3, 4) The probability of being biased to 1, 2, 3, 4) increases. (Conversely, when left circularly polarized light is irradiated, the probability that the magnetic quantum number m _F = 0 is biased to any one of 0, −1, −2, −3, and −4 increases.)
Alternatively, when the right-handed circularly polarized light is irradiated to the cesium atom, the alkali metal atom that has been irradiated with the right-handed circularly polarized light has four magnetic fields for the F = 3 ground level (first ground level 33). The probability that atoms are biased and exist in the quantum numbers (m _F = 0, 1, 2, 3) increases (conversely, when irradiated with light of left circular polarization, the magnetic quantum numbers m _F = 0, −1, −2) , −3 is likely to exist in a biased manner).

USP 6320472

According to the above explanation, the probability that an alkali metal atom exists for each magnetic quantum number m _F is biased. (Whether the alkali metal atom is at the ground level of F = 4 or the ground level of F = 3 is almost the same in terms of probability.) An alkali metal atom exists in a ground level other than m _F = 0 such as the magnetic quantum number m _F = 1, 2, 3, 4, and the problem that the probability of the EIT phenomenon cannot be increased any more. is there.
The present invention has been made in view of these problems, by transitioning the number of alkali metal atoms present in the magnetic quantum number m _F other than the magnetic quantum number m _F = 0 in the ground level of m _F = 0 An object of the present invention is to provide an atomic oscillator in which the peak value of the EIT signal at the magnetic quantum number m _F = 0 is increased.

  SUMMARY An advantage of some aspects of the invention is to solve at least a part of the problems described above, and the invention can be implemented as the following forms or application examples.

[Application Example 1]
The atomic oscillator of this application example includes an alkali metal atom that generates an electromagnetically induced transmission phenomenon, a DC magnetic field generating unit that causes Zeeman splitting of the alkali metal atom by applying a DC magnetic field to the alkali metal atom, and the alkali metal. An alternating magnetic field generating means for applying a predetermined alternating magnetic field to the atom, wherein the alternating magnetic field generating means has a frequency difference ΔF corresponding to an energy difference ΔE having different magnetic quantum numbers mF in the Zeeman splitting as the predetermined alternating magnetic field. An alternating magnetic field equal to is given .

When a DC magnetic field is applied to an alkali metal atom, Zeeman splitting occurs. Since the EIT signal subjected to Zeeman splitting is distributed to each ground level, the probability that an alkali metal atom exists at the ground level of mF = 0 is lowered, and the level of the EIT signal is lowered. Therefore, mF =
In order to increase the probability that an alkali metal atom at the zero ground level exists, circularly polarized light is irradiated to the alkali metal atom. As a result, for example, an alkali metal atom irradiated with right circularly polarized light has nine magnetic quantum numbers (mF = −4) for the F = 4 ground level (second ground level 34).
, -3, -2, -1, 0, 1, 2, 3, 4), five magnetic quantum numbers (mF = 0, 1, 2, 4)
The probability of being biased to 3, 4) increases. Alternatively, with respect to the ground level of F = 3 (first ground level 33), the probability that atoms are biased to four magnetic quantum numbers (mF = 0, 1, 2, 3) increases. However, in this state, the level of the EIT signal at mF = 0 is higher than that of linearly polarized light, but the level at other mFs is also higher, so that the E at mF = 0 is not necessarily efficient.
IT level cannot be raised. Therefore, in the present invention, there is provided AC magnetic field generating means for applying an AC magnetic field equal to a frequency difference ΔF corresponding to an energy difference ΔE having different magnetic quantum numbers mF in the Zeeman splitting to alkali metal atoms. As a result, the number of alkali metal atoms present in the magnetic quantum number mF other than the magnetic quantum number mF = 0 is shifted to the ground level of mF = 0, and the peak value of the EIT signal at the magnetic quantum number mF = 0 is increased. can do.

  [Application Example 2] DC magnetic field detection means for detecting the strength of the DC magnetic field is provided, and the AC magnetic field generation means generates an AC magnetic field having a predetermined frequency based on the strength of the DC magnetic field detected by the DC magnetic field detection means. It is characterized by giving to the alkali metal atom.

When a DC magnetic field is applied to an alkali metal atom, Zeeman splitting occurs. At this time, an energy difference ΔE having different magnetic quantum numbers m _F and a frequency difference ΔF corresponding to the energy difference are generated. When a direct-current magnetic field, circularly polarized resonance light, and an alternating-current magnetic field equal to ΔF are applied, the alkali metal atom at the Zeeman level of the magnetic quantum number m _F = + 1 is changed to the state of the magnetic quantum number m _F = 0. And transition. Thereby, the number of alkali metal atoms in the Zeeman level of the magnetic quantum number m _F = 0 can be increased.

  Application Example 3 The AC magnetic field generation means includes a frequency control means for generating a frequency control signal based on the intensity of the DC magnetic field detected by the DC magnetic field detection means, and a voltage whose frequency is controlled according to the frequency control signal. A control oscillator, and a coil that generates the AC magnetic field when an output signal of the voltage control oscillator is input are provided.

  The DC magnetic field is generated by passing a current from a DC power supply to the coil. However, when the power supply voltage fluctuates, the current flowing through the coil changes, and the strength of the DC magnetic field fluctuates. The alternating magnetic field needs to be generated at a frequency corresponding to the strength of the direct magnetic field. Therefore, in the present invention, the intensity of the DC magnetic field is detected, and a control signal corresponding to the intensity is given to the voltage controlled oscillator. Thereby, the frequency of the alternating magnetic field can be controlled following the fluctuation of the direct magnetic field.

  Application Example 4 The frequency control means includes storage means for storing frequency information corresponding to the intensity of the DC magnetic field detected by the DC magnetic field detection means, and based on the frequency information read from the storage means. The frequency control signal is generated.

  The relationship between the DC magnetic field intensity and the AC magnetic field frequency may be changed continuously, but in order to simplify the circuit, the frequency information of the AC magnetic field corresponding to the DC magnetic field intensity is stored in a table. The frequency information corresponding to the detected DC magnetic field intensity is read from the table and output. As a result, the circuit configuration can be simplified.

(A) is a diagram showing the relationship between the frequency difference and the magnetic field strength when the quantum number F = 4, (b) is a diagram showing the relationship between the frequency difference and the magnetic field strength when the quantum number F = 3, (c) is It is a figure which shows the energy level of a ground level when Zeeman splits. 1 is a block diagram showing a configuration of an atomic oscillator according to a first embodiment of the present invention. It is a block diagram which shows the structure of the atomic oscillator which concerns on the 2nd Embodiment of this invention. (A) is a block diagram showing one embodiment of the frequency control means of the present invention, (b) is a diagram showing the relationship between the DC magnetic field strength and the DC magnetic field detection voltage, (c) is the DC magnetic field detection voltage and the control voltage The figure which shows a relationship, (d) is a figure which shows the relationship between a control voltage and an oscillation frequency. It is a block diagram which shows other embodiment of the frequency control means of this invention. It is a figure explaining the principle of an EIT system. (A) is shown in FIG. 3 is a diagram illustrating FIG. 3 and FIG. FIG. It is an energy level diagram of Cs atom.

Hereinafter, the present invention will be described in detail with reference to embodiments shown in the drawings. However, the components, types, combinations, shapes, relative arrangements, and the like described in this embodiment are merely illustrative examples and not intended to limit the scope of the present invention only unless otherwise specified. .
The present invention is characterized in that a strong direct current magnetic field (about 3 gauss) is applied to the alkali metal atom, and an alternating current magnetic field having a frequency corresponding to the strength of the direct current magnetic field is applied to the alkali metal atom.

FIG. 1 is a diagram showing the relationship between the frequency difference and the magnetic field strength at quantum numbers F = 4 and F = 3. 1A is a diagram showing the relationship between the frequency difference and the magnetic field strength when the quantum number F = 4, and FIG. 1B is a diagram showing the relationship between the frequency difference and the magnetic field strength when the quantum number F = 3. FIG.1 (c) is a figure which shows the energy level of a ground level at the time of Zeeman splitting.
For example, the ground level (first ground level 33) of the cesium atom with the quantum number F = 3 shown in FIG. 1C will be described as an example. The magnetic quantum numbers m _F = −3, −2, −1, With respect to 0, +1, +2, and +3, energy levels of ground levels whose magnetic quantum numbers m _F are different from each other by 1 are respectively expressed as ΔE (−3, −2) 21, ΔE (−2, −1) 22, and ΔE ( −1,0) 23, ΔE (0, + 1) 24, ΔE (+ 1, + 2) 25, ΔE (+ 2, + 3) 26, and the frequency difference corresponding to each ΔE is ΔF (−3, −2), When a strong magnetic field is applied to an alkali metal atom when ΔF (−2, −1), ΔF (−1, 0), ΔF (0, +1), ΔF (+1, +2), ΔF (+2, +3) , ΔF have different values from each other, the present inventors have noted that each of the straight lines 21 to 26 in FIG. Interval is different). When a weak DC magnetic field is applied to the alkali metal atom, each ΔF is substantially equal.

Therefore, by using the feature that ΔF has different values, for example, an alkali metal atom, a strong DC magnetic field parallel to the resonance light, a right circular polarization resonance light, and a frequency equal to ΔF (0, +1). When the AC magnetic field is given, the alkali metal atom in the Zeeman level of the magnetic quantum number m _F = + 1 transitions to the state of the magnetic quantum number m _F = 0 (arrow in FIG. 1C). ). (Same idea as microwave irradiation in the double resonance method) At this time, the alkali metal atom originally in the Zeeman level of the magnetic quantum number m _F = 0 does not transition to the Zeeman level of m _F = -1. This is because even when an AC magnetic field is applied to an alkali metal atom, ΔF (0, + 1) and ΔF (−1,0) have different values, so that only a transition from m _F = + 1 → 0 occurs. _This is because the transition from _F = 0 → m _F = −1 does not occur. In this way, in the ground level of F = 3 (first ground level 33), the number of atoms existing in the magnetic quantum number m _F = 0 can be increased, and the occurrence probability of the EIT phenomenon can be sufficiently increased. Can do.
The frequency of the alternating magnetic field may be controlled so that not only the transition of m _F = + 1 → 0 but also the transition of m _F = + 2 → 0 and m _F = + 3 → 0 occurs. Further, the F = 4 ground level of the cesium atom is the same as the example of the F = 3 ground level.

  FIG. 2 is a block diagram showing a configuration of the atomic oscillator according to the first embodiment of the present invention. An atomic oscillator 100 according to the present invention includes a first laser beam (light source) 1 for generating an EIT phenomenon in an alkali metal atom and a semiconductor laser (light source) 1 that generates a second beam of resonance, and a laser beam generated from the semiconductor laser 1. Λ / 4 wave plate 2 that circularly polarizes la, atomic cell 3 in which alkali metal atoms are enclosed, light detection means 5 that detects the intensity of resonance light 3a emitted from atomic cell 3, and predetermined alkali metal atoms DC magnetic field generating means 4 for applying a direct-current magnetic field of a certain intensity, AC magnetic field generating means 8 for applying an alternating magnetic field having a predetermined frequency corresponding to the strength of the direct-current magnetic field to alkali metal atoms, and resonant light output from the light detecting means 5 And a control means 10 for controlling the frequency difference between the first resonance light and the second resonance light so as to cause the alkali metal atom to develop an EIT phenomenon. It is configured Te. The AC magnetic field generating means 8 includes an oscillator 7 that oscillates the frequency of the AC magnetic field, and a coil 6 that generates an AC magnetic field when an output signal of the oscillator 7 is input.

When a DC magnetic field is applied to an alkali metal atom, Zeeman splitting occurs. Since the EIT signal subjected to Zeeman splitting is distributed to each ground level, the probability that an alkali metal atom exists at the ground level of m _F = 0 is lowered, and the level of the EIT signal is lowered. Therefore, in order to increase the existence probability of the alkali metal atom at the ground level of m _F = 0, the circularly polarized light 2a is irradiated to the alkali metal atom. As a result, for example, an alkali metal atom that has been irradiated with right-circularly polarized light has nine magnetic quantum numbers (m _F = 4) for the ground level (second ground level 34) having a quantum number F = 4. -4, -3, -2, -1, 0, 1, 2, 3, 4) Probability of being biased to five magnetic quantum numbers (m _F = 0, 1, 2, 3, 4) Becomes higher. Alternatively, with respect to the ground level of the quantum number F = 3 (the first ground level 33), there is a high probability that atoms are biased in four magnetic quantum numbers (m _F = 0, 1, 2, 3). Become.
However, in this state, the level of the EIT signal at m _F = 0 is higher than that of linearly polarized light, but the level at other m _F is also higher, so the EIT level at m _F = 0 is not necessarily efficiently. Can't be high. Therefore, in the present embodiment, an AC magnetic field generating means 8 is provided that applies an AC magnetic field having a predetermined frequency according to the strength of the DC magnetic field to the alkali metal atoms. Accordingly, by transitioning the number of alkali metal atoms present in the magnetic quantum number m _F other than the magnetic quantum number m _F = 0 in the ground level of m _F = 0, the EIT signal in the magnetic quantum number m _F = 0 The peak value can be increased.

FIG. 3 is a block diagram showing a configuration of an atomic oscillator according to the second embodiment of the present invention. The atomic oscillator 110 of the present invention is different from that shown in FIG. 2 in that the direct-current magnetic field detection means 11 for detecting the strength of the direct-current magnetic field of the direct-current magnetic field generation means 4 and the direct-current magnetic field detection means 11 A frequency control means 12 for generating a frequency control signal based on the strength of the magnetic field and a voltage controlled oscillator 13 whose frequency is controlled according to the frequency control signal are further provided.
As described above, when a DC magnetic field is applied to an alkali metal atom, Zeeman splitting occurs. At this time, an energy difference ΔE having different magnetic quantum numbers m _F and a frequency difference ΔF corresponding to the energy difference are generated. When a DC magnetic field, circularly polarized resonance light 2a, and an AC magnetic field equal to ΔF are applied, the alkali metal atom in the Zeeman level of the magnetic quantum number m _F = + 1 is in the state of the magnetic quantum number m _F = 0. Transition to. Thereby, the number of alkali metal atoms in the Zeeman level of the magnetic quantum number m _F = 0 can be further increased.
The DC magnetic field is generated by passing a current from a DC power supply to the coil. However, when the power supply voltage fluctuates, the current flowing through the coil changes, so that the strength of the DC magnetic field fluctuates. The alternating magnetic field needs to be generated at a frequency corresponding to the strength of the direct magnetic field. Therefore, in this embodiment, the intensity of the DC magnetic field is detected and a control signal corresponding to the intensity is given to the voltage controlled oscillator 13. Thereby, the frequency of the alternating magnetic field can be controlled following the fluctuation of the direct magnetic field.

  FIG. 4A is a block diagram showing an embodiment of the frequency control means of the present invention. For example, the frequency control means 12 of this embodiment includes an amplifier 12a, a variable resistor R2 that feeds back the output of the amplifier 12a to an inverting input, and a resistor R1 that grounds the inverting input, and the resistors R1 and R2 The amplification factor is determined by the ratio of. The DC magnetic field detection means 11 outputs a detection voltage corresponding to the detected magnetic field intensity (FIG. 4B). The detected voltage is received by the non-inverting input of the amplifier 12a of the frequency control means 12, and the strength of the magnetic field is converted into a control voltage by the amplification factor determined by the ratio of the resistors R1 and R2, and output to the voltage controlled oscillator 13 (FIG. (C)). The voltage controlled oscillator 13 oscillates the voltage controlled oscillator 13 at an oscillation frequency corresponding to the control voltage (FIG. 4 (d)).

FIG. 5 is a block diagram showing another embodiment of the frequency control means of the present invention. For example, the frequency control means 12 includes an A / D converter 12a that converts an analog signal into a digital signal, a non-volatile memory 12b that stores a control voltage having a frequency value corresponding to a detection voltage of the intensity of the DC magnetic field, And a D / A converter 12c that converts a digital value of the control voltage read from the memory 12b into an analog voltage.
A detection voltage corresponding to the intensity of the magnetic field detected by the DC magnetic field detection means 11 is converted into a digital signal by the A / D converter 12a, and a digital voltage value stored in the nonvolatile memory 12b corresponding to this detection voltage is read out. . The digital voltage value is converted to an analog value by the D / A converter 12 c and output to the voltage controlled oscillator 13. The voltage controlled oscillator 13 oscillates the voltage controlled oscillator 13 at an oscillation frequency corresponding to the control voltage converted into an analog value.

  DESCRIPTION OF SYMBOLS 1 Semiconductor laser, 2 (lambda) / 4 wavelength plate, 3 atomic cell, 4 DC magnetic field generation means, 5 Photodetection means, 6 Coil, 7 Oscillator, 8 AC magnetic field generation means, 9 Center wavelength control means, 10 Control means, 11 DC Magnetic field detection means, 12 Frequency control means, 13 Voltage controlled oscillator, 14 AC magnetic field generation means, 30 Excitation level, 31 First resonance light, 32 Second resonance light, 33 First ground level, 34 Second ground level , 100, 110 Atomic oscillator

Claims (7)

An alkali metal atom that generates an electromagnetically induced transmission phenomenon;
The Rukoto given DC magnetic field to the alkali metal atom, a DC magnetic field generating means to cause Zeeman splitting in the alkali metal atom,
AC magnetic field generating means for applying a predetermined AC magnetic field to the alkali metal atoms,
The AC magnetic field generating means gives an AC magnetic field equal to a frequency difference ΔF corresponding to an energy difference ΔE having different magnetic quantum numbers m F in the Zeeman splitting as the predetermined AC magnetic field.
An atomic oscillator characterized by that. The alternating magnetic field generating means, said a predetermined alternating magnetic field, the atomic oscillator according to claim 1, wherein the alternating magnetic field of predetermined frequency corresponding to the intensity of the DC magnetic field, characterized in that given to the alkali metal atoms.   The atomic oscillator according to claim 1, further comprising a DC magnetic field detection unit that detects the intensity of the DC magnetic field. The AC magnetic field generating means includes
The atomic oscillator according to claim 1, further comprising a frequency control unit that generates a frequency control signal based on the intensity of the DC magnetic field. The AC magnetic field generating means includes
The atomic oscillator according to claim 4, further comprising a voltage-controlled oscillator whose frequency is controlled based on the frequency control signal. The frequency control means includes
It has a memory | storage means which memorize | stores the frequency information corresponding to the intensity | strength of the said DC magnetic field detected by the said DC magnetic field detection means, The said frequency control signal is produced | generated based on the frequency information read from the said memory | storage means The atomic oscillator according to claim 4 or 5. The AC magnetic field generating means includes
The atomic oscillator according to claim 5, further comprising a coil that generates the alternating magnetic field when an output signal from the voltage controlled oscillator is input.

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