Quantum sensor element and measuring device

Abstract

This technology enables the measurement of both electric and magnetic fields surrounding power equipment using a single diamond quantum sensor. [Solution] A quantum sensor element 1 in which an ensemble NV center is generated in a diamond 12, wherein the diamond 12 is a flat plate having a main surface and a side surface intersecting the main surface, the surface orientation is the main surface (110) and the side surface (111), and of the multiple NV axes A, B, C, D of the ensemble NV center, the first NV axis A and the second NV axis D are arranged parallel to the main surface.

Description

[Technical Field]

[0001] The present invention relates to a quantum sensor element in which ensemble NV centers are generated in diamond, and a measuring device equipped with this element for measuring electric and magnetic fields generated around an object to be measured. [Background technology]

[0002] Electricity is indispensable in modern society, and power facilities are essential infrastructure. Power facilities, including transformers, switches, and transmission lines, have few opportunities to stop once they are in operation, and if a failure occurs in such power facilities, the impact on society will be significant. For this reason, power facilities are equipped with various measuring instruments corresponding to the various physical quantities to be measured, in order to quickly detect failures in the power facilities.

[0003] For example, in the early stages of a power plant failure, it is known that partial discharge generates minute, extremely short pulse-like magnetic fields (hereinafter referred to as magnetic field spikes) within the power plant. Power plants are equipped with measuring instruments to measure the magnetic fields generated around them. In addition to such measuring instruments for measuring magnetic fields, power plants are also equipped with measuring instruments to measure the electric fields generated around them, as well as measuring instruments to measure the current and voltage flowing through them.

[0004] In recent years, diamond has also attracted attention as a material for sensor elements that measure magnetic fields. In the crystal structure of diamond, complex defects called nitrogen-vacancy centers can sometimes be observed. These nitrogen-vacancy centers consist of a nitrogen atom that replaces a carbon atom in the crystal lattice and a vacancy (where a carbon atom is missing) adjacent to that nitrogen atom, and are also called NV centers (Nitrogen Vacancy centers).

[0005] An NV center is a state in which electrons are trapped in a vacancy (negative charge state, hereafter referred to as "NV"). -In this case, it exhibits a magnetic property called electron spin. - The electron spin state of diamond changes in response to an external magnetic field, and since this electron spin state can be measured at room temperature, diamond containing NV centers is increasingly being used as a material for magnetic field sensor elements. For example, Patent Document 1 discloses a device that detects magnetic field spikes generated in power facilities by using diamond NV centers as a magnetic field sensor.

[0006] The Hamiltonian describing electron spin has shown that electron spins at NV centers can function not only as magnetic field sensors, but also as electric field sensors, temperature sensors, and mechanical quantity (pressure) sensors. Therefore, diamond containing NV centers is expected to be used as electric field sensors, temperature sensors, and mechanical quantity sensors. Sensors that use NV centers in diamond to measure physical quantities such as magnetic fields, electric fields, temperature, and mechanical quantities are called diamond quantum sensors. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-131861 [Overview of the project] [Problems that the invention aims to solve]

[0008] To detect power equipment failures as quickly as possible, it is desirable to measure not only the magnetic field but also the electric field. Although the electron spins of the NV centers contained in diamond quantum sensors function as both magnetic and electric field sensors, there have been no previous examples of measuring both electric and magnetic fields with a single diamond quantum sensor. There is a need to measure both the electric and magnetic fields generated around power equipment with a single diamond quantum sensor.

[0009] The object of the present invention is to enable the measurement of both the electric field and the magnetic field generated around power facilities using a single diamond quantum sensor.

Means for Solving the Problems

[0010] The present invention for solving the above problems includes, for example, the following aspects. (Item 1) A quantum sensor element in which an ensemble of NV centers is generated in a diamond, The diamond is in a flat plate shape having a main surface and side surfaces intersecting the main surface, the plane orientation is the main surface (110) and the side surface (111), A quantum sensor element in which, among a plurality of NV axes of the ensemble of NV centers, a first NV axis and a second NV axis are arranged parallel to the main surface. (Item 2) The quantum sensor element according to Item 1, An electromagnetic wave irradiation unit that repeatedly irradiates the quantum sensor element with an electromagnetic wave for operating the electron spin state of the quantum sensor element that changes due to the interaction with the electric field and magnetic field generated around the measurement object, A physical quantity measurement unit that measures the electric field and the magnetic field respectively based on the electron spin state after the interaction with the electric field and the magnetic field, Comprising, The physical quantity measurement unit, Calculates the intensity of the electric field based on the electron spin state of the first NV axis, A measuring device that calculates the intensity of the magnetic field based on the electron spin state of the second NV axis. (Item 3) A bias magnetic field is applied to the quantum sensor element in the <11 - 2> direction or the <-1 - 12> direction, The physical quantity measurement unit, Measures the electric field along the <1 - 10> direction or the <-110> direction, The measuring device according to Item 2 that measures the magnetic field along the <-1 - 12> direction or the <11 - 2> direction. (Item 4) The electromagnetic wave irradiation unit, For measuring the electric field, irradiate the electromagnetic wave at a first frequency, The measuring device according to item 2 or 3, which irradiates the electromagnetic wave at a second frequency for measuring the magnetic field. (Item 5) The first frequency is a frequency near zero magnetic field, The measuring device according to item 4, wherein the second frequency is a frequency away from zero magnetic field. (Item 6) The physical quantity measuring unit includes a light irradiation unit that irradiates the quantum sensor element with light for reading information on the phase of the electron spin state after interacting with the electric field and the magnetic field, a detection unit that detects changes generated in the quantum sensor element by the irradiation of the light, a data processing unit that reads out the phase information from the detected changes and calculates the intensity of the electric field and the intensity of the magnetic field respectively based on the read phase information, The measuring device according to any one of items 2 to 5, further comprising (Item 7) The light irradiation unit irradiates the quantum sensor element with the light that excites the electron spin state from the <111> direction, The detection unit according to item 6, which detects a change in the emission intensity of fluorescence emitted from the quantum sensor element from the <111> direction. (Item 8) The light irradiation unit irradiates the quantum sensor element with the light that excites the electron spin state from the <11 - 2> direction, The detection unit according to item 6, which detects a change in the emission intensity of fluorescence emitted from the quantum sensor element from the <11 - 2> direction. (Item 9) The thickness of the flat diamond is 100 μm or more and 1 mm or less, and the measuring device according to any one of items 2 to 8. (Item 10) The electromagnetic wave irradiation unit is located at the axis of the branched transmission line. <111> A measuring apparatus according to any one of items 2 to 9, comprising open stub type resonators arranged parallel to the direction or the <-1-1-1> direction, wherein the electromagnetic waves are applied perpendicular to the first NV axis and the second NV axis. [Effects of the Invention]

[0011] According to the present invention, both electric and magnetic fields generated around power equipment can be measured using a single diamond quantum sensor. [Brief explanation of the drawing]

[0012] [Figure 1] This diagram schematically shows the general configuration of a measuring device according to one embodiment of the present invention. [Figure 2] This figure schematically shows an example of the specific configuration of the measuring device shown in Figure 1. [Figure 3] This diagram schematically shows the energy levels of electrons at the NV-center of diamond. [Figure 4] This is an example pulse sequence for sensing an alternating magnetic field using the optically detected magnetic resonance (ODMR) method. [Figure 5] This diagram illustrates the crystal structure of diamond. (A) shows the crystal structure of NV centers in diamond. (B) shows the four orientation directions of NV centers within the diamond crystal. [Figure 6] This is a diagram illustrating the arrangement of the diamond plate and the object. [Figure 7] This diagram illustrates the crystal orientation of a diamond plate in which an ensemble NV center is formed, and the four NV axes of the ensemble NV center. [Figure 8] This is a diagram illustrating the antenna used in this embodiment. [Figure 9] This is an example of a magnetic resonance signal obtained by the optically detected magnetic resonance (ODMR) method. [Modes for carrying out the invention]

[0013] Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. In the following description and drawings, the same reference numerals indicate the same or similar components, and therefore, redundant explanations of the same or similar components will be omitted.

[0014] In this specification, a physical quantity refers to a quantity whose dimensions are determined under a certain system in physics and which can be expressed as a multiple of a defined physical unit. Examples of physical quantities include magnetic fields, electric fields, temperature, and mechanical quantities (mechanical stress, pressure, etc.). Magnetic fields, electric fields, temperature, and mechanical quantities include physical quantities that do not change over time and physical quantities whose direction changes over time. That is, magnetic fields include static magnetic fields and alternating magnetic fields, electric fields include electrostatic fields and alternating electric fields, temperature includes static temperature and alternating temperature (temperature oscillation), and mechanical quantities include static mechanical quantities and alternating mechanical quantities.

[0015] In this specification, the terms "surface orientation" (surface index) and "direction index" (direction index) are defined as follows: When a surface orientation is described and an equivalent surface exists for that surface orientation, the described surface orientation refers to both the literal surface orientation and its equivalent surface. Similarly, when a direction index is described and an equivalent direction exists for that direction index, the described direction index refers to both the literal direction index and its equivalent direction.

[0016] In this embodiment, the power equipment to be measured is a power transmission line, and a measuring device equipped with a sensor element according to one embodiment of the present invention measures the electric and magnetic fields generated around the power transmission line.

[0017] [Device configuration] Figure 1 is a schematic diagram showing the general configuration of a measuring device 10 according to one embodiment of the present invention. Figure 2 is a schematic diagram showing an example of a specific configuration of the measuring device 10 shown in Figure 1.

[0018] The measuring device 10 (hereinafter also simply referred to as device 10) comprises a sensor element 1, an electromagnetic wave irradiation unit 2, and a physical quantity measuring unit 3. In this embodiment, the sensor element 1 is attached to the tip of the probe 11 of the device 10.

[0019] Sensor element 1 is a quantum sensor element. In this embodiment, sensor element 1 is a diamond 12 crystal having color centers, and NV centers are used as color centers. An NV center is a composite (composite defect) of nitrogen (N) substituted for a carbon atom and a vacancy (V) adjacent to the nitrogen. In this embodiment, sensor element 1 is pre-generated in a predetermined region on the diamond 12 crystal by a known method. Exemplarily, the region contains approximately several thousand (concentration: ~1 × 10⁻¹⁶) 12 / cm -3 Multiple sensor elements 1 are generated. In this embodiment, sensor elements 1 are ensemble NV centers. An ensemble NV center represents a collection of many NV centers.

[0020] In other words, the sensor element 1 according to this embodiment is a quantum sensor element in which ensemble NV centers are generated in a diamond 12, the diamond 12 being a flat plate having a main surface and a side surface intersecting the main surface, the plane orientation being the main surface (110) and the side surface (111), and of the multiple (four) NV axes of the ensemble NV center, the first NV axis and the second NV axis are arranged parallel to the main surface. The ingenuity applied to the arrangement of the NV axes with respect to the crystal plane of the diamond 12 in the sensor element 1 will be described later with reference to Figure 7.

[0021] The electron spin state of the sensor element 1 is changed by the interaction 8 with the object 9. In this embodiment, the object 9 is a power transmission line (power equipment), and the interaction 8 is an interaction due to an electric field and a magnetic field. When the interaction 8 is due to an electric field and a magnetic field, the electron spin state of the color center of the sensor element 1 becomes a state corresponding to the strength of the electric field and magnetic field generated around the power transmission line, which is the object 9. A bias magnetic field is applied to the sensor element 1 using, for example, a magnetic field generator (e.g., a coil) not shown in the figure.

[0022] The electromagnetic wave irradiation unit 2 irradiates the sensor element 1 with electromagnetic waves to manipulate the electron spin state of the sensor element 1 by magnetic resonance. As an example, in this embodiment, the electromagnetic wave irradiation unit 2 includes a known microwave (MW) oscillator 21, a switch 22 that irradiates electromagnetic waves (microwaves) in a pulsed form, and an amplifier 23. The switch 22 and amplifier 23 can be configured in any way. In this embodiment, the electromagnetic wave irradiation unit 2 irradiates the sensor element 1 with electromagnetic waves in a pulsed form to manipulate the electron spin state of the sensor element 1.

[0023] Various pulse sequences can be used in the electromagnetic wave pulse sequence that the electromagnetic wave irradiation unit 2 irradiates onto the sensor element 1 to generate magnetic resonance. For example, when sensing an AC magnetic field using photodetected magnetic resonance (ODMR) on electron spins in the sensor element, the electromagnetic wave is irradiated onto the sensor element using a pulse sequence based on the Hahn echo method of the spin echo method. Similarly, when sensing a static magnetic field using photodetected magnetic resonance, the electromagnetic wave is irradiated onto the sensor element using a pulse sequence based on the Ramsey method of the spin echo method. AC electric fields and electrostatic fields can also be sensed using the same pulse sequences as AC magnetic fields and static magnetic fields.

[0024] The electromagnetic wave irradiation unit 2 irradiates the sensor element 1 with electromagnetic waves through an electromagnetic wave irradiation antenna 14 positioned near the sensor element 1. The antenna 14 is formed on the diamond 12 crystal using a conductive metal, for example, by lithography. The antenna 14 will be described later with reference to Figure 8.

[0025] In this embodiment, the electromagnetic wave irradiation unit 2 irradiates electromagnetic waves at a first frequency for measuring the electric field and electromagnetic waves at a second frequency for measuring the magnetic field. In this embodiment, the first frequency is a frequency near zero magnetic field, and the second frequency is a frequency away from zero magnetic field. The fact that the frequencies of the electromagnetic waves irradiated for measuring the electric field and the magnetic field are different, and that the first frequency for measuring the electric field is a frequency near zero magnetic field and the second frequency for measuring the magnetic field is a frequency away from zero magnetic field, will be explained in more detail later with reference to Figure 9.

[0026] The physical quantity measuring unit 3 measures a physical quantity based on the change in the electron spin state of the sensor element 1 after it has been altered by the interaction 8 with the object 9. In this embodiment, the physical quantity measuring unit 3 measures the electric field and magnetic field generated around the power equipment, which is the object 9. The physical quantity measuring unit 3 comprises a light irradiation unit 31, a detection unit 32, and a data processing unit 33.

[0027] The light irradiation unit 31 irradiates the sensor element 1 with light 30 to read the phase information of the electron spin state of the sensor element 1 after it has interacted with the object 9. The light irradiation unit 31 also irradiates the sensor element 1 with light 30 to initialize the electron spin state of the sensor element 1. As an example, in this embodiment, the light irradiation unit 31 comprises a light source 311, an acoustic optical modulator (AOM) 312, and an objective lens 313. The acoustic optical modulator 312 and the objective lens 313 can be configured in any configuration.

[0028] The light source 311 emits light 30 for reading the phase information of the electron spin state of the sensor element 1 after it has interacted with the object 9. The light source 311 also emits light 30 for exciting and initializing the electron spin state of the sensor element 1. The wavelength of the light 30 emitted by the light source 311 is determined according to the type of sensor element 1. In this embodiment, the light source 311 emits laser light with a wavelength of 532 nm (green). For example, various known laser generators can be used as the light source 311. In this embodiment, the light source 311 is a semiconductor laser that emits green laser light.

[0029] The objective lens 313 focuses the light 30 emitted from the light source 311 and irradiates the region on the diamond crystal 12 where the sensor element 1 is generated. For example, the spot size of the laser beam focused on the diamond crystal 12 is approximately 2 μm in diameter. As the spot size of the laser beam decreases, the intensity of the laser beam per unit area increases, and the efficiency of the photocurrent generated in the conductive band of the diamond also increases.

[0030] In the configuration illustrated in Figure 2, the laser beam spot is positioned to cover the region on the diamond crystal 12 where the sensor element 1 is generated. Preferably, the laser beam spot can be positioned at an offset location from approximately the center of the region where the sensor element 1 is generated.

[0031] The detection unit 32 detects changes occurring in the sensor element 1. In this embodiment, the detection unit 32 detects the light 39 emitted from the sensor element 1 and detects the magnetic resonance signal as a change in emission intensity using a known photodetection magnetic resonance (ODMR) method. In this case, the detection unit 32 can be, for example, a known photodiode. For example, an avalanche photodiode can be used as the photodiode.

[0032] In this embodiment, the electromagnetic wave irradiation unit 2 irradiates the operating electromagnetic waves in a pulsed form. Therefore, in this embodiment, detection is specifically performed using the Pulsed Optically Detected Magnetic Resonance (pODMR) method.

[0033] The data processing unit 33 is connected to the detection unit 32 and reads the phase information of the electron spin state of the sensor element 1 after it has interacted with the object 9 from the changes detected by the detection unit 32. Based on the read phase information, it calculates the electric field strength and magnetic field strength, respectively. The data processing unit 33 includes an electric field strength calculation unit 331 and a magnetic field strength calculation unit 332.

[0034] The data processing unit 33 can be, for example, a well-known general-purpose computer or various information terminal devices such as a smartphone. The data processing unit 33 may be integrated with the device 10, or, as shown in the figure, it may be provided outside the device 10 and connected to the device 10 via a wired or wireless network 99.

[0035] The electric field strength calculation unit 331 calculates the electric field strength based on the electron spin state of the first NV axis among the multiple (four) NV axes of the sensor element 1. The magnetic field strength calculation unit 332 calculates the magnetic field strength based on the electron spin state of the second NV axis among the multiple (four) NV axes of the sensor element 1. As described above, in this embodiment, both the first NV axis and the second NV axis are NV axes among the multiple (four) NV axes of the ensemble NV center, arranged parallel to the principal surface (110) in a flat diamond 12 whose surface orientation is the principal surface (110) and side surface (111).

[0036] [Detection principle] In the present invention, the intensities of the electric and magnetic fields generated around the power facility 9, which is the object, are measured using the quantum sensor 1. The magnetic resonance signal used for calculating the intensities of the electric and magnetic fields is detected by the optical detection magnetic resonance (ODMR) method. Thereby, the intensities of the electric and magnetic fields are measured without electrically connecting directly to the power facility 9, which is the object.

[0037] In the present invention, in the quantum sensor 1, the arrangement of the NV axis with respect to the crystal plane of the diamond 12 is devised. Thereby, both the electric and magnetic fields generated around the power facility 9 can be measured by a single diamond quantum sensor 1.

[0038] First, the principle and procedure for detecting the magnetic resonance signal by the optical detection magnetic resonance (ODMR) method will be described below, and the method for calculating the electric field intensity and the magnetic field intensity from the detected magnetic resonance signal will be described. Next, the devised arrangement of the NV axis with respect to the crystal plane of the diamond 12, which is applied in the quantum sensor 1, will be described.

[0039] <Detection of Magnetic Resonance Signal by Optical Detection Magnetic Resonance (ODMR) Method> FIG. 3 is a diagram schematically showing the energy levels of electrons at the NV center of diamond. - It is a diagram schematically showing the energy levels of electrons at the center of the diamond NV.

[0040] In the present embodiment, the NV center of diamond is used as the sensor element 1. The ground state of the NV center is a spin triplet state with magnetic quantum numbers m s = -1, 0, +1, and in the steady state at room temperature, all levels are equally distributed in the ground state.

[0041] The electron with magnetic quantum number m s = 0 in the ground state transitions to the excited state when irradiated with laser light having a wavelength of 532 nm (green), emits red fluorescence, and relaxes to the ground state with magnetic quantum number m s = 0.

[0042] On the other hand, the electron with magnetic quantum number m sWhen an electron with a magnetic quantum number of =0 is irradiated with microwaves at a resonance frequency of 2.87 GHz, electron spin resonance (ESR) occurs, and the magnetic quantum number m s It transitions to a doubly degenerate ground state with a magnetic quantum number m = ±1. s Electrons with a magnetic quantum number of m = ±1 transition to an excited state when irradiated with laser light of wavelength 532 nm (green), and then, with a certain probability, s It returns to the ground state of =0. This series of processes is a non-radiative transition that does not emit fluorescence.

[0043] Thus, the process of emitting red fluorescence involves magnetic resonance, where electrons reach a magnetic quantum number m. s This becomes less likely when the ground state is ±1. Also, the magnetic quantum number m s The double degenerate ground state of =±1 is separated by Zeeman splitting in proportion to the strength of the external magnetic field, and therefore the fluorescence intensity also changes depending on the magnetic quantum number m of the electrons. s It changes depending on whether the state is ±1 or not. Therefore, when the microwave frequency is swept around 2.87 GHz, the magnetic resonance signal can be detected as the point where the red fluorescence intensity decreases.

[0044] Figure 4 shows an example pulse sequence for sensing an alternating magnetic field using the optically detected magnetic resonance (ODMR) method. The pulse sequence of the electromagnetic wave used for operation shown in Figure 4 is a pulse sequence based on the Hahn echo method of the spin echo technique.

[0045] State I represents the state in which electron spins have been initialized by laser irradiation. In the Bloch sphere, a notation that represents quantum states on a unit sphere, electron spins are aligned along the z-axis, which is the quantization axis.

[0046] Next, in state II, a π / 2 pulse is applied to tilt the electron spin along the quantization axis to a plane perpendicular to the quantization axis. The electron spin is then tilted to the xy-plane of the Bloch sphere. Subsequently, in state III, the electron spin, tilted to the xy-plane, undergoes phase relaxation during a predetermined time τ0 due to interaction with the alternating magnetic field and the static magnetic field. The strength of the interaction corresponds to the strength of the magnetic field felt by the electron spin.

[0047] After a predetermined time τ0 has elapsed in state III, a π pulse is irradiated in state IV to reverse the electron spin, which has been phase-relaxed by interaction with the object being measured, in a plane. From state III to state IV, the electron spin undergoes phase relaxation while rotating in the xy plane of the Bloch sphere. In this process, in the re-converged state V, the static magnetic field component is canceled out as the electron spin re-converges, but the AC magnetic field component is not canceled out because its intensity is reversed compared to state III.

[0048] After a predetermined time τ0 has elapsed while the electron spin is phase-relaxed in state V, a π / 2 pulse is irradiated in state VI to project the phase-relaxed electron spin onto the quantization axis. The electron spin, which was located in the xy-plane of the Bloch sphere, is projected onto the z-axis, which is the quantization axis, and aligned along the z-axis.

[0049] Subsequently, in state VII, the sensor element is irradiated with laser light, and the phase information of the electron spin state after interaction is read out by detecting the light emitted from the sensor element. This measurement of the magnetic resonance signal (phase information) related to the spin state using such a pulse sequence is performed repeatedly to improve the signal-to-noise ratio by integrating the signal intensity.

[0050] In the Hahn echo pulse sequence illustrated in Figure 4, the electron spin undergoes phase relaxation while rotating in the xy-plane of the Bloch sphere from state III to state V. Magnetic resonance (MRT) detects the signal generated when the electron spin undergoes this phase relaxation as a magnetic resonance signal. The time τ between π / 2 pulses corresponds to the period from state III to state V during which the electron spin undergoes phase relaxation, and this time τ determines the sensitivity of the measurement. This is because the degree to which the electron spin undergoes phase relaxation due to interaction with the magnetic field corresponds to the strength of the magnetic field felt by the electron spin.

[0051] <Method for calculating electric and magnetic field strength based on magnetic resonance signals> In optically detected magnetic resonance (ODMR) spectroscopy, the phase information (magnetic resonance signal) of the electron spin state of the sensor element 1 after interaction with the object 9 is detected as a change in emission intensity. The detected phase information corresponds to the physical quantity of the object. Therefore, by appropriately processing the detected phase information of the electron spin state after interaction, the physical quantity of the object can be calculated. The physical quantity of the object can be calculated based on the Hamiltonian of the electron spin.

[0052] Hamiltonian H of electron spin gs It can be expressed by the following formula.

number

[0053] Here, μ B This is a Bohr magneton, and g e is the g-factor of the electron, and h is Planck's constant. Vector S is the electron spin. Vector B is the applied magnetic field. D gs S is the zero-field splitting constant. x ,S y ,S z These are the x, y, and z components of the electron spin S, respectively. gs ⊥ E is the electric dipole moment. x ,E y These are the x and y components of the electric field, respectively.

[0054] First item

number

[0055] The second and third terms are terms resulting from dipole interactions (i.e., spin-to-spin interactions). Second term

number

number

[0056] Therefore, the magnetic field strength can be calculated based on the first term. The temperatures and mechanical quantities can be calculated based on the second term. The electric field strength can be calculated based on the third term.

[0057] <Techniques for arranging the NV axes relative to the crystal planes of diamond> Figure 5 is a diagram illustrating the crystal structure of diamond. (A) shows the crystal structure of NV centers in diamond. (B) shows the four orientation directions of NV centers within the diamond crystal.

[0058] As shown in Figure 5(A), an NV center in diamond is a diamond crystal in which a carbon atom (C) is replaced by a pair of nitrogen atoms (N) and a vacancy. 3vIt has symmetry, and as shown in Figure 5(B), in the direction of the axis (NV axis) connecting the nitrogen atom (N) and the vacancy (V), within the diamond crystal, <111> There are four equivalent directions (

[0111] , [-111], [1-11], [11-1]). Hereafter, these four NV axes located at the NV center will be referred to as NV axis A, NV axis B, NV axis C, and NV axis D, respectively.

[0059] Figure 6 is a diagram illustrating the arrangement of the diamond plate and the object.

[0060] Sensor element 1 is a quantum sensor element in which ensemble NV centers are generated in diamond 12. As shown in Figure 6, diamond 12 is a flat plate having a main surface and a side surface intersecting the main surface, with the surface orientation being the main surface (110) and the side surface (111). An electric current i flows through the power transmission line, which is the object 9. In this embodiment, the device 10 measures the electric field E and magnetic field B generated around the power transmission line, which is the object 9, in a non-contact manner with high sensitivity, using the arrangement of sensor element 1 (diamond 12) and object 9 as shown in Figure 6.

[0061] Figure 7 is a diagram illustrating the crystal orientation of a diamond plate in which an ensemble NV center is generated, and the four NV axes possessed by the ensemble NV center. Figure 7 shows the four NV axes (NV axis A, NV axis B, NV axis C, NV axis D) shown in Figure 5(B).

[0062] As shown in Figure 7, in a flat diamond 12 whose surface orientation is the principal surface (110) and side surface (111), the first and second NV axes of the multiple (four) NV axes of the ensemble NV center are arranged parallel to the principal surface. In the illustrated example, NV axis A and NV axis D are arranged parallel to the principal surface (110) of the diamond 12.

[0063] This section explains why the first and second NV axes of the ensemble NV center are positioned parallel to the principal plane (110).

[0064] In this embodiment, as shown in the arrangement of the flat diamond 12, the object 9, and the NV axes (NV axis A, NV axis D) in Figures 6 and 7, the electric field E to be measured is perpendicular to the (110) plane and <111> The diamond 12's surface orientation, the object 9, and the NV axis are positioned such that they are perpendicular to the NV axis (NV axis A) of the direction. In addition, the magnetic field B to be measured is parallel to the (110) plane and <111> The diamond 12's face orientation, the object 9, and the NV axis are positioned so that they are perpendicular to the NV axis of direction (NV axis A).

[0065] At this time, the electric field E and magnetic field B to be measured are perpendicular, and the NV axis in the other direction (NV axis D) is perpendicular to the electric field E and at an angle of approximately 19.5° from perpendicular to the magnetic field B. Of the four existing NV axes (NV axis A, NV axis B, NV axis C, NV axis D), <111> The NV axis in the direction (NV axis A) is perpendicular to the magnetic field B, so while the sensitivity to magnetic field B is the lowest, the sensitivity to electric field E is the highest. In contrast, the other NV axis in a different direction (NV axis D) is perpendicular to electric field E and at an angle of approximately 19.5° from perpendicular to magnetic field B, so the sensitivity to magnetic field becomes dominant.

[0066] Therefore, in the illustrated example, it can be seen that measuring the electric field using NV axis A and the magnetic field using NV axis D, among the four existing NV axes, is highly sensitive and effective for measuring both the electric and magnetic fields using a single sensor element 1.

[0067] The direction in which the light irradiation unit 31 irradiates the sensor element 1 with light 30 and the detection unit 32 detects the light 39 emitted from the sensor element 1 will be explained.

[0068] Refer to Figure 7. The light irradiation unit 31 emits light 30 that excites the electron spin state. <111> The sensor element 1 is illuminated from a direction, and the detection unit 32 detects the change in the emission intensity of the fluorescence 39 emitted from the sensor element 1. <111> Detection is performed from a specific direction. Alternatively, the light irradiation unit 31 irradiates the sensor element 1 with light 30 that excites the electron spin state from the <11-2> direction, and the detection unit 32 detects the change in the emission intensity of the fluorescence 39 emitted from the sensor element 1 from the <11-2> direction.

[0069] The direction of the bias magnetic field when it is applied to the sensor element 1 will be explained. Refer to Figure 7. A bias magnetic field is applied to the sensor element 1 in the <11-2> direction or the <-1-12> direction, and the physical quantity measuring unit 3 measures the electric field E along the <1-10> direction or the <-110> direction and the magnetic field B along the <-1-12> direction or the <11-2> direction.

[0070] Figure 8 is a diagram illustrating the antenna 14 used in this embodiment. (A) is a schematic perspective view of the antenna. (B) is a diagram illustrating the direction of electromagnetic waves irradiated from the antenna to the sensor element.

[0071] As shown in (A), in this embodiment, an open stub type microwave resonator is used as the antenna 14. As shown in (B), electromagnetic waves are emitted from the antenna 14, and a magnetic field is applied in a direction perpendicular to the plane of the paper.

[0072] Antenna 14 is connected to the axes 141, 141 of the branched transmission line. <111> The electromagnetic wave irradiation unit 2 is configured using open stub type resonators arranged parallel to the direction or the <-1-1-1> direction, and applies electromagnetic waves through the antenna 14 perpendicular to the first NV axis and the second NV axis. As shown in Figure 7, in the illustrated example, the first NV axis and the second NV axis are NV axis A and NV axis D, and are arranged parallel to the main surface (110) of the diamond 12. The axes 141,141 of the transmission line apply the magnetic field of the electromagnetic wave perpendicular to the main surface (110), i.e., perpendicular to NV axis A and NV axis D.

[0073] Refer to Figures 6 and 8. Preferably, the thickness d of the flat diamond 12 is 100 μm or more and 1 mm or less. More preferably, the thickness d is 100 μm or more and 500 μm or less. Most preferably, the thickness d is 100 μm or more and 300 μm or less. By reducing the thickness d of the flat diamond 12, the uniformity of the electromagnetic waves emitted from the antenna 14 and irradiated onto the diamond 12 and the electric field strength can be increased.

[0074] Figure 9 shows an example of a magnetic resonance signal obtained by the photodetector magnetic resonance (ODMR) method. In the graph in Figure 9, the vertical axis represents fluorescence intensity, and the horizontal axis represents the frequency of the electromagnetic wave (microwave) irradiated onto the sensor element 1. The static magnetic field (bias magnetic field) B is applied in the <11-2> direction.

[0075] An ensemble NV center is generated in the sensor element 1, and as shown in the graph in Figure 9, a waveform with a peak is observed for each of the four NV axes of the sensor element 1. In this embodiment, the electric field strength calculation unit 331 calculates the electric field strength based on peak A in the figure corresponding to NV axis A, and the magnetic field strength calculation unit 332 calculates the magnetic field strength based on peak D in the figure corresponding to NV axis D. When the magnetic field component parallel to NV axis A is zero, there should ideally be only one peak, but due to quantum mechanical effects, the intensity of the central part of the peak may decrease, causing zero-field splitting where the peak splits into two, and the electric field strength is calculated taking this into account.

[0076] Referring to Figure 9 below, we will provide further explanation regarding the fact that the frequencies of the electromagnetic waves irradiated for measuring the electric field and the magnetic field are different, and that the first frequency for measuring the electric field is a frequency near zero magnetic field, while the second frequency for measuring the magnetic field is a frequency far from zero magnetic field.

[0077] First, in the magnetic resonance signal shown in the graph of Figure 9, the reason why the peak frequencies of the signals differ for each of the four NV axes A to D is because each of the four NV axes experiences a different magnetic field strength (magnetic field sensitivity). If there is no bias magnetic field B (zero magnetic field), the peak frequencies of the signals on all four NV axes in the graph will all coincide with the peak frequency of NV axis A (approximately 2870 MHz).

[0078] The magnetic field sensitivity is determined by the angle (denoted by θ, for example) between the NV axis and the bias magnetic field B, and the effective magnetic field strength B' felt by the NV axis is B' = Bcosθ. As described above, in this embodiment, of the four NV axes, the electric field is measured using NV axis A and the magnetic field is measured using NV axis D. In the example shown in the graph of Figure 9, the bias magnetic field is applied in the <11-2> direction.

[0079] Therefore, in this case, with the NV axis arrangement shown in Figure 7, the angle θ between NV axis A and bias magnetic field B is 90°, and the effective magnetic field strength B' felt by NV axis A is B'=0, resulting in the smallest effective magnetic field strength B'. Thus, the peak frequency position of the signal of NV axis A used for measuring the electric field is the same as the frequency position when there is no bias magnetic field B. On the other hand, with the four NV axis arrangement shown in Figure 7, NV axis D is the NV axis closest to an angle θ between the NV axis and bias magnetic field B of 0° or 180° (i.e., cosθ=1), so the effective magnetic field strength B' is also the largest. Thus, the peak frequency position of the signal of NV axis D used for measuring the magnetic field is the furthest from the peak frequency position of the signal of NV axis A (in this embodiment, the same frequency position when there is no bias magnetic field B).

[0080] As described above, according to the quantum sensor element 1 of one embodiment, both the electric field E and the magnetic field B generated around the power equipment 9 can be measured by a single diamond quantum sensor 1.

[0081] The sensor element 1 has four NV axes at the center of the diamond ensemble NV, with the surface orientation being the main surface (110) and the side surface (111). Two of these axes, which form an angle of 109.5°, are arranged parallel to the main surface (110). As a result, the sensitivity of one NV axis (NV axis A) to the electric field is improved, and the sensitivity of the other NV axis (NV axis D) to the magnetic field is improved. Thus, according to the quantum sensor element 1 of this embodiment, it is possible to improve sensitivity to both electric and magnetic fields, and both the electric field E and magnetic field B generated around the power equipment 9 can be measured by a single diamond quantum sensor 1.

[0082] Furthermore, the measuring device 10 according to one embodiment includes a quantum sensor element 1 according to one embodiment, and measures both the electric field E and magnetic field B generated around the power equipment 9. One sensor element 1 is sufficient for the measuring device 10 to measure the electric field E and magnetic field B, and it is not necessary to provide multiple sensor elements 1 separately for electric field measurement and magnetic field measurement.

[0083] [Other forms] Although the present invention has been described above with reference to specific embodiments, the present invention is not limited to the embodiments described above.

[0084] In the embodiment described above, the electromagnetic wave irradiation unit 2 irradiates the sensor element 1 with electromagnetic waves using a pulse sequence based on the spin echo method. However, the pulse sequence of electromagnetic waves irradiated onto the sensor element 1 is not limited to a pulse sequence based on the spin echo method. The pulse sequence of electromagnetic waves irradiated onto the sensor element 1 by the electromagnetic wave irradiation unit 2 only needs to be able to generate magnetic resonance. For example, the electromagnetic wave irradiation unit 2 may irradiate the sensor element 1 with electromagnetic waves using a pulse sequence that observes a free induction decay (FID) signal.

[0085] In the embodiment described above, the power equipment referred to as object 9 is a power transmission line, and the measuring device 10 measures the electric and magnetic fields generated around the power transmission line. However, the power equipment referred to as object 9 is not limited to a power transmission line. The power equipment may include, for example, power transmission and distribution equipment such as transformers and switches. [Explanation of Symbols]

[0086] 1. Sensor element (Diamond ensemble NV center) 2 Electromagnetic wave irradiation section 3 Physical quantity measurement section 8 Interaction 9. Object (power lines) 10 Measuring device 11 probes 12 Diamond Crystals 14 Antennas 21 Microwave (MW) Oscillators 22 switches 23 Amplifier 30 light 31 Light-irradiating section 311 Light source 312 Acousto-optical modulation element (AOM) 313 Objective lens 32 Detection unit 33 Data Processing Unit 331 Electric Field Strength Calculation Unit 332 Magnetic field strength calculation unit 39 Fluorescence 99 Network

Claims

1. A quantum sensor element in which ensemble NV centers are generated in diamond, The diamond is in the shape of a flat plate having a main surface and a side surface intersecting the main surface, and the surface orientation is the main surface (110) and the side surface (111). A quantum sensor element in which, of the multiple NV axes of the ensemble NV center, the first NV axis and the second NV axis are arranged parallel to the main plane.

2. A quantum sensor element according to claim 1, An electromagnetic wave irradiation unit repeatedly irradiates the quantum sensor element with electromagnetic waves to manipulate the electron spin state of the quantum sensor element, which changes due to its interaction with the electric and magnetic fields generated around the object to be measured, A physical quantity measuring unit that measures the electric field and the magnetic field, respectively, based on the electron spin state after interaction with the electric field and the magnetic field, Equipped with, The aforementioned physical quantity measuring unit is Based on the electron spin state of the first NV axis, the strength of the electric field is calculated. A measuring device that calculates the strength of the magnetic field based on the electron spin state of the second NV axis.

3. A bias magnetic field is applied to the quantum sensor element in the direction of <11-2> or <-1-12>. The aforementioned physical quantity measuring unit is The electric field along the <1-10> direction or the <-110> direction is measured. The measuring device according to claim 2, which measures the magnetic field along the <-1-12> direction or the <11-2> direction.

4. The electromagnetic wave irradiation unit is For the purpose of measuring the electric field, the electromagnetic wave is irradiated at a first frequency. The measuring apparatus according to claim 2 or 3, wherein the electromagnetic waves are irradiated at a second frequency for measuring the magnetic field.

5. The first frequency mentioned above is a frequency near zero magnetic field, The measuring device according to claim 4, wherein the second frequency is a frequency away from the zero magnetic field.

6. The aforementioned physical quantity measuring unit is A light irradiation unit that irradiates the quantum sensor element with light for reading information about the phase of the electron spin state after it has interacted with the electric field and the magnetic field, A detection unit for detecting changes occurring in the quantum sensor element due to the irradiation of the aforementioned light, A data processing unit reads out the phase information from the detected change, and calculates the electric field strength and the magnetic field strength, respectively, based on the read-out phase information. The measuring device according to claim 2, further comprising:

7. The light irradiation unit irradiates the quantum sensor element with the light that excites the electron spin state from the <111> direction, The measuring device according to claim 6, wherein the detection unit detects a change in the emission intensity of fluorescence emitted from the quantum sensor element from the <111> direction.

8. The light irradiation unit irradiates the quantum sensor element with the light that excites the electron spin state from the direction of <11-2>, The measuring device according to claim 6, wherein the detection unit detects a change in the emission intensity of fluorescence emitted from the quantum sensor element from the <11-2> direction.

9. The measuring device according to claim 2, wherein the thickness of the flat diamond is 100 μm or more and 1 mm or less.

10. The electromagnetic wave irradiation unit is configured using an open stub type resonator in which the axes of the branched transmission lines are arranged parallel to the <111> direction or the <-1-1-1> direction, and the electromagnetic waves are applied perpendicular to the first NV axis and the second NV axis, as described in claim 2.

Images