Quantum sensor element, magnetic field detection device, method for manufacturing quantum sensor element, and head observation device

Abstract

A quantum sensor element 10 has a diamond body 1 that includes nitrogen-vacancy centers in the crystal structure thereof. The diamond body 1 has: an optical waveguide region 2 that includes a nitrogen-vacancy center and extends in the thickness direction; and a boundary layer 3 that surrounds and demarcates an optical waveguide region 2 when viewed from the thickness direction. The optical waveguide region 2 has an optical emission end 2a at one end in the thickness direction. The boundary layer 3 reflects red light generated from the nitrogen-vacancy center within the optical waveguide region 2 and guides the red light to the optical emission end 2a.

Description

Quantum sensor element, magnetic field detection device, method for manufacturing a quantum sensor element, and head observation device

[0001] This invention relates to a technique for detecting weak magnetic fields generated by neural activity in the human brain or other sources, or magnetic fields at other inspection sites (objects under inspection or spaces under inspection), using the nitrogen-vacancy centers of diamond.

[0002] Magnetoencephalography (MEG) is a method for measuring brain activity. MEG can non-invasively measure the weak magnetic fields generated by brain activity. Specifically, MEG uses a superconducting quantum interference device (SQUID) that utilizes the Josephson effect to measure the weak magnetic fields generated in the brain. Such a MEG is described, for example, in Patent Document 1.

[0003] Japanese Patent Publication No. 2022-186358

[0004] Fei He et al., "Tailoring femtosecond 1.5-μm Bessel beams for manufacturing high-aspect-ratio through-silicon vias", Scientific Reports 7, Article number: 40785 (2017)

[0005] <Problem 1> However, in MEG, it is necessary to cool the SQUID with liquid helium to maintain a superconducting state.

[0006] Therefore, it is conceivable to use the nitrogen-vacancy centers of diamond, which have magnetic field sensitivity equivalent to that of SQUIDs without requiring a superconducting state, to detect (e.g., measure) weak magnetic fields in objects under test (e.g., human brains, solar panels, semiconductor chips, etc.) or spaces under test. In this case, it is desirable to increase the measurement sensitivity of weak magnetic fields in minute local areas (for example, local areas with a size of around 20 μm, smaller than the element of a SQUID) in order to enable magnetic field detection (e.g., measurement) at the cellular level. It is also desirable to be able to detect magnetic fields with a time resolution commensurate with nerve transmission speed, etc.

[0007] <Problem 2> Furthermore, the spatial resolution of local information of brain neural activity obtained using MEG is limited to the size of the SQUID element (for example, on the order of centimeters).

[0008] Therefore, there is a need for quantum sensor elements that can detect (e.g., measure) magnetic fields (e.g., weak magnetic fields) in the object being tested (e.g., the human brain, solar panels, semiconductor chips, etc.) or the space being tested with higher spatial resolution than SQUID elements. By using such quantum sensor elements, it becomes possible to obtain more detailed local information on brain nerve activity, for example. For example, by detecting magnetic fields generated from the axons of nerve cells with high spatial resolution, it becomes possible to record nerve location and nerve transmission state. It is expected that such high spatial resolution magnetic field detection data can be utilized, for example, in the following (1) to (3).

[0009] (1) To elucidate information transmission within the brain by directly observing the activity of brain nerve cells, and to understand the mechanisms of thinking, memory, consideration, and prediction. (2) To be able to distinguish whether a person's memory-related symptoms are early-stage dementia or age-related forgetfulness. (3) To build a communication support system for people who have difficulty communicating due to neurological diseases or accidents.

[0010] The object of the present invention is to provide a technology that can solve at least some of the problems described above.

[0011] An object according to one aspect of the present invention is to provide a technology that enables the detection sensitivity of a magnetic field (e.g., a weak magnetic field) in a minute localized area (e.g., a location smaller than the element of a SQUID) when detecting (e.g., measuring) a magnetic field using the nitrogen-vacancy center of a diamond, or in addition to the above, enables the detection of a magnetic field with a high temporal resolution commensurate with nerve transmission speed, etc.

[0012] Another object of the present invention, according to another aspect, is to provide a technique that enables the detection of magnetic fields (e.g., weak magnetic fields) with higher spatial resolution than SQUID when detecting magnetic fields using nitrogen-vacancy centers in diamond.

[0013] A quantum sensor element according to one aspect of the present invention has a diamond body containing nitrogen-vacancy centers in its crystal structure, the diamond body having an optical waveguide region extending in the thickness direction and containing the nitrogen-vacancy centers, and a boundary layer surrounding the optical waveguide region so as to demarcate it when viewed from the thickness direction, the optical waveguide region having an optical emission end at one end in the thickness direction, and the boundary layer reflects red light generated from the nitrogen-vacancy centers within the optical waveguide region and guides it to the optical emission end.

[0014] A magnetic field detection device according to one aspect of the present invention includes the above-mentioned quantum sensor element, which is placed at the location where a weak magnetic field is detected, and the nitrogen-vacancy center has a magnetic quantum number m Ｓ The state of = 0 and the magnetic quantum number m Ｓ = +1 or m Ｓ The system comprises a microwave source capable of irradiating the diamond body with microwaves at a resonant frequency that causes a transition between the state of -1 and the state of the diamond body, an excitation light source that irradiates the diamond body with excitation green light, and an image generation device that generates an image of the outer surface of the diamond body.

[0015] A method for manufacturing a quantum sensor element according to one aspect of the present invention is a method for manufacturing a quantum sensor element as described above, comprising: (A) preparing a diamond for the element which will be the diamond body; and (B) moving the focusing portion of the laser light in the diamond for the element over an irradiation area that extends in the circumferential direction so as to surround a predetermined area when viewed from the thickness direction of the diamond for the element, thereby modifying the irradiation area into the boundary layer, so that the predetermined area partitioned by the boundary layer becomes the optical waveguide area.

[0016] According to one aspect of the present invention, when detecting a magnetic field using the nitrogen-vacancy center of a diamond, it becomes possible to increase the detection sensitivity of a magnetic field (e.g., a weak magnetic field) in a minute localized area, or in addition, to detect a magnetic field with a high temporal resolution commensurate with nerve transmission speed, etc. According to another aspect of the present invention, when detecting a magnetic field using the nitrogen-vacancy center of a diamond, it becomes possible to detect a magnetic field (e.g., a weak magnetic field) with a higher spatial resolution than a SQUID.

[0017] This is a perspective view showing an example of the configuration of a quantum sensor element according to the first embodiment of the present invention. This is a perspective view showing another example of the configuration of a quantum sensor element according to the first embodiment of the present invention. This shows the crystal structure of a diamond body having nitrogen-vacancy centers. This shows the energy levels of the nitrogen-vacancy centers in diamond. This is a perspective view schematically showing each of the numerous nitrogen-vacancy centers in the optical waveguide region as a sphere. This is another perspective view schematically showing each of the numerous nitrogen-vacancy centers in the optical waveguide region as a sphere. This is a schematic diagram showing the red fluorescence of nitrogen-vacancy centers excited by green light in the case of Figure 4A. This is a flowchart showing a method for manufacturing a quantum sensor element according to the first embodiment. This is an explanatory diagram showing a method for forming a boundary layer. This is another explanatory diagram showing a method for forming a boundary layer. This is a perspective view showing an example of the configuration of a quantum sensor element according to the second embodiment of the present invention. This is a perspective view showing another example of the configuration of a quantum sensor element according to the second embodiment of the present invention. This is a schematic diagram showing the optical waveguide region viewed in the thickness direction of the diamond body in Figure 8B. This is a schematic diagram showing another example of the configuration when the optical waveguide region is viewed in the thickness direction of the diamond body. This is a schematic diagram showing yet another configuration example when viewing the optical waveguide region in the thickness direction of the diamond body. This is a perspective view showing a configuration example of a quantum sensor element according to the third embodiment of the present invention. This is a plan view of the quantum sensor element shown in Figure 12. This is a schematic diagram showing a magnetic field detection device according to an embodiment of the present invention. This is a view along the 14B-14B arrow in Figure 14A. This shows configuration example 1 of a head observation device according to an embodiment of the present invention. This shows configuration example 2 of a head observation device according to an embodiment of the present invention. This is data obtained in an experimental example, showing the relationship between microwave frequency and red light intensity. This is data obtained in an experimental example, showing the relationship between the current value of the copper wire and the microwave frequency at which the red light intensity is minimized. This is an image of the surface of the diamond body obtained in an experimental example. This is a graph describing the magnetic field strength at each coordinate shown in Figure 19A by the amount of microwave frequency shift. This shows a configuration example of a magnetic field detection device without a reflector. This shows a configuration example when each optical waveguide region is surrounded by a single boundary layer. This shows another configuration example when each optical waveguide region is surrounded by a single boundary layer.

[0018] Embodiments of the present invention will be described based on the drawings. In the drawings, the same reference numerals are given to the common parts in each figure, and redundant descriptions are omitted. In each figure, since the characteristic parts are emphasized, the scales of each part are not accurate.

[0019] [First Embodiment]FIG. 1A is a perspective view showing a configuration example of a quantum sensor element 10 according to the first embodiment of the present invention. The quantum sensor element 10 has a diamond body 1. The diamond body 1 is formed of diamond containing a nitrogen-vacancy center in its crystal structure. The nitrogen-vacancy center is excited by green light and emits red light when transitioning from this excited state to the ground state. The quantum sensor element 10 is for detecting (for example, measuring) a weak magnetic field using such a nitrogen-vacancy center. The weak magnetic field may be a magnetic field generated by human brain nerve activity, a magnetic field of the same magnitude as the magnetic field, or a magnetic field of other magnitudes.

[0020] (Nitrogen-Vacancy Center and Red Fluorescence)FIG. 2 shows the crystal structure of the diamond body 1 having a nitrogen-vacancy center. In FIG. 2, C represents a carbon atom, N represents a nitrogen atom, and V represents a vacancy. As shown in FIG. 2, the nitrogen-vacancy center is a composite defect (hereinafter also simply referred to as a nitrogen-vacancy center) composed of a nitrogen atom (Nitrogen) substituted for a carbon atom and a vacancy generated by the removal of a carbon atom adjacent to the nitrogen atom in the diamond crystal lattice. The nitrogen-vacancy center is also denoted as an NV center.

[0021] The nitrogen-vacancy center is excited by green light and emits red light when transitioning from this excited state to the ground state. The red fluorescence by the nitrogen-vacancy center will be described based on FIG. 3.

[0022] FIG. 3 shows the energy levels of the nitrogen-vacancy center. Each nitrogen-vacancy center of the diamond body 1 captures one electron and has six electrons. In this state, each nitrogen-vacancy center has a spin quantum number S = 1, and in the ground state and the excited state, the magnetic quantum number m ＳIt forms a spin triplet state of = -1, 0, +1. In the state where no external electric field or magnetic field is applied to the nitrogen-vacancy center, the ground-state nitrogen-vacancy center is excited by green light (e.g., green laser) GL with a wavelength of about 495 - 570 nm (e.g., 532 nm). When the excited nitrogen-vacancy center returns from the excited state to the ground state, it emits red light RL with a wavelength of about 630 - 800 nm (e.g., 637 nm).

[0023] The probability of red fluorescence of the nitrogen-vacancy center varies according to the magnetic quantum number as follows. When the nitrogen-vacancy center is in the ground state with magnetic quantum number m Ｓ = 0 and is excited by green light, the probability of non-radiative transition is higher when the nitrogen-vacancy center is in the ground state with m Ｓ = ±1 and is excited by green light. That is, by irradiating the nitrogen-vacancy center with microwaves at the resonance frequency (about 2.87 GHz when no magnetic field is applied to the nitrogen-vacancy center), the transition probability of the energy level of the nitrogen-vacancy center from the state with magnetic quantum number m Ｓ = 0 to the state with magnetic quantum number m Ｓ = ±1 increases. As a result, when the excited state with m Ｓ = ±1 falls to the ground state, the probability of passing through non-radiative transition increases, so the intensity of red fluorescence decreases. More specifically, in the state where green light is irradiating the nitrogen-vacancy center of the diamond body 1, regardless of whether the electron spin state of the nitrogen-vacancy center is m Ｓ = 0 or m Ｓ = ±1, it is excited by green light and transitions from this excited state to the ground state to become an electron spin state with m Ｓ = 0. Therefore, in this state, the nitrogen-vacancy centers with m Ｓ = 0 exist more than the nitrogen-vacancy centers with m Ｓ = ±1. Thus, red fluorescence occurs from the diamond body 1 due to green light. Next, in this state, by irradiating the nitrogen-vacancy center of the diamond body 1 with microwaves at the resonance frequency, the electron spin state of the nitrogen-vacancy center changes from m Ｓ = 0 to m Ｓ = ±1, and m Ｓfrom m = ±1 Ｓ although any change to m = 0 occurs, Ｓ since there are many nitrogen-vacancy centers with m = 0, as a result, Ｓ from m = 0 Ｓ many changes to m = ±1 occur. As a result, the intensity of the red fluorescence decreases.

[0024] (Configuration of the quantum sensor element) The diamond body 1 of the quantum sensor element 10 according to the first embodiment has an optical waveguide region 2 extending in the thickness direction (hereinafter also simply referred to as the thickness direction) of the diamond body 1, and a boundary layer 3 surrounding so as to partition the optical waveguide region 2 when viewed from the thickness direction. The boundary layer 3 is a layer that forms the boundary between the optical waveguide region 2 and another region (diamond region) of the diamond body 1. Note that the diamond body 1 may have dimensions of 1 cm or more and 10 cm or less in each direction (for example, each of two mutually orthogonal directions) when viewed from its thickness direction, but may be appropriately set according to the use of the quantum sensor element 10 or the like.

[0025] The optical waveguide region 2 is a minute region of diamond containing nitrogen-vacancy centers in its crystal structure. FIG. 1A shows the case where the shape of the optical waveguide region 2 is a cylindrical shape having a central axis in the thickness direction, and FIG. 1B is a perspective view showing the case where the shape of the optical waveguide region 2 is a quadrangular prism shape having a central axis in the thickness direction. The quantum sensor element 10 of FIG. 1B is the same as the case of FIG. 1A except that the shape of the optical waveguide region 2 is different from that of FIG. 1A.

[0026] Note that the optical waveguide region 2 may actually have a vertically long (elongated) shape in the thickness direction rather than the shapes shown in FIGS. 1A and 1B. The shape of the optical waveguide region 2 may be a cylindrical shape having a central axis in the thickness direction, or may be a prismatic shape (for example, a quadrangular prism) having a central axis in the thickness direction, or may be another shape (for example, a shape close to the cylindrical shape or the prismatic shape).

[0027] The optical waveguide region 2 has an optical emission end 2a at one end in the thickness direction. The optical emission end 2a may be a part of the surface 1a of the diamond body 1. The optical emission end 2a may be an optical emission surface. The boundary layer 3 reflects the red light generated from the nitrogen-vacancy center within the optical waveguide region 2 and guides it to the optical emission end 2a. That is, the red light generated from the nitrogen-vacancy center within the optical waveguide region 2 is guided by the boundary layer 3 through the optical waveguide region 2 to the optical emission end 2a.

[0028] The boundary layer 3 reflects red light as described above because its refractive index is different from that of the diamond in the optical waveguide region 2. In this embodiment, the boundary layer 3 is made of graphite. The boundary layer 3 is formed inside the diamond body 1 so as to surround the optical waveguide region 2 when viewed from the thickness direction of the diamond body 1 as described above.

[0029] The quantum sensor element 10 according to this embodiment may further have a reflector 4. The reflector 4 covers the other end (other end face) of the optical waveguide region 2. The reflector 4 is provided on the back surface 1b in the thickness direction of the diamond body 1. The reflector 4 reflects the red light generated when the nitrogen-vacancy center in the optical waveguide region 2 transitions from an excited state to a ground state. The reflector 4 may be, for example, a film that reflects red light in this way. The reflector 4 transmits a magnetic field (the magnetic field to be detected). Such a reflector 4 may be a dielectric multilayer film formed on the back surface 1b of the diamond body 1. However, the reflector 4 is not limited to a dielectric multilayer film, and may be a boundary layer 3 or something else. The reflector 4 may be omitted as described later.

[0030] The reflective portion 4 may be provided on the entire back surface 1b of the diamond body 1. For example, a dielectric multilayer film as the reflective portion 4 may be formed on the entire back surface 1b of the diamond body 1.

[0031] (Optical Waveguide Region and its Function) Numerous nitrogen-vacancy centers exist within the optical waveguide region 2. Figures 4A and 4B are perspective views schematically showing each of the numerous nitrogen-vacancy centers within the optical waveguide region 2 as a sphere. Figure 4A shows the cylindrical optical waveguide region 2 in Figure 1A, and Figure 4B shows the rectangular prism-shaped optical waveguide region 2 in Figure 1B.

[0032] When the quantum sensor element 10 is used to detect a weak magnetic field, green light is incident on the optical waveguide region 2. As a result, the nitrogen-vacancy centers within the optical waveguide region 2 are excited from the ground state to the excited state by the green light, and emit red light when they return from the excited state to the ground state.

[0033] Figure 5 is a schematic diagram showing the red fluorescence of nitrogen-vacancy centers excited by green light in the case of Figure 4A. The boundary layer 3 of the optical waveguide region 2 guides the red light generated from the nitrogen-vacancy centers within the optical waveguide region 2 to the light emission end 2a. That is, a portion of the red light generated from the nitrogen-vacancy centers within the optical waveguide region 2 is reflected by the boundary layer 3 forming the outer surface of the optical waveguide region 2, as shown in Figure 3. As a result, the red light is guided to the light emission end 2a while being confined within the optical waveguide region 2, and is emitted from the light emission end 2a. Another portion of the red light generated from the nitrogen-vacancy centers within the optical waveguide region 2 is similarly guided to the opposite side of the light emission end 2a, as shown in Figure 3, but is reflected by the reflector 4 and guided to the light emission end 2a. In this way, the optical waveguide region 2 functions as an optical waveguide that guides red light to the light emission end 2a. This function can also be obtained for optical waveguide regions 2 having shapes other than cylindrical (for example, optical waveguide region 2 in Figure 4B).

[0034] The optical waveguide region 2 may be a region extending in the thickness direction from the surface 1a to the back surface 1b of the diamond body 1. Therefore, the dimensions of the optical waveguide region 2 in the thickness direction may be the same as the thickness of the diamond body 1. The thickness of the diamond body 1 (i.e., the dimension in the thickness direction) may be a value in the range of 100 μm or more and 500 μm or less (250 μm in one example), but is not limited to this range and may be less than 100 μm (for example, about 90 μm) or greater than 500 μm (for example, about 1 mm).

[0035] The optical waveguide region 2 is a minute region when viewed from the thickness direction (hereinafter simply referred to as the thickness direction) of the diamond body 1. The dimensions of the cross-section of the optical waveguide region 2 and the optical emission end 2a, which are in a plane perpendicular to the thickness direction, may be 100 μm or less. In this case, the dimensions of the cross-section and the optical emission end 2a may be on the order of μm (for example, 2 μm, 3 μm, or 5 μm), or they may be on the order of μm (for example, 2 μm, 3 μm, or 5 μm) or more and below a predetermined upper limit. This upper limit may be, for example, 100 μm, 75 μm, 50 μm, 35 μm, 25 μm, 20 μm, 10 μm, or 7 μm. However, according to the present invention, the dimensions of the cross-section and the optical emission end 2a of the optical waveguide region 2 are not limited to the above range and may be set according to the application of the quantum sensor element 10, etc.

[0036] Furthermore, the dimensions of the cross-section and the optical emission end 2a may refer to the largest dimension among the dimensions in each direction perpendicular to the thickness direction when viewed from the thickness direction. Also, the dimensions of the cross-section and the optical emission end 2a refer to the dimensions of the region demarcated by the boundary layer 3 (the inner surface of the boundary layer 3) in the optical waveguide region 2, and are the dimensions of the region that does not include the boundary layer 3.

[0037] The thickness of the boundary layer 3 may be smaller than the dimensions of the cross-section and the optical emission end 2a of the optical waveguide region 2. For example, the thickness of the boundary layer 3 may be in the range of 0.5 μm or more and 2 μm or less (approximately 1 μm in one example), but is not limited to this range.

[0038] The optical waveguide region 2 may be a region that is elongated vertically in the thickness direction. For example, the optical waveguide region 2 may be a region that extends in a long, narrow shape in the thickness direction. The length of the optical waveguide region 2 (i.e., the dimensions of the optical waveguide region 2 in the thickness direction) may be 2 times or more, 3 times or more, 5 times or more, or 10 times or more the dimensions of the above cross-section of the optical waveguide region 2 in a plane perpendicular to the thickness direction (the maximum value of the dimensions of said cross-section), but is not limited to these ranges.

[0039] Furthermore, as described above, the optical waveguide region 2 does not need to be completely demarcated as long as it can reflect a sufficient amount of red light from the nitrogen-vacancy center within the optical waveguide region 2 and guide it to the light emission end 2a. In other words, there may be parts of the optical waveguide region 2 that are not demarcated by the boundary layer 3. For example, in the diamond body 1, the boundary layer 3 that demarcates the optical waveguide region 2 may extend discontinuously in the circumferential direction of the optical waveguide region 2. That is, the boundary layer 3 may have one or more discontinuous points in the circumferential direction of the optical waveguide region 2 in a part or the whole of the boundary layer 3 in the thickness direction, and the boundary layer 3 may have one or more discontinuous points in the thickness direction in a part or the whole of the boundary layer 3 in the circumferential direction of the optical waveguide region 2.

[0040] (Method for Manufacturing Quantum Sensor Elements) The method for manufacturing the quantum sensor element 10 described above will be explained with reference to Figure 6. Figure 6 is a flowchart of the manufacturing method according to the first embodiment. This manufacturing method includes the following steps S1 to S5.

[0041] In step S1, a diamond for the element 11 (see Figure 7A or Figure 7B described later) that will become the diamond body 1 is prepared. This diamond for the element 11 corresponds to the diamond body 1 in which the boundary layer 3 has not yet been formed. The diamond for the element 11 prepared in step S1 may or may not contain nitrogen-vacancy centers in its crystal structure. The diamond for the element 11 may be in the form of a sheet of diamond.

[0042] The diamond 11 for the element prepared in step S1 may be, for example, a synthetic diamond or a natural diamond. The synthetic diamond may be, for example, a CVD (Chemical Vapor Deposition) diamond formed by the CVD method, or a CVD diamond formed by the High Pressure High Temperature method.

[0043] In step S2, the irradiation area surrounding the predetermined area that will become the optical waveguide region 2 is irradiated with laser light, thereby modifying the irradiation area and transforming it into the boundary layer 3. This irradiation area is an area in the element diamond 11 that extends in the thickness direction and also extends circumferentially (for example linearly) so as to surround the predetermined area when viewed from the thickness direction. In step S2, the focusing portion of the laser light is moved (scanned) across the irradiation area by controlling an appropriate optical system through which the laser light passes in the element diamond 11. As a result, the irradiation area is modified with laser light and transformed into the boundary layer 3, and the predetermined area partitioned by the boundary layer 3 becomes the optical waveguide region 2. The laser light used in step S2 may be a femtosecond laser light. The femtosecond laser light used in step S2 (in each of the following examples) may, for example, have a wavelength of 532 nm, a pulse width of 280 fs (femtoseconds), a pulse energy of 80 mW, and a pulse repetition frequency of 200 kHz, but is not limited to this example.

[0044] In one example, the laser beam used in step S2 may have an elongated focused portion in the direction of propagation of the laser beam, such as the Bessel beam described in Non-Patent Document 1. In this case, in step S2, the laser beam is irradiated onto the element diamond 11 in the thickness direction, and the focused portion is moved in the circumferential direction across the irradiated area, thereby modifying the irradiated area and transforming it into the boundary layer 3.

[0045] In this case, the length of the focused portion of the laser beam in the direction of propagation of the laser beam (the thickness direction of the element diamond 11) may be greater than or equal to the thickness of the element diamond 11, and in one example, it may be on the order of millimeters. In this case, in step S2, as shown in Figure 7, the focused portion F of the laser beam L (the portion shown by the shaded area in Figure 7A) may be moved in the circumferential direction indicated by arrow A so as to circle the predetermined region R once, in the thickness direction of the element diamond 11. This modifies the irradiated area with the laser beam and transforms it into the boundary layer 3 without moving the focused portion F in the thickness direction, and the predetermined region R partitioned by the boundary layer 3 becomes the optical waveguide region 2.

[0046] In another example, the laser beam used in step S2 has a point-shaped focal point. In this case, in step S2, the laser beam is irradiated onto the element diamond 11 in the thickness direction, and the irradiated area is modified and transformed into the boundary layer 3 by moving the focal point circumferentially and in the thickness direction across the irradiated area. For example, while keeping the position of the focal point F of the laser beam L (circular portion shown by the shaded area in Figure 7B) constant in the circumferential direction surrounding a predetermined area R (circumferential direction shown by arrow A in Figure 7B), the focal point F of the laser beam L is moved in the thickness direction (direction shown by arrow B in Figure 7B) from the surface 11a to the back surface of the element diamond 11. The speed of this movement may be, for example, 0.6 μm / sec. Next, the position of the focusing portion F of the laser beam L is shifted in the circumferential direction A surrounding the predetermined region R. While maintaining the shifted position of the focusing portion F, the focusing portion F of the laser beam L is again moved in the thickness direction (the direction indicated by arrow B in Figure 7B) from the surface 11a to the back surface of the element diamond 11. By repeating this process, the irradiated region is modified with laser light and transformed into the boundary layer 3.

[0047] Alternatively, while keeping the position of the laser beam focusing portion F (the circular portion shown by the shaded area in Figure 7B) constant in the thickness direction of the element diamond 11, the laser beam focusing portion is moved in the circumferential direction indicated by arrow A so as to complete one revolution around a predetermined region R. Next, the position of the laser beam focusing portion F is shifted in the thickness direction of the element diamond 11 (the direction indicated by arrow B in Figure 7B), and while maintaining the shifted position of the focusing portion F, the laser beam focusing portion F is again moved in the circumferential direction indicated by arrow A so as to complete one revolution around the predetermined region R. By repeating this process, the irradiated area is modified with laser light and transformed into the boundary layer 3.

[0048] By performing step S2, the boundary layer 3 is formed in the element diamond 11 as described above, and the predetermined region R demarcated by the boundary layer 3 becomes the optical waveguide region 2. The element diamond 11 after performing step S2 corresponds to the diamond body 1 described above.

[0049] In step S3, the diamond for the device 11 is annealed to form nitrogen-vacancy centers in the diamond for the device 11. In this case, the diamond for the device 11 prepared in step S1 may already contain nitrogen (nitrogen atoms) and vacancies due to nitrogen ion implantation or electron beam irradiation. The annealing treatment in step S3 may be performed with the diamond for the device 11 placed in a nitrogen atmosphere. The annealing treatment may also be performed, for example, at 1000°C for 3 hours. Through such annealing treatment, nitrogen (nitrogen atoms) and vacancies combine in the diamond for the device 11 to form nitrogen-vacancy centers. As a result, the number of nitrogen-vacancy centers in the diamond for the device 11 increases, or the diamond for the device 11 comes to have nitrogen-vacancy centers.

[0050] If the outer surface of the diamond element 11 becomes graphite during the annealing process in step S3, the graphite portion of the outer surface of the diamond element 11 is removed by chemical etching or the like.

[0051] In step S4, a laser beam is irradiated onto the predetermined region R (i.e., the optical waveguide region 2) of the device diamond 11 (i.e., the diamond body 1) containing nitrogen (nitrogen atoms), thereby forming vacancies and creating nitrogen-vacancy centers from these vacancies and nitrogen. The laser beam used in step S4 may be, for example, a femtosecond laser beam. This femtosecond laser beam has an energy of 80 mW and moves its focal point through the interior of the device diamond 11 in the thickness direction at a speed of 0.6 μm / sec. As a result of step S4, for example, the density of nitrogen-vacancy centers in the optical waveguide region 2 becomes higher than the density of nitrogen-vacancy centers in the diamond regions of the diamond body 1 other than the optical waveguide region 2.

[0052] In step S5, a reflective portion 4 is formed on the back surface of the element diamond 11 in the thickness direction. For example, a dielectric multilayer film as the reflective portion 4 is formed on the back surface of the element diamond 11 (diamond body 1) by vacuum deposition.

[0053] By steps S1 to S5, the quantum sensor element 10 is formed. That is, the element diamond 11 and the predetermined region R after steps S1 to S5 are the diamond body 1 and the optical waveguide region 2 of the quantum sensor element 10, respectively. Step S3 and step S4, or both, may be omitted. For example, if an element diamond 11 having a sufficient amount of nitrogen-vacancy centers is prepared in step S1, then step S3 and step S4, or both, may be omitted.

[0054] (Effects of the First Embodiment) The quantum sensor element 10 of the first embodiment provides the following effects (A) to (D).

[0055] (A) The quantum sensor element 10 according to this embodiment has a diamond body 1 as a diamond containing nitrogen-vacancy centers in its crystal structure. The diamond body 1 has an optical waveguide region 2 extending in the thickness direction. The optical waveguide region 2 has an optical emission end 2a at one end in the thickness direction. The boundary layer 3 demarcates the optical waveguide region 2 and reflects the red light generated from the nitrogen-vacancy centers within the optical waveguide region 2, guiding it to the optical emission end 2a. As a result, the red light from each nitrogen-vacancy center within the optical waveguide region 2 is reflected by the outer surface (boundary layer 2) of the optical waveguide region 2, confined and focused within the optical waveguide region 2, and guided to the optical emission end 2a, where it is emitted.

[0056] Therefore, the red emission intensity from the light-emitting edge 2a is significantly higher than (for example) the red emission intensity from other regions of the diamond body 1. Thus, in the quantum sensor element 10 utilizing the nitrogen-vacancy center of the diamond, the detection sensitivity of weak magnetic fields can be increased in the optical waveguide region 2, which is a minute local region (for example, a region smaller than the element of a SQUID).

[0057] (B) The quantum sensor element 10 has a boundary layer 3 that demarcates the optical waveguide region 2. The boundary layer 3 is formed inside the diamond body 1 so as to surround the optical waveguide region 2 when viewed from the thickness direction. The boundary layer 3 has a different refractive index from the diamond of the optical waveguide region 2, and therefore reflects red light from the nitrogen-vacancy center in the optical waveguide region 2. The boundary layer 3 may be formed of graphite, for example. The optical waveguide region 2 can be demarcated by such a boundary layer 3.

[0058] (C) The quantum sensor element 10 has a reflector 4 that covers the other end (other end face) of the optical waveguide region 2 in the thickness direction. The reflector 4 reflects the red light generated from the nitrogen-vacancy center within the optical waveguide region 2. As a result, the red light generated from the nitrogen-vacancy center within the optical waveguide region 2 that has been guided by the boundary layer 3 to the side opposite the optical emission end 2a is reflected by the reflector 4 and guided by the boundary layer 3 to the optical emission end 2a. In this way, the red light emission intensity from the optical emission end 2a can be further increased.

[0059] (D) The density of nitrogen-vacancy centers in optical waveguide region 2 is higher than the density of nitrogen-vacancy centers in regions of the diamond body 1 other than optical waveguide region 2, so the red emission intensity in optical waveguide region 2 is relatively higher.

[0060] [Second Embodiment] A quantum sensor element 10 according to a second embodiment of the present invention will be described with reference to Figures 8A and 8B. Regarding the second embodiment, matters not described below are the same as in the first embodiment.

[0061] Figures 8A and 8B are perspective views showing examples of the configuration of a quantum sensor element 10 according to a second embodiment of the present invention. Figure 8A is a schematic diagram showing the case where the shape of the optical waveguide region 2 is cylindrical with a central axis in the thickness direction, and Figure 8B is a schematic diagram showing the case where the shape of the optical waveguide region 2 is a rectangular prism with a central axis in the thickness direction. The quantum sensor elements 10 in Figures 8A and 8B are the same except that the shape of the optical waveguide region 2 is different from each other.

[0062] Figure 9 is a schematic diagram showing the optical waveguide region 2 as viewed in the thickness direction in Figure 8B. According to the second embodiment, for example, as shown in Figures 8A to 9, the boundary layer 3 is formed inside the diamond body 1 so as to surround the optical waveguide region 2 in two or more layers when viewed from the thickness direction. In this case, the boundary layer 3 may be formed inside the diamond body 1 so as to surround the optical waveguide region 2 in multiple layers when viewed from the thickness direction. Here, multiple layers may mean three or more layers (for example, three, four, or five layers). In the example of Figures 8A and 8B, the boundary layer 3 is formed so as to surround the optical waveguide region 2 in four layers.

[0063] The double or more boundary layers 3 may be two or more boundary layers 3 that are separated from each other at intervals in each direction perpendicular to the central axis (thickness axis) of the optical waveguide region 2, as shown in Figures 8A to 9. In this case, each boundary layer 3 may be the same as the boundary layer 3 described above, referring to Figure 1A, etc. Of the two or more boundary layers 3, the space between each pair of adjacent boundary layers 3 may be occupied by diamond that constitutes a part of the diamond body 1.

[0064] The spacing between adjacent pairs of boundary layers 3 may be on the order of micrometers (e.g., 1 μm, 2 μm, or 3 μm), but is not limited thereto. Furthermore, adjacent pairs of boundary layers 3 may be connected to each other at one or more locations in the circumferential direction surrounding the optical waveguide region 2 without the above-mentioned spacing being maintained. Such boundary layers 3 can be applied not only when the optical waveguide region 2 has a prismatic shape, as shown in Figure 9, but also when the optical waveguide region 2 has other shapes (e.g., cylindrical shape).

[0065] Figure 10 is a schematic diagram showing another configuration example when the optical waveguide region 2 is viewed from the thickness direction of the diamond body 1. Of the two or more boundary layers 3, some of the boundary layers 3 or each boundary layer 3 may have one or more discontinuities 3d in the circumferential direction of the optical waveguide region 2 in a part or all range of the boundary layer 3 in the thickness direction of the diamond body 1, as shown in Figure 10. Also, although not shown, the boundary layer 3 may have one or more discontinuities in the thickness direction in a part or all range of the boundary layer 3 in the circumferential direction of the optical waveguide region 2. Such a boundary layer 3 may be applied not only when the optical waveguide region 2 has a substantially rectangular prism shape as shown in Figure 10, but also when the optical waveguide region 2 has other shapes (e.g., cylindrical shape). The discontinuities 3d may occur, for example, when the intensity and irradiation time of the laser light for forming the boundary layer 3 are partially insufficient.

[0066] Figure 11 is a schematic diagram showing another configuration example when the optical waveguide region 2 is viewed from the thickness direction. As shown in Figure 11, the double or more (e.g., multiple) boundary layers 3 may extend from the optical waveguide region 2 (for example, in a spiral shape as shown in Figure 11, or in a polygonal shape) while rotating around the optical waveguide region 2 when viewed from the thickness direction, and while transitioning from a predetermined position on the outer edge of the optical waveguide region 2 to the outside of the optical waveguide region 2 (towards the side away from the optical waveguide region 2).

[0067] Each portion of the boundary layer 3 is separated by a gap from other portions adjacent to it in the direction away from the optical waveguide region 2 within the boundary layer 3. The space between these adjacent portions may be occupied by diamond, which constitutes part of the diamond body 1. Such a boundary layer 3 can be applied not only when the optical waveguide region 2 has a substantially cylindrical shape, as shown in Figure 11, but also when the optical waveguide region 2 has other shapes (e.g., prismatic shape). The above-mentioned gap between adjacent portions in the boundary layer 3 that surrounds the optical waveguide region 2 in two or more layers may be on the order of micrometers (e.g., 1 μm, 2 μm, or 3 μm), but is not limited thereto.

[0068] In the second embodiment, the dimensions of each part of the optical waveguide region 2 (the dimensions in the thickness direction, the cross-section of the optical waveguide region 2 in a plane perpendicular to the thickness direction, and the dimensions of the optical emission end 2a) may be the same as those described in the first embodiment.

[0069] (Method for manufacturing a quantum sensor element) The method for manufacturing the quantum sensor element 10 according to the second embodiment is the same as the method for manufacturing the quantum sensor element 10 described in the first embodiment, except that it is not described below.

[0070] In the second embodiment, when forming multiple boundary layers 3 as shown in Figure 8A or Figure 8B, step S2 described above is performed for each boundary layer 3 after step S1. That is, step S2 described above is performed for each of the multiple irradiation regions corresponding to each of the multiple boundary layers 3. This forms the multiple boundary layers 3.

[0071] Even when forming a boundary layer 3 as shown in Figure 11, the irradiation area is modified with the laser light and transformed into the boundary layer 3 by moving the focused portion of the laser light across the irradiation area where the boundary layer 3 is formed. For example, if the laser light has an elongated focused portion that is longer than or equal to the thickness of the element diamond 11 in the direction of propagation, the focused portion of the laser light is moved so that, in the thickness direction of the element diamond 11, the entire length of the irradiation area is included in the focused portion of the laser light, and the focused portion moves across the irradiation area, circling a predetermined area, and moving from a predetermined position on the outer edge of the predetermined area to the outside of the predetermined area (away from the predetermined area). This modifies the irradiation area and transforms it into the boundary layer 3 as shown in Figure 11.

[0072] After forming two or more boundary layers 3 in step S2, the process proceeds to step S3, and steps S3 to S5 are performed as described above.

[0073] (Effects of the second embodiment) According to the quantum sensor element 10 of the second embodiment, in addition to the effects (A) to (D) of the first embodiment described above, the following effect (E) can be obtained.

[0074] (E) When viewed from the thickness direction of the diamond body 1, the boundary layer 3 is formed inside the diamond body 1 so as to surround the optical waveguide region 2 in two or more layers. With a single boundary layer 3, even if some of the red light leaks out from the optical waveguide region 2 inside the boundary layer 3 to the outside, this leaked light can be suppressed by the double or more boundary layers 2. In other words, with double or more (e.g., multiple) boundary layers 3, the leakage of red light from the inside to the outside can be suppressed or eliminated.

[0075] [Third Embodiment] A quantum sensor element 10 according to a third embodiment of the present invention will be described with reference to Figures 12 and 13. Regarding the third embodiment, matters not described below are the same as those in the first or second embodiment.

[0076] Figure 12 is a perspective view showing an example of the configuration of a quantum sensor element 10 according to a third embodiment of the present invention. Figure 13 is a plan view of the quantum sensor element 10 shown in Figure 12, as seen from the surface 1a side of the diamond body 1.

[0077] According to the third embodiment, when viewed from the thickness direction, a plurality of optical waveguide regions 2 are arranged. The arrangement of the plurality of optical waveguide regions 2 may be a two-dimensional arrangement along the surface 1a of the diamond body 1, as shown in Figure 12. For example, as shown in Figure 12, the plurality of optical waveguide regions 2 may be arranged in a matrix when viewed from the thickness direction. In this case, in each column, a plurality of (four in Figure 13) optical waveguide regions 2 may be arranged linearly in the arrangement direction of that column (up and down direction in Figure 13), and in each row, a plurality of (six in Figure 13) optical waveguide regions 2 may be arranged linearly in the arrangement direction of that row.

[0078] The arrangement of the multiple optical waveguide regions 2 may be a one-dimensional arrangement (linear or curved) along the surface 1a of the diamond body 1.

[0079] The dimensions of each of the multiple optical waveguide regions 2 formed in the diamond body 1 (the dimensions in the thickness direction, the cross-section of the optical waveguide region 2 in a plane perpendicular to the thickness direction, and the dimensions of the optical emission end 2a) may be the same as those described in the first embodiment.

[0080] In the third embodiment, for each optical waveguide region 2, a boundary layer 3 surrounding the optical waveguide region 2 is formed inside the diamond body 1 when viewed from the thickness direction. Here, the boundary layer 3 for each optical waveguide region 2 may surround the optical waveguide region 2 in two or more layers (for example, multiple layers as shown in Figure 13), as in the second embodiment, or it may surround the optical waveguide region 2 in a single layer, as in the first embodiment.

[0081] When viewed from the thickness direction, the spacing between the boundary layers 2 of adjacent optical waveguide regions 2 (or the outermost edges of the boundary layers 2 in the case of two or more boundary layers) may be on the order of micrometers (for example, 1 μm or more, 2 μm, 3 μm, or 5 μm) or more, and on the order of 10 μm or less (for example, 10 μm or more, 20 μm, 30 μm, or 50 μm or less), but is not limited to this.

[0082] The reflective portion 4 may extend continuously along the back surface 1b of the diamond body 1 across the other ends (other end faces) of each of the numerous optical waveguide regions 2. In this case, the reflective portion 4 may be formed over the entire back surface 1b of the diamond body 1. For example, a dielectric multilayer film as the reflective portion 4 may be formed over the entire back surface 1b of the diamond body 1.

[0083] (Method for manufacturing a quantum sensor element) The method for manufacturing the quantum sensor element 10 according to the third embodiment is the same as the method for manufacturing the quantum sensor element 10 described in the first or second embodiment, except that the points not described below are the same.

[0084] In the second embodiment, in step S1, a diamond for the element 11 is prepared having a surface 11a of a size that can form a plurality of optical waveguide regions 2.

[0085] In step S2, for each of the multiple predetermined regions corresponding to the multiple optical waveguide regions 2 in the element diamond 11, laser light is irradiated onto the irradiation region that demarcates the predetermined region, similar to the first or second embodiment described above, thereby modifying the irradiation region and transforming it into a boundary layer 3.

[0086] After forming multiple (for example, many) boundary layers 3 in step S2, step S3 is performed, and then step S4 is performed for each irradiation region of the element diamond 11. After that, step S5 is performed.

[0087] (Effects of the Third Embodiment) According to the quantum sensor element 10 of the third embodiment, in addition to the effects (A) to (E) of the first or second embodiment described above, the following effect (F) can be obtained.

[0088] (F) Since the optical waveguide regions 2 of minute dimensions are arranged, it is possible to measure weak magnetic fields with a spatial resolution corresponding to the dimensions of the optical waveguide regions 2. That is, since the multiple arranged optical waveguide regions 2 are substantially independent of each other by their respective boundary layers 3, it is possible to detect (e.g., measure) the magnetic field for each optical waveguide region 2 based on the intensity of the red light from the optical emission end 2a of the optical waveguide region 2. In this way, it is possible to detect the magnetic field with a spatial resolution corresponding to the dimensions of the optical waveguide regions 2 (for example, it is possible to measure the distribution of magnetic field strength). This spatial resolution can be made to about 10 μm. Therefore, for example, it is possible to detect weak magnetic fields of a few picotesla (pT) caused by the neural activity of the human brain with a spatial resolution (spatial resolution of about 10 μm) that is comparable to the dimensions of nerve cells in the human brain.

[0089] [Magnetic Field Detection Device] Figure 14A is a schematic diagram showing an example of the configuration of a magnetic field detection device 20 according to an embodiment of the present invention. Figure 14B is a view taken along the line 14B-14B in Figure 14A. The magnetic field detection device 20 comprises a quantum sensor element 10 according to any of the first to third embodiments described above, a magnetic field application device 21, a microwave source 22, an excitation light source 23, and an image generation device 24.

[0090] The quantum sensor element 10 is placed at the location where a weak magnetic field is detected (for example, the measurement location). In this embodiment, as shown in the example in Figure 14A, the quantum sensor element 10 is placed in a position close to (for example, in contact with) the surface 31a of the object under inspection 31. In this state, the back surface 1b of the diamond body 1 is in close proximity to and facing the surface 31a of the object under inspection 31. In the example in Figure 14A, the reflective portion 4 faces (for example, in contact with) the surface 31a of the object under inspection 31. In one example, the object under inspection 31 is a human head, and the location where the weak magnetic field is detected is near the nerve cells of the brain of the human head 31. However, according to the present invention, the magnetic field detection device 20 may be applied to detection locations of other magnetic fields (for example, weak magnetic fields). For example, the object under inspection 31 may be a solar power generation panel, a semiconductor chip, a lithium battery, a lithium-ion battery, etc. For example, defects in such an object under inspection 31 and their locations can be detected by detecting a magnetic field.

[0091] The magnetic field application device 21 applies a magnetic field (e.g., a static magnetic field) in a predetermined direction (in the example of Figure 14A, the left-right direction in this figure) to a target area including the optical waveguide region 2 in the diamond body 1. In the case of the quantum sensor element 10 according to the third embodiment, this target area is a range that includes multiple or many optical waveguide regions 2. The predetermined direction in which the magnetic field is applied is the electron spin state of the nitrogen-vacancy center (magnetic quantum number m Ｓ This is the direction in which the magnetic field is applied that splits the ±1) energy level into two levels by the Zeeman effect. The magnetic field application device 21 may be composed of permanent magnets 21a, for example, as shown in Figure 14A, or it may be composed of electromagnets, but is not limited to this. In the example of Figure 14A, a pair of permanent magnets 21a are arranged so as to sandwich the diamond body 1 in a direction perpendicular to the thickness direction of the diamond body 1 (the left-right direction in this figure).

[0092] In this way, the magnetic field applied by the magnetic field application device 21 determines the electron spin state (magnetic quantum number m) of the numerous nitrogen-vacancy centers in the target range of the quantum sensor element 10. Ｓ The state (±1) is split into two levels by the Zeeman effect (see Figure 3).

[0093] The microwave source 22 controls the nitrogen-vacancy center with a magnetic quantum number m Ｓ Electron spin state = 0 and magnetic quantum number m Ｓ = ±1 (that is, m Ｓ = +1 or m ＳThe microwave source 22 is configured to irradiate the diamond body 1 with microwaves at a resonant frequency that causes a transition between the electron spin state of -1. For example, the microwave source 22 may be capable of irradiating microwaves of a single frequency which is the resonant frequency, or it may be capable of irradiating microwaves in a frequency band that includes the resonant frequency. In the former case, the microwave source 22 may be configured so that the single frequency is variable. Also, when a magnetic field is applied to the quantum sensor element 10 by the magnetic field application device 21 as described above, the microwave source 22 may be configured to irradiate the diamond body 1 with microwaves of two resonant frequencies. For example, the microwave source 22 may be capable of irradiating microwaves of a single frequency which is one of the two resonant frequencies, or it may be capable of irradiating microwaves in a frequency band that includes the two resonant frequencies. In the former case, the microwave source 22 may be configured so that the single frequency is variable (for example, adjustable to either of the two resonant frequencies). The two resonant frequencies are determined by the magnetic quantum number m Ｓ Electron spin state = 0 and magnetic quantum number m Ｓ The resonance frequency that causes the nitrogen-vacancy center to transition between the electron spin state of +1 and the magnetic quantum number m Ｓ Electron spin state = 0 and magnetic quantum number m Ｓ This is the resonance frequency that causes the nitrogen-vacancy center to transition between the electron spin state of -1 and the current state.

[0094] The microwave source 22 may have a plurality of antennas 22a to 22e, for example, as shown in Figure 14B. As shown in Figure 14B, when viewed from the thickness direction of the diamond body 1, each of the plurality of antennas 22a to 22e may be formed by a conductor (for example, concentric circles) surrounding the target area. When an electric current is passed through each of these conductors, microwaves are radiated from each of the antennas 22a to 22e as described above.

[0095] Multiple antennas 22a to 22e radiate microwaves in different narrow frequency bands onto the diamond body 1, for example. These frequency bands include the aforementioned resonance frequencies (or the two resonance frequencies if the magnetic field application device 21 is used). With such multiple antennas 22a to 22e, microwaves in a wide frequency band (for example, a continuous frequency band) can be radiated onto the diamond body 1. Note that the magnetic field application device 21 is not required.

[0096] The microwave source 22 is not limited to the above-described configuration having multiple antennas 22a to 22e (for example, the microwave source 22 may have only one of the multiple antennas 22a to 22e described above). In this case, the microwave source 22 may be configured to change the wavelength of the microwaves irradiated onto the diamond body 1. For example, the microwave source 22 may be provided with an operating unit for changing the wavelength of the microwaves to be irradiated (e.g., a single frequency or frequency band), and the wavelength of the microwaves irradiated onto the diamond body 1 (a single frequency or frequency band) may be changed by operating this operating unit.

[0097] The excitation light source 23 irradiates the target area of ​​the optical waveguide region 2 on the diamond body 1 (for example, its surface 1a) with excitation green light having a wavelength of approximately 495 to 570 nm (for example, 532 nm). The excitation light source 23 may be a laser light source, and the excitation green light may be laser light. In the case of the quantum sensor element 10 of the third embodiment, the excitation light source 23 irradiates the diamond body 1 (for example, its surface 1a) with green light such that a plurality (for example, many) of adjacent optical waveguide regions 2 are included in the irradiation range of the green light (for example, green laser light).

[0098] The image generation device 24 generates an image of the portion of the surface 1a of the diamond body 1 that is irradiated with the aforementioned green light. The image generation device 24 generates the above image by receiving red light from the surface 1a of the diamond body 1 via an optical system (for example, an optical system including a microscope or optical member 25, not shown). The image generation device 24 may be, for example, a CCD camera. The image generation device 24 generates an image of a range spanning multiple optical waveguide regions 2 on the surface 1a of the diamond body 1. The magnetic field detection device 20 may have a display 28 that displays the image generated by the image generation device 24. The optical member 25 may be a half mirror or a dichroic mirror that transmits either red fluorescence or excitation green light and reflects the other. The excitation light source 23 irradiates the optical waveguide region 2 of the target range on the diamond body 1 (for example, its surface 1a) with excitation green light via the optical member 25.

[0099] (Effects of the magnetic field detection device of the embodiment) Using a quantum sensor element 10 in which multiple or numerous optical waveguide regions 2 are arranged in an array or the like, a magnetic field (e.g., a weak magnetic field of several picotesla) can be detected at each of these optical waveguide regions 2 at once with high spatial resolution (e.g., a spatial resolution of about 10 μm) using an image generation device 24. Therefore, a weak magnetic field can be detected with high spatial resolution and in a short time at the location of each optical waveguide region 2 over a relatively wide area in which the optical waveguide regions 2 are arranged.

[0100] Furthermore, the diamond body 1, which is provided with multiple or numerous optical waveguide regions 2, can be formed to a relatively large size for easier support. Therefore, the diamond body 1 can be stably positioned by supporting it with appropriate means so that multiple or numerous optical waveguide regions 2 are located close to the surface 1a of the object to be inspected 31. This allows multiple or numerous optical waveguide regions 2 to be stably positioned simultaneously near the surface 1a of the object to be inspected 31.

[0101] This point is advantageous when detecting magnetic fields generated from brain nerve cells, as follows: The weak magnetic field generated from the axons of human nerve cells decreases in strength inversely proportional to the square of the distance from the point of origin. Therefore, in order to detect such weak magnetic fields, in addition to very high magnetic field sensitivity, a structure that allows the detection element to be brought close to the head and stable detection operation are required. In this regard, the magnetic field detection device 20 of this embodiment, as described above, allows multiple or numerous optical waveguide regions 2 having very high magnetic field sensitivity to be simultaneously and stably positioned close to the surface 31a of the human head 31, thereby achieving not only very high magnetic field sensitivity but also a stable structure and detection operation.

[0102] Furthermore, the magnitude of a weak magnetic field can also be measured as follows: (i) While irradiating the surface 1a of the diamond body 1 with green light using the excitation light source 23, the surface 1a of the diamond body 1 is irradiated with microwaves of a single frequency (single wavelength) using the microwave source 22, and the surface 1a of the diamond body 1 is imaged by the image generation device 24 to generate an image, while the frequency of the microwaves is changed. At this time, the magnetic field described above may be applied by the magnetic field application device 21. (ii) Based on the image generated in (i) above, the microwave frequency at which the intensity of red fluorescence is lowest is identified as the resonance frequency. (iii) By performing (i) and (ii) above in advance when there is no weak magnetic field of the object to be measured, the resonance frequency identified in (ii) above is set as the reference resonance frequency. (iv) By performing (i) and (ii) above in the presence of a weak magnetic field of the object to be measured (i.e., at the measurement location of the weak magnetic field), the resonance frequency identified in (ii) above is set as the measured resonance frequency. (v) The difference between this measured resonance frequency and the reference resonance frequency is determined as the shift amount. (vi) The magnitude of the weak magnetic field is determined from the shift amount determined in (v) above. That is, since the shift amount and the magnitude of the weak magnetic field are proportional, this proportional relationship is determined in advance by experimentation, etc., and the magnitude of the weak magnetic field is determined based on this proportional relationship and the shift amount determined in (v) above. Note that the resonance frequency in (ii) above is m Ｓ = 0 and m Ｓ The resonance frequency may be one that transitions the nitrogen-vacancy center between = +1 and m Ｓ = 0 and mＳ This could also be a resonance frequency that transitions the nitrogen-vacancy center between -1 and -1.

[0103] Furthermore, if two resonance frequencies exist due to the Zeeman effect caused by the magnetic field generated by the magnetic field application device 21, the two resonance frequencies may be identified in (ii) above. In this case, instead of (iii) to (vi) above, the following (vii) to (x) may be performed. (vii) Beforehand, perform (i) and (ii) above in a state where there is no weak magnetic field of the object to be measured, and determine the difference between the two resonance frequencies identified in (ii) above as the reference frequency difference. (viiii) Perform (i) and (ii) above in a state where there is a weak magnetic field of the object to be measured (i.e., at the measurement point of the weak magnetic field), and determine the difference between the two resonance frequencies identified in (ii) above as the measured frequency difference. (ix) Determine the difference between this measured frequency difference and the reference frequency difference as the frequency difference change. (x) Determine the magnitude of the weak magnetic field from the frequency difference change obtained in (ix) above. In other words, the relationship between the change in frequency difference and the magnitude of the weak magnetic field is determined in advance through experiments or other means, and the magnitude of the weak magnetic field is determined based on this relationship and the change in frequency difference obtained in (ix) above.

[0104] [Head Observation Device] (Configuration Example 1) Configuration Example 1 of the head observation device 30 having the magnetic field detection device 20 described above will be explained below. Figure 15 is a schematic diagram showing Configuration Example 1 of the head observation device 30. The head observation device 30 is a device for observing changes in the amount of at least one of oxyhemoglobin and deoxyhemoglobin in the blood in a local area of ​​the brain in the head of a human or animal (for example, a change in the ratio of the amounts of oxyhemoglobin and deoxyhemoglobin). The head observation device 30 comprises at least one magnetic field detection device 20, a wearable body 32, and a static magnetic field application device 33. In Figure 15, a cross-section of the wearable body 32 is shown. Note that the wearable body 32 may be omitted, as will be described later.

[0105] The wearer 32 can be attached to the head of a human or animal (hereinafter simply referred to as the head). In the example of Figure 15, the head is a human head 31 outlined by a dashed line. The wearer 32 can be attached to the head from the outside so as to cover the cerebral cortex inside the head. Here, "covering the cerebral cortex" may mean partially covering the cerebral cortex (for example, a predetermined area of ​​the cerebral cortex) or covering the entire cerebral cortex. Also, "attaching" may mean placing the wearer 32 over the head as in Figure 15, or it may mean wrapping the wearer 32 around the head (for example, using a band-like or string-like member provided on the wearer 32). The wearable body 32, which can be placed over the head, may be helmet-shaped or hat-shaped, or may include a part of a helmet-shaped or hat-shaped body. In these cases, the wearable body 32 may be made of the same material as the helmet or hat (e.g., plastic or cloth), or it may be made of an elastic material (e.g., an elastic material such as rubber) so that it deforms to conform to the shape of the head when worn and fits the head.

[0106] As shown in the example in Figure 15, the head observation device 30 may have multiple (e.g., many) magnetic field detection devices 20. Each magnetic field detection device 20 may include the configuration described above (the configuration described above based on Figure 14A). However, each magnetic field detection device 20 does not have to have the magnetic field application device 21 described above, as in the case described above. The number of magnetic field detection devices 20 constituting the head observation device 30 may be just one.

[0107] The quantum sensor elements 10 (diamond body 1, or diamond body 1 and reflector 4) of each magnetic field detection device 20 are attached to the mounting body 32. For example, although not shown in the figures, the outer edge of the diamond body 1 of the quantum sensor element 10 may be attached to the inner surface 32a of the mounting body 32 directly or via other members using adhesive or the like.

[0108] Furthermore, for each magnetic field detection device 20, as shown in the example in Figure 15, a microwave source 22 and a magnetic field application device 21 may be attached to the mounting body 32 together with the quantum sensor element 10. For example, although not shown, the outer edge of the diamond body 1 of the quantum sensor element 10 may be attached to the inner surface 32a of the mounting body 32 via the microwave source 22 and the magnetic field application device 21 using adhesive or the like. Power for transmitting microwaves may be supplied to the microwave source 22 through wiring (not shown). This wiring may be connected to the microwave source 22, for example, through a wiring through-hole (not shown) provided in the mounting body 32.

[0109] In the example shown in Figure 15, each of the multiple magnetic field detection devices 20 has a microwave source 22, but the head observation device 30 may have one microwave source 22 for each of the multiple magnetic field detection devices 20. In this case, the microwave source 22 may irradiate each of the diamond bodies 1 of the multiple quantum sensor elements 10 with microwaves at a resonant frequency. The microwaves at this resonant frequency will cause the nitrogen-vacancy center of the diamond body 1 to reach a magnetic quantum number m Ｓ The state of = 0 and the magnetic quantum number m Ｓ = +1 or m Ｓ Transition between the state = -1 and the current state.

[0110] The static magnetic field application device 33 applies a static magnetic field to the head. The static magnetic field application device 33 may be an electromagnet or a permanent magnet.

[0111] Furthermore, the magnetic field detection device 20 may also include an optical guide section 27 in addition to the above-described configuration. The optical guide section 27 may be, for example, an optical fiber. Green light from the excitation light source 23 enters the rear end surface (not shown) of the optical guide section 27 via the optical member 25 (see Figure 14A), propagates through the optical guide section 27, and is irradiated from the front end surface 27a of the optical guide section 27 onto the surface 1a of the diamond body 1 of the quantum sensor element 10. Red light from the surface 1a of the diamond body 1 enters the front end surface 27a of the optical guide section 27, propagates through the optical guide section 27, and enters the optical member 25 from the rear end surface of the optical guide section 27.

[0112] The tip of such an optical guide portion 27 may be attached to the mounting body 32. The tip of the optical guide portion 27 may be positioned, for example, in a through hole 32b provided in the mounting body 32. Alternatively, the tip of the optical guide portion 27 may be attached to the mounting body 32 such that its tip surface 27a is optically connected to the through hole 32b. In this case, green light from the tip surface 27a of the optical guide portion 27 enters the surface 1a of the diamond body 1 through the through hole 32b, and red light from the diamond body 1 enters the tip surface 27a of the optical guide portion 27 through the through hole 32b.

[0113] The mounting body 32 is common to multiple magnetic field detection devices 20. Therefore, multiple through holes 32b corresponding to the optical guide portion 27 of each of the multiple magnetic field detection devices 20 are formed in the mounting body 32 at different positions.

[0114] Such a head observation device 30 can observe human brain activity in the same way as fMRI (functional magnetic resonance imaging). That is, the head observation device 30 can perform observations as follows: (a1) to (a4).

[0115] (a1) For example, as shown in Figure 15, the wearable body 32 to which the quantum sensor element 10 is attached is attached to the head of the person or animal to be tested. In addition, the head and the static magnetic field application device 33 are moved to adjust their relative positions so that the static magnetic field application device 33 can apply a static magnetic field to the head (the region to which the quantum sensor element 10 is facing). The static magnetic field application device 33 may be attached to a suitable structure.

[0116] (a2) In the state described in (a1), a static magnetic field is applied to the head by the static magnetic field application device 33, and green light is shone onto the diamond body 1 of the quantum sensor element 10 from the excitation light source 23 (see Figure 14A). Due to this static magnetic field, oxyhemoglobin in the blood flowing through the head (e.g., the cerebral cortex) is diamagnetic and therefore points in the opposite direction to the static magnetic field. In addition, the irradiation with green light causes red fluorescence to be emitted from the surface 1a of each diamond body 1, and an image of this is generated by the image generation device 24 and displayed on the display 28.

[0117] (a3) In the state described in (a2) above, by irradiating each diamond body 1 with microwaves of the resonant frequency using the microwave source 22, the nitrogen-vacancy center of each diamond body 1 is brought to a magnetic quantum number m Ｓ The state of = 0 and the magnetic quantum number m Ｓ = +1 or m Ｓ The state is transitioned between -1 and the following state. This weakens the red fluorescence from the surface 1a of each diamond body 1. This can be determined from the image displayed on the display 28. The frequency of the microwaves irradiated onto each diamond body 1 by the microwave source 22 does not need to be changed from the frequency in (a3) ​​in the following (a4) and (a5).

[0118] (a4) In the state described in (a3) ​​above, when brain activity occurs in the head, oxygen is consumed in that area, increasing the amount of deoxygenated hemoglobin. Since deoxygenated hemoglobin is paramagnetic, it aligns in the same direction as the static magnetic field. Due to the resulting change in the magnetic field (fluctuation in the magnetic field), the red fluorescence from the surface of the corresponding diamond body 1 becomes stronger than in the state described in (a3) ​​above. This change in the magnetic field changes the resonance frequency, disrupting the resonance of the nitrogen-vacancy center, and the magnetic quantum number m Ｓ This is because there are more nitrogen-vacancy centers with a value of 0. The way in which the red fluorescence intensifies in this way (its location, the change in that location, and the intensity of the red fluorescence) can be determined from the image displayed on the display 28.

[0119] As shown in (a4) above, the location where the red fluorescence intensifies can be identified as the location of brain activity response based on the image displayed on the display 28. For example, in the state shown in (a3) ​​above, the subject person or animal is stimulated, and the location where the red fluorescence intensifies can be identified based on the image. While it is also possible to observe the location of brain activity response with fMRI, the head observation device 30 according to this configuration example 1 can observe the location of brain activity response (the location where the red light intensifies) (for example, in real time) with higher spatial resolution (about 10 μm, for example, a spatial resolution of 5 to 33 μm) and temporal resolution than fMRI. Thus, the head observation device 30 can identify the location where deoxygenated hemoglobin increases as the location of brain activity response with a spatial resolution of about 10 μm and high temporal resolution.

[0120] Such a head observation device 30 can also be used in the following ways: Based on observations from an fMRI device, a region within the head that you want to observe with higher resolution or temporal resolution is specified. Brain activity is observed in the specified region as described in the processes (a1) to (a4) above.

[0121] In addition, instead of (a4) above, the following observation (a5) is also possible.

[0122] (a5) In the state described in (a3) ​​above, if a cerebral hemorrhage occurs in the head, a large amount of oxyhemoglobin flows to the site of the hemorrhage, and the area where this large amount of oxyhemoglobin is present expands. As a result, a change in the magnetic field due to the large amount of oxyhemoglobin occurs at the site of the hemorrhage and in the area, and, as in the case of (a4) above, the red fluorescence from the diamond body 1 or the area corresponding to the site of the hemorrhage and in the area becomes stronger. Therefore, it becomes possible to identify the location and area of ​​the cerebral hemorrhage based on the image displayed on the display 28.

[0123] In the example configuration 1, the attachment 32 may be omitted. In this case, in the above process (a1), the quantum sensor element 10 of each magnetic field detection device 20 may be attached to the head using appropriate means such as adhesive tape or a band. In this case, the microwave source 22 or the magnetic field application device 21 may be coupled to the quantum sensor element 10, or it may be placed separately in an appropriate position.

[0124] (Configuration Example 2) A head observation device 30 comprising the magnetic field detection device 20 and the fMRI device 40 described above will be explained below. Figure 16 is a schematic diagram showing Configuration Example 2 of such a head observation device 30. The head observation device 30 is a device capable of observing changes in at least one of oxyhemoglobin and deoxyhemoglobin in the blood of the head of a human subject. The head observation device 30 is used with the quantum sensor element 10 of the magnetic field detection device 20 attached to the head of a person.

[0125] The fMRI apparatus 40 includes a static magnetic field application device 41, a gradient magnetic field application device 42, a transmitting and receiving device 43, a signal processing device 44, and a display 45. The configuration and functions of the fMRI apparatus 40 may be the same as those of known fMRI apparatuses, except for those not described below.

[0126] The static magnetic field application device 41 applies a static magnetic field to the subject's head. At this time, the subject is lying on the bed 46 of the fMRI device 40, for example.

[0127] The gradient magnetic field application device 42 applies a gradient magnetic field to the head in addition to the static magnetic field provided by the static magnetic field application device 41. A gradient magnetic field refers to a magnetic field whose strength varies depending on the location within the head. The gradient magnetic field provides a magnetic field strength distribution in a predetermined direction relative to the static magnetic field.

[0128] The transmitting / receiving device 43 transmits an electromagnetic signal (high-frequency signal) to a region within the head to which a static magnetic field and a gradient magnetic field are applied by the static magnetic field application device 41 and the gradient magnetic field application device 42, and receives a nuclear magnetic resonance signal generated from the head by the electromagnetic signal. The transmitting / receiving device 43 may have a common coil that transmits the electromagnetic signal and receives the nuclear magnetic resonance signal. That is, the common coil may perform both the transmission of the electromagnetic signal and the reception of the nuclear magnetic resonance signal. Alternatively, the transmitting / receiving device 43 may have a transmitting coil that transmits the electromagnetic signal and a receiving coil that receives the nuclear magnetic resonance signal.

[0129] The signal processing device 44 generates an fMRI image representing the location where a magnetic field change occurred in the head structure, based on the nuclear magnetic resonance signal received by the transmitting / receiving device 43 and an image representing the head structure. Here, the magnetic field change may be a fluctuation in the magnetic field, caused by a change in the ratio of oxygenated hemoglobin to deoxygenated hemoglobin in the blood. Each pixel in the fMRI image has a pixel value that represents the intensity of the nuclear magnetic resonance signal from the location corresponding to that pixel, or a pixel value that represents the change in the intensity of the nuclear magnetic resonance signal at a reference time. The display 45 displays the fMRI image generated by the signal processing device 44.

[0130] The magnetic field detection device 20, when the amount of at least one of oxyhemoglobin and deoxyhemoglobin changes under the static magnetic field applied by the static magnetic field application device 41 in a local region of the head opposite the quantum sensor element 10, generates an image corresponding to the change (hereinafter also simply referred to as a red fluorescence image) using the image generation device 24.

[0131] The configuration of the magnetic field detection device 20 in this configuration example 2 may be the same as the configuration of the magnetic field detection device 20 in the configuration example 1 described above. For example, the magnetic field detection device 20 in this configuration example 2 may have the optical guide unit 27 described above. Also, in this configuration example 2, multiple magnetic field detection devices 20 may be provided, as in the configuration example 1 described above, or there may be only one magnetic field detection device 20.

[0132] The head observation device 30 may further include a head-mounted body 32. This head-mounted body 32 may be the same as the head-mounted body 32 in the above-described configuration example 1, except for the following point: In addition to the quantum sensor element 10, a transmitting / receiving device 43 may also be attached to the head-mounted body 32. The transmitting / receiving device 43 (i.e., one or more of the common coils, or one or more of the transmitting coils and one or more of the receiving coils) may be attached, for example, to the outer surface of the head-mounted body 32. The transmitting / receiving device 43 may be attached to the structure of the fMRI device 40 at a location other than the head-mounted body 32.

[0133] Such a head observation device 30 can perform observations as follows: (b1) to (b4).

[0134] (b1) For example, as shown in Figure 16, a wearable device 32 to which a quantum sensor element 10 (see Figure 15 of Configuration Example 1) is attached is placed on the subject's head, and the subject lies down in a predetermined position on the bed 46 of the fMRI device 40. In Figure 16, the subject is depicted by a dashed line.

[0135] (b2) In the state described in (b1) above, a static magnetic field is applied to the head by the static magnetic field application device 41, and a gradient magnetic field is applied to the head in addition to the static magnetic field by the gradient magnetic field application device 42, while green light is irradiated onto the diamond body 1 from the excitation light source 23 (see Figure 14A). Due to this static magnetic field, the oxyhemoglobin in the blood flowing in the head (e.g., the cerebral cortex) is diamagnetic and therefore faces in the opposite direction to the static magnetic field. In addition, due to the irradiation of green light, red fluorescence is emitted from the surface 1a of each diamond body 1, and an image of this is generated by the image generation device 24 and displayed on the display 28.

[0136] (b3) In the state described in (b2) above, the transmitting / receiving device 43 transmits an electromagnetic signal to the head and receives a nuclear magnetic resonance signal generated from the head by the electromagnetic signal. Based on this, the signal processing device 44 generates an fMRI image as described above, using the nuclear magnetic resonance signal and the like. This fMRI image is displayed on the display 45.

[0137] (b4) In the state described in (b3) above, when brain activity occurs in the head, oxygen in that area is consumed, increasing the amount of deoxygenated hemoglobin. Since deoxygenated hemoglobin is paramagnetic, it aligns itself in the same direction as the static magnetic field. This causes a change in the magnetic field, and this change in the magnetic field can be confirmed in the fMRI image displayed on the display 45.

[0138] (b5) On the other hand, in the state described in (b2) above, each magnetic field detection device 20 irradiates the diamond body 1 with microwaves of the resonant frequency using the microwave source 22, thereby irradiating the nitrogen-vacancy center of the diamond body 1 with a magnetic quantum number m Ｓ The state of = 0 and the magnetic quantum number m Ｓ = +1 or m Ｓ The state is transitioned between -1 and the current state. This weakens the red fluorescence from the surface of each diamond body 1. This can be determined from the image (hereinafter also referred to as the red fluorescence image) generated by the image generation device 24 and displayed on the display 28. The frequency of the microwaves irradiated onto each diamond body 1 by the microwave source 22 does not need to be changed from the frequency in (a3) ​​in the following (b6).

[0139] (b6) In the state described in (b5) above, when brain activity occurs in the head, oxygen is consumed in that area, increasing the amount of deoxygenated hemoglobin. Since deoxygenated hemoglobin is paramagnetic, it aligns in the same direction as the static magnetic field. Due to the resulting change in the magnetic field (fluctuation in the magnetic field), the red fluorescence from the surface of the corresponding diamond body 1 becomes stronger than in the state described in (b5) above. This change in the magnetic field changes the resonance frequency, disrupting the resonance of the nitrogen-vacancy center, and the magnetic quantum number m Ｓ This is because there are more nitrogen-vacancy centers with a value of 0. The way in which the red fluorescence intensifies in this way (its location, the change in that location, and the intensity of the red fluorescence) can be determined from the image displayed on the display 28.

[0140] (b6) may also be carried out as follows: A person can view the fMRI image generated in (b4) above and identify, for example, a region of the brain (cerebral cortex) that they wish to observe with higher spatial or temporal resolution. A magnetic field detection device 20 (quantum sensor element 10) corresponding to the identified region can then be used to generate a red fluorescence image representing the change in the magnetic field of that region. This allows the region to be observed with high spatial and temporal resolution.

[0141] Note that the display 28 and the display 45 may be separate, or they may be configured as a single common display.

[0142] (Experimental Example) Using the magnetic field detection device 20 described above, the magnetic field generated by an electric current flowing through a copper wire with a diameter of 25 μm was detected. That is, in Figure 14A, the experiment was conducted by placing a copper wire in place of the object under test 31. For cases where no current was flowing through the copper wire, and for cases where currents of 1 mA, 5 mA, 10 mA, and 20 mA were flowing through the copper wire, a single-frequency microwave was irradiated onto the diamond body 1 from the microwave source 22 while the surface 1a of the diamond body 1 was irradiated with green laser light, and the frequency of the microwave was varied from approximately 2.75 GHz to approximately 2.28 GHz.

[0143] Figure 17 shows the normalized intensity of red light in a specific optical waveguide region 2 adjacent to the copper wire in the image generated by the image generation device 24 for each value of the current flowing through the copper wire. In Figure 17, the horizontal axis represents the microwave frequency, and the vertical axis represents the normalized intensity of red light in the optical waveguide region 2.

[0144] As shown in Figure 17, three minimums occur in the distribution of red light intensity with respect to microwave frequency. Of these minimums, the rightmost and leftmost minimums in Figure 17 correspond to the magnetic quantum number m of the nitrogen-vacancy center. ＳThe values ​​of ±1 correspond to the two spin states split by the Zeeman effect, and the minimum value in the center of Figure 17 corresponds to an isotope of carbon without a nuclear magnetic moment. As can be seen from Figure 17, as the current increases, the frequency at which the red light intensity takes its minimum value increases. Figure 19B, described later, is a graph showing the amount of frequency shift (hereinafter referred to as frequency shift) at which the red light intensity takes its minimum value for each optical waveguide region 2.

[0145] Figure 18 shows the relationship between the current value of the copper wire and the microwave frequency at which the red light intensity is minimized, based on the results in Figure 17. Figure 18 also shows the magnitude of the magnetic field generated at the specific optical waveguide region 2 by the current in the copper wire. As can be seen from Figure 18, the magnitude of the magnetic field and the amount of microwave frequency shift are approximately proportional. Therefore, it can be seen that the magnetic field detection device 20 according to this embodiment can accurately measure the magnitude of a weak magnetic field. In this example, the experiment was conducted with a magnetic field on the order of microtesla (μT), but the magnetic field detection sensitivity of the nitrogen-vacancy center is on the order of picotesla (pT). Therefore, by using the quantum sensor element and magnetic field detection device of the present invention (for example, the quantum sensor element 10 and magnetic field detection device 20 according to the above-described embodiment), it is possible to detect weak magnetic fields on the order of picotesla (pT). For example, a weak magnetic field of several picotesla (pT) generated from the axons of nerve cells due to neural activity in the human brain can be detected by the quantum sensor element 10 and magnetic field detection device 20 according to the above-described embodiment.

[0146] Figure 19A shows an image generated by an image generation device 24 while the surface 1a of the diamond body 1 is irradiated with green laser light and microwaves at the resonant frequency, as described above. The image is taken from the thickness direction of the surface 1a of the diamond body 1. In Figure 19A, the X and Y axes indicate position, and the position ranges in the X and Y axes are indicated by the numbers 1 to 4. The position of each optical waveguide region 2 is specified by the combination of the corresponding numbers in the X and Y coordinates. That is, at each of the numbers 1 to 4 in the X axis direction, multiple optical waveguide regions 2 are arranged in the Y axis direction corresponding to each number in the Y axis direction. In Figure 19A, the copper wire actually on the back side of the image is drawn for reference.

[0147] Figure 19A contains numerous optical waveguide regions 2. Each of these optical waveguide regions 2 is surrounded by multiple boundary layers 3, and its shape, when viewed from the thickness direction of the diamond body 1, is approximately square, with each side measuring about 30 μm.

[0148] Figure 19A shows an image of a copper wire with no current flowing through it, where a green laser beam is broadly irradiated around the area enclosed by the dashed line. In Figure 19A, the area enclosed by the dashed line is the region of the five optical waveguide regions 2 and their multiple boundary layers 3, where the intensity of the red light is higher than in other regions. As shown in Figure 19A, for each optical waveguide region 2, the intensity of the red light is increased in the area inside the outermost boundary layer 3 surrounding that optical waveguide region 2.

[0149] As can be seen from Figure 19A, the intensity of red light can be detected with a spatial resolution of the dimensions of the optical waveguide region 2 (approximately 30 μm).

[0150] Figure 19B is a graph that describes the magnetic field strength for each coordinate system in the optical waveguide region 2 shown in Figure 19A, using the X and Y coordinate axes of Figure 19A and the Z axis representing the frequency shift, in terms of the amount of microwave frequency shift. In other words, Figure 19B shows the frequency shift obtained by switching the current flowing through the copper wire on and off while changing the microwave frequency. The magnitude of the frequency shift indicates the magnitude of the magnetic field, and the sign of the frequency shift value indicates the direction of the magnetic field.

[0151] Furthermore, on the right side of the copper wire in Figure 19A, the frequency shift value becomes negative, as shown in Figure 19B. Therefore, the direction of the magnetic field can be determined by the sign of the frequency shift value.

[0152] Therefore, as described above, by irradiating the surface 1a of the diamond body 1 with green laser light and irradiating the diamond body 1 with microwaves at the resonant frequency, and by continuously imaging the surface 1a of the diamond body 1 with the image generation device 24 to generate an image, it becomes possible to detect the location of the weak magnetic field generation (location of change in red light intensity) and the movement of the weak magnetic field generation location in real time with a spatial resolution of the dimensions of the optical waveguide region 2 (for example, about 30 μm or 20 μm or less). As a result, the location of a weak magnetic field (a magnetic field of about 2 μT in this embodiment) and the change (movement) of the position of said magnetic field can be detected in real time with high spatial resolution (for example, about 30 μm or 20 μm or less) and high temporal resolution commensurate with nerve transmission speed, etc.

[0153] Such effects can also be obtained for detecting magnetic fields generated by the neural activity of the human brain, as follows. The quantum sensor element 10 according to the third embodiment is placed on the surface of a person's head (near the brain), and while irradiating the surface 1a of the diamond body 1 with green laser light and microwaves at the resonant frequency of the diamond body 1, the surface 1a of the diamond body 1 is continuously imaged by the image generation device 24 to generate an image. Based on this image, it becomes possible to detect in real time the location of the generation of a weak magnetic field (location of the intensity change of red light) and the change (movement) of the location of the generation of the weak magnetic field generated by the neural activity of the brain as neural activity of the brain. For example, nerve cells in the brain transmit information by firing (a phenomenon in which the potential inside the nerve cell temporarily increases), and it becomes possible to detect such activity as the generation of a magnetic field and the change in the location of the generation of the magnetic field using the quantum sensor element 10. As a result, it becomes possible to obtain more detailed local information of brain neural activity (nerve location and nerve transmission state).

[0154] Furthermore, in order to measure specific individual brain nerve transmissions, multiple or numerous quantum sensor elements 10 may be placed near the surface of the target scalp, and inverse problem solving methods such as exploratory estimation methods and optimization estimation methods may be performed based on magnetic field detection data obtained using these quantum sensor elements 10.

[0155] The present invention is not limited to the embodiments described above, and various modifications can be made within the scope of the technical idea of ​​the present invention. For example, the quantum sensor element 10, the magnetic field detection device 20, and the method for manufacturing the quantum sensor element 10 according to the embodiments of the present invention do not have to have all of the above-described items, and may have only some of the above-described items.

[0156] Furthermore, to the extent that at least some of the above-mentioned problems can be solved, or to the extent that at least some of the effects described herein can be obtained, one or more of the claims and components described herein can be omitted, or any combination of the claims and components described herein is possible.

[0157] Alternatively, you may adopt one or both of the following modification examples 1 and 2. In this case, the points not mentioned below are the same as those described above.

[0158] (Modification Example 1) In the first to third embodiments described above, the reflector 4 may be omitted. In this case, a portion (for example, half) of the red light from the nitrogen-vacancy center in the optical waveguide region 2 is guided to the optical emission end 2a of the optical waveguide region 2.

[0159] In the case where the reflective section 4 is omitted, the other configurations of the magnetic field detection device 20 may be the same as in the case of Figure 14A described above, or they may be the configuration shown in Figure 20. In the latter case, the matters described below will differ from those in the case of Figure 14A, while the matters not described below will be the same as those in the case of Figure 14A.

[0160] The inspection space Sa, which serves as the magnetic field detection point, may be a space adjacent to the back surface 1b of the diamond body 1 (the area enclosed by the dashed line in Figure 20), as shown in Figure 20, or it may be a space adjacent to the front surface 1a of the diamond body 1, as shown in Figure 20.

[0161] The image generation device 24 is positioned on the back surface 1b side of the diamond body 1. The image generation device 24 generates an image of the back surface 1b of the diamond body 1 (an example of the outer surface of the diamond body 1). This image may be an image of the portion of the back surface 1b that overlaps with the portion of the surface 1a of the diamond body 1 that is irradiated with the aforementioned green light in the thickness direction of the diamond body 1. This image may include multiple or a large number of optical waveguide regions 2.

[0162] The image generation device 14 receives red light from the back surface 1b of the diamond body 1 via an optical system and generates the above image. The optical system may include a filter 26 that does not transmit green light but transmits red light, and a microscope (not shown).

[0163] In addition, in Figure 20, the space under inspection Sa may be replaced with the object under inspection 31 that transmits red light.

[0164] (Modification Example 2) In the first to third embodiments described above, the boundary layer 3 may be formed inside the diamond body 1 so as to completely surround the optical waveguide region 2 when viewed from the thickness direction of the diamond body 1, provided that it can sufficiently confine the red light generated from the nitrogen-vacancy center within the optical waveguide region 2 within the optical waveguide region 2.

[0165] For example, the boundary layer 3 may be formed inside the diamond body 1 so as to surround the optical waveguide region 2 in a single layer if it has a thickness of 3 μm or more, thereby sufficiently confining the red light generated from the nitrogen-vacancy center within the optical waveguide region 2. On the other hand, if the boundary layer 3 has a thickness of less than 3 μm, it may be formed so as to surround the optical waveguide region 2 in a double or more layer when viewed from the thickness direction of the diamond body 1, as described above.

[0166] Figure 21A shows an example configuration when this modified example 2 is adopted for the quantum sensor element 10 in the third embodiment, and is a plan view seen from the surface 1a side of the diamond body 1. As shown in Figure 21A, for each optical waveguide region 2, the boundary layer 3 surrounding that optical waveguide region 2 may be separated from the boundary layer 3 surrounding other optical waveguide regions 2.

[0167] Figure 21B shows another configuration example when this modified example 2 is adopted for the quantum sensor element 10 in the third embodiment, and is a plan view seen from the surface 1a side of the diamond body 1. As shown in Figure 21B, a lattice-shaped boundary layer 3 (lattice drawn with thick solid lines in Figure 21B) is formed when viewed from the thickness direction of the diamond body 1, and multiple (for example, many) optical waveguide regions 2 may be partitioned by the lattice-shaped boundary layer 3. As a result, adjacent optical waveguide regions 2 can be partitioned by a portion of the common boundary layer 3 located between them.

[0168] 1 Diamond body 1a Front surface 1b Back surface 2 Optical waveguide region 2a Optical emission end 3 Boundary layer 3d Discontinuity 4 Reflector (dielectric multilayer film) 10 Quantum sensor element 11 Diamond for element 20 Magnetic field detection device 21 Magnetic field application device 21a Permanent magnet 22 Microwave source 22a-22e Antenna 23 Excitation light source 24 Image generation device 25 Optical components (half mirror, dichroic mirror) 26 Filter 27 Optical guide section 27a Front surface 28 Display 30 Head observation device 31 Head 31a Front surface 32 Wearable body 32a Inner surface 32b Through hole 33 Static magnetic field application device 40 fMRI device 41 Static magnetic field application device 42 Gradient magnetic field application device 43 Transceiver 44 Signal processing device 45 Display 46 Bed Sa Examination space

Claims

1. A quantum sensor element having a diamond body containing nitrogen-vacancy centers in its crystal structure, wherein the diamond body has an optical waveguide region extending in the thickness direction and containing the nitrogen-vacancy centers, and a boundary layer surrounding the optical waveguide region so as to demarcate it when viewed from the thickness direction, the optical waveguide region having an optical emission end at one end in the thickness direction, and the boundary layer reflects red light generated from the nitrogen-vacancy centers within the optical waveguide region and guides it to the optical emission end.

2. The quantum sensor element according to claim 1, wherein the boundary layer is formed of graphite inside the diamond body.

3. A quantum sensor element according to claim 1 or 2, having a reflective portion that covers the other end of the optical waveguide region in the thickness direction, wherein the reflective portion reflects the red light generated from the nitrogen-vacancy center within the optical waveguide region.

4. The quantum sensor element according to any one of claims 1 to 3, wherein, when viewed from the thickness direction, the boundary layer is formed inside the diamond body so as to surround the optical waveguide region in two or more layers.

5. The quantum sensor element according to claim 4, wherein, when viewed from the thickness direction, the boundary layer is formed inside the diamond body so as to enclose the optical waveguide region in multiple layers.

6. The quantum sensor element according to any one of claims 1 to 5, wherein the optical waveguide region is a region that is elongated vertically in the thickness direction.

7. The quantum sensor element according to any one of claims 1 to 6, wherein the density of nitrogen-vacancy centers in the optical waveguide region is higher than the density of nitrogen-vacancy centers in the diamond region other than the optical waveguide region in the diamond body.

8. A quantum sensor element according to any one of claims 1 to 7, wherein, when viewed from the thickness direction, a plurality of optical waveguide regions are arranged, and for each optical waveguide region, when viewed from the thickness direction, the boundary layer surrounding the optical waveguide region is formed.

9. The quantum sensor element according to claim 8, wherein, when viewed from the thickness direction, a grid-like boundary layer is formed, and the plurality of optical waveguide regions are demarcated by the grid-like boundary layer.

10. A method for manufacturing a quantum sensor element according to any one of claims 1 to 8, comprising: (A) preparing a diamond for the element which will be the diamond body; and (B) moving a laser beam focusing portion over an irradiation region that extends circumferentially so as to surround a predetermined region when viewed from the thickness direction of the diamond for the element, thereby modifying the irradiation region into the boundary layer, so that the predetermined region demarcated by the boundary layer becomes the optical waveguide region.

11. The method for manufacturing a quantum sensor element according to claim 10, wherein the laser light has an elongated focusing portion in the direction of propagation of the laser light, and in (B), the laser light is irradiated onto the diamond for the element in the thickness direction, and the focusing portion is moved in the circumferential direction across the irradiated area, thereby modifying the irradiated area into the boundary layer.

12. The method for manufacturing a quantum sensor element according to claim 10, wherein the laser light has a point-shaped focusing portion, and in (B), the laser light is irradiated onto the diamond for the element in the thickness direction, and the focusing portion is moved in the circumferential direction and in the thickness direction across the irradiated area, thereby modifying the irradiated area into the boundary layer.

13. (C) After (B) above, the diamond for the element is subjected to an annealing treatment to bond vacancies and nitrogen in the diamond for the element to form the nitrogen-vacancy center, the method for manufacturing a quantum sensor element according to any one of claims 10 to 12.

14. The method for manufacturing a quantum sensor element according to any one of claims 10 to 13, wherein in (A) above, a diamond for the element having the nitrogen-vacancy center is prepared.

15. The method for manufacturing a quantum sensor element according to claim 10, wherein the diamond for the element contains nitrogen, and (D) after (B), a laser beam is irradiated onto the predetermined region of the diamond for the element to form a vacancy and to form the nitrogen-vacancy center from the vacancy and the nitrogen.

16. A quantum sensor element according to any one of claims 1 to 9, wherein the quantum sensor element is placed at a location for detecting a weak magnetic field, and the magnetic quantum number m Ｓ The state of = 0 and the magnetic quantum number m Ｓ = +1 or m Ｓ A magnetic field detection device comprising: a microwave source capable of irradiating the diamond body with microwaves at a resonant frequency that transitions the nitrogen-vacancy center between the state of -1 and the state of -1; an excitation light source that irradiates the diamond body with excitation green light; and an image generation device that generates an image of the front or back surface of the diamond body.

17. A head observation device comprising the magnetic field detection device according to claim 16, wherein the quantum sensor element is attached to the head of a person or animal and used, further comprising a static magnetic field application device for applying a static magnetic field to the head.

18. The head observation device according to claim 17, comprising a wearable body that can be attached to the head of a human or animal, wherein the quantum sensor element is attached to the wearable body, and the quantum sensor element is attached to the head when the wearable body is attached to the head.

19. A head observation device comprising an fMRI apparatus and a magnetic field detection device according to claim 16, wherein the quantum sensor element is attached to the head of a person, the fMRI apparatus comprising: a static magnetic field application device for applying a static magnetic field to the head; a gradient magnetic field application device for applying a gradient magnetic field to the head in addition to the static magnetic field; a transmitting and receiving device for transmitting an electromagnetic signal to the head and receiving a nuclear magnetic resonance signal generated from the head by the electromagnetic signal; and a signal processing unit for generating an fMRI image representing the location where a magnetic field change occurs in the structure based on the nuclear magnetic resonance signal and an image representing the structure of the head, wherein the magnetic field detection device generates an image corresponding to the change when the amount of at least one of oxyhemoglobin and deoxyhemoglobin changes under the static magnetic field in a region of the head facing the quantum sensor element, the image generation device.

20. The head observation device according to claim 19, further comprising a wearable body that can be attached to the head, wherein the transmitting and receiving device and the quantum sensor element are attached to the wearable body.

Images