Atomic wave interferometer

Abstract

To suppress the influence of an environmental magnetic field in an atomic wave interferometer.SOLUTION: An atomic wave interferometer according to an aspect of the invention includes an atomic beam source, a first Raman light generator, a second Raman light generator, a third Raman light generator, and a detector. The atomic beam source emits atoms of nuclear spin 0 in a first metastable state. The first Raman light generator generates first Raman light that separates atoms in a first metastable state into atoms in the first metastable state and atoms in a second metastable state. The second Raman light generator generates second Raman light for reversing the atoms in the first metastable state after the separation to the second metastable state and the atoms in the second metastable state after the separation to the first metastable state. The third Raman light generator generates third Raman light for separating the atoms in the first metastable state after the reversal into the atoms in the first metastable state and the atoms in the second metastable state after the reversal into the atoms in the first metastable state and the atoms in the second metastable state. The detector detects a result of superimposing the two atoms in the second metastable state separated by the third Raman light.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The disclosed technology relates to a Mach-Zehnder atomic wave interferometer using atomic beams. [Background technology]

[0002] An atomic wave interferometer is known that uses atomic waves to form a Mach-Zehnder interferometer (Non-Patent Document 1). Figure 1 shows a schematic diagram of an atomic wave interferometer. An atomic wave in quantum mechanical state |1> incident from position A is separated into quantum mechanical state |1> and quantum mechanical state |2> at position B. Hereinafter, "quantum mechanical state" will be abbreviated to simply "state." The states are reversed at positions C and D to close the path, and each state is further separated at position E, causing state |1> to overlap in the E→G direction and state |2> to overlap in the E→F direction, causing interference. When atoms acquire a phase difference Δφ between paths BCE and BDE, the number of atoms incident from position A is N0, and the number of atoms in state |1> detected at position G and the number of atoms in state |2> detected at position F are as follows:

number

[0003] The atomic wave interferometer outputs the atomic state N |1> or N |2> By measuring this, we can read the difference Δφ in the phase that the atomic wave acquires between the two paths. The phase difference Δφ acquired by the atomic waves includes a phase proportional to the acceleration a of the system including the atomic wave interferometer and the angular velocity Ω, so by extracting these components, it can be used as an accelerometer or gyroscope. Atomic wave interferometers are expected to be applied as next-generation high-end inertial sensors.

[0004] The most common type of atomic wave interferometer is one that uses stimulated Raman transitions between the hyperfine structures of alkali atoms. Figure 2 shows the levels used in stimulated Raman transitions and the state separation and state reversal of atomic waves caused by Raman light. Alkali atoms have fine structure levels |1> and |2> in the ground state. Irradiating an alkali atom with light of angular frequencies ω1 and ω2 causes stimulated Raman transitions. |i> is a virtual level.

[0005] An atomic beam in state |1> is incident from position A in the positive direction of the x-axis. At position B, light with angular frequency ω1 is irradiated in the positive direction of the y-axis, and light with angular frequency ω2 is irradiated in the negative direction of the y-axis, causing half of the quantum mechanical states of the alkali atoms to transition to |2>. The alkali atoms in state |2> gain momentum (h / 2πc)(ω1+ω2) in the positive direction of the y-axis, where h is Planck's constant and c is the speed of light. Hereinafter, the mixed light irradiated at position B will be referred to as the π / 2 pulse first Raman light.

[0006] At positions C and D, light with an angular frequency of ω1 is irradiated in the positive direction of the y-axis, and light with an angular frequency of ω2 is irradiated in the negative direction of the y-axis, reversing state |1> to state |2> and state |2> to state |1>. When transitioning from state |2> to state |1> at position C, the alkali atom loses momentum (h / 2πc)(ω1 + ω2) along the y-axis and moves along the x-axis. At position D, the alkali atom transitioning from state |1> to state |2> gains momentum (h / 2πc)(ω1 + ω2) in the positive direction of the y-axis. Hereinafter, the mixed light irradiated at positions C and D is referred to as the π-pulse second Raman light.

[0007] At E, light with an angular frequency of ω1 is irradiated in the positive direction of the y-axis, and light with an angular frequency of ω2 is irradiated in the negative direction of the y-axis, causing half of the state |1> after the reversal to transition to state |2>. Also, half of the state |2> after the reversal is caused to transition to state |1>. An atom in state |1> after path BCE and an atom in state |1> after path BDE are made to interfere in the direction E → G, and an atom in state |2> after path BCE and an atom in state |2> after path BDE are made to interfere in the direction E → F. Hereinafter, the mixed light irradiated at position E is called the π / 2 pulse third Raman light.

[0008] In atomic wave interferometers that use Raman transitions (two-photon transitions), the detuning required to control the probability of interstate transitions is achieved by adjusting the frequency difference between ω1 and ω2. While high-precision absolute frequency stabilization is still in the basic research stage, relative frequency stabilization is already being commercialized (for example, optical frequency combs) and can be performed relatively easily. [Prior art documents] [Patent documents]

[0009] [Patent Document 1] Japanese Patent Application Publication No. 2020-91239 [Non-patent literature]

[0010] [Non-Patent Document 1] TL Gustavson, PRECISION ROTATION SENSING USING ATOM INTERFEROMETRY, A DISSERTATION SUBMITTED TO THE DEPARTMENT OF PHYSICS AND THE COMMITTEE ON GRADUATE STUDIES OF STANFORD UNIVERSITY, 2000. [Non-patent document 2] N. Marliere, "DESIGN AND SETUP OF AN ATOM INTERFEROMETER GYROSCOPE USING A STRONTIUM THERMAL BEAM", Master Thesis submitted to the University of Oklahoma, 2022. Summary of the Invention [Problem to be solved by the invention]

[0011] When considering applications to high-end sensors such as inertial navigation, it is expected that they will be used in environments where there are many external disturbances such as environmental magnetic fields, so it is important to suppress the effects of these disturbances.

[0012] [Conventional method 1] The type of atomic wave interferometer constructed using the stimulated Raman transition between the hyperfine structures of alkali atoms mentioned above uses an energy state with a magnetic quantum number of 0, which is insensitive to magnetic fields, to suppress fluctuations in energy levels (first-order Zeeman shift) caused by environmental magnetic fields. However, because the hyperfine structure originates from the nuclear magnetic moment, a level shift (second-order Zeeman shift) proportional to the square of the magnetic field strength occurs, resulting in a phase difference. This will be explained using Figure 3.

[0013] The quantum mechanical state (phase) of an atom is determined by the difference between the energy of the atom and the relative frequency of the two lasers that cause the Raman transition (Δω laser =ω1-ω2). When the energy of an atom changes due to the environmental magnetic field, the phase acquired by the atom changes. The second-order Zeeman shift that occurs in the energy level of the hyperfine structure under the environmental magnetic field B is called Δω ZS As (B), when the energy difference between states |1> and |2> and the relative frequency of the two lasers of the Raman light match, the magnetic field component φ of Δφ B is given by the following formula:

number

[0014] For simplicity, let us consider the case where the magnetic field applied to the atomic wave interferometer is B0 in the first half (before positions C and D) and B0+ΔB in the second half (after positions C and D). Then, let α be the coefficient of the magnetic field response of the hyperfine structure (response to the square of the magnetic field), and φ B can be estimated as follows:

number

[0015] [Conventional method 2] Atoms with a nuclear spin of 0 do not undergo a second-order Zeeman shift, so if we could construct an atomic wave interferometer using these atoms, we could suppress the effects of environmental magnetic fields. On the other hand, atoms with no nuclear spin do not have a hyperfine structure, so we cannot construct an atomic wave interferometer using Raman transitions between hyperfine structures. A method has also been proposed for constructing an atomic wave interferometer by coupling between the ground state and metastable state using the ultra-narrow linewidth optical transition of alkaline earth atoms with nuclear spin 0 (Non-Patent Document 2). This will be explained using Figure 4.

[0016] An atomic beam in state |1> is incident from position A in the positive direction of the x-axis. At position B, light with an angular frequency of ω3 is irradiated in the positive direction of the y-axis, causing half of the atoms' quantum mechanical states to transition to |2>. The alkaline-earth atoms in state |2> gain momentum in the positive direction of the y-axis. At position D, ω3 causes all states |1> to transition to states |2>. At position C, the emission of ω3 is induced, causing all states |2> to transition to states |1>. At position E, half of C → E is transitioned to state |2>, and atoms in state |2> via path BCE and atoms in state |2> via path BDE are made to interfere in the direction E → F. Also, half of D → E is transitioned to state |1>, and atoms in state |1> via path BCE and atoms in state |1> via path BDE are made to interfere in the direction E → G.

[0017] As with conventional method 1, an energy state with a magnetic quantum number of 0 is used to suppress fluctuations in energy levels (first-order Zeeman shift) due to environmental magnetic fields. Even when using the ground state and metastable state, a level shift (diamagnetic effect) proportional to the square of the magnetic field strength and a resulting phase difference occur, but the energy shift due to the diamagnetic effect is four to five orders of magnitude smaller than the energy shift due to the second-order Zeeman effect. Therefore, compared to conventional method 1, the influence of environmental magnetic fields can be significantly reduced. However, in atomic wave control using one-photon transitions, the detuning to control the probability of state-to-state transitions is given by adjusting ω3, so a change in ω3 itself changes the detuning, making atomic wave control difficult unless the absolute frequency of the laser is stable. In order to stabilize the absolute frequency of the laser light with high precision, a complex mechanism such as an atomic clock is required in addition to the atomic wave interferometer.

[0018] [Conventional method 3] Conventional methods 1 and 2 are interferometers that utilize the superposition of internal states and momentum states. It is also possible to create an interferometer that utilizes only the momentum state of atoms (Patent Document 1). In this case, the atomic waves propagate in the same internal state (energy level), so even if the internal state changes due to the influence of the environmental magnetic field, the change is uniform on both paths, so there is no effect on interference. However, this method requires a high-quality atomic beam with a momentum width of hk / 2π or less in the y-axis direction. Obtaining a high-quality atomic beam requires a complex mechanism, such as using an ultra-narrow linewidth optical transition, as in Patent Document 1, making it difficult to implement. [Means for solving the problem]

[0019] In order to solve the above problems, an atomic wave interferometer according to the disclosed technique includes an atomic beam source, a first Raman light generation unit, a second Raman light generation unit, a third Raman light generation unit, and a detector. The atom beam source emits atoms with nuclear spin 0 in a first metastable state. The first Raman light generating unit generates first Raman light that separates atoms in the first metastable state into atoms in the first metastable state and atoms in the second metastable state. The second Raman light generating section generates second Raman light that reverses the state of the atoms in the first metastable state after separation to the second metastable state, and reverses the state of the atoms in the second metastable state after separation to the first metastable state. The third Raman light generating unit separates atoms in the first metastable state after the inversion into the first metastable state and the second metastable state, and generates third Raman light that separates atoms in the second metastable state after the inversion into the first metastable state and the second metastable state. The detector detects the result of superposition of the two second metastable state atoms separated by the third Raman light. [Effects of the Invention]

[0020] By constructing an atomic wave interferometer using two-wavelength Raman transitions between metastable states for atoms with nuclear spin 0, it is possible to eliminate the effect of the second-order Zeeman shift, which was unavoidable in conventional atomic wave interferometers constructed using Raman transitions between hyperfine structures of alkali atoms, and to suppress the effect of environmental magnetic fields on the atomic wave interferometer by four to five orders of magnitude. In addition, compared to conventional solutions that require absolute frequency stabilization using complex mechanisms such as atomic clocks, it is now possible to construct an atomic wave interferometer with relative frequency stabilization using an easily achievable optical frequency comb. [Brief explanation of the drawings]

[0021] [Figure 1] A schematic diagram of an atomic wave interferometer. [Figure 2] A diagram illustrating a type of atomic wave interferometer constructed using stimulated Raman transitions between hyperfine structures. [Figure 3] This is a diagram illustrating the case where an atomic wave interferometer constructed using stimulated Raman transitions between hyperfine structures is placed in a magnetic field gradient. [Figure 4] A diagram illustrating a type of atomic wave interferometer constructed using ultra-narrow linewidth optical transitions. [Figure 5] 1 is a diagram illustrating energy levels used in an atomic wave interferometer of the disclosed technology. [Figure 6] 1A and 1B are diagrams for explaining control of an atomic beam in an atomic wave interferometer of the disclosed technique. [Figure 7]FIG. 1 is a functional block diagram of an atomic wave interferometer according to a first embodiment. [Figure 8] 2A to 2C are diagrams for explaining control and detection of an atomic beam in the atomic wave interferometer of the first embodiment. [Figure 9] 10A and 10B are diagrams for explaining control and detection of an atomic beam in an atomic wave interferometer according to a second modified example. [Figure 10] FIG. 10 is a functional block diagram of an atomic wave interferometer according to a second modified example. DETAILED DESCRIPTION OF THE INVENTION

[0022] Hereinafter, embodiments of the disclosed technology will be described in detail. Note that components having the same functions are assigned the same numbers, and duplicated descriptions will be omitted.

[0023] [Energy levels] First, the energy levels used in the atomic wave interferometer according to the disclosed technique will be described with reference to FIG. The disclosed technology controls the internal state and momentum of an atomic wave using stimulated Raman transitions that use the first and second metastable states. Because it is a two-photon transition, a two-wavelength laser with stable relative frequency can be used.

[0024] [Atomic species] Next, atomic species suitable for Raman transitions between metastable states will be described. <Required conditions> (1) Nuclear spin is 0 If the nuclear spin is 0, the second-order Zeeman shift does not occur. (2) The lifetime T of the metastable state is longer than the transit time of the interferometer. If the total length of the interferometer is L and the speed of the atom is v, the transit time L / v is approximately 1 msec, so T must be greater than 1 msec.

[0025] <Control conditions> The control of the atomic beam in the atomic wave interferometer of the disclosed technique will be described with reference to FIG. First, atoms in the ground state are excited to the second metastable state by pumping light. The internal state and momentum state of the atomic wave are controlled by inducing Raman transitions between the second metastable state and the first stable state. The interference result of the first metastable state is detected with the probe light. To achieve the above control, it is desirable that the atomic species satisfy the following conditions. (3) It is easy to pump from the ground state to the metastable state. (4) have closed optical transitions that allow probing metastable states; (5) The wavelengths of Raman light, λ1 and λ2, are close to each other.

[0026] [First embodiment] 7 is a functional block diagram showing an example configuration of an atomic wave interferometer 7 according to the first embodiment. The atomic wave interferometer 7 includes a first laser light source 71, a second laser light source 72, splitters 73-1 to 73-3, attenuators 74-1 to 74-6, an atomic beam source 75, a third laser light source 77, a multiplexer 78, a fourth laser light source 79, an interference wave detector 80, and an optical frequency comb 81. FIG. 8 is a diagram illustrating an example of control of atomic waves by the atomic wave interferometer 7. Ba is used as the atomic species, and (6s5d) 3 D1 is the first metastable state, (6s5d) 3 D2 is the second metastable state, (6s6p) 1 Raman transitions are induced using P1 as a virtual level. The wavelength λ1 of the Raman light absorbed / generated in the transition between the virtual level and the first metastable state is 1131 nm, and the wavelength λ2 of the Raman light absorbed / generated in the transition between the virtual level and the second metastable state is 1108 nm. The following description will be given with reference to FIGS. 7 and 8.

[0027] <Raman light generation> The Raman light is generated to separate and reverse the state of the atomic waves. The relative frequencies of the first laser light source 71 and the second laser light source 72 are stabilized by an optical frequency comb 81. Laser light (wavelength λ1) generated by first laser light source 71 is split into two by splitter 73-3, one output is split into three by splitter 73-1, and the intensity is adjusted by attenuators 74-1, 74-2, and 74-3 to produce laser light 76-2, 76-4, and 76-6 of wavelength λ1. The other output from splitter 73-3 is used for pumping atomic beams, which will be described later. Laser light (wavelength λ2) generated by the second laser light source 72 is split into three by a splitter 73-2, and the intensities are adjusted by attenuators 74-4, 74-5, and 74-6 to produce laser light 76-1, 76-3, and 76-5 of wavelength λ2. The mixed light of the laser beams 76-1 and 76-2 is the π / 2 pulse first Raman light, the mixed light of the laser beams 76-3 and 76-4 is the π pulse second Raman light, and the mixed light of the laser beams 76-5 and 76-6 is the π / 2 pulse third Raman light.

[0028] <Atomic beam pumping> From the atomic beam source 75, the state (6s 2 ) 1 The Ba atomic beam of S0 is emitted from the third laser light source 77 at a wavelength λ pump The pumping light of wavelength λ1 output from the demultiplexer 73-3 is multiplexed by the multiplexer 78 to form a state (6s 2 ) 1 Ba atoms are irradiated with the S0 Ba atomic beam, and the Ba atoms are converted into the second metastable state ((6s5d) 3 D2).

[0029] <Stimulated Raman transition> The first Raman light of the π / 2 pulse is 3 Ba atomic wave of D2 state 3 D2 and 3 Separate into D1. The second π-pulse Raman light reverses the state of the separated Ba atoms. The third Raman light from the π / 2 pulse is in the inverted state. 3 D2 3 D2 and 3 D1 shows the state after the reversal 3 D1 3 D1 and 3 Separate into D2.

[0030] <Detection> Two states separated by the π / 2 pulse third Raman light 3 D1 is overlapped and interferes. The interference results were irradiated with probe light of 602 nm wavelength from the fourth laser light source 79 (5d6p). 3 The Ba atoms are excited to P0, and the fluorescence emitted by the Ba atoms is detected by an interference wave detector 80. As shown in equation (1), the detected fluorescence intensity is 3 It is proportional to the proportion of Ba atoms in the D1 state. 3 The phase difference Δφ between path 1 and path 2 is calculated from the proportion of Ba atoms in the D1 state, and the acceleration and angular velocity occurring in the interferometer are calculated from Δφ.

[0031] The above is the description of the first embodiment.

[0032] [First Modification] In the first embodiment, Ba 3 D1 and 3 D2 was used in two metastable states, but Ba 3 D1, 3 D2, 3 D3, 1 Any two levels selected from D2 may be used as metastable states.

[0033] The atomic species may be a boson isotope of an alkaline earth or alkaline earth-like atom instead of Ba. For example, if Mg, Ca, or Sr is used as the atomic species, the metastable state 3 P0, 3 P1, 3 Any two levels selected from P2 may be used for the metastable state. Alternatively, the atomic species can be Cd, Hg, or Yb, and the two metastable states are 3 P0 and 3 P2 may also be used.

[0034] The pumping light, Raman light, and probe light may be modified to suit the selected atomic species and two levels. This concludes the description of the first modified example.

[0035] [Second Modification] In the first embodiment, two metastable states were used for the stimulated Raman transition levels. Alternatively, two levels, the ground state and the metastable state, may be used. In this case, compared to the case where two metastable states are used, the implementation of condition (5) "The wavelengths of the Raman light, λ1 and λ2, must be close" is disadvantageous. However, since the lower level side of the Raman transition is the ground state, there is no need to pump the atomic beam, which has the advantage of simplifying the device configuration. Figure 9 shows the atomic species Ba, with the ground state (6s 2 ) 1 S0, metastable state (6s5d) 3 The wavelength λ1 of the Raman light absorbed / generated in the transition between the virtual level and the ground state is 554 nm, and the wavelength λ2 of the Raman light absorbed / generated in the transition between the virtual level and the metastable state is 1108 nm. 10 is a functional block diagram showing an example of the configuration of an atomic wave interferometer 10 according to the second modification. The configuration of the atomic wave interferometer 10 is almost the same as that shown in functional block diagram 7 of the first embodiment, but since atomic beam pumping is not performed, the demultiplexer 73-3, third laser light source 77, and multiplexer 78 are not required. The following description will be given with reference to FIGS. 9 and 10.

[0036] <Raman light generation> As in the first embodiment, a π / 2 pulsed first Raman light, a π pulsed second Raman light, and a π / 2 pulsed third Raman light are formed. The output of the first laser light source 71 is input directly to the demultiplexer 73-1.

[0037] <Stimulated Raman transition> The first Raman light of the π / 2 pulse is 1 Ba atomic wave of S0 1 S0 and 3 Separate into D1. The second π-pulse Raman light reverses the state of the separated Ba atoms. The third Raman light from the π / 2 pulse is in the inverted state. 3 D1 3 D1 and 1 S0 is the state after reversal1 S0 1 S0 and 3 Separate into D1.

[0038] <Detection> Two states separated by the π / 2 pulse third Raman light 3 D1 is overlapped and interferes. The interference results were irradiated with probe light of 602 nm wavelength from the fourth laser light source 79 (5d6p). 3 The Ba atoms are excited to P0, and the fluorescence emitted by the Ba atoms is detected by an interference wave detector 80.

[0039] This concludes the description of the second modified example. [Explanation of symbols]

[0040] 7,10 Atomic wave interferometer 71 First laser light source 72 Second laser light source 73-1 to 73-3 splitters 74-1 to 74-6 Attenuators 75 Atomic radiation source 77 Third laser light source 78 Multiplexer 79 4th laser light source 80 Interference Detector 81 Optical Frequency Comb

Claims

1. an atomic beam source that emits atoms with nuclear spin 0 in a first metastable state; a first Raman light generating unit that generates first Raman light that separates atoms in the first metastable state into the first metastable state and a second metastable state; a second Raman light generating unit that generates second Raman light that inverts the atoms in the first metastable state after the separation to the second metastable state and the atoms in the second metastable state after the separation to the first metastable state; a third Raman light generating unit that separates atoms in the first metastable state after the inversion into the first metastable state and a second metastable state, and separates atoms in the second metastable state after the inversion into the first metastable state and a second metastable state; a detector for detecting the result of superposing the two atoms in the second metastable state separated by the third Raman light; An atomic wave interferometer equipped with

2. 2. The atomic wave interferometer according to claim 1, the atom with nuclear spin 0 is Ba, 3 D 1 , 3 D 2 , 3 D 3 , 1 D 2 Two levels were selected from the above to form the first metastable state and the second metastable state. Atomic wave interferometer.

3. 3. The atomic wave interferometer according to claim 2, The atomic beam source irradiates ground-state Ba atoms with 554 nm and 1131 nm light. 3 D 2 to generate the atomic beam; The detector detects light at 602 nm. 3 D 1 Detecting atoms of Atomic wave interferometer.

4. 2. The atomic wave interferometer according to claim 1, the atom with nuclear spin 0 is any one of Mg, Ca, and Sr, 3 P 0 , 3 P 1 , 3 P 2 Two levels were selected from the above to form the first metastable state and the second metastable state. Atomic wave interferometer.

5. 2. The atomic wave interferometer according to claim 1, the atom with nuclear spin 0 is any one of Cd, Hg, and Yb, 3 P 0 the first metastable state, 3 P 2 is set to the second metastable state, or 3 P 0 the second metastable state, 3 P 2 is set as the first metastable state. Atomic wave interferometer.

6. an atomic beam source that emits atoms with nuclear spin 0 in the ground state; a first Raman light generating unit that generates first Raman light that separates the atoms in the ground state into the ground state and a metastable state; a second Raman light generating unit that generates second Raman light that inverts the atoms in the ground state after the separation into the metastable state and the atoms in the metastable state after the separation into the ground state; a third Raman light generating unit that separates atoms in the ground state after the inversion into the ground state and the metastable state, and separates atoms in the metastable state after the inversion into the ground state and the metastable state; a detector for detecting the result of superposing the two metastable atoms separated by the third Raman light; An atomic wave interferometer equipped with

7. 7. An atomic wave interferometer according to claim 6, The atom with nuclear spin 0 is Ba, and the metastable state is 3 D 1 is Atomic wave interferometer.

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