Quantum sensor

Abstract

This quantum sensor comprises an element body layer having a color center, a signal line, and a ground line. The signal line has a first parallel line and a second parallel line that extend in parallel and through which high-frequency currents flow in parallel. When the element body layer is viewed in plan, the color center is present at least in an opening between the first parallel line and the second parallel line in the element body layer.

Description

Quantum chem Cross-reference of related applications

[0001] This application is a related application to Japanese Patent Application No. 2024-195991, filed on November 8, 2024, and claims priority based on the said Japanese Patent Application. All contents of the said Japanese Patent Application are incorporated herein by reference as constituting this specification.

[0002] The technologies disclosed herein relate to quantum sensors.

[0003] Development is underway on quantum sensors that detect physical quantities (e.g., magnetic fields, electric fields, temperature, or pressure) using optically detected magnetic resonance (ODMR). Japanese Patent Publication No. 2022-128554 discloses an example of this type of quantum sensor.

[0004] In quantum sensors utilizing photodetection magnetic resonance, an alternating magnetic field is applied to the element body layer containing the color center in order to excite the electrons present in the color center. It is desirable that the alternating magnetic field be applied in a direction parallel to the main surface of the element body layer. Japanese Patent Application Publication No. 2022-128554 discloses a technique for applying an alternating magnetic field in a direction parallel to the main surface of the element body layer by passing high-frequency currents with opposite phases through a pair of coils arranged vertically above and below the element body layer. However, such quantum sensors suffer from the problem of having a complex structure. This specification aims to provide a quantum sensor with a simple structure.

[0005] The quantum sensor disclosed herein may comprise an element body layer having a color center, a signal line, and a ground line. The signal line may have a first parallel line and a second parallel line extending in parallel and carrying high-frequency currents in parallel. When the element body layer is viewed from above, at least the color center may be provided in an opening between the first parallel line and the second parallel line within the element body layer.

[0006] When high-frequency currents flow in parallel through the first and second parallel transmission lines, which extend parallel to each other, an alternating magnetic field is applied to the element body layer directly below the aperture between the first and second parallel transmission lines, in a direction parallel to the main surface of the element body layer. In the above quantum sensor, a color center exists in the element body layer directly below the aperture. Therefore, electrons present in the color center are excited by the alternating magnetic field applied in a direction parallel to the main surface of the element body layer. Furthermore, the above quantum sensor can allow at least one of the excitation light irradiated onto the color center and the fluorescence emitted from the color center to pass through the aperture between the first and second parallel transmission lines. Thus, the above quantum sensor has the necessary functions to utilize photodetection magnetic resonance and has a simple structure.

[0007] This figure shows the energy levels of the NV centers of a diamond when no external magnetic field is applied. This figure shows the energy levels of the NV centers of a diamond when an external magnetic field is applied. This figure shows the ODMR spectrum when no external magnetic field is applied. This figure shows the ODMR spectrum when an external magnetic field is applied. This figure is a schematic diagram illustrating the configuration of a quantum sensor system. This figure is a schematic diagram showing a plan view of a quantum sensor according to one embodiment. This figure is a schematic diagram showing a cross-sectional view of a quantum sensor according to one embodiment, corresponding to the IV-IV line in Figure 3. This figure is a schematic diagram showing a cross-sectional view of a quantum sensor according to one embodiment, corresponding to the V-V line in Figure 3. This figure shows an example in which the excitation light generation unit and the photodetector unit are connected to the quantum sensor 10. This figure shows an example in which the excitation light generation unit and the photodetector unit are connected to the quantum sensor 10. This figure shows an example in which the excitation light generation unit and the photodetector unit are connected to the quantum sensor 10. This figure is for explaining the alternating magnetic field generated around the signal line. This figure shows an example in which the quantum sensor is placed directly below the object to be measured. This is a schematic diagram showing a modified quantum sensor, (A) a plan view and (B) a B-B cross-sectional view within the plan view. This is a schematic diagram showing a modified quantum sensor, (A) a plan view and (B) a B-B cross-sectional view within the plan view. This is a schematic diagram showing a modified quantum sensor, (A) a plan view and (B) a B-B cross-sectional view within the plan view. This is a schematic diagram showing a plan view of a quantum sensor having a modified signal line. This is a schematic diagram showing a cross-sectional view of a quantum sensor having a modified signal line.

[0008] (Operating Principle of Optically Detected Magnetic Resonance) Before explaining the configuration of the quantum sensor disclosed in this specification, the operating principle of detecting a physical quantity using optically detected magnetic resonance will be explained. Hereinafter, the case where the magnetic resonance material is diamond and the physical quantity to be measured is an external magnetic field will be described as an example.

[0009] Figures 1A and 1B show the energy levels of the NV center of diamond. The electrons present in the NV center form an electron spin triplet state with m ｓ = 0, +1, -1. The electrons in the ground state are excited by green excitation light of 515 nm. The electrons in the excited state are relaxed to the ground state by a direct transition accompanied by red emission of 637 nm or an indirect transition (i.e., a non-emission process) via the spin singlet state. m ｓ The electrons in the state of m = 0 are relaxed to the ground state by direct transition with a high probability. On the other hand, the probability that the electrons in the state of m ｓ = ±1 are relaxed to the ground state via a non-emission process is higher than that of the electrons in the state of m ｓ = 0. Therefore, the electrons in the ground state with m ｓ = 0 emit strong light during relaxation, and the electrons in the ground state with m ｓ = ±1 emit weak light during relaxation.

[0010] Here, when no external magnetic field is applied, as shown in Figure 1A, the states of the electrons with m ｓ = ±1 are degenerate. In this case, the resonance frequencies when the ground state of the electrons is excited from m ｓ = 0 to m ｓ = ±1 are both 2.87 GHz. Therefore, as shown in Figure 1C, the emission intensity is observed to be weak at the resonance frequency of f ＋ = f － On the other hand, when an external magnetic field is applied, as shown in Figure 1B, the degeneracy of the states of the electrons with m ｓ = +1 and m ｓ = -1 is lifted by Zeeman splitting. In this case, the resonance frequency f when the ground state of the electrons is excited from m ｓ = 0 to m ｓ = +1 ＋This is a frequency higher than 2.87 GHz, and the ground state of the electron is m ｓ = from 0 to m ｓ Resonance frequency f when excited to -1 － This is a frequency lower than 2.87 GHz. Therefore, as shown in Figure 1D, there are two resonant frequencies f ＋ , f － A weak emission intensity is observed at each of these. The difference between the two resonance frequencies (f ＋ -f － ) is proportional to the magnitude of the external magnetic field.

[0011] A quantum sensor utilizing optical magnetic resonance measures the strength of an external magnetic field based on the above operating principle. The quantum sensor applies an external magnetic field, irradiates a diamond NV center with green excitation light, and sweeps with microwaves. It acquires the ODMR spectrum of the red fluorescence emitted from the NV center and measures the strength of the external magnetic field based on the resonance frequency of the acquired ODMR spectrum. An embodiment of the quantum sensor based on the above operating principle is described below. Note that the operating principle for detecting physical quantities remains the same even when the magnetic resonance material is a material other than diamond (e.g., silicon carbide), and even when the physical quantity being measured is a physical quantity other than an external magnetic field. For example, if the physical quantity is temperature, the temperature change is m ｓ = 0 state and m ｓ Because it causes a change in the magnitude of the energy difference between the ±1 states, i.e., a shift in the resonance frequency, it can be measured in the same way as an external magnetic field.

[0012] (Configuration of the quantum sensor system) As shown in Figure 2, the quantum sensor system 1 comprises a quantum sensor 10, an excitation light generation unit 20, a high-frequency signal generation unit 30, a photodetection unit 40, and a control unit 50.

[0013] The quantum sensor 10 is a sensor element that includes a magnetic resonance material having a color center, as will be described later. The quantum sensor 10 is not particularly limited, but may, for example, be attached to the tip of a sensor probe, or it may be integrally incorporated into a device such as a power device.

[0014] The excitation light generation unit 20 is configured to generate excitation light and irradiate the quantum sensor 10 with the generated excitation light. The excitation light generation unit 20 may include a light source such as a light-emitting diode.

[0015] The high-frequency signal generation unit 30 is configured to generate a high-frequency current for generating microwaves and to supply the generated high-frequency current to the quantum sensor 10. The high-frequency signal generation unit 30 may also include, for example, a high-frequency signal source.

[0016] The light detection unit 40 is configured to detect fluorescence emitted from the color center. The light detection unit 40 may include, for example, a photodetector such as a photodiode.

[0017] The control unit 50 controls the operation of the excitation light generation unit 20, the high-frequency signal generation unit 30, and the photodetection unit 40. The control unit 50 may be composed of a computer having, for example, memory and an arithmetic unit. The memory stores a physical quantity detection program. The arithmetic unit is composed of a microprocessor including a CPU or the like. The arithmetic unit performs the physical quantity detection process by executing the physical quantity detection program stored in the memory.

[0018] As shown in Figures 3 to 5, the quantum sensor 10 includes an element body layer 12 having a color center 18 (i.e., a light-emitting point defect), a signal line 14, and a ground line 16. The quantum sensor 10 in this example is configured as a microstrip line. The material of the element body layer 12 is not particularly limited, but may be, for example, diamond having NV centers consisting of substituted nitrogen and vacancies, or silicon carbide (SiC) having VSi centers of silicon vacancies. The element body layer 12 is a flat plate-shaped member and has a first main surface S1 and a second main surface S2. The signal line 14 and the ground line 16 are not particularly limited, but may be, for example, metal foil such as aluminum. The signal line 14 and the ground line 16 are not particularly limited, but may be formed by depositing a film on the surface of the element body layer 12 using, for example, sputtering technology or vapor deposition technology.

[0019] Here, for the sake of explanation, we define a coordinate system. The direction parallel to the first principal surface S1 and the second principal surface S2 is defined as the X direction, the direction parallel to the first principal surface S1 and the second principal surface S2 and perpendicular to the X direction is defined as the Y direction, and the direction perpendicular to both the X and Y directions is defined as the Z direction. Furthermore, the first principal surface S1 is defined as the top surface, and the second principal surface S2 is defined as the bottom surface.

[0020] The signal line 14 is arranged on a part of the first main surface S1 of the element body layer 12. The signal line 14 extends linearly along the Y direction, from one side to the other side of the element body layer 12 in the Y direction. The signal line 14 has a first end 22 and a second end 24 at both ends in the Y direction. A high-frequency current generated by the high-frequency signal generation unit 30 is input to either the first end 22 or the second end 24. Therefore, the high-frequency current transmitted through the signal line 14 flows in the direction connecting the first end 22 and the second end 24, that is, along the Y direction.

[0021] An opening 15 is formed in a part of the signal line 14 between the first end 22 and the second end 24. The opening 15 is not particularly limited, but for example, it may be a rectangular shape with its long side extending in the Y direction. A first parallel line 14a is arranged on one side of the opening 15 in the X direction, and a second parallel line 14b is arranged on the other side of the opening 15 in the X direction. The first parallel line 14a and the second parallel line 14b extend parallel to each other with the opening 15 in between. In this example, each of the first parallel line 14a and the second parallel line 14b further extends in a straight line parallel to the longitudinal direction of the signal line 14, i.e., the Y direction. The first parallel line 14a and the second parallel line 14b are identical in shape and are symmetrical with respect to the center line of the signal line 14 extending in the Y direction.

[0022] The width 15W of the aperture 15 (see Figure 3), measured in a direction perpendicular to the direction of the high-frequency current flowing through the signal line 14, i.e., along the X direction, is appropriately adjusted according to the wavelength of the high-frequency current transmitted through the signal line 14. The width 15W of the aperture 15 is not particularly limited, but may be as large as, for example, several tens of micrometers.

[0023] A color center 18 exists in at least a portion of the element body layer 12. When the element body layer 12 is viewed from above, that is, when viewed from the Z direction, the color center 18 is at least located within the opening 15 of the signal line 14 within the element body layer 12. Furthermore, the color center 18 is formed closer to the first main surface S1 than to the second main surface S2 within the element body layer 12. More specifically, the color center 18 is formed in the area of ​​the element body layer 12 that includes the first main surface S1.

[0024] The grounding line 16 is arranged across the entire surface of the second main surface S2 of the element body layer 12. The grounding line 16 is fixed at GND potential.

[0025] Figures 6 to 8 show connection examples in which the excitation light generation unit 20 and the photodetection unit 40 are connected to the quantum sensor 10. In the quantum sensor 10, at least one of the excitation light irradiated from the excitation light generation unit 20 and the fluorescence emitted from the color center 18 passes through the aperture 15 of the signal line 14. The example in Figure 6 is one in which both the excitation light and fluorescence pass through the aperture 15 of the signal line 14. The excitation light and fluorescence may be separated using an optical system such as a beam splitter 60. The example in Figure 7 is one in which the excitation light passes through the aperture 15 of the signal line 14 and the fluorescence passes through the side surface of the element body layer 12. The example in Figure 8 is one in which the fluorescence passes through the aperture 15 of the signal line 14 and the excitation light passes through the side surface of the element body layer 12.

[0026] (Effects of the quantum sensor) As shown in Figure 9, when the high-frequency current generated by the high-frequency signal generation unit 30 propagates through the signal line 14, an alternating magnetic field is generated within the element body layer 12. In the basic mode (i.e., the lowest-order propagation mode) of the signal line 14, which is a planar waveguide, the alternating magnetic field is generated to circulate around the signal line 14, as shown by the dashed arrow. As described above, the width 15W of the aperture 15 of the signal line 14 is appropriately adjusted according to the wavelength of the high-frequency current transmitted through the signal line 14, and is adjusted to be sufficiently small. As a result, even though an aperture 15 is formed in the signal line 14, an alternating magnetic field is generated in the element body layer 12 directly below the aperture 15 in a direction parallel to the main surfaces S1 and S2 of the element body layer 12, that is, in a direction parallel to the XY plane. In the quantum sensor 10, a color center 18 exists in the element body layer 12 directly below the aperture 15. Therefore, an alternating magnetic field is applied to the electrons present in the color center 18 in a direction parallel to the XY plane. Furthermore, in the quantum sensor 10, the signal line 14 and the color center 18 are located in close proximity. As a result, the amplitude of the alternating magnetic field is large and applied to the color center 18 without significant attenuation.

[0027] For the alternating magnetic field applied to the element body layer 12 directly below the aperture 15 to be parallel to the XY plane, it is desirable that the phases of the high-frequency current propagating through the first parallel line 14a and the high-frequency current propagating through the second parallel line 14b coincide in the X direction. In other words, it is desirable that no electric field is generated between the first parallel line 14a and the second parallel line 14b. In the quantum sensor 10, when the element body layer 12 is viewed from above, the first parallel line 14a and the second parallel line 14b have the same shape. Therefore, the above state is obtained in the quantum sensor 10, and the alternating magnetic field applied to the element body layer 12 directly below the aperture 15 is parallel to the XY plane.

[0028] Furthermore, in the quantum sensor 10, as shown in FIGS. 6 to 8, at least one of the excitation light irradiated from the excitation light generation unit 20 and the fluorescence emitted from the color center 18 passes through the opening 15 of the signal line 14. Therefore, when the excitation light passes through the opening 15 of the signal line 14, it becomes possible to efficiently irradiate the color center 18 with the excitation light. When the fluorescence passes through the opening 15 of the signal line 14, it becomes possible to sensitively detect the fluorescence emitted from the color center 18.

[0029] As described above, the quantum sensor 10 has the functions necessary for utilizing optically detected magnetic resonance and has a simple structure. Further, since the quantum sensor 10 has a simple structure, it can be arranged near the measurement object. For example, as shown in FIG. 10, the quantum sensor 10 can be arranged directly below the measurement object. In this case, the distance between the color center 18 and the measurement object becomes short, and the physical quantity (for example, magnetic field) to be measured can be detected with high sensitivity.

[0030] The quantum sensor 10 is not limited to the case where it is arranged directly below the measurement object, and the measurement object may be integrated with the element body layer 12. The material of the element body layer 12 is the same as the semiconductor layer of a power device such as diamond or silicon carbide. Therefore, by forming the signal line 14 and the ground line 16 in the region of interest in the semiconductor layer of the power device, the quantum sensor 10 can be integrally incorporated into the semiconductor layer of the power device. As described above, since the quantum sensor 10 has a simple structure, it can be integrally incorporated into other devices.

[0031] The quantum sensor 10 generates an alternating magnetic field using a waveguide-type transmission line. Compared with the resonator structure (i.e., antenna) that has been commonly used, such a waveguide-type transmission line has a wide frequency range in which impedance matching is possible. Therefore, the quantum sensor 10 can also handle cases where the difference between the two resonance frequencies (see FIG. 1) is wide, and has the characteristic of having a wide detection range of physical quantities.

[0032] The quantum sensor 10 is configured as a microstrip line, and its characteristic impedance can be designed based on the line width of the signal line 14 and the thickness of the element body layer 12. Compared with the conventionally often used resonator structure (i.e., antenna), it has a small structure while being able to sufficiently suppress the reflection of high-frequency currents from several hundred MHz to several GHz. For example, in order to suppress the reflection of high-frequency currents from several hundred MHz to several GHz, a conventionally often used resonator structure (i.e., antenna) requires a size from several mm to several cm. On the other hand, a waveguide-type transmission line can suppress the reflection of high-frequency currents from several hundred MHz to several GHz even with a line width from several tens of μm to several hundreds of μm.

[0033] (Modified examples of the quantum sensor) Hereinafter, several modified examples of the quantum sensor will be exemplified. Components having the same functions as the above-described quantum sensor 10 are denoted by the same reference numerals, and their descriptions are omitted. Also, the features of each modified example described below can be combined as appropriate.

[0034] The quantum sensor 10A shown in FIG. 11 and the quantum sensor 10B shown in FIG. 12 are configured as coplanar lines. The quantum sensors 10A and 10B configured as coplanar lines can design their characteristic impedance based on the ratio of the line width of the signal line 14 and the distance between the signal line 14 and the ground line 16. Therefore, the quantum sensors 10A and 10B are useful when there is no freedom in the thickness of the element body layer 12. As shown in the quantum sensor 10C shown in FIG. 13, it may also be configured as a grounded coplanar line.

[0035] The quantum sensor 10D shown in FIG. 14 is configured such that the first parallel line 14a and the second parallel line 14b extend over the entire range between the first end 22 and the second end 24 of the signal line 14. Therefore, the aperture 15 formed in the signal line 14 also extends over the entire range between the first end 22 and the second end 24 of the signal line 14. The quantum sensor 10D having such a signal line 14 can secure a wide sensing area.

[0036] The quantum sensor 10E shown in Figure 15 is configured such that the signal line 14 is embedded within the element body layer 12. Alternatively, the ground line 16 may be embedded within the element body layer 12, or both the signal line 14 and the ground line 16 may be embedded within the element body layer 12. A quantum sensor 10E with such a configuration can also exhibit the same effects as the quantum sensor described above.

[0037] In each of the quantum sensors described above, the aperture 15 formed in the signal line 14 was rectangular. Various shapes can be used for the aperture 15. The shape of the aperture 15 may be, for example, circular, elliptical with the signal propagation direction as the major axis, rhombic, or elongated, meandering along the signal propagation direction. When the width 15W of the aperture 15 (see Figure 3) is constant along the signal propagation direction (for example, when the aperture 15 is rectangular), the distribution of the alternating magnetic field applied to the element body layer 12 directly below the aperture becomes uniform. Therefore, the sensing position can be arbitrarily set within the aperture 15.

[0038] The following summarizes the features of the technology disclosed in this specification. Note that each of the technical elements described below is an independent technical element, and exhibits technical usefulness either individually or in various combinations.

[0039] (Aspect 1) A quantum sensor comprising: an element body layer having a color center; a signal line and a ground line, wherein the signal line has a first parallel line and a second parallel line that extend in parallel and through which high-frequency currents flow in parallel, and when the element body layer is viewed in plan, at least the color center is located within an opening between the first parallel line and the second parallel line in the element body layer.

[0040] (Aspect 2) The quantum sensor according to aspect 1, further comprising a light detection unit, wherein the light detection unit is configured to detect the fluorescence emitted from the color center that has passed through the aperture.

[0041] (Aspect 3) The quantum sensor according to aspect 1 or 2, further comprising an excitation light generating unit, wherein the excitation light generating unit is configured to irradiate the color center with excitation light passing through the aperture.

[0042] (Aspect 4) The quantum sensor according to any one of aspects 1 to 3, wherein the element body layer has a first main surface and a second main surface, the signal line is disposed on the first main surface of the element body layer, and the ground line is disposed on the second main surface of the element body layer.

[0043] (Aspect 5) The quantum sensor according to any one of aspects 1 to 3, wherein the element body layer has a first main surface and a second main surface, the signal line is disposed on the first main surface of the element body layer, and the ground line is also disposed on the first main surface of the element body layer.

[0044] (Aspect 6) The quantum sensor according to any one of aspects 1 to 3, wherein at least one of the signal line and the ground line is embedded in the element body layer.

[0045] (Aspect 7) The quantum sensor according to any one of aspects 1 to 6, wherein the signal line is a conductive film including a first end and a second end, and the first parallel line and the second parallel line extend on both sides of the opening provided in a part of the conductive film between the first end and the second end.

[0046] (Aspect 8) The quantum sensor according to aspect 7, wherein the signal line extends in a straight line between the first end and the second end, and each of the first parallel line and the second parallel line extends parallel to the longitudinal direction of the signal line.

[0047] (Aspect 9) The quantum sensor according to aspect 8, wherein the first parallel line and the second parallel line are configured to have the same shape.

[0048] (Aspect 10) A quantum sensor according to any one of aspects 1 to 9, wherein the object to be measured is integrated with the element body layer.

[0049] Although specific examples of the present invention have been described in detail above, these are merely illustrative and do not limit the scope of the claims. The technologies described in the claims include various modifications and changes to the specific examples illustrated above. Furthermore, the technical elements described in this specification or drawings exhibit technical usefulness individually or in various combinations, and are not limited to the combinations described in the claims at the time of filing. In addition, the technologies illustrated in this specification or drawings can achieve multiple objectives simultaneously, and achieving even one of these objectives itself constitutes technical usefulness.

Claims

1. A quantum sensor comprising: an element body layer having a color center; a signal line and a ground line, wherein the signal line has a first parallel line and a second parallel line extending in parallel and carrying high-frequency currents in parallel, and when the element body layer is viewed in plan view, at least the color center is located within an opening between the first parallel line and the second parallel line in the element body layer.

2. The quantum sensor according to claim 1, further comprising a photodetector, wherein the photodetector is configured to detect the fluorescence emitted from the color center that has passed through the aperture.

3. The quantum sensor according to claim 1, further comprising an excitation light generating unit, wherein the excitation light generating unit is configured to irradiate the color center with excitation light passing through the aperture.

4. The quantum sensor according to claim 1, wherein the element body layer has a first main surface and a second main surface, the signal line is disposed on the first main surface of the element body layer, and the ground line is disposed on the second main surface of the element body layer.

5. The quantum sensor according to claim 1, wherein the element body layer has a first main surface and a second main surface, the signal line is disposed on the first main surface of the element body layer, and the ground line is also disposed on the first main surface of the element body layer.

6. The quantum sensor according to claim 1, wherein at least one of the signal line and the ground line is embedded within the element body layer.

7. The quantum sensor according to claim 1, wherein the signal line is a conductive film including a first end and a second end, and the first parallel line and the second parallel line extend on both sides of the opening provided in a part of the conductive film between the first end and the second end.

8. The quantum sensor according to claim 7, wherein the signal line extends in a straight line between the first end and the second end, and each of the first parallel line and the second parallel line extends parallel to the longitudinal direction of the signal line.

9. The quantum sensor according to claim 8, wherein the first parallel line and the second parallel line are configured to have the same shape when the element body layer is viewed in plan view.

10. The quantum sensor according to any one of claims 1 to 9, wherein the object to be measured is integrated with the element body layer.

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