Quantum interference device, atomic oscillator, and control method

Abstract

To provide a quantum interference device that can realize a quantum interference effect having high frequency stability for magnetic field variation.SOLUTION: A quantum interference device 100 comprises: a space 2; and an alkali metal atom cell 3. A static magnetic field having a specific direction and intensity is applied to the space 2. The alkali metal atom cell 3 is provided within the space 2. Alkali metal atoms are filled in the alkali metal atom cell 3. A quantum interference state of the alkali metal atoms is generated by applying the static magnetic field to the alkali metal atom cell 3 and injecting excitation light having at least two different frequency components. A frequency component associated with formation of the quantum interference state, of frequency components of the excitation light is light including linear polarization being the same polarization direction to each other. The static magnetic field applied to the space 2 is adjusted to suppress variation for a magnetic field for a transition frequency between ground levels forming the quantum interference state.SELECTED DRAWING: Figure 21

Description

[Technical Field]

[0001] The present invention relates to a quantum interference device, an atomic oscillator, and a control method. [Background technology]

[0002] Atomic oscillators that oscillate based on the energy transition of alkali metal atoms are known as oscillators with long-term, highly accurate oscillation characteristics. In relation to this technology, Patent Document 1 discloses an atomic cell module, a method for controlling the magnetic field of an atomic cell, and a quantum interference device and electronic device that use the atomic cell module and have high frequency stability. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2014-053841 Summary of the Invention [Problem to be solved by the invention]

[0004] In the technology disclosed in Patent Document 1, problems with the magnetic field control method and structural problems make it difficult to obtain a quantum interference effect with high frequency stability against magnetic field fluctuations.

[0005] The object of the present disclosure has been made to solve such problems, and is to provide a quantum interference device, an atomic oscillator, and a control method that can achieve a quantum interference effect with high frequency stability against magnetic field fluctuations. [Means for solving the problem]

[0006] The quantum interference device according to the present disclosure comprises a space to which a static magnetic field of a specific direction and strength is applied, and an alkali metal atom cell disposed inside the space and containing alkali metal atoms, wherein the static magnetic field is applied to the alkali metal atom cell, and excitation light having at least two different frequency components is incident thereon, thereby generating a quantum interference state of the alkali metal atoms, and among the frequency components of the excitation light, frequency components involved in the formation of the quantum interference state are light containing linearly polarized light having the same polarization direction, and the static magnetic field is adjusted so that fluctuations in the resonant frequency, which is the transition frequency between ground levels that form the quantum interference state, with respect to the magnetic field are suppressed.

[0007] The atomic oscillator according to the present disclosure also includes a quantum interference device and a mechanism for adjusting the oscillation frequency based on the quantum interference state.

[0008] In addition, the control method disclosed herein involves irradiating excitation light having at least two different frequency components onto an alkali metal atom cell in which alkali metal atoms are sealed, detecting the light that has passed through the alkali metal atom cell, measuring the transmitted light spectrum to detect CPT resonance, and controlling the static magnetic field applied to the alkali metal atom cell so that fluctuations in the resonant frequency of the CPT resonance with respect to the magnetic field are suppressed. [Effects of the Invention]

[0009] According to the present disclosure, it is possible to provide a quantum interference device, an atomic oscillator, and a control method that can realize a quantum interference effect with high frequency stability against magnetic field fluctuations. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 illustrates the hyperfine structure of a cesium atom. [Figure 2] Schematic diagram of CPT resonance appearing in the transmitted light spectrum. [Figure 3] FIG. 10 is a diagram showing an example of the excitation structure of CPT resonance detected when circularly polarized excitation light is incident. [Figure 4] FIG. 10 is a diagram showing an example of an excitation structure of CPT resonance detected when linearly polarized excitation light is incident. [Figure 5] FIG. 10 is a diagram showing the magnetic field dependence of the resonance frequencies of (0,0), (+1,-1), and (-1,+1) resonances. [Figure 6] FIG. 1 is a functional block diagram of a quantum interference device according to a first embodiment. [Figure 7] 4 is a flowchart showing the operation of the quantum interference device according to the first embodiment. [Figure 8] FIG. 10 is a functional block diagram of a quantum interference device according to a second embodiment. [Figure 9] 10 is a flowchart showing the operation of the quantum interference device according to the second embodiment. [Figure 10] FIG. 10 is a functional block diagram of a quantum interference device according to a third embodiment. [Figure 11] 10 is a flowchart showing the operation of the quantum interference device according to the third embodiment. [Figure 12] FIG. 10 is a structural diagram of an atomic oscillator according to a fourth embodiment. [Figure 13] FIG. 10 is a diagram showing the configuration of an atomic oscillator 120 according to a fifth embodiment. [Figure 14] FIG. 13 is a schematic diagram showing a frequency spectrum of frequency-modulated excitation light according to the fifth embodiment. [Figure 15] FIG. 11 is a diagram showing the magnetic field dependence of the transmitted light spectrum detected when linearly polarized excitation light is incident on the alkali metal atom cell according to the fifth embodiment. [Figure 16] FIG. 11 is a diagram showing the magnetic field dependence of the resonance frequency of the CPT resonance detected when linearly polarized excitation light is incident on the alkali metal atom cell according to the fifth embodiment. [Figure 17] FIG. 11 is a diagram showing the excitation light intensity dependency of the transmitted light spectrum detected when linearly polarized excitation light is incident on the alkali metal atom cell according to the fifth embodiment. [Figure 18]FIG. 11 is a diagram showing the excitation light intensity dependence of the full width at half maximum of the CPT resonance detected when linearly polarized excitation light is incident on the alkali metal atom cell, according to the fifth embodiment. [Figure 19] FIG. 10 is a diagram showing the magnetic field dependence of the transmitted light spectrum detected when circularly polarized excitation light is incident on an alkali metal atom cell. [Figure 20] FIG. 10 is a diagram showing the magnetic field dependence of the resonance frequency of the CPT resonance detected when circularly polarized excitation light is incident on the alkali metal atom cell. [Figure 21] FIG. 10 is a functional block diagram of a quantum interference device according to a sixth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] (Summary of Embodiments of the Present Disclosure) Hereinafter, the present embodiment will be described in detail with reference to the drawings. Prior to describing the embodiments of the present disclosure, an overview of the embodiments of the present disclosure will be described.

[0012] There are several types of atomic oscillators, which are devices for measuring time with high precision. For example, there is an oscillation method that utilizes the quantum interference effect, as described below. Figure 1 shows the hyperfine structure of a cesium atom. As an alkali metal atom, cesium atoms have six electrons as a result of the interaction between the total angular momentum of the electrons and the nuclear spin, as shown in Figure 1. 2 S 1 / 2 The ground level of 6 2 P 1 / 2 and the excited level of 6 2 P 3 / 2 In other words, in this case, the cesium atom has two levels, F=3,4, and 2 S 1 / 2 and two levels F=3,4. 2 P 1 / 2 and four levels F=2,3,4,5. 2 P 3 / 2 Among these, the ground level 6 2 S1 / 2 The transition frequency between F=3 and F=4 (the transition frequency between the ground levels) is f hfs = 9 192 631 770 Hz. This frequency f hfs By using the time information obtained from this, it is possible to realize seconds based on the SI unit system (International System of Units). The transition frequency between these ground states shifts due to factors such as interactions with external electromagnetic fields and collisions between cesium atoms and buffer gas. In particular, the change in transition frequency caused by a static magnetic field is called the Zeeman shift.

[0013] When a cesium atom in the ground state is irradiated with resonant light having a frequency corresponding to the energy difference between these levels, the cesium atom may absorb the resonant light and transition to an excited state. In addition, as a reverse process, a cesium atom in an excited state may emit resonant light and transition to the ground state. Here, 6 2 S 1 / 2 The ground level of 6 2 P 1 / 2 The resonant light with a frequency corresponding to the energy difference with the excited level of 6 is called the D1 line. 2 S 1 / 2 The ground level of 6 2 P 3 / 2 The resonant light having a frequency corresponding to the energy difference with the excited level of is called the D2 line.

[0014] In particular, 6 2 S 1 / 2 Two ground levels of F=3,4 and 6 2 P 1 / 2 The three levels consisting of the excited levels of F = 3, 4 are called Λ-type three levels because Λ-type transitions due to the absorption and emission of the D1 line are possible. 2 S 1 / 2 F=3 and 6 2 P 1 / 2 The transition between any of the excited levels is called transition #1, and the light having a frequency that is near-resonant with transition #1 is called pump light #1. In other words, the frequency of pump light #1 is the same as the transition frequency of transition #1 or is different by a certain detuning frequency.2 S 1 / 2 F=4 and 6 2 P 1 / 2 The transition between any of the excited levels is called transition #2, and the light having a frequency that is near-resonant with transition #2 is called pump light #2. In other words, the frequency of pump light #2 is the same as the transition frequency of transition #2, or it differs by a certain detuning frequency. Now, consider the simultaneous irradiation of these pump lights (pump light #1 and pump light #2) onto gaseous cesium atoms. At this time, the difference frequency between the irradiated pump light #1 and pump light #2 is the frequency that is near-resonant with two ground levels (6 2 S 1 / 2 F=3 and 6 2 S 1 / 2 When the transition frequency of the two ground levels coincides with the transition frequency of the quantum coherence state (dark resonance state), a quantum interference effect (called CPT (Coherent Population Trapping)) occurs, suppressing excitation to the excited level.

[0015] Figure 2 is a schematic diagram of the CPT resonance that appears in the transmitted light spectrum. For example, if the transmitted light spectrum is measured while sweeping the difference frequency between pump light #1 and pump light #2, the transmitted light of a cesium atom is detected. When the difference frequency matches the transition frequency between the ground levels, the transmitted light reaches a peak, as shown in Figure 2, and the CPT resonance is detected. The difference frequency between the pump lights at this time is called the resonant frequency. By detecting the resonant frequency of the CPT resonance and controlling the difference frequency between the pump lights to match the transition frequency between the two ground levels, a high-precision oscillator utilizing the quantum interference effect can be realized. Note that while cesium atoms have been used as an example here, similar atomic oscillators utilizing the quantum interference effect can also be realized with alkali metal atoms with similar atomic structures, such as rubidium, sodium, and potassium.

[0016] In the atomic oscillator using the CPT method described above, the resonant frequency of the CPT resonance is used as the reference for the oscillation frequency. To realize a precise atomic oscillator, it is necessary to take into account the Zeeman effect, in which energy fluctuates under a magnetic field depending on the magnetic quantum number.

[0017] Figure 3 shows an example of the excitation structure of CPT resonance detected when circularly polarized excitation light is incident. For example, when an external magnetic field is applied to a cesium atom, the energy shift due to the Zeeman effect results in a 6 2 S 1 / 2 The F=3 level has a magnetic quantum number m F It splits into seven magnetic sublevels: ±0, ±1, ±2, ±3. 2 S 1 / 2 The level of F=4 is m F = 0, ±1, ±2, ±3, ±4. As a result, the transition frequencies between the magnetic sublevels are different from each other, so when a magnetic field is applied to the cesium atom, multiple CPT resonances with different resonance frequencies can be detected. Here, the set of magnetic sublevels |F=3,m F =i〉 and |F=4,m F For simplicity, the transmitted light spectrum due to the dark resonance state formed by (i,j) is called the "(i,j) resonance."

[0018] In general, for atomic oscillators that require high frequency stability, it is preferable to detect the CPT resonance, which has a small fluctuation in the resonant frequency with respect to the magnetic field, and use it to control the oscillation frequency. For example, |F=3,m F =0〉 and |F=4,m F =0〉, none of the magnetic sublevels undergo a first-order Zeeman shift, and the energy shift due to the application of a magnetic field is smaller than that of other magnetic sublevels. Therefore, the (0,0) resonance arising from these dark resonance states is widely used in CPT-type atomic oscillators for cesium atoms. In Figure 3, the (0,0) resonance is indicated by the dashed arrow.

[0019] Furthermore, in order to determine the resonance frequency with high precision, it is preferable to detect a single CPT resonance, avoiding the increase in the resonance linewidth due to the superposition of multiple CPT resonances. Generally, in a CPT atomic oscillator, a magnetic field is applied to an alkali metal atomic gas cell to make the interval frequency between multiple resonance frequencies larger than the resonance linewidth, and a single CPT resonance without overlap is detected. In other words, in a CPT atomic oscillator, the resonance frequency is varied by applying a magnetic field to an alkali metal atomic gas cell, and a single CPT resonance without overlap is detected.

[0020] Here, whether a dark resonance state can be formed between specific magnetic sublevels is determined by the polarization state of the excitation light and the frequency components of the excitation light. For example, the (0,0) resonance resulting from the dark resonance state having the excitation structure shown in Figure 3 is detected when the polarization states of excitation light #1 and excitation light #2 are both the same circularly polarized light. Since other CPT resonances that can occur under this polarization condition are affected by the first-order Zeeman shift, applying a magnetic field of about several tens of μT (T: Tesla) allows the detection of a non-overlapping (0,0) resonance.

[0021] Furthermore, in CPT atomic oscillators, magnetic field correction devices with magnetic field shielding and magnetic field cancellation functions are provided to avoid fluctuations in the resonance frequency due to higher-order Zeeman effects and to improve frequency stability against magnetic field fluctuations. Technology related to these magnetic field correction devices is disclosed, for example, in Patent Document 1. However, the magnetic field correction device described in Patent Document 1 above was unable to achieve sufficient performance. The reasons for this are as follows.

[0022] The first reason is that it is difficult to completely demagnetize the magnetic field generated in alkali metal atoms using only an external magnetic field shielding device. For example, Patent Document 1 discloses a technology for performing demagnetization operations in response to detection signals from a magnetic detection unit. However, with magnetic field correction using such a feedback system, it is difficult to respond to magnetic fields that fluctuate in a time shorter than the feedback time constant. Therefore, with the technology disclosed in Patent Document 1, it is difficult to completely demagnetize the magnetic field generated in alkali metal atoms.

[0023] The second reason is that a magnetic shield may be provided to suppress fluctuations in the external magnetic field that occur at the position of the alkali metal atomic gas cell. To improve the magnetic field shielding performance as in Patent Document 1, a bulky magnetic shield must be provided, which limits the miniaturization of the atomic oscillator. Therefore, to provide a compact atomic oscillator, it is preferable to have an oscillation mechanism with high frequency stability against fluctuations in the external magnetic field.

[0024] The technology according to the present embodiment has been made in consideration of the problem of the deterioration of frequency stability of atomic oscillators due to fluctuations in the external magnetic field as described above. That is, the technology according to the present embodiment can provide a quantum interference device and an atomic oscillator that utilize the quantum interference effect and have high frequency stability against fluctuations in the magnetic field generated inside an alkali metal atomic gas cell.

[0025] Figure 4 shows an example of the excitation structure of CPT resonance detected when linearly polarized excitation light is incident. When detecting the CPT resonance of cesium atoms, if the excitation light is linearly polarized, the (0,0) resonance is not detected, but the (+1,-1) resonance and (-1,+1) resonance resulting from the dark resonance state having the excitation structure shown in Figure 4 are detected. In Figure 4, the (+1,-1) resonance is indicated by a dashed arrow, and the (-1,+1) resonance is indicated by a solid arrow. |F=3,m F =+1〉 and |F=4,m F=-1〉, all magnetic sublevels produce approximately the same first-order Zeeman shift, so the (+1,-1) resonance exhibits a small change in resonance frequency with respect to a magnetic field, comparable to that of the (0,0) resonance. Similarly, the (-1,+1) resonance exhibits a small change in resonance frequency with respect to a magnetic field, comparable to that of the (0,0) resonance. Therefore, these CPT resonances can be used in CPT atomic oscillators. That is, this embodiment is configured to irradiate alkali metal electrons with linearly polarized excitation light. Furthermore, as described below, when linearly polarized excitation light is used under a certain magnetic field, a CPT resonance can be detected whose resonance frequency is more stable with respect to magnetic field fluctuations than the (0,0) resonance detected when the excitation light is circularly polarized.

[0026] FIG. 5 shows the magnetic field dependence of the resonance frequencies of the (0,0) resonance, the (+1,-1) resonance, and the (-1,+1) resonance. FIG. 5 shows the magnetic field dependence of the resonance frequencies of the (0,0) resonance, the (+1,-1) resonance, and the (-1,+1) resonance, obtained from calculations of the energy difference between the magnetic sublevels of cesium atoms, including higher-order Zeeman shifts. Here, the direction opposite to the propagation direction of the excitation light is the positive direction of the applied magnetic field. In FIG. 5, the magnetic field dependence of the resonance frequency of the (0,0) resonance is shown by a dashed line, the magnetic field dependence of the resonance frequency of the (+1,-1) resonance is shown by a dashed line, and the magnetic field dependence of the resonance frequency of the (-1,+1) resonance is shown by a solid line.

[0027] The shift of each resonance frequency due to an external magnetic field (magnetic field shift; the variation of the resonance frequency with respect to the magnetic field) is smallest at the magnetic field where the resonance frequency is at its minimum. For example, the resonance frequency with a gradient of 1.2 Hz / μT or less is achieved at the (0,0) resonance from -15 μT to +15 μT. Similarly, the resonance frequency with a gradient of 1.2 Hz / μT or less is achieved at the (+1,-1) resonance from -154 μT to -124 μT, and at the (-1,+1) resonance from +124 μT to +154 μT. In particular, the resonance frequency shift at the (-1,+1) resonance is smallest at a magnetic field of +139 μT. Therefore, detection of non-overlapping CPT resonances with minimal influence of magnetic field fluctuations can be achieved by applying a specific static magnetic field, determined by the atomic species, to alkali-metal atoms using linearly polarized excitation light.

[0028] The atomic oscillator according to this embodiment includes a space to which a static magnetic field with controllable magnetic field strength is applied, an alkali metal atomic cell in which alkali metal atoms are sealed, and linearly polarized excitation light that is incident on the alkali metal atomic cell and has at least two frequency components, the difference frequency of which is approximately equal to the transition frequency between the ground states. The alkali metal atomic cell is placed at a predetermined position in the space to which the static magnetic field is applied.

[0029] The quantum interference device according to this embodiment includes a space to which a static magnetic field of a specific direction and specific strength is applied, an alkali metal atom cell in which alkali metal atoms are sealed, and excitation light incident on the alkali metal atom cell, the excitation light having at least two frequency components and whose difference frequency is approximately equal to the transition frequency between ground states. Here, the alkali metal atom cell is arranged so that its interior is located above the space to which the static magnetic field is applied. The quantum interference device generates a quantum interference state of the alkali metal atoms by irradiating the alkali metal atoms with excitation light. The quantum interference device includes frequency components of the excitation light that contribute to the formation of the quantum interference state, the frequency components including linearly polarized light having the same polarization direction, and a magnetic field generating device for suppressing fluctuations in the transition frequency between ground states that form the quantum interference state due to changes in the magnetic field.

[0030] Here, when detecting CPT resonance using the method of this embodiment, the fluctuation of the resonance frequency against fluctuations in the external magnetic field is small. Therefore, it is possible to provide a quantum interference device and an atomic oscillator with high frequency stability against fluctuations in the magnetic field. In the example of Figure 5, by applying a magnetic field (139 μT) to the alkali metal atomic cell that maximizes the stability of the resonance frequency against fluctuations in the magnetic field of the (-1, +1) resonance, it is possible to provide a quantum interference device and an atomic oscillator with high frequency stability against fluctuations in the external magnetic field.

[0031] (First embodiment) Hereinafter, embodiments will be described with reference to the drawings. For clarity of explanation, the following description and drawings have been omitted and simplified as appropriate. In addition, the same elements in each drawing are designated by the same reference numerals, and duplicate explanations have been omitted as necessary.

[0032] [Configuration Description] FIG. 6 is a functional block diagram of a quantum interference device 100 according to a first embodiment. The quantum interference device 100 according to this embodiment includes excitation light 1, a space 2, an alkali metal atom cell 3, and a photodetector 4. The excitation light 1 has at least two different frequency components. A static magnetic field substantially parallel to the incident direction of the excitation light 1 is applied to the space 2. That is, the space 2 functions as a magnetic field application space. A static magnetic field in the opposite direction (opposite direction) to the incident direction of the excitation light 1 may be applied to the space 2. A static magnetic field in the same direction as the incident direction of the excitation light 1 may also be applied to the space 2. That is, it is sufficient that a static magnetic field parallel to the incident direction of the excitation light 1 is applied to the space 2 in the same direction or opposite direction. Alkali metal atoms are sealed in the alkali metal atom cell 3. The alkali metal atom cell 3 is disposed at a predetermined position within the space 2. The photodetector 4 detects light (transmitted light) that has passed through the alkali metal atom cell 3.

[0033] As described above, the pump light 1 has at least two different frequency components. The pump light 1 may also have three or more different frequency components, with the difference frequency between two of these frequency components being approximately equal to the transition frequency between two magnetic sublevels that form the dark resonance state of the alkali metal atom. Preferably, the difference frequency of the pump light 1 can be realized by a mechanism capable of sweeping within a range of approximately 1 MHz. Note that, as long as resonance detection is possible, the sweep range need not be approximately 1 MHz. For example, the sweep range may be narrower than 1 MHz, e.g., approximately 10 kHz. The two frequency components contained in the pump light 1, whose difference frequency is approximately equal to the transition frequency between the ground levels of the alkali metal atom, are light containing linearly polarized light with the same polarization direction. For example, when light of a certain frequency contained in the pump light 1 is linearly polarized, the pump light 1 contains light whose frequency differs by the transition frequency between the ground levels of the alkali metal atom, and this light may have a polarization component parallel to the linearly polarized light. That is, the pump light 1 has two frequency components with polarization components parallel to each other and a difference frequency substantially equal to the transition frequency between the ground levels of the alkali metal atoms. Pump light 1 that satisfies these conditions can be realized, for example, by modulating single-wavelength light emitted from a semiconductor laser or the like with a frequency substantially equal to half the transition frequency between the ground levels to generate sidebands. Alternatively, pump light 1 that satisfies these conditions can be realized, for example, by combining two single-wavelength light beams emitted from two semiconductor lasers or the like that have a mechanism for controlling the difference frequency.

[0034] The space 2 to which the static magnetic field is applied includes a region including the inside of the alkali metal atom cell 3. For example, a coil is placed inside the space 2 so as to cover the alkali metal atom cell 3, and the position and shape of the coil and the direction and magnitude of the current applied to the coil are adjusted, thereby realizing control of the direction and strength of the static magnetic field applied to the space 2. As a result, a static magnetic field of a specific direction and specific strength is applied to the space 2.

[0035] The alkali metal atom cell 3 contains alkali metal atoms having a Λ-type three-level energy. The alkali metal atoms contained in the alkali metal atom cell 3 may be, for example, cesium atoms, rubidium atoms, sodium atoms, or potassium atoms. The container of the alkali metal atom cell 3 is preferably made of a transparent material such as glass, which has a high transmittance for the excitation light 1. In addition to the alkali metal atoms, the alkali metal atom cell 3 may contain a buffer gas that does not contribute to the absorption of the excitation light 1, in order to reduce the effect of collisions of the gaseous alkali metal atoms with the container wall. The alkali metal atom cell 3 may also include a temperature control device that does not obstruct the optical path of the excitation light 1, in order to control the saturated vapor pressure of the gaseous alkali metal atoms. The temperature control device may be, for example, a resistance heater.

[0036] Excitation light 1 is incident on the alkali metal atom cell 3, and a portion of the incident light is transmitted through the alkali metal atom cell 3. The light detection unit 4 has a device that detects light that has transmitted through the alkali metal atom cell 3 (transmitted light). The light detection unit 4 is realized by using, for example, a photodiode. The light detection unit 4 can be realized by a photodetector, which is a light detection means.

[0037] Here, quantum interference device 100 is a device that generates a quantum interference state of alkali metal atoms by irradiating excitation light 1 onto the alkali metal atoms. Furthermore, among the frequency components of excitation light 1, the frequency components involved in the formation of the quantum interference state are linearly polarized light whose difference frequency coincides with the transition frequency between ground states and has the same polarization direction. Furthermore, quantum interference device 100 may also have a magnetic field generator (corresponding to static magnetic field application device 8, described later) for suppressing fluctuations in the transition frequency between ground states that form the quantum interference state due to changes in magnetic field. The magnetic field generator may be provided in space 2.

[0038] [Explanation of operation] 7 is a flowchart showing the operation of the quantum interference device 100 according to the first embodiment. The flowchart shown in FIG. 7 shows a control method (adjustment method, detection method) executed by the quantum interference device 100 according to the first embodiment. The operation shown in FIG. 7 may be realized by a control device (for example, a control means such as the control device 20 described later) provided in the quantum interference device 100 according to the first embodiment. The operation in this embodiment will be described with reference to the flowchart shown in FIG. 7.

[0039] When detecting the quantum interference effect (CPT resonance), the transmitted light is detected while sweeping the difference frequency of the excitation light 1 (S112 to S116). First, the sweep range of the difference frequency of the excitation light 1 is set to a predetermined value (step S112). Specifically, the quantum interference device 100 sets the sweep range of the difference frequency of the excitation light 1 to a range that includes the resonance frequency of the CPT resonance and is wider than the full width at half maximum of the CPT resonance. Preferably, the quantum interference device 100 sets the sweep range of the difference frequency of the excitation light 1 to a range in which both the (-1, +1) resonance and the (+1, -1) resonance are expected to be detected.

[0040] Next, the strength of the magnetic field (applied magnetic field) applied to the alkali metal atom cell 3 is set to a predetermined value (step S114). Specifically, the quantum interference device 100 sets the strength of the magnetic field applied to the alkali metal atom cell 3 to a value that is expected to minimize the magnetic field shift of the resonant frequency of the (-1, +1) resonance (the variation of the resonant frequency with respect to the magnetic field). This value can be calculated from the Zeeman effect occurring in the magnetic sublevels, and is, for example, 139 μT when the alkali metal atoms sealed in the alkali metal atom cell 3 are cesium atoms, as shown in FIG. 5.

[0041] Under these conditions, the quantum interference device 100 sweeps the frequency difference of the excitation light 1 while making the excitation light 1 incident on the alkali metal atom cell 3 and detects the transmitted light (step S116). Then, the quantum interference device 100 varies the applied magnetic field and performs similar detection. Specifically, the quantum interference device 100 makes the excitation light 1 incident on the alkali metal atom cell 3 and detects the transmitted light with the photodetector 4, thereby measuring the transmitted light spectrum and detecting the CPT resonance. Then, to evaluate the magnetic field shift of the resonance frequency, the quantum interference device 100 slightly varies the applied magnetic field, for example, by about 10 μT, and performs similar transmitted light detection. This makes it possible to detect CPT resonance whose resonance frequency is stable against fluctuations in the external magnetic field (i.e., whose magnetic field shift is small).

[0042] The quantum interference device 100 determines whether or not the (-1, +1) resonance is detected from the obtained transmitted light spectrum (step S118). When linearly polarized excitation light 1 is irradiated onto alkali metal electrons, the (-1, +1) resonance and the (+1, -1) resonance, whose resonance frequency shift due to a magnetic field is small, are detected, and therefore, it can be determined whether or not the (-1, +1) resonance is detected from these resonance frequencies.

[0043] If the (-1, +1) resonance is not detected (NO in S118), the quantum interference device 100 corrects the setting value of the sweep range of the difference frequency (step S120). Then, the process flow returns to S114. Specifically, the quantum interference device 100 expands the sweep range of the difference frequency, and again sets the applied magnetic field (S114) and detects the transmitted light, i.e., measures the transmitted light spectrum (S116).

[0044] On the other hand, if the (-1, +1) resonance is detected (YES in S118), the quantum interference device 100 determines whether the magnetic field shift of the resonance frequency is within the allowable range (step S130). That is, the quantum interference device 100 determines whether the magnetic field shift of the resonance frequency is suppressed. Specifically, the quantum interference device 100 determines whether the magnitude of the magnetic field-induced shift of the resonance frequency is within the allowable range, for example, 1.2 Hz / μT or less. That is, the quantum interference device 100 determines whether the gradient of the resonance frequency (corresponding to the magnetic field shift) with respect to the applied magnetic field is within a predetermined range. The predetermined range is, for example, "-1.2 Hz / μT or more and 1.2 Hz / μT or more." Alternatively, the predetermined range may be, for example, "-10 Hz / μT or more and 10 Hz / μT or more."

[0045] If the magnitude of the magnetic field shift of the resonant frequency is outside the allowable range (NO in S130), the quantum interference device 100 corrects the setting value of the applied magnetic field (step S132). Then, the process flow returns to S116. Specifically, for example, if the magnetic field shift of the resonant frequency is positive (i.e., 0<1.2 Hz / μT<“magnetic field shift”), the quantum interference device 100 resets the applied magnetic field to be smaller. On the other hand, if the magnetic field shift of the resonant frequency is negative (i.e., 0>−1.2 Hz / μT>“magnetic field shift”), the quantum interference device 100 resets the applied magnetic field to be larger. Then, the quantum interference device 100 again performs transmitted light detection, i.e., measurement of the transmitted light spectrum (S116).

[0046] On the other hand, if the magnitude of the magnetic field shift of the resonant frequency is within the allowable range (YES in S130), the quantum interference device 100 determines the set value of the applied magnetic field (step S140). Then, the adjustment of the applied magnetic field is terminated. Through this process, the static magnetic field applied to the space 2 is adjusted so as to suppress the magnetic field shift of the transition frequency (resonant frequency) between ground levels that form the quantum interference state. Furthermore, for example, a control device (control means) controls the magnetic field applied to the space 2 (alkali metal atom cell 3) based on the transmitted light spectrum. Furthermore, for example, a control device (control means) controls the applied magnetic field so that the gradient of the resonant frequency with respect to the applied magnetic field (corresponding to the magnetic field shift) is within a predetermined range. This controls the difference frequency of the excitation light, making it possible to generate a quantum interference state of the alkali metal atoms. This also applies to other embodiments.

[0047] [Effect description] According to the quantum interference device 100 of the first embodiment, by generating the applied magnetic field adjusted by the above-described method at a position inside the alkali metal atom cell, it is possible to detect CPT resonance, whose resonance frequency is stable against fluctuations in the external magnetic field. Then, by performing feedback control on the difference frequency of the excitation light so as to lock to the detected resonance frequency, an atomic oscillator with high frequency stability against fluctuations in the external magnetic field is realized. That is, by realizing an atomic oscillator having a mechanism for adjusting the oscillation frequency of the excitation light (the difference frequency of the excitation light) based on the resonance frequency (quantum interference effect) detected by the quantum interference device 100, an atomic oscillator with high frequency stability against fluctuations in the external magnetic field is realized. In other words, it is possible to control (feedback control) the difference frequency of the excitation light based on the transmitted light spectrum detected by the photodetector 4 (photodetector), thereby generating a quantum interference state of the alkali metal atoms.

[0048] (Second embodiment) Next, a second embodiment will be described. For clarity of explanation, the following description and drawings have been omitted and simplified as appropriate. In addition, in each drawing, the same elements are given the same reference numerals, and duplicate explanations are omitted as necessary.

[0049] [Configuration Description] 8 is a functional block diagram of a quantum interference device 100 according to the second embodiment. The quantum interference device 100 according to the second embodiment includes excitation light 1, a light generating unit 5 that generates the excitation light 1, a space 2, an alkali metal atom cell 3, and a light detecting unit 4. The excitation light 1, the space 2, the alkali metal atom cell 3, and the light detecting unit 4 are substantially the same as those according to the first embodiment, and therefore description thereof will be omitted.

[0050] The light generating unit 5 functions as a light generating means. The light generating unit 5 generates excitation light 1 having at least two frequency components. The light generating unit 5 has a mechanism for modulating the amount of excitation light, which is realized, for example, by a voltage-controllable optical attenuator. The light generating unit 5 includes a light source 5a, a frequency modulation unit 5b, and a light intensity modulation unit 5c. The light source 5a outputs monochromatic light. The frequency modulation unit 5b performs frequency modulation on the monochromatic light output from the light source 5a. The light intensity modulation unit 5c performs light intensity modulation on the monochromatic light output from the light source 5a. The excitation light 1 is generated by frequency modulation and light intensity modulation on the monochromatic light output from the light source 5a. The light generating unit 5 is configured to modulate the intensity of the excitation light. The light generating unit 5 can be controlled by a control device (e.g., a control means such as the control device 20 described later) provided in the quantum interference device 100.

[0051] [Explanation of operation] 9 is a flowchart showing the operation of the quantum interference device 100 according to the second embodiment. The flowchart shown in FIG. 9 shows a control method (adjustment method, detection method) executed by the quantum interference device 100 according to the second embodiment. The operation shown in FIG. 9 may be realized by a control device (for example, a control means such as the control device 20 described later) provided in the quantum interference device 100 according to the second embodiment. The operation in the second embodiment will be described with reference to the flowchart shown in FIG. 9.

[0052] When detecting the quantum interference effect (CPT resonance), the transmitted light is detected while sweeping the difference frequency of the excitation light 1 (S212 to S216). First, similar to S112 in FIG. 7, the quantum interference device 100 sets the sweep range of the difference frequency of the excitation light 1 to a predetermined value (step S212). The quantum interference device 100 also sets the intensity of the excitation light 1 to a predetermined value (step S213). Specifically, the quantum interference device 100 controls the light generating unit 5 to set the intensity of the excitation light 1 to a predetermined value. Similarly to S114 in FIG. 7, the quantum interference device 100 also sets the strength of the magnetic field (applied magnetic field) applied to the alkali metal atom cell 3 to a predetermined value (step S214).

[0053] 7, the quantum interference device 100 causes the excitation light 1 to enter the alkali metal atom cell 3 while sweeping the frequency difference of the excitation light 1, and detects the transmitted light (step S216). Then, the quantum interference device 100 performs a similar detection by varying the applied magnetic field. That is, the quantum interference device 100 measures the transmitted light spectrum by causing the excitation light 1 generated by the light generating unit 5 to enter the alkali metal atom cell 3 and detecting the transmitted light with the light detecting unit 4. Then, in order to evaluate the magnetic field shift of the resonance frequency, the quantum interference device 100 minutely varies the applied magnetic field and performs a similar transmitted light detection.

[0054] 7, quantum interference device 100 determines whether or not (-1, +1) resonance is detected from the obtained transmitted light spectrum (step S218). If (-1, +1) resonance is not detected (NO in S218), quantum interference device 100 corrects the set value of the sweep range of the difference frequency (step S220), similar to S120 in Fig. 7. Then, the process flow returns to S213, and CPT resonance is detected again.

[0055] On the other hand, if the (-1, +1) resonance is detected (YES in S218), the quantum interference device 100 determines whether or not the CPT resonance is superimposed (step S222). Specifically, the quantum interference device 100 determines whether or not the (-1, +1) resonance and the (+1, -1) resonance are superimposed from the obtained transmitted light spectrum.

[0056] If CPT resonance is superimposed (YES in S222), the quantum interference device 100 corrects the set value of the light intensity (step S224). Then, the process flow returns to S214. Specifically, the quantum interference device 100 attenuates the intensity of the excitation light 1, and again sets the applied magnetic field (S214) and detects the transmitted light, i.e., measures the transmitted light spectrum (S216).

[0057] On the other hand, if the CPT resonance is not overlapping, that is, if the (-1, +1) resonance is detected without overlapping (NO in S222), the quantum interference device 100 determines whether the magnetic field shift of the resonance frequency is within the allowable range (step S230), similar to S130 in FIG. 7. If the magnitude of the magnetic field shift of the resonance frequency is outside the allowable range (NO in S230), the quantum interference device 100 corrects the setting value of the applied magnetic field (step S232), similar to S132 in FIG. 7. Then, the process flow returns to S216. That is, the quantum interference device 100 again detects transmitted light, that is, measures the transmitted light spectrum (S216).

[0058] On the other hand, if the magnitude of the magnetic field shift of the resonance frequency is within the allowable range (YES in S230), the quantum interference device 100 determines the set values ​​of the light intensity and the applied magnetic field (step S240). Then, the adjustment of the light intensity and the applied magnetic field is terminated. Through this process, the static magnetic field applied to the space 2 is adjusted so as to suppress the magnetic field shift of the transition frequency (resonance frequency) between the ground levels that form the quantum interference state. Furthermore, the light intensity of the excitation light is also adjusted so as to prevent multiple CPT resonances from superimposing. For example, the light intensity of the excitation light can be controlled by a control device (control means) based on the transmitted light spectrum.

[0059] [Effect description] According to the quantum interference device 100 of the second embodiment, by adjusting the magnetic field applied to the alkali metal atom cell 3 and the intensity of the excitation light 1 incident on the alkali metal atom cell 3, CPT resonance, whose resonant frequency is stable against fluctuations in the external magnetic field, is detected without overlap. As a result, feedback control is performed on the difference frequency so as to lock to the detected resonant frequency, thereby realizing an atomic oscillator with high frequency stability against fluctuations in the external magnetic field. That is, by controlling (feedback control) the intensity of the excitation light based on the transmitted light spectrum detected by the photodetector 4, CPT resonance, whose resonant frequency is stable against fluctuations in the external magnetic field, is realized without overlap. For example, as shown in FIGS. 17 and 18 (described later), when the difference frequency of the excitation light is swept in a frequency region separated from the resonant frequency of the optical absorption characteristic due to the quantum interference effect by the full width at half maximum or less of the optical absorption characteristic, a state is realized in which the quantum interference effect arising from only one pair of magnetic sublevels contributes to the transmitted light spectrum.

[0060] (Third embodiment) Next, a third embodiment will be described. For clarity of explanation, the following description and drawings have been omitted and simplified as appropriate. In addition, in each drawing, the same elements are given the same reference numerals, and duplicate explanations are omitted as necessary.

[0061] [Configuration Description] 10 is a functional block diagram of a quantum interference device 100 according to the third embodiment. The quantum interference device 100 according to the third embodiment includes an optical trapping system. The quantum interference device 100 according to the third embodiment also includes excitation light 1, a magnetic field generator 2A, an atom trapping cell 6, a magneto-optical trapping system 7, and a photodetector 4.

[0062] As in the above-described embodiment, the excitation light 1 has at least two different frequency components. Gaseous alkali metal atoms are sealed in the atom trapping cell 6. The excitation light 1 is incident on the atom trapping cell 6. The magnetic field generator 2A applies a static magnetic field to a predetermined position inside the atom trapping cell 6.

[0063] The atom trapping cell 6 corresponds to the alkali metal atom cell 3. Like the alkali metal atom cell 3, the atom trapping cell 6 contains alkali metal atoms with a Λ-type three-level energy. The alkali metal atoms contained in the atom trapping cell 6 may be, for example, cesium atoms, rubidium atoms, sodium atoms, or potassium atoms. The material constituting the container of the atom trapping cell 6 is preferably a transparent material, such as glass, that has a high transmittance for the excitation light 1 and the light for atom trapping.

[0064] The magneto-optical trapping system 7 generates cooled atoms inside the atom trapping cell 6. The magneto-optical trapping system 7 functions as an optical trapping system that traps atoms using light. The magneto-optical trapping system 7 achieves trapping of alkali metal atoms, for example, by applying an optical electric field and a trapping magnetic field to the atom trapping cell 6 for atom trapping. The light detection unit 4 detects light that has passed through the atom trapping cell 6 (transmitted light).

[0065] Compared with the quantum interference device 100 according to the above-described embodiments, the quantum interference device 100 according to the third embodiment has a significantly smaller effect on the quantum interference effect due to collisions between alkali metal atoms and the cell inner wall, alkali metal atoms, or buffer gas. This is because the atoms in the optically trapped atom trapping cell 6 have a significantly slower movement speed than the atoms in the alkali metal atom cell, and therefore the number of collisions per unit time is smaller. Therefore, the third embodiment can realize a quantum interference device 100 with higher accuracy.

[0066] [Explanation of operation] 11 is a flowchart showing the operation of the quantum interference device 100 according to the third embodiment. The flowchart shown in FIG. 11 shows a control method (adjustment method, detection method) executed by the quantum interference device 100 according to the third embodiment. The operation shown in FIG. 11 may be realized by a control device (for example, control means such as the control device 20 described later) provided in the quantum interference device 100 according to the third embodiment. The operation in this embodiment will be described with reference to the flowchart shown in FIG. 11.

[0067] First, the quantum interference device 100 sets the trapping magnetic field and the optical electric field to predetermined values ​​(step S302). Specifically, the quantum interference device 100 sets the optical electric field and the trapping magnetic field of the magneto-optical trapping system 7 so that the alkali metal atoms are trapped at predetermined positions in the atom trapping cell 6.

[0068] The quantum interference device 100 determines whether the alkali metal atom is trapped at the predetermined position (step S304). If the alkali metal atom is not trapped at the predetermined position (NO in S304), the quantum interference device 100 resets the trapping magnetic field and the optical electric field (step S306). Then, the process flow returns to S304. That is, the processes of S304 and S306 are repeated until the alkali metal atom is trapped at the predetermined position.

[0069] On the other hand, if the alkali metal atom is trapped at the predetermined position (YES in S304), the quantum interference device 100 sets the sweep range of the difference frequency of the excitation light 1 to a predetermined value (step S312), similar to S112 in Fig. 7. Furthermore, the quantum interference device 100 sets the strength of the magnetic field (applied magnetic field) applied to the alkali metal atom cell 3 to a predetermined value (step S314), similar to S114 in Fig. 7.

[0070] Under these conditions, the quantum interference device 100 detects the transmitted light (detects CPT resonance) (step S316). Specifically, the quantum interference device 100 temporarily removes the trapping optical electric field and trapping magnetic field, and while sweeping the frequency difference of the excitation light 1, the quantum interference device 100 causes the excitation light 1 to enter the atom trapping cell 6 and detects the transmitted light. The quantum interference device 100 then performs similar detection by varying the applied magnetic field. That is, after trapping the cooled atoms at a predetermined position, the quantum interference device 100 temporarily removes the trapping optical electric field and trapping magnetic field, causes the excitation light 1 to enter the atom trapping cell 6, and detects the transmitted light with the photodetector 4, thereby measuring the transmitted light spectrum. In this way, the quantum interference device 100 detects the CPT resonance.

[0071] 7, quantum interference device 100 determines whether or not (-1, +1) resonance is detected from the obtained transmitted light spectrum (step S318). If (-1, +1) resonance is not detected (NO in S318), quantum interference device 100 corrects the set value of the sweep range of the difference frequency (step S320), similar to S120 in Fig. 7. Then, the process flow returns to S314, and CPT resonance is detected again.

[0072] On the other hand, if the (-1, +1) resonance is detected (YES in S318), the quantum interference device 100 determines whether the magnetic field shift of the resonance frequency is within the allowable range (step S330), similar to S130 in FIG. 7. If the magnitude of the magnetic field shift of the resonance frequency is outside the allowable range (NO in S330), the quantum interference device 100 corrects the setting value of the applied magnetic field (step S332), similar to S132 in FIG. 7. Then, the process flow returns to S316. That is, the quantum interference device 100 again detects transmitted light, i.e., measures the transmitted light spectrum (S316).

[0073] On the other hand, if the magnitude of the magnetic field shift of the resonant frequency is within the allowable range (YES in S330), the quantum interference device 100 determines the setting value of the applied magnetic field (step S340). Then, the adjustment of the applied magnetic field to the atom trapping cell 6 is completed. Through this process, the static magnetic field applied to the space 2 is adjusted so as to suppress the magnetic field shift of the transition frequency (resonant frequency) between the ground levels that form the quantum interference state. Note that FIG. 11 corresponds to a modified processing flow of the first embodiment, but is not limited to this configuration. The third embodiment can be applied not only to the first embodiment but also to the second embodiment. In other words, the light intensity may be adjusted in the third embodiment.

[0074] [Effect description] According to the quantum interference device 100 of the third embodiment, by detecting CPT resonance using cooled atoms formed by the magneto-optical trap system 7, it is possible to ignore fluctuations in the resonance frequency and signal linewidth of CPT resonance caused by the influence of buffer gas. Therefore, as an effect of the quantum interference device 100 of the third embodiment, it is possible to detect CPT resonance with a highly stable resonance frequency and a narrow resonance linewidth compared to when an alkali metal atom cell containing a buffer gas is used. Therefore, it is possible to provide a quantum interference device 100 (atomic oscillator) with high frequency stability against fluctuations in the magnetic field.

[0075] (Fourth embodiment) Next, a fourth embodiment will be described. For clarity of explanation, the following description and drawings have been omitted and simplified as appropriate. In addition, the same elements in each drawing are given the same reference numerals, and duplicated explanations are omitted as necessary.

[0076] [Configuration Description] FIG. 12 is a structural diagram of an atomic oscillator 110 according to a fourth embodiment. The atomic oscillator 110 shown in FIG. 12 is a small atomic oscillator with a simplified magnetic field shielding device (magnetic field shielding function). The atomic oscillator 110 includes a light generating unit 5 that generates excitation light, an alkali metal atomic cell 3 on the optical path of the excitation light, a light detecting unit 4 that detects light transmitted through the alkali metal atomic cell 3, and a static magnetic field application device 8. A magnetic field shielding device (not shown) with a simplified magnetic field shielding function is provided to cover the outside of the static magnetic field application device 8. The atomic oscillator 110 may be included in the quantum interference device 100 described above. In other words, the quantum interference device 100 described above may include the atomic oscillator 110.

[0077] The light generating unit 5 generates excitation light having at least two frequency components. Here, the two frequency components contained in the excitation light, whose difference frequency is approximately equal to the transition frequency between the ground levels of the alkali metal atoms, are linearly polarized light having the same polarization direction. The excitation light can be generated, for example, by a light source such as a semiconductor laser that oscillates linearly polarized light. For example, sidebands are generated by driving the semiconductor laser with a frequency-modulated current, thereby realizing excitation light that is linearly polarized light having at least two frequency components.

[0078] The alkali metal atom cell 3 contains alkali metal atoms having a Λ-type three-level energy. As described above, the alkali metal atoms contained in the alkali metal atom cell 3 may be, for example, cesium atoms, rubidium atoms, sodium atoms, or potassium atoms. The alkali metal atom cell 3 is made of a transparent material, such as glass, that has a high transmittance for excitation light. In addition to the alkali metal atoms, the alkali metal atom cell 3 may contain a buffer gas that does not contribute to absorbing the excitation light, in order to reduce the effect of collisions of the gaseous alkali metal atoms with the container wall. The alkali metal atom cell 3 may also include a temperature control mechanism that is shaped so as not to obstruct the optical path of the excitation light or is made of a transparent material that has a high transmittance for the excitation light.

[0079] The light detection unit 4 detects light (transmitted light) that has passed through the alkali metal atom cell 3. In other words, the light detection unit 4 has a device that detects light that has passed through the alkali metal atom cell 3. The light detection unit 4 is realized by using, for example, a photodiode. The light detection unit 4 can be configured with a photodetector that is a light detection means.

[0080] The static magnetic field application device 8 applies a static magnetic field to a predetermined position inside the alkali metal atom cell 3. The static magnetic field application device 8 can be realized, for example, by arranging a coil so as to cover the alkali metal atom cell 3. The static magnetic field application device 8 can correspond to the magnetic field generation device 2A according to the third embodiment.

[0081] Here, as in the above-described embodiment, the quantum interference device 100 can be realized by the light generating unit 5, the alkali metal atom cell 3, and the light detecting unit 4. Furthermore, the atomic oscillator 110 may have a mechanism for adjusting the oscillation frequency based on the quantum interference effect (CPT) detected by the method according to the above-described embodiment. That is, the atomic oscillator 110 may have the quantum interference device 100 and a mechanism for adjusting the oscillation frequency based on the quantum interference effect (CPT).

[0082] [Effect description] According to the atomic oscillator 110 of the fourth embodiment, the magnetic field applied to the alkali metal atom cell 3 can be adjusted using the method described in the above embodiments to suppress the influence of fluctuations in the external magnetic field on the quantum interference effect. This allows for the detection of CPT resonance with minimized fluctuations in the resonant frequency due to fluctuations in the external magnetic field. Here, when detecting non-overlapping CPT resonance, using the (-1,1) resonance results in smaller fluctuations in the resonant frequency due to the magnetic field compared to the (0,0) resonance. Therefore, if there is an allowable frequency fluctuation range, the corresponding magnetic field range is wider for the (-1,1) resonance than for the (0,0) resonance. Therefore, to ensure a certain frequency stability, the allowable range of fluctuating magnetic field at a given position inside the alkali metal atom cell 3 is broadened. This eliminates the need for high magnetic field shielding performance in this embodiment, allowing the use of a simple magnetic shield with a low shielding factor (magnetic field shielding performance index). Furthermore, when the environmental magnetic field is weak, the magnetic shield can be eliminated. This allows for the elimination or simplification of the magnetic shield, thereby achieving a more compact atomic oscillator 110.

[0083] (Fifth embodiment) Next, a fifth embodiment will be described. For clarity of explanation, the following description and drawings have been omitted and simplified as appropriate. In addition, the same elements in each drawing are given the same reference numerals, and duplicated explanations are omitted as necessary. The fifth embodiment shows an example of an atomic oscillator capable of detecting quantum interference effects.

[0084] Fig. 13 is a diagram showing the configuration of an atomic oscillator 120 according to a fifth embodiment. A method for detecting the quantum interference effect will be described with reference to Fig. 13. The atomic oscillator 120 according to the fifth embodiment includes a light source 9, a current controller 10, an optical attenuator 11, a signal generator 12, an optical modulator 13, a collimating lens 14, a λ / 2 plate 15, a magnetic shielding device 16, a photodetector 17, and a control device 20. The magnetic shielding device 16 is provided with an alkali metal atom cell 3 and a static magnetic field application device 8.

[0085] The control device 20 may be realized by, for example, a computer. Therefore, the control device 20 has, as its hardware configuration, an arithmetic device such as a processor, a storage device such as a memory or a disk, a communication device, and a UI (User Interface). The control device 20 controls the operations of the current controller 10, the optical attenuator 11, and the signal generator 12. The control device 20 may control the operations of the current controller 10, the optical attenuator 11, and the signal generator 12 according to the detection result of the optical detector 17. The control device 20 may also control the static magnetic field application device 8 according to the detection result of the optical detector 17. The optical detector 17 may be realized by a photodetector, which is a light detection means.

[0086] The current controller 10 outputs a driving current to the light source 9 under the control of, for example, the control device 20. In response to this driving current, the light source 9 outputs a frequency f c For example, the light source 9 emits a single-wavelength laser beam with a carrier wavelength of 894.593 nm. The optical attenuator 11 is, for example, a variable optical attenuator. The optical attenuator 11 attenuates the laser beam emitted from the light source 9 under the control of, for example, the control device 20. The optical attenuator 11 performs amplitude modulation on the laser beam emitted from the light source 9. This generates a laser beam with any optical intensity.

[0087] The signal generator 12 generates a signal at a frequency f m The optical attenuator 11 outputs the modulated signal to the optical modulator 13. The optical modulator 13 performs optical modulation by combining the modulated signal with the laser light output from the optical attenuator 11. As a result, a frequency f c This light output from the optical modulator 13 becomes the pump light.

[0088] 14 is a schematic diagram showing the frequency spectrum of frequency-modulated excitation light. As shown in FIG. 14, the frequency f c The sideband f of the laser light c -f m and f c +f mThe difference frequency between the two sidebands is 2f m In this way, the difference frequency 2f m For example, the frequency f of the modulation signal is m is set to about 4.596 GHz, pump light containing two frequency components with a difference frequency of about 9.192 GHz is generated.

[0089] The excitation light generated by the optical modulator 13 is propagated through an optical fiber. Under the conditions described above, the excitation light propagated through the optical fiber is collimated by a collimating lens 14. For example, the excitation light passes through the collimating lens 14 to become laser light with a beam diameter of approximately 7 mm. Furthermore, the collimated laser light (excitation light) becomes linearly polarized light by passing through a λ / 2 plate 15, which is a polarizing plate.

[0090] The linearly polarized excitation light is incident on the alkali metal atom cell 3 provided in the magnetic shielding device 16. For example, the alkali metal atom cell 3 is filled with cesium atoms, which are alkali metal atoms, and 1.33 kPa of nitrogen gas, which is a buffer gas. The alkali metal atom cell 3 is formed in a cylindrical shape, for example, with a diameter of 20 mm and a height of 20 mm. The static magnetic field application device 8 applies a static magnetic field to the inside of the alkali metal atom cell 3. The static magnetic field is applied to the alkali metal atom cell 3 in a direction that is substantially parallel to and opposite to the optical path of the excitation light. The alkali metal atom cell 3 is provided inside the magnetic shielding device 16 formed of a magnetic shielding container in order to enhance magnetic field stability. The light (laser light) that has passed through the alkali metal atom cell 3 is converged via the collimating lens 14 and detected by the photodetector 17. As a result, the control device 20 acquires the amount of light (laser light) that has passed through the alkali metal atom cell 3. For example, the light detection unit 17 may measure the amount of light of the laser light (transmitted light) and transmit information indicating the amount of light to the control device 20.

[0091] Fig. 15 is a diagram showing the magnetic field dependence of the transmitted light spectrum detected when linearly polarized excitation light is incident on the alkali metal atom cell 3 according to the fifth embodiment. Fig. 16 is a diagram showing the magnetic field dependence of the resonance frequency of the CPT resonance detected when linearly polarized excitation light is incident on the alkali metal atom cell 3 according to the fifth embodiment. Fig. 17 is a diagram showing the excitation light intensity dependence of the transmitted light spectrum detected when linearly polarized excitation light is incident on the alkali metal atom cell 3 according to the fifth embodiment. Fig. 18 is a diagram showing the excitation light intensity dependence of the full width at half maximum of the CPT resonance detected when linearly polarized excitation light is incident on the alkali metal atom cell 3 according to the fifth embodiment.

[0092] While keeping the applied magnetic field constant, the control device 20 controls the signal generator 12 to sweep the difference frequency of the excitation light, while measuring the amount of transmitted light with the photodetector 17. Then, the strength of the applied magnetic field is changed from 0 μT to 425 μT, and similar measurements are performed. As a result, two CPT resonances corresponding to the (-1, +1) resonance and the (+1, -1) resonance are detected, as shown in Figure 15.

[0093] Furthermore, as shown in Figure 16, in the magnetic field range where the applied magnetic field is 425 μT or less, the resonant frequencies of the (-1, +1) and (+1, -1) resonances agree well with the calculation of the magnetic field dependence of the resonant frequency shown in Figure 5. In particular, the resonant frequency of the (-1, +1) resonance shown in Figure 16, when a magnetic field of 139 μT is applied, has a gradient of the magnetic field shift (resonant frequency) relative to the applied magnetic field that is 0, as in the case of Figure 5 (i.e., the magnetic field shift (shift of the resonant frequency) is minimized). Note that f at 0 μT hfs The frequency difference between this and 9,192,631,770 Hz is due to the frequency shift caused by the inclusion of buffer gas (nitrogen).

[0094] When CPT resonance is used in an atomic oscillator, the shift in the resonance frequency with respect to the applied magnetic field affects the frequency stability against fluctuations in the external magnetic field. When the (-1, +1) resonance is used for frequency oscillation with a static magnetic field of 139 μT applied, the amount of shift in the resonance frequency is 9.2 Hz or less and the magnetic field gradient of the resonance frequency is 1.2 Hz / μT or less with respect to a magnetic field fluctuation of 15 μT. Therefore, the method shown in the above-described embodiment can provide a quantum interference device and an atomic oscillator with high frequency stability against magnetic field fluctuations.

[0095] Furthermore, when using CPT resonance for frequency oscillation, it is preferable to detect a signal consisting of a single CPT resonance to improve frequency stability. As shown in Figure 16, when a static magnetic field of 139 μT is applied, the resonance frequencies of the (-1, +1) and (+1, -1) resonances are 3.10 kHz apart. To detect these separately, it is preferable that the full width at half maximum of the CPT resonance is smaller than half the difference in the resonance frequencies. For example, the linewidth of the CPT resonance can be adjusted by controlling the power broadening caused by the optical intensity of the excitation light.

[0096] Furthermore, when a static magnetic field of 139 μT is applied and the optical intensity of the excitation light is changed by controlling the optical attenuator 11, and CPT resonance is detected, the line width (full width at half maximum) of the CPT resonance increases with the optical intensity, as shown in Figure 17. In the example of Figure 17, the intensity of the excitation light is set to 0.3 μW / mm 2 to 4.5 μW / mm 2 The amount of transmitted light is measured by the light detection unit 17 while sweeping the difference frequency of the excitation light for each light intensity.

[0097] In addition, for example, in this embodiment, as shown in FIG. 18, the light intensity of the excitation light incident on the alkali metal atom cell 3 is set to about 4 μW / mm 2By setting the frequency of the excitation light beam to the frequency domain, a CPT resonance with a full width at half maximum of 1.5 kHz or less can be detected. This result suggests that the method described in the second embodiment can provide a quantum interference device with higher frequency stability. In other words, when the difference frequency of the excitation light is swept in a frequency domain that is separated from the resonance frequency of the optical absorption characteristic due to the quantum interference effect by the full width at half maximum or less of the optical absorption characteristic, a state is realized in which the quantum interference effect arising from only one pair of magnetic sublevels contributes to the transmitted light spectrum.

[0098] In this embodiment, linearly polarized excitation light is incident on the alkali metal atom cell 3. Here, a case will be described in which circularly polarized excitation light is incident on the alkali metal atom cell 3 by, for example, placing a λ / 4 plate in addition to the λ / 2 plate 15 on the optical path of the excitation light.

[0099] FIG. 19 shows the magnetic field dependence of the transmitted light spectrum detected when circularly polarized excitation light is incident on the alkali metal atom cell 3. FIG. 20 shows the magnetic field dependence of the resonant frequency of the CPT resonance detected when circularly polarized excitation light is incident on the alkali metal atom cell 3. When circularly polarized excitation light is incident on the alkali metal atom cell 3, the (0,0) resonance is detected as shown in FIG. 19. Also, in this case, as shown in FIG. 20, the variation of the resonant frequency with respect to the applied magnetic field can be approximated by a quadratic function. When the applied magnetic field is 0 μT, the gradient of the resonant frequency with respect to the applied magnetic field becomes 0. This result is consistent with the calculation of the magnetic field dependence of the resonant frequency of the (0,0) resonance shown in FIG. 5. However, around 0 μT, CPT resonance between higher-order magnetic sublevels is superimposed, and the linewidth of the detected resonance signal is strongly affected by external magnetic field fluctuations, making it unsuitable for frequency oscillation. Therefore, it is preferable to incident linearly polarized excitation light on the alkali metal atom cell 3.

[0100] (Sixth embodiment) Next, a sixth embodiment will be described. For clarity of explanation, the following description and drawings have been omitted and simplified as appropriate. In addition, in each drawing, the same elements are given the same reference numerals, and duplicate explanations are omitted as necessary.

[0101] 21 is a functional block diagram of a quantum interference device 100 according to the sixth embodiment. The quantum interference device 100 according to the sixth embodiment has a space 2 and an alkali metal atom cell 3. A static magnetic field of a specific direction and strength is applied to the space 2. The alkali metal atom cell 3 is provided inside the space 2. Furthermore, alkali metal atoms are sealed in the alkali metal atom cell 3.

[0102] Here, a static magnetic field is applied to the alkali metal atom cell 3, and excitation light having at least two different frequency components is incident thereon, thereby generating a quantum interference state of the alkali metal atoms. Furthermore, of the frequency components of the excitation light, the frequency components involved in the formation of the quantum interference state have a difference frequency that matches the transition frequency between ground states and have linear polarization in the same polarization direction. Furthermore, the static magnetic field applied to the space 2 is adjusted so that fluctuations (magnetic field shifts) with respect to the magnetic field are suppressed for the resonance frequency, which is the transition frequency between ground states that form the quantum interference state. With this configuration, the quantum interference device 100 according to the sixth embodiment can achieve a quantum interference effect with high frequency stability against magnetic field fluctuations.

[0103] (Variation) The present invention is not limited to the above-described embodiments, and can be modified as appropriate without departing from the spirit of the present invention. For example, any two or more of the above-described embodiments can be applied to each other. In addition, the order of the processes in the flowcharts shown in Figures 7, 9, and 11 can be changed as appropriate. In addition, one or more of the processes in each flowchart can be omitted.

[0104] The processes shown in each flowchart may be implemented by an information processing device such as a computer (such as the control device 20). Here, the information processing device (such as the control device 20) has an arithmetic device such as a CPU (Central Processing Unit) and a storage device such as a memory or a disk. For example, the processes shown in each flowchart may be implemented by the arithmetic device executing a program stored in the storage device.

[0105] The program includes instructions (or software code) that, when loaded into a computer, cause the computer to perform one or more functions described in the embodiments. The program may be stored in a non-transitory computer-readable medium or a tangible storage medium. By way of example and not limitation, computer-readable media or tangible storage media include random-access memory (RAM), read-only memory (ROM), flash memory, solid-state drive (SSD) or other memory technologies, CD-ROM, digital versatile disk (DVD), Blu-ray® disk or other optical disk storage, magnetic cassette, magnetic tape, magnetic disk storage or other magnetic storage device. The program may also be transmitted on a transitory computer-readable medium or communication medium. By way of example and not limitation, transitory computer-readable media or communication media include electrical, optical, acoustic, or other forms of propagated signals.

[0106] A part or all of the above-described embodiments can be described as, but not limited to, the following supplementary notes. (Appendix 1) A space to which a static magnetic field of a specific direction and strength is applied; an alkali metal atom cell provided inside the space and containing alkali metal atoms; and the static magnetic field is applied to the alkali metal atom cell, and excitation light having at least two different frequency components is incident thereon, thereby generating a quantum interference state of the alkali metal atoms; Among the frequency components of the excitation light, frequency components involved in forming the quantum interference state are light containing linearly polarized light having the same polarization direction, The static magnetic field is adjusted so that fluctuations of a resonance frequency, which is a transition frequency between ground levels forming the quantum interference state, with respect to the magnetic field are suppressed. Quantum interference device. (Appendix 2) a light detecting means for detecting light transmitted through the alkali metal atom cell; a control means for controlling the static magnetic field so as to suppress the fluctuations based on a transmitted light spectrum corresponding to the light detected by the light detection means; 2. The quantum interference device of claim 1, further comprising: (Appendix 3) the control means controls the static magnetic field so that the fluctuation falls within a predetermined range. 3. The quantum interference device of claim 2. (Appendix 4) a light generating means for modulating the intensity of the excitation light; and the control means controls the amount of the excitation light based on the transmitted light spectrum corresponding to the light detected by the light detection means. 4. The quantum interference device of claim 2 or 3. (Appendix 5) an optical trapping system that traps the cooled alkali metal atoms in the alkali metal atom cell; 5. The quantum interference device of claim 1, further comprising: (Appendix 6) The alkali metal atom is at least one of a cesium atom, a rubidium atom, a sodium atom, and a potassium atom. 6. A quantum interference device according to any one of claims 1 to 5. (Appendix 7) A quantum interference device according to any one of claims 1 to 6; a mechanism for adjusting an oscillation frequency based on the quantum interference state; An atomic oscillator having (Appendix 8) An excitation light having at least two different frequency components is incident on an alkali metal atom cell in which alkali metal atoms are sealed; By detecting the light transmitted through the alkali metal atomic cell, the transmitted light spectrum is measured to detect the CPT resonance. controlling a static magnetic field applied to the alkali metal atom cell so that fluctuations in the resonant frequency of the CPT resonance with respect to the magnetic field are suppressed; Control method. (Appendix 9) controlling the static magnetic field so that the fluctuation is within a predetermined range; 9. The control method according to claim 8. (Appendix 10) controlling the amount of the excitation light based on the transmitted light spectrum corresponding to the detected light; 10. The control method according to claim 8 or 9. (Appendix 11) When the CPT resonance is superimposed, the amount of the excitation light is changed. 11. The control method of claim 10. [Explanation of symbols]

[0107] 1. Excitation light 2 space 2A magnetic field generator 3 Alkali metal atomic cell 4. Light detection unit 5 Light generating unit 5a light source 5b Frequency modulation section 5c Optical intensity modulation section 6 Atomic trap cell 7. Magneto-optical trap system 8. Static magnetic field application device 9 light source 10 Current Controller 11 Optical attenuator 12 Signal Generator 13 Optical Modulator 14 Collimating Lens 15 λ / 2 plate 16 Magnetic field shielding device 17 Light detection unit 20 Control device 100 Quantum Interference Device 110 Atomic Oscillator 120 Atomic Oscillator

Claims

1. A light generating means for generating excitation light; A space to which a static magnetic field of a specific direction and strength is applied; an alkali metal atom cell provided inside the space and containing alkali metal atoms, which are at least one of cesium atoms, rubidium atoms, sodium atoms, and potassium atoms; a light detecting means for detecting light transmitted through the alkali metal atom cell; a control means for controlling the static magnetic field based on a transmitted light spectrum corresponding to the light detected by the light detection means; and A static magnetic field is applied to the space in a direction parallel to or opposite to the direction of incidence of the excitation light, the static magnetic field is applied to the alkali metal atom cell, and the excitation light having at least two different frequency components is incident thereon, thereby generating a quantum interference state of the alkali metal atoms; a difference frequency of two of the at least two different frequency components is equal to a transition frequency between two magnetic sublevels forming the quantum interference state of the alkali metal atom; Among the frequency components of the excitation light, frequency components involved in forming the quantum interference state are light containing linearly polarized light having the same polarization direction, the light detecting means detects transmitted light in a state where a static magnetic field set to a predetermined setting value is applied; the control means controls the static magnetic field so that a change in a resonance frequency, which is a transition frequency between ground levels forming the quantum interference state, with respect to the magnetic field falls within a predetermined range; When a CPT resonance corresponding to the quantum interference state of the alkali metal atom is detected from the transmitted light spectrum and the variation of the resonance frequency with respect to the magnetic field is not within an allowable range, the control means corrects the setting value of the applied static magnetic field, and the light detection means detects the transmitted light again; When the CPT resonance is detected from the transmission light spectrum and the variation of the resonance frequency with respect to the magnetic field is within an allowable range, the control means determines a setting value of the static magnetic field to be applied. Quantum interference device.

2. The light generating means modulates the intensity of the excitation light, the control means controls the amount of the excitation light based on the transmitted light spectrum corresponding to the light detected by the light detection means so that the CPT resonance corresponding to the quantum interference state formed between two magnetic sublevels does not overlap with the CPT resonance corresponding to the quantum interference state formed between other two magnetic sublevels. The quantum interference device of claim 1 .

3. an optical trapping system that traps the cooled alkali metal atoms in the alkali metal atom cell; 3. The quantum interference device of claim 1, further comprising:

4. The light detection means detects the transmitted light while sweeping the difference frequency of the excitation light, If the CPT resonance is not detected from the transmitted light spectrum obtained by detecting the transmitted light, the control means corrects the set sweep range of the difference frequency, and the light detection means detects the transmitted light again.

4. A quantum interference device according to any one of claims 1 to 3.

5. A quantum interference device according to any one of claims 1 to 4; a mechanism for adjusting an oscillation frequency based on the quantum interference state; An atomic oscillator having

6. Generating excitation light, the excitation light having at least two different frequency components is incident on an alkali metal atom cell provided inside a space to which a static magnetic field parallel to the direction of incidence of the excitation light or a direction opposite to the direction of incidence of the excitation light is applied, the alkali metal atom cell containing at least one alkali metal atom selected from the group consisting of cesium atoms, rubidium atoms, sodium atoms, and potassium atoms; detecting light transmitted through the alkali metal atom cell; controlling the static magnetic field based on a transmitted light spectrum corresponding to the detected light; the static magnetic field is applied to the alkali metal atom cell, and the excitation light having at least two different frequency components is incident thereon, thereby generating a quantum interference state of the alkali metal atoms; a difference frequency of two of the at least two different frequency components is equal to a transition frequency between two magnetic sublevels forming a quantum interference state of the alkali metal atom; Among the frequency components of the excitation light, frequency components involved in forming the quantum interference state are light containing linearly polarized light having the same polarization direction, Detecting transmitted light while applying a static magnetic field set to a predetermined value; controlling the static magnetic field so that a change in a resonance frequency, which is a transition frequency between ground levels forming the quantum interference state, with respect to a magnetic field falls within a predetermined range; If a CPT resonance corresponding to the quantum interference state of the alkali metal atoms is detected from the transmitted light spectrum, and the variation of the resonance frequency with respect to the magnetic field is not within the allowable range, the setting value of the applied static magnetic field is corrected and the transmitted light is detected again; If the CPT resonance is detected from the transmission light spectrum and the variation of the resonance frequency with respect to the magnetic field is within an allowable range, a setting value of the static magnetic field to be applied is determined. Control method.

7. and controlling the amount of the excitation light based on the transmitted light spectrum corresponding to the detected light so that the CPT resonance corresponding to the quantum interference state formed between two magnetic sublevels does not overlap with the CPT resonance corresponding to the quantum interference state formed between the other two magnetic sublevels. The control method according to claim 6.

8. Detecting transmitted light while sweeping the difference frequency of the excitation light; If the CPT resonance is not detected from the transmitted light spectrum obtained by detecting the transmitted light, the set sweep range of the difference frequency is corrected and the transmitted light is detected again. The control method according to claim 6 or 7.

Images