JP2016015363A - Quantum interference device and atomic oscillator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a quantum interference device capable of improving expression efficiency and reducing the deterioration of an EIT signal intensity or an S/N ratio, and an atomic oscillator.SOLUTION: A quantum interference device 10 includes a cell 11 sealing a metal atom 28 therein, and a light source 15 irradiating a laser beam 20 with an angle of irradiation θ to the inside of the cell 11. The inner width of the cell 11 in a cross section that intersects with a direction of radiation of the laser beam 20 increases toward the direction of irradiation.

Description

  The present invention relates to a quantum interference device and an atomic oscillator having the quantum interference device.

As an oscillator having long-term highly accurate oscillation characteristics, an atomic oscillator that oscillates based on energy transition of an alkali metal atom such as rubidium (Rb) or cesium (Cs) is known.
In general, the operating principle of an atomic oscillator is divided into a method using a double resonance phenomenon by light and microwave, and a method using a quantum interference effect (CPT: Coherent Population Trapping) by two lights having different frequencies (wavelengths). Although broadly classified, atomic oscillators utilizing the quantum interference effect can be made smaller than atomic oscillators utilizing the double resonance phenomenon, and in recent years, they are expected to be mounted on various devices.

  An atomic oscillator using the quantum interference effect includes a gas cell in which metal atoms in a gas state are sealed, a light emitting unit that irradiates the metal atoms in the gas cell with laser light including two resonance lights having different frequencies, and a gas cell that passes through the gas cell. A light detecting unit for detecting the laser beam and an optical component provided between the light emitting unit and the gas cell.

  Then, when the frequency difference of the resonance light is a specific value, an electromagnetically induced transparency (EIT) phenomenon occurs in which both of the two resonance lights are transmitted without being absorbed by the metal atoms in the gas cell, An EIT signal, which is a steep signal generated with the EIT phenomenon, is detected by a photodetector. Since the EIT signal has an eigenvalue determined by the type of metal atom, by detecting this EIT signal, a highly accurate oscillator that oscillates at a stable frequency can be configured.

  Conventionally, the atomic oscillator as described above, for example, as described in Japanese Patent Application Laid-Open No. H10-260260, has a laser beam on the optical axis between a laser beam oscillation source that supplies a laser beam as resonance light and a gas cell. Convex lenses and concave lenses capable of expanding the light beam in a range narrower than the internal space of the gas cell are arranged, and the laser light beam is expanded when the laser light passes through these lenses.

  By adopting such a configuration, laser light is uniformly irradiated to metal atoms in the internal space of the gas cell, and light-atom interaction can be caused with most metal atoms, and the line width of the EIT signal (detection intensity) It is disclosed that the half-value width is reduced and the detection intensity of the EIT signal is increased.

JP 2009-164331 A

  However, in order to meet the demand for miniaturization of quantum interference devices (atomic oscillators), light having an emission angle (hereinafter referred to as diffusion) between the light source part of the resonance light (laser light oscillation source) and the cell (gas cell). It has become difficult to arrange light flux adjusting parts such as convex lenses and concave lenses that adjust the width (light flux) of light (referred to as light) according to the inner width (inner wall) of the cell in the cross section that intersects the light irradiation direction. .

  Therefore, as described in Patent Document 1, in the direction of resonance light irradiation, when the diffused light is irradiated as the resonance light to the cell of the quantum interference device having the inner wall parallel to the optical axis of the resonance light Since there is no component for adjusting the luminous flux of the resonant light on the optical axis, the resonant light has a radiation angle in a state where it is emitted from the light source part toward the cell, and the cell is continuously expanded while expanding the luminous flux. Advancing inside, the metal (metal atom) enclosed in the cell is irradiated. Further, in order to reduce the line width of the EIT signal, the resonance light is adjusted so that the resonance light does not hit the inner wall of the cell.

  For this reason, on the light source side of the cell, the luminous flux of the resonant light is much smaller than the cross-sectional area of the inner wall of the cell, so there are many metals that are not irradiated with the resonant light inside the cell. The resonance light irradiated to the cell can cause a light-atom interaction only with a part of the metal atoms inside the cell, and the expression efficiency is lowered. As a result, there is a problem that the intensity of the EIT signal or the S / N ratio is lowered.

  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 application examples or forms.

  Application Example 1 A quantum interference device according to this application example includes a cell enclosing a metal and a light source unit that emits light having a radiation angle inside the cell, and intersects the irradiation direction of the light. The inner width of the cell in the cross section is increased toward the irradiation direction.

  According to this application example, the inner width of the cell in the cross section intersecting with the irradiation direction of the diffused light (hereinafter referred to as the inner width of the cell) is increased along the luminous flux of the diffused light. Evenly diffused light is irradiated to the metal. As a result, the metal enclosed in the cell efficiently absorbs light, and the expression efficiency is increased without wasting the internal space of the cell. Therefore, even if the quantum interference device is downsized and no light beam adjusting component is disposed, it is possible to reduce the decrease in the intensity of the EIT signal or the S / N ratio. The radiation angle refers to an angle formed by light positioned outside the diffused light flux and the optical axis.

  Furthermore, since the inner width of the cell can be configured in a range slightly larger than the luminous flux of the diffused light, it is difficult for the diffused light to hit the inner wall of the cell, and the irradiation of the metal near the inner wall can be reduced. As a result, the line width of the EIT signal is reduced, and a high quality and large EIT signal can be obtained. Therefore, a highly accurate and compact quantum interference device can be obtained.

  Application Example 2 The quantum interference device according to the application example is characterized in that the radiation angle of the radiation angle is in a range of 1 degree to 90 degrees.

  According to this application example, when the radiation angle is smaller than 1 degree, among the metals enclosed in the cell, the number of metals that are not irradiated with diffused light increases, and thus the metal inside the cell is uniformly irradiated with diffused light. When trying to do so, the cell becomes long in the direction parallel to the optical axis of the diffused light. When the radiation angle is larger than 90 degrees, it becomes impossible to make the diffused light incident so as not to hit the inner wall of the cell. Therefore, if the radiation angle is in the range of 1 to 90 degrees, the quantum interference device can be downsized. In addition, a radiation angle means the magnitude | size of a radiation angle.

  Application Example 3 In the quantum interference device according to the application example described above, the thickness of the cell is increased in the irradiation direction.

  According to this application example, the thickness of the cell increases toward the irradiation direction of the diffused light so that the outer width of the cell is parallel to the optical axis of the diffused light. It becomes possible to make it easy to fix. Accordingly, the positioning accuracy of the cell is improved, and the irradiation direction (optical axis) can be stabilized for a long time, so that the long-term stability of the oscillation frequency can be improved.

  Furthermore, since the wall thickness of the cell on the opposite side to the light source part is smaller than the wall thickness of the cell wall on the light source part side, the cell wall on the opposite side to the light source part has good heat dissipation, The temperature is lower than the surroundings. Therefore, the cooling efficiency is good and the solidification of the metal inside the cell is concentrated in the cell on the side opposite to the light source unit. Therefore, compared with the case where solidification of metal occurs in an unspecified part of the cell, the temperature distribution of the cell is stably maintained, so that frequency fluctuation can be reduced.

  Application Example 4 In the quantum interference device according to the application example described above, the metal reservoir for storing metal is provided near the end of the cell on the side opposite to the end on the light source unit side. To do.

  According to this application example, as described above, the temperature of the cell wall on the side opposite to the light source unit is lower than the surroundings. Therefore, solidification of the metal inside the cell is concentrated in the metal reservoir provided near the end opposite to the light source unit, and the solidified metal is efficiently collected in the metal reservoir. Therefore, it is possible to reduce blocking of the diffused light irradiated to the inside of the cell.

  That is, the amount of solidified metal can be easily seen visually compared to the case where no metal reservoir is provided. As a result, it can be seen that the concentration of metal in the cell in a gaseous state is insufficient and the concentration is lowered, so that the timing when maintenance and inspection of the quantum interference device is necessary can be grasped.

  Application Example 5 In the quantum interference device according to the application example described above, the inner wall of the cell has a tapered shape that widens in the light irradiation direction.

  According to this application example, by expanding the inner width of the cell into a tapered shape, it becomes possible to follow the luminous flux of the diffused light, the diffused light is hard to hit the inner wall of the cell, and the metal near the inner wall of the cell is irradiated. In this way, light is evenly applied to the metal enclosed in the cell. Therefore, a useless space inside the cell is reduced, and the quantum interference device can be efficiently downsized.

  Application Example 6 In the quantum interference device according to the application example described above, the inner wall inside the cell has a step shape along the irradiation direction of the light.

  According to this application example, it becomes easy to manufacture the inner wall of the cell along the luminous flux of the diffused light, so that the cost of the quantum interference device can be reduced.

  Application Example 7 The quantum interference device according to the application example includes a light receiving unit having a light receiving region larger than a width of the light incident on the cell.

  According to this application example, since the light receiving unit can receive the diffused light emitted from the light source unit without missing it, the light detection accuracy can be improved.

  Application Example 8 An atomic oscillator according to this application example includes the quantum interference device described above.

  According to this application example, since the quantum interference device that can reduce the intensity of the EIT signal or the S / N ratio can be reduced without arranging a light flux adjusting component, a small and highly accurate atomic oscillator is provided. Can be provided.

1 is an overall configuration diagram of a quantum interference device according to a first embodiment. 1 is a schematic diagram of a quantum interference device according to a first embodiment. Explanatory drawing of the energy state of an alkali metal. The graph which shows the relationship between the frequency difference of two light radiate | emitted from a light source part, and the intensity | strength of the light detected by a light-receiving part. Schematic of the quantum interference apparatus according to the second embodiment. The schematic diagram of the quantum interference device concerning modification 1 of a 2nd embodiment. The schematic diagram of the quantum interference device concerning modification 2 of a 2nd embodiment. 1 is an overall configuration diagram of an atomic oscillator having a quantum interference device according to a first embodiment. FIG.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following drawings, the scale of each layer and each member is made different from the actual scale so that each layer and each member can be recognized.

[Configuration of quantum interference device]
First, the configuration of the quantum interference device 10 of the present invention will be described. The quantum interference device 10 of the present invention can be applied to, for example, a magnetic sensor, a quantum memory, and the like in addition to an atomic oscillator 100 described later.

<First Embodiment>
FIG. 1 is an overall configuration diagram of a quantum interference device 10 according to the first embodiment. FIG. 2 is a schematic diagram of the quantum interference device 10 according to the first embodiment.
A quantum interference device 10 illustrated in FIG. 1 is a quantum interference device that controls output by using light absorption characteristics due to a quantum interference effect when two resonant lights having different frequencies are incident.

  Hereinafter, a specific configuration of the quantum interference device 10 of the present embodiment will be described in order with reference to FIGS. 1 and 2. Since the gist of the present invention is the structure of the quantum interference device 10, a detailed description of the frequency control of the quantum interference device 10 is omitted.

  As shown in FIG. 1, the quantum interference device 10 includes a cell 11, a light source unit 15, a light receiving unit 16, a control unit 41, a heater 31, a temperature sensor 32, and a coil 33, and further includes the cell 11 and the light receiving unit 16. , A heater 31, a temperature sensor 32, and a magnetic shield 36 that houses the coil 33.

  More specifically, as shown in FIG. 2, the quantum interference device 10 includes a cell 11 in which metal atoms 28 in a gas state are sealed, and light (diffused light) having an emission angle θ in the metal atoms 28. The light source unit 15 that is a light source that supplies the laser beam 20 (resonant light) and the light receiving unit 16 that detects the emitted light 22 transmitted through the cell 11 on the optical axis 21 of the laser beam 20 emitted from the light source unit 15. And. Note that the radiation angle θ refers to an angle formed by the optical axis 21 and the light positioned on the outermost side of the light beam of the laser light 20.

  That is, the laser light 20 emitted from the light source unit 15 enters the internal space 19 of the cell 11 through the incident window 17 of the cell 11 and radiates so as to form a truncated cone or a cone in the internal space 19 of the cell 11. The light is transmitted while being diffused, emitted from the exit window 18 of the cell 11, and finally the light receiving unit 16 detects the intensity as the emitted light 22.

(cell)
The cell 11 is composed of a pair of a body 12 having an opening having an open side surface, an incident window 17 that seals one of the openings, and an exit window 18 that blocks the other opening. Thus, an internal space 19 in which metal atoms 28 are enclosed is formed. In the cell 11, an imaginary line connecting the center portion of the entrance window 17 and the center portion of the exit window 18 on a plane perpendicular to the optical axis 21 connecting the light source portion 15 and the light receiving portion 16 with a straight line has an optical axis. 21 are arranged so as to overlap with each other.

  The metal atoms 28 are enclosed in the internal space 19 of the cell 11 and exist at a constant concentration in a gaseous state according to a saturated vapor pressure determined from the temperature and vacuum degree of the internal space 19. In the present embodiment, cesium (Cs), which is a quantum absorber, is sealed as the metal atom 28, and further, an inert gas such as nitrogen or a rare gas such as argon or neon or a nitrogen gas is sealed as necessary. It may be.

  The body 12 is a hollow frustum-shaped casing extending in the direction of the optical axis 21, and the inner wall 14 of the cell 11 maintains an inner width slightly larger than the luminous flux of the laser light 20, while the laser light 20 The taper shape is increased so as to follow the light flux of the laser beam 20 toward the irradiation direction. That is, an angle formed by the inner wall 14 of the cell 11 and the optical axis 21 (hereinafter referred to as an inclination angle η) becomes substantially the same as the radiation angle θ of the laser light 20 in the irradiation direction of the laser light 20. ing. The inner width refers to the width (size) of the inner wall 14 of the cell 11 having a cross section that intersects the irradiation direction of the laser beam 20.

  On the other hand, the outer wall 13 of the cell 11 is parallel to the inner wall 14 in the irradiation direction of the laser light 20, in other words, the wall thickness sandwiched between the outer wall 13 and the inner wall 14 of the body 12 of the cell 11 ( (Hereinafter referred to as “thickness”).

  The material constituting the body 12 may be any material that has a certain rigidity and does not deform, dissolve, or corrode at the operating temperature of the quantum interference device 10. That is, a glass material, a crystal, a metal material, a resin material, a silicon material, and the like can be given. In consideration of workability and bondability with the entrance window 17 and the exit window 18, it is preferable to use a glass material and a silicon material.

  Among these, it is more preferable to use a silicon material. Because, even when forming a small cell 11 such that the width and height of the cell 11 are 10 mm or less, a highly accurate body 12 can be easily formed using a fine processing technique such as etching, This is because the size of the cell 11 can be reduced.

  Next, the incident window 17 transmits the laser light 20 emitted from the light source unit 15 and incident on the internal space 19 of the cell 11. The emission window 18 emits from the internal space 19 of the cell 11 and exits. The laser beam 20 to be the incident light 22 is transmitted and each has a plate shape. Accordingly, the material constituting the entrance window 17 and the exit window 18 is not particularly limited as long as it has transparency to the laser light 20. Therefore, for example, a silicon material, a glass material, a crystal, and the like can be given, but it is preferable to use the same material as that of the body 12 in consideration of thermal expansion.

  In particular, when the entrance window 17 and the exit window 18 are made of a glass material, the body 12 made of a silicon material, and the entrance window 17 and the exit window 18 can be simply and airtightly joined by an anodic bonding method. it can. Depending on the thickness of the entrance window 17 and the exit window 18 and the intensity of the laser light 20, the entrance window 17 and the exit window 18 can be made of a silicon material.

  Here, an example of a manufacturing method of the cell 11 in which the metal atoms 28 are encapsulated using a fine processing technique such as etching will be described. First, a silicon substrate containing a silicon material is etched to form through holes in a tapered shape to form the body 12. Next, a glass substrate containing a glass material as the entrance window 17 is bonded so as to block one opening of the body 12, and metal atoms 28 are put into an internal space 19 formed inside the body 12.

  Next, similarly, the internal space 19 of the cell 11 becomes an airtight space by joining another glass substrate as the exit window 18 so as to seal the other opening of the body 12. In this case, as a method for joining the body 12 to the entrance window 17 and the exit window 18, in addition to the above-described anode joining method, a joining method using an adhesive, a direct joining method, or the like can be used. Then, in accordance with the outer dimensions of the cell 11, the joined one is cut using a dicing apparatus or the like, thereby completing the cell 11 in which the metal atoms 28 are enclosed.

  Moreover, you may perform enclosure of the metal atom 28 as follows. An introduction hole (not shown) for introducing metal atoms 28 is formed in a part of the body 12, a vent pipe (not shown) is connected to the introduction hole, and a certain amount is fixed by a vacuum pump (not shown). Depressurize to vacuum. And in the state which vaporized the metal atom 28, it inject | pours into the internal space 19 of the cell 11 from a vent pipe, and seals an introduction hole after that.

  Alternatively, the body 12, the entrance window 17, and the exit window 18 may be joined in an atmosphere in which the metal atoms 28 exist in a gas, or the metal atoms 28 are put into a glass tube having both ends open, You may enclose by heating and melt | dissolving. In such a case, when the metal atom 28 is sealed, the saturation vapor pressure of the metal atom 28 is taken into consideration so that the metal atom 28 does not precipitate at room temperature and the temperature of the cell 11 when the quantum interference device 10 is operated. It is necessary to adjust the degree of vacuum and the temperature appropriately.

  The shape of the body 12 of the cell 11 has been described as a hollow truncated cone shape. However, the laser light 20 that is diffused light does not strike the inner wall 14 of the cell 11 in the irradiation direction of the laser light 20. Any configuration may be used as long as it is tapered so as to follow the luminous flux of the laser beam 20.

  Since the cross section of the laser beam 20 intersecting with the irradiation direction of the diffused light is circular, the shape of the body 12 of the cell 11 is optimally a truncated cone shape considering the expression efficiency of the metal atoms 28, but is limited to the truncated cone shape. For example, the shape may be a polygonal frustum shape having a polygonal cross section such as a rectangular frustum shape having a rectangular cross section or a hexagonal frustum shape having a hexagonal cross section, or may be an elliptical frustum shape having an elliptical cross section.

  In addition, the quantum interference device 10 of the present embodiment is preferably configured such that the radiation angle of the laser light 20 is in the range of 1 degree to 90 degrees. This is because when the radiation angle is smaller than 1 degree, among the metal atoms 28 enclosed in the internal space 19 of the cell 11, the number of metal atoms 28 that are not irradiated with the laser beam 20 increases. Therefore, if the laser light 20 is uniformly irradiated to the metal atoms 28 in the internal space 19 of the cell 11, the cell 11 becomes long in the direction parallel to the optical axis 21 of the laser light 20, and the radiation angle is 90 degrees. If it is larger, the laser beam 20 cannot be incident so as not to strike the inner wall 14 of the cell 11.

  For the above reasons, the quantum interference device 10 can be miniaturized as long as the radiation angle is in the range of 1 to 90 degrees. In particular, the quantum interference device 10 is parallel to the optical axis 21 of the laser light 20. When the size and the in-plane direction perpendicular to the optical axis 21 are reduced, it is preferable that the radiation angle is 10 degrees or more and 30 degrees or less. If the radiation angle is set within the above numerical range, the size can be reduced.

  From the above, since the metal atoms 28 sealed in the internal space 19 of the cell 11 are uniformly distributed in the internal space 19 of the cell 11, when the laser light 20 is irradiated to the metal atom 28, the cell The cell 11 having the body 12 in which the inner wall 14 of the laser beam 11 radially expands along the radiation angle θ of the laser light 20 toward the irradiation direction of the laser light 20 is parallel to the optical axis 21 of the laser light 20. Compared with a cell having a body, more irradiation is possible.

  That is, by configuring the quantum interference device 10 with the cell 11 having the body 12 that radially spreads along the radiation angle θ of the laser light 20, the metal atoms 28 enclosed in the internal space 19 of the cell 11 are evenly distributed. Laser light 20 is irradiated. Accordingly, the quantum interference device 10 is further miniaturized, and the intensity of the EIT signal or the S / N ratio is lowered even if a lens for adjusting the luminous flux of diffused light such as a convex lens or a concave lens is not disposed on the optical axis 21. Can be reduced.

(Light source)
Next, the light source unit 15 is configured to emit laser light 20 having _two oscillation frequencies (ω _1, ω ₂ ), that is, coupling light and probe light, simultaneously in the same direction. It can be changed independently for each frequency. As a result, two laser beams 20 having different frequencies are simultaneously irradiated onto the metal atoms 28 enclosed in the internal space 19 of one cell 11, and the frequency of the laser beams 20 is controlled to absorb light accompanied by an EIT signal. The metal atom 28 can be performed.

  The light source unit 15 may be anything that can emit resonant light. For example, a semiconductor laser such as a vertical cavity surface emitting laser (VCSEL) or an edge emitting laser may be used. it can. The light source unit 15 is temperature adjusted to a predetermined temperature by a temperature adjusting element (a heating resistor, a Peltier element, etc.) (not shown).

(Light receiving section)
Next, if the light receiving unit 16 has frequency characteristics having light detection sensitivity for detecting the intensity of the emitted light 22 that is transmitted through the internal space 19 of the cell 11 and emitted in the variable frequency region of the laser light 20. For example, a photodetector (light receiving element) such as a solar cell or a photodiode can be used.

  Since the emitted light 22 spreads radially while traveling in the irradiation direction of the laser light 20, the light receiving area of the light receiving unit 16 is larger than the width (light flux) of the laser light 20 incident on the inside of the cell 11. . Furthermore, the light receiving unit 16 is arranged close to the cell 11 within a distance range where the emitted light 22 can be captured without leaking.

(heater)
When the quantum interference device 10 is operated, the heater 31 heats the metal atoms 28 in the cell 11 to an appropriate temperature at which the EIT phenomenon occurs with the gas atom having a desired concentration. The heater 31 generates heat when energized. For example, the heater 31 includes a heating resistor provided on the outer surface of the cell 11. Such a heating resistor is formed using, for example, a chemical vapor deposition method (CVD) such as plasma CVD or thermal CVD, a dry plating method such as vacuum deposition, a sol-gel method, or the like.

When this heating resistor is provided in the entrance window 17 or the exit window 18 of the cell 11, a material having transparency to resonant light, for example, ITO (Indium Tin Oxide), IZO (Indium Zinc Oxide), In ₃ The transparent electrode material is an oxide such as O ₃ , SnO ₂ , Sb-containing SnO ₂ , and Al-containing ZnO.

  The heater 31 is not particularly limited as long as it can heat the cell 11, and may be non-contact with the cell 11. Further, the cell 11 may be heated using a Peltier element instead of the heater 31 or in combination with the heater 31. Such a heater 31 is electrically connected to a temperature control unit 43 of a control unit 41, which will be described later, via a wiring (not shown) and is energized.

(Temperature sensor)
The temperature sensor 32 detects the temperature of the heater 31 or the cell 11. Based on the detection result of the temperature sensor 32, the heat generation amount of the heater 31 is controlled. By this control, the metal atoms 28 inside the cell 11 can be maintained at a desired temperature.

  The installation position of the temperature sensor 32 may be, for example, on the heater 31 or on the outer surface of the cell 11. As the temperature sensor 32, various known temperature sensors such as a thermistor and a thermocouple can be used. The temperature sensor 32 is electrically connected to a temperature control unit 43 of a control unit 41 (described later) via wiring (not shown) and is energized.

(coil)
When the coil 33 is energized, a magnetic field in a direction parallel to the optical axis 21 of the laser beam 20 is generated in the internal space 19 of the cell 11 to cause Zeeman splitting. As a result, it is possible to widen the gap between the degenerated energy levels of the metal atoms 28 existing in the internal space 19 to improve the resolution, and to reduce the line width of the EIT signal. The magnetic field generated from the coil 33 may be either a DC magnetic field or an AC magnetic field, or may be a magnetic field in which a DC magnetic field and an AC magnetic field are superimposed.

  The installation position of the coil 33 may be wound, for example, along the outer wall 13 of the body 12 of the cell 11 so as to constitute a solenoid type, or a pair of coils via the cell 11 so as to constitute a Helmholtz type. May be opposed to each other. The coil 33 is electrically connected to a magnetic field control unit 44 of the control unit 41, which will be described later, via wiring (not shown). As a result, the coil 33 can be energized.

(Magnetic shield)
The magnetic shield 36 is configured by a housing whose outer shape is a block shape, and contains the cell 11, the light receiving unit 16, the heater 31, the temperature sensor 32, and the coil 33 therein as described above. The magnetic shield 36 has magnetic shielding properties and shields the metal atoms 28 in the cell 11 from an external magnetic field. Thereby, since the magnetic field generated from the coil 33 can be stabilized inside the magnetic shield 36, the stability of the output of the quantum interference device 10 can be improved.

  The constituent material of the magnetic shield 36 is not particularly limited as long as it is a material having magnetic shielding properties, and examples thereof include soft magnetic materials such as Fe and various iron-based alloys (silicon iron, permalloy, amorphous, Sendust, Kovar). It is done. Among them, from the viewpoint of excellent magnetic shielding properties, Fe—Ni alloys such as Kovar and Permalloy can be used.

  Further, a plurality of leads (not shown) protrude from the magnetic shield 36, and these are electrically connected to the light receiving unit 16, the heater 31, the temperature sensor 32, and the coil 33 through wiring. Each lead is electrically connected to the wiring board by a connector or the like. As this connector, for example, a flexible substrate or a socket can be used.

(Control part)
The control unit 41 includes a resonance light control unit 42 that controls the frequencies of the two laser beams 20 of the light source unit 15, and a temperature control unit 43 that controls the temperature of the metal atoms 28 enclosed in the internal space 19 of the cell 11. And a magnetic field controller 44 for controlling the magnetic field applied to the cell 11. As described below, the control unit 41 controls the heater 31, the coil 33, and the light source unit 15, and in this embodiment, is configured by an IC (Integrated Circuit) chip.

Based on the detection result of the light receiving unit 16, the resonant light control unit 42 causes the frequency difference (ω ₁ −ω ₂ ) between the two laser beams 20 to be a specific frequency (specific value) ω _{0 of the} metal atom 28. In addition, the frequencies (ω ₁ , ω ₂ ) of the _two laser beams 20 emitted from the light source unit 15 are controlled. A specific configuration of the resonant light control unit 42 will be described later.

The temperature control unit 43 can maintain the cell 11 within a desired temperature range by controlling energization to the heater 31 based on the detection result of the temperature sensor 32.
The magnetic field control unit 44 controls energization of the coil 33 so that the magnetic field generated from the coil 33 is constant.

  From the above, according to the first embodiment, the inner wall 14 of the cell 11 increases radially along the radiation angle θ of the laser light 20 in the irradiation direction of the laser light 20, in other words, By making the inclination angle η of the inner wall 14 of the cell 11 in the direction of the optical axis 21 substantially the same as the radiation angle θ of the laser light 20, the laser light is uniformly distributed on the metal atoms 28 enclosed in the internal space 19 of the cell 11. 20 is irradiated.

  For this reason, the quantum interference device 10 has been miniaturized, and the metal enclosed in the internal space 19 of the cell 11 is not disposed on the optical axis 21 such as a convex lens or a concave lens. It is possible to improve the expression efficiency and reduce the intensity of the EIT signal or the S / N ratio from decreasing without the atoms 28 efficiently absorbing light and wasting the internal space 19 of the cell 11.

  Furthermore, since the inner width of the inner wall 14 of the cell 11 is configured to be slightly larger than the luminous flux of the laser beam 20, the laser beam 20 is difficult to hit the inner wall 14 and the metal atoms 28 near the inner wall 14 are irradiated. Can be reduced. As a result, the line width of the EIT signal is reduced, and a high quality and large EIT signal can be obtained. Therefore, a highly accurate and compact quantum interference device 10 can be obtained.

[Principle of quantum interference device]
Next, the principle of the quantum interference device 10 will be described.
FIG. 3 is an explanatory diagram of the energy state of the alkali metal, and FIG. 4 is a graph showing the relationship between the frequency difference between the two lights emitted from the light source unit 15 and the intensity of the light detected by the light receiving unit 16.

  As described above, in the quantum interference device 10, the laser light 20 is emitted from the light source unit 15 toward the cell 11, and the light receiving unit 16 detects the emitted light 22 transmitted through the cell 11. In the internal space 19 of the cell 11, metal atoms 28 are uniformly enclosed in a gas state, and the metal atoms 28 have energy levels of a three-level system as shown in FIG. There can be three states: two ground states having different levels (ground states α and β) and one resonance state. The ground state α is an energy state lower than the ground state β.

The laser light 20 emitted from the light source unit 15 includes two resonance lights 1 and 2 having different frequencies, and when the two resonance lights 1 and 2 are irradiated onto the metal atom 28 in a gas state as described above. Depending on the difference (ω ₁ −ω ₂ ) between the frequency ω ₁ of the resonant light ₁ and the frequency ω ₂ of the resonant light 2, the light absorptance (light transmittance) in the metal atoms 28 of the resonant lights 1 and 2 changes. To do.

When the difference (ω ₁ −ω ₂ ) between the frequency ω ₁ of the resonant light ₁ and the frequency ω ₂ of the resonant light 2 coincides with the frequency corresponding to the energy difference between the ground state α and the ground state β, the ground state Resonance from α and β to the resonance state stops. At this time, both the resonance lights 1 and 2 are transmitted without being absorbed by the metal atom 28. Such a phenomenon is called an electromagnetically induced transparency (EIT) phenomenon.

For example, when the light source unit 15 fixes the frequency ω ₁ of the resonant light 1 and changes the frequency ω ₂ of the resonant light ₂ , the difference between the frequency ω ₁ of the resonant light ₁ and the frequency ω ₂ of the resonant light 2 ( When ω ₁ −ω ₂ ) matches the frequency corresponding to the energy difference between the ground state α and the ground state β, the detection intensity of the light receiving unit 16 increases sharply as shown in FIG.

  Such a steep signal is detected as an EIT signal. Since the EIT signal has an eigenvalue determined by the type of the metal atom 28, a highly accurate oscillator or magnetic sensor can be configured, for example, by using this EIT signal.

Second Embodiment
A quantum interference device 10a according to a second embodiment of the present invention will be described with reference to FIG.
FIG. 5 is a schematic diagram of a quantum interference device 10a according to the second embodiment. The quantum interference device 10a according to the second embodiment is different in the shape of the body 12 of the cell 11 from the quantum interference device 10 according to the first embodiment. The parts common to the first embodiment will be denoted by the same reference numerals, description thereof will be omitted, and parts different from the first embodiment will be mainly described.

(cell)
As shown in FIG. 5, the quantum interference device 10a according to the second embodiment also includes a cell 11a, a light source unit 15, and a light receiving unit 16, as in the first embodiment. An internal space 19 in which metal atoms 28 are enclosed is formed.

  As in the first embodiment, the inner wall 14a of the body 12a of the cell 11a of the quantum interference device 10a according to the second embodiment has an inclination angle η substantially the same as the radiation angle θ of the laser light 20 in the irradiation direction of the laser light 20. And has a tapered shape. On the other hand, since the outer wall 13a of the body 12a of the cell 11a is parallel to the optical axis 21, the outer shape of the cell 11a is cylindrical. That is, in the cell 11a, the thickness of the body 12a on the light source unit 15 side is thicker than that of the body 12a on the opposite side to the light source unit 15 side (hereinafter referred to as the light receiving unit 16 side).

  The inner wall 14a is not limited to a truncated cone shape as long as the laser light 20 that is diffused light does not hit the inner wall 14a of the cell 11a. For example, the inner wall 14a has a rectangular pyramid shape with a hexagonal cross section. A polygonal pyramid shape with a polygonal cross section, such as a pyramid shape, or an elliptical cone shape with an elliptical cross section may be used. On the other hand, the outer wall 13a is not limited to the cylindrical shape shown in FIG. 5, but may be a polygonal column shape, an elliptical shape, or a combination thereof, and can be freely selected regardless of the inner wall 14a.

From the above, according to the quantum interference device 10a according to the second embodiment, the following effects can be obtained in addition to the effects of the first embodiment.
By extending the outer wall 13a of the body 12a of the cell 11a in parallel with the optical axis 21 in the irradiation direction of the laser light 20, the body 12a of the cell 11a can be easily fixed to another structure. As a result, the positioning accuracy of the cell 11a is improved, and the irradiation direction of the laser beam 20 or the optical axis 21 can be stabilized in the long term.

  Furthermore, since the thickness of the cell 11a on the light receiving unit 16 side is smaller than the thickness of the cell on the light source unit 15 side, the heat dissipation is good and the temperature is lower than the surroundings. Therefore, the cooling efficiency is good, and solidification of the metal atoms 28 in the gas state inside the cell 11a is concentrated on the light receiving unit 16 side of the cell 11a. Therefore, the temperature distribution of the cell 11a is stably maintained as compared with the case where the solidification of the metal atom 28 occurs in an unspecified part of the cell 11a. Therefore, improvement in frequency stability can be expected, and long-term reliability can also be improved.

<Modification 1>
A quantum interference device 10b according to Modification 1 of the second embodiment will be described with reference to FIG. FIG. 6 is a schematic diagram of a quantum interference device 10b according to Modification 1 of the second embodiment. In addition, the quantum interference apparatus 10b which concerns on the modification 1 differs in the shape of the inner wall 14a of the trunk | drum 12a of the cell 11a from the quantum interference apparatus 10a of the said 2nd Embodiment. The parts common to the first embodiment or the second embodiment will be denoted by the same reference numerals and the description thereof will be omitted, and the parts different from the second embodiment will be mainly described.

(cell)
As shown in FIG. 6, the quantum interference device 10b according to Modification 1 also has an inner wall 14b of the body 12b of the cell 11b that increases along the irradiation direction of the laser light 20, as in the second embodiment. The outer wall 13 b of 12 b extends parallel to the optical axis 21. That is, the inner wall 14 b of the body 12 b extends along the radiation angle θ of the laser light 20, and the outer wall 13 b is parallel to the optical axis 21.

  Unlike the second embodiment, the quantum interference device 10b according to the first modification has the inner wall 14b of the cell 11b having a step shape along the irradiation direction of the laser light 20. In FIG. 6, a diagram is shown that gradually spreads from the entrance window 17 to the exit window 18 in four stages, but may be two stages, three stages, or may be spread in five stages or more. Moreover, you may spread, combining with a taper shape.

  With such a configuration, it becomes easy to manufacture the inner wall 14b of the cell 11b, so that the cost of the cell 11b can be reduced. Therefore, the time for manufacturing the quantum interference device 10b is shortened, which can contribute to cost reduction. The fact that the inner wall 14b of the cell 11b, which is a feature of the first modification of the second embodiment, has a step shape along the irradiation direction of the laser light 20, can also be applied to the first embodiment. It is.

<Modification 2>
A quantum interference device 10c according to Modification 2 of the second embodiment will be described with reference to FIG. FIG. 7 is a schematic diagram of a quantum interference device 10c according to the second modification of the second embodiment. Note that the quantum interference device 10c according to the modification 2 is different from the quantum interference device 10a of the second embodiment in the shape of the body 12a of the cell 11a. The parts common to the first embodiment or the second embodiment will be denoted by the same reference numerals and the description thereof will be omitted, and the parts different from the second embodiment will be mainly described.

(cell)
As shown in FIG. 7, the quantum interference device 10 c according to the modification 2 also has an emission angle of the laser light 20 toward the irradiation direction of the laser light 20 by the inner wall 14 c of the body 12 c of the cell 11 c as in the second embodiment. Since the outer wall 13c of the body 12c of the cell 11c is parallel to the optical axis 21, the outer shape of the cell 11c has a cylindrical shape. Yes. That is, in the cell 11c, the thickness of the body 12c on the light source unit 15 side is thicker than the thickness of the body 12c on the light receiving unit 16 side.

  Furthermore, unlike the second embodiment, the quantum interference device 10c according to the second modification has a metal reservoir 29 that accumulates metal atoms 28 at the lower part in the direction in which gravity acts at the end on the light receiving unit 16 side inside the cell 11c. Is provided. As described above, since the thickness of the body 12 is small on the light receiving unit 16 side, heat dissipation is better than that on the light source unit 15 side, and the temperature is lower than the surroundings.

  Not all of the metal atoms 28 in the cell 11c exist in a gas state, but a part of the metal atom 28 becomes a liquid by being deposited (condensed) as a surplus in a low temperature portion of the cell 11c. For this reason, the solidification of the metal atoms 28 in the gas state inside the cell 11 c occurs in a concentrated manner in the metal reservoir 29, and the metal atoms 28 can be efficiently collected in the metal reservoir 29.

  That is, the amount of the solidified metal atom 28 can be easily visually recognized as compared with the case where the metal reservoir 29 is not provided. As a result, it can be seen that the concentration of the metal sealed in the gas state inside the cell 11c is reduced, and therefore the timing at which maintenance and inspection of the quantum interference device 10c is necessary can be grasped.

  Furthermore, after a long period of time, cesium (Cs) is absorbed by the cell 11c, and the cesium (Cs) concentration inside the cell 11c may gradually decrease. However, the quantum interference device 10c according to the modification 2 may be used. According to the above, since the metal reservoir 29 is provided in a part of the inside of the cell 11c, the cesium (Cs) can be added by replenishing the metal reservoir 29 with liquid or solid cesium (Cs). A decrease in concentration can be reduced. Therefore, it is possible to use the quantum interference device 10c for a long time without maintenance and inspection.

[Atomic oscillator]
FIG. 8 is an overall configuration diagram of the atomic oscillator 100 including the quantum interference device 10 according to the first embodiment. The overall configuration of the atomic oscillator 100 having the quantum interference device 10 will be specifically described with reference to FIGS.

  As shown in FIG. 8, the atomic oscillator 100 includes a center frequency control unit 110, a semiconductor laser 120, an atomic cell 130, a magnetic field generation unit 140, a photodetector 150, an amplifier 160, a detection unit 170, a modulation unit 180, an oscillator 190, The detection unit 200, the oscillator 210, the modulation unit 220, the oscillator 230, the frequency conversion unit 240, the detection unit 250, the oscillator 260, the modulation unit 270, the oscillator 280, and the modulation unit 290 are configured.

  Note that the semiconductor laser 120, the atomic cell 130, the magnetic field generation unit 140, and the photodetector 150 in FIG. 8 correspond to the light source unit 15, the cell 11, the coil 33, and the light receiving unit 16 in FIG. Further, the center frequency control means 110, the amplifier 160, the detection means 170, the modulation means 180, the oscillator 190, the detection means 200, the oscillator 210, the modulation means 220, the oscillator 230, the frequency conversion means 240, the detection means 250, the oscillator 260, the modulation means. A circuit composed of 270, the oscillator 280, and the modulation means 290 corresponds to the resonant light control unit 42 in FIG.

  As described above with reference to FIG. 2, the semiconductor laser 120 (light source unit 15) includes two lasers having different frequencies so that the metal atoms 28 enclosed in the atomic cell 130 (cell 11) efficiently cause the EIT phenomenon. Light 20 is emitted to irradiate the metal atoms 28.

  For example, when a laser diode driver that supplies a driving current to the semiconductor laser 120 is used as the center frequency control unit 110, the semiconductor laser 120 is configured to superimpose an alternating current output from the modulation unit 290 on the driving current. The emitted laser beam 20 can be modulated. The output of the modulation means 290 is feedback-controlled so that the light corresponding to the modulation component becomes the resonance light 1 or the resonance light 2 for the metal atom 28.

  The photodetector 150 detects the light transmitted through the atomic cell 130 and outputs a signal having an intensity corresponding to the detected amount of light. The output signal of the photodetector 150 is amplified by the amplifier 160 and input to the detection means 170, the detection means 200, and the detection means 250.

  The detector 170 synchronously detects the output signal of the amplifier 160 based on the oscillation signal of the oscillator 190. The modulation unit 180 modulates the output signal of the detection unit 170 with the oscillation signal of the oscillator 190. The oscillator 190 may oscillate at a low frequency of about several tens Hz to several hundreds Hz, for example.

  Then, the center frequency control unit 110 controls the center frequency of the laser light 20 emitted from the semiconductor laser 120 in accordance with the output signal of the modulation unit 180. The center frequency is stabilized by a feedback loop passing through the semiconductor laser 120, the atomic cell 130, the photodetector 150, the amplifier 160, the detection unit 170, the modulation unit 180, and the center frequency control unit 110.

  Next, the detection means 200 synchronously detects the output signal of the amplifier 160 using the oscillation signal of the oscillator 230. The oscillator 210 is an oscillator whose oscillation frequency changes according to the magnitude of the output signal of the detection means 200, and can be realized by, for example, a voltage controlled crystal oscillator (VCXO). Here, the oscillator 210 oscillates at about 10 MHz, for example, and this oscillation signal becomes the output signal of the atomic oscillator 100.

  Modulating means 220 modulates the output signal of oscillator 210 with the oscillation signal of oscillator 230. For example, the oscillator 230 may oscillate at a low frequency of about several tens Hz to several hundreds Hz.

  The frequency conversion unit 240 converts the output signal of the modulation unit 220 into a half of the frequency difference corresponding to the energy difference between the two ground levels of the metal atom 28 with the magnetic quantum number m = 0 enclosed in the atomic cell 130 ( In the case of a cesium atom, the signal is converted to a signal having a frequency equal to (9.1926 GHz / 2 = 4.5963 GHz). The frequency conversion means 240 can be realized by, for example, a PLL (Phase Locked Loop) circuit.

  The frequency conversion means 240 outputs the output signal of the modulation means 220 to a frequency difference (cesium atom) corresponding to the energy difference between the two ground levels of the metal atom 28 with the magnetic quantum number m = 0 enclosed in the atomic cell 130. In this case, the signal may be converted to a signal having a frequency equal to 9.1926 GHz.

  Next, the detection unit 250 synchronously detects the output signal of the amplifier 160 using the oscillation signal of the oscillator 280. The oscillator 260 is an oscillator whose oscillation frequency changes according to the magnitude of the output signal of the detection means 250, and can be realized, for example, by a voltage controlled crystal oscillator (VCXO). Here, the oscillator 260 oscillates at a frequency Δω (for example, about 1 MHz to 10 MHz) that is sufficiently small with respect to the frequency corresponding to the width of the Doppler spread of the excitation level of the metal atom 28 enclosed in the atomic cell 130.

  Modulating means 270 modulates the output signal of oscillator 260 with the oscillation signal of oscillator 280. The oscillator 280 may oscillate at a low frequency of about several tens Hz to several hundreds Hz, for example.

  Modulating means 290 modulates the output signal of frequency converting means 240 by the output signal of modulating means 270 (the output signal of modulating means 270 may be modulated by the output signal of frequency converting means 240). The modulation means 290 can be realized by a frequency mixer (mixer), a frequency modulation (FM) circuit, an amplitude modulation (AM) circuit, or the like. Then, the laser light 20 emitted from the semiconductor laser 120 is modulated based on the output of the modulation means 290, and the resonance light 1 and the resonance light 2 are generated.

  In the atomic oscillator 100 having such a configuration, the frequency difference between the resonant light 1 and the resonant light 2 emitted from the semiconductor laser 120 is the energy difference between the two ground levels of the metal atoms 28 enclosed in the atomic cell 130. If the frequency does not exactly match the frequency corresponding to, the metal atom 28 does not cause the EIT phenomenon, so that the detection amount of the photodetector 150 changes extremely sensitively according to the frequencies of the resonant light 1 and the resonant light 2. .

Therefore, the output of the frequency conversion means 240 is provided by a feedback loop passing through the semiconductor laser 120, the atomic cell 130, the photodetector 150, the amplifier 160, the detection means 200, the oscillator 210, the modulation means 220, the frequency conversion means 240, and the modulation means 290. Feedback control is applied so that the frequency of the signal exactly matches a frequency equal to ½ of the frequency difference corresponding to the energy difference between the two ground levels of the metal atom 28 with the magnetic quantum number m = 0.
Therefore, the oscillator 210 existing in the feedback loop also oscillates at an extremely stable oscillation frequency, and the frequency accuracy of the output signal of the atomic oscillator 100 can be increased.

  Further, the intensity of the magnetic field applied to the atomic cell 130 changes under the influence of the geomagnetic field and the influence of temperature change, but according to the present embodiment, feedback control is performed in consideration of the influence of the geomagnetic field and the influence of temperature change. It takes. Therefore, it is possible to provide the atomic oscillator 100 with higher accuracy by canceling the influence of disturbance.

  From the above, when the atomic oscillator 100 includes the quantum interference device 10 of the present embodiment, EIT expression efficiency can be significantly improved without increasing the volume of the cell 11. As a result, it is possible to realize the atomic oscillator 100 in which the peak of the EIT signal becomes higher and steeper and the oscillation can be maintained with extremely stable frequency stability.

  Further, according to the atomic oscillator 100 of the present embodiment, the atomic oscillator 100 is further miniaturized, so that the cell 11 (even if the lens for adjusting the light beam such as a convex lens or a concave lens is not disposed on the optical axis 21 of the resonance light. The metal atoms 28 enclosed in the internal space 19 of the atomic cell 130) efficiently absorb light, improve the expression efficiency without wasting the internal space 19 of the cell 11, and increase the intensity of the EIT signal, or A decrease in the S / N ratio can be reduced. Therefore, it is advantageous for cost reduction and miniaturization.

  DESCRIPTION OF SYMBOLS 1, 2 ... Resonant light, 10 ... Quantum interference apparatus, 11 ... Cell, 12 ... Body, 13 ... Outer wall, 14 ... Inner wall, 15 ... Light source part, 16 ... Light-receiving part, 17 ... Incident window, 18 ... Emission window, 19 ... Internal space, 20 ... Laser light, 21 ... Optical axis, 22 ... Emission light, 28 ... Metal atom, 29 ... Metal reservoir, 31 ... Heater, 32 ... Temperature sensor, 33 ... Coil, 36 ... Magnetic shield, 41 ... Control part 42 ... Resonant light control part 43 ... Temperature control part 44 ... Magnetic field control part 100 ... Atomic oscillator 110 110 Central frequency control means 120 ... Semiconductor laser 130 ... Atomic cell 140 ... Magnetic field generation means DESCRIPTION OF SYMBOLS 150 ... Photodetector, 160 ... Amplifier, 170 ... Detection means, 180 ... Modulation means, 190 ... Oscillator, 200 ... Detection means, 210 ... Oscillator, 220 ... Modulation means, 230 ... Oscillator, 240 ... Frequency conversion means, 2 0 ... detecting means, 260 ... oscillator, 270 ... modulating unit, 280 ... oscillator, 290 ... modulating unit, theta ... radiation angle, eta ... tilt angle.

Claims (8)

A cell containing metal,
A light source unit that emits light having a radiation angle inside the cell, and
The quantum interference device according to claim 1, wherein an inner width of the cell in a cross section intersecting with the irradiation direction of the light increases toward the irradiation direction.   The quantum interference device according to claim 1, wherein the radiation angle is in a range of 1 degree to 90 degrees.   3. The quantum interference device according to claim 1, wherein a thickness of the cell increases toward the irradiation direction. 4.   4. The quantum interference device according to claim 3, wherein a metal reservoir for storing metal is provided near an end of the cell opposite to an end on the light source side.   5. The quantum interference device according to claim 1, wherein an inner wall of the cell has a tapered shape that expands in the light irradiation direction. 6.   5. The quantum interference device according to claim 1, wherein an inner wall of the cell has a step shape along an irradiation direction of the light. 6.   7. The quantum interference device according to claim 1, further comprising a light receiving unit having a light receiving region larger than a width of light incident on the cell.   An atomic oscillator comprising the quantum interference device according to claim 1.

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