Magnetic field intensity estimation method

Abstract

To provide an estimation method that can improve the accuracy of estimating magnetic field intensity and improve workability.SOLUTION: A magnetic field intensity estimation method includes: a position change amount calculation step of using one peak in a spectrum of first fluorescence emitted from a first color center to calculate the amount of change of the position of the peak when a magnetic field is applied to a diamond element and when a magnetic field is not applied to the diamond element; a temperature change amount calculation step of using one peak in a spectrum of second fluorescence emitted from a second color center to calculate the amount of change of the temperature of the peak when the magnetic field is applied to the diamond element and when the magnetic field is not applied to the diamond element; a correction step of correcting the amount of change of the position by using the amount of change of the temperature; and an estimation step of estimating magnetic field intensity when the magnetic field is applied on the basis of the amount of change of the position after the correction.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a method for estimating magnetic field strength, and more particularly to a method for estimating magnetic field strength using a diamond element. [Background technology]

[0002] Diamond elements are devices that utilize the property of nitrogen-vacancy complexes (NV centers) present inside diamonds, which sensitively detect environmental changes and change their quantum state, and are expected to be used as highly sensitive sensors for magnetic fields, electric fields, temperature, strain, etc. In addition to NV centers, diamond elements can also contain silicon-vacancy complexes (SiV centers) and germanium-vacancy complexes (GeV centers), and these complexes containing NV centers are called color centers.

[0003] As a method for estimating magnetic field strength using a diamond element, for example, as described in the following Patent Document 1, a method is known in which two ODMR (optically detected magnetic resonance) peaks are used to estimate the magnetic field strength from the interval between these peaks. More specifically, by utilizing the property (Zeeman effect) in which the resonance frequency of the quantum state changes depending on the magnetic field strength, green excitation light is irradiated onto the NV center while a magnetic field is applied, and microwaves are swept to obtain the spectrum of red fluorescence emitted from the NV center, and the magnetic field strength is estimated based on two ODMR peaks (i.e., resonance frequencies) from the obtained spectrum. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2022-098572 Summary of the Invention [Problem to be solved by the invention]

[0005] The position of the ODMR peak is also affected by temperature. However, the above estimation method does not take into account the effect of temperature on the position change, so it is difficult to say that the accuracy of estimating the magnetic field strength is good. In addition, with the above estimation method, when the strength of the magnetic field to be estimated is large, the distance between the two ODMR peaks becomes large and the microwave sweep range becomes wide, so it takes time to acquire the spectrum, and there is still room for improvement in workability.

[0006] The present invention has been made to solve such technical problems, and has an object to provide an estimation method that can improve the estimation accuracy of magnetic field strength and improve operability. [Means for solving the problem]

[0007] The magnetic field strength estimation method of the present invention is a method for estimating magnetic field strength, which involves irradiating an excitation light onto a diamond element having at least a first color center and a second color center different from the first color center, sweeping a microwave, acquiring a spectrum of fluorescence emitted from the diamond element, and estimating magnetic field strength based on the acquired spectrum, and is characterized in including a position change amount calculation step of calculating a position change amount of the peak when a magnetic field is applied to the diamond element and when a magnetic field is not applied, using one peak of the spectrum of the first fluorescence emitted from the first color center, a temperature change amount calculation step of calculating a temperature change amount of the peak when a magnetic field is applied to the diamond element and when a magnetic field is not applied, using one peak of the spectrum of the second fluorescence emitted from the second color center, a correction step of correcting the position change amount using the temperature change amount, and an estimation step of estimating the magnetic field strength when a magnetic field is applied based on the position change amount after correction.

[0008] In the method for estimating magnetic field strength according to the present invention, one peak in the spectrum of the first fluorescence emitted from the first color center is used to calculate the amount of change in position of the peak, and one peak in the spectrum of the second fluorescence emitted from the second color center is used to calculate the amount of change in temperature of the peak. Then, the amount of change in position is corrected using the calculated amount of change in temperature, and the magnetic field strength is estimated based on the amount of change in position after the correction. In this way, the influence of temperature can be eliminated, and the estimation accuracy of the magnetic field strength can be improved compared to the conventional method. In addition, since the magnetic field strength is estimated using one peak in the spectrum of the acquired fluorescence, the sweep range of the microwave is smaller than in the conventional method using two peaks, and the time required to acquire the fluorescent spectrum can be shortened. As a result, the work time required for estimating the magnetic field strength can be shortened, and the workability can be improved.

[0009] In the method for estimating magnetic field strength according to the present invention, it is preferable that the first color center is a nitrogen-vacancy complex, the second color center is a group IV element other than carbon-vacancy complex, and at least the spectrum of the second fluorescence is a photoluminescence spectrum. In this way, it is possible to further improve the accuracy of estimating magnetic field strength by taking advantage of the respective characteristics of the first and second color centers.

[0010] In the method for estimating magnetic field strength according to the present invention, it is preferable that in the position change amount calculation step and the temperature change amount calculation step, the spectra of the first fluorescence and the second fluorescence are obtained within 300 seconds after the excitation light is irradiated onto the diamond element in a state where a magnetic field of 50 μT or less is applied. In this way, the effect of correcting the temperature change amount can be more effectively achieved.

[0011] Furthermore, in the method for estimating magnetic field strength according to the present invention, in the position change amount calculation step and the temperature change amount calculation step, a temperature change is calculated by calculating a lower limit value of the magnetic field strength to be estimated×3.8×10 5It is preferable to acquire the spectra of the first fluorescent light and the second fluorescent light when the temperature is equal to or higher than the above range, thereby making it possible to more effectively correct the amount of temperature change. Effect of the Invention

[0012] According to the present invention, it is possible to improve the accuracy of estimating the magnetic field strength and to improve the workability. [Brief description of the drawings]

[0013] [Figure 1] FIG. 2 is a schematic diagram showing the configuration of a magnetic field intensity estimation device used to estimate magnetic field intensity. [Diagram 2] FIG. 13 is a diagram for explaining estimation of magnetic field strength using one peak. [Diagram 3] FIG. 2 is a schematic diagram for explaining an estimation method according to the present embodiment. [Figure 4] FIG. 13 is a diagram showing the relationship between irradiation time and wavelength. [Diagram 5] FIG. 11 is a schematic diagram for explaining Example 2 and Example 3. [Figure 6] FIG. 13 shows the PL spectrum of Example 3. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] Hereinafter, an embodiment of the method for estimating magnetic field strength according to the present invention will be described with reference to the drawings. In the following description, unless otherwise specified, the spectrum indicates the intensity of the detected fluorescence, and has the same meaning as the fluorescence intensity. In addition, "emitted fluorescence" has the same meaning as "luminescence". For example, the fluorescence emitted from the NV center and the luminescence of the NV center have the same meaning, and are only different in expression.

[0015] [About the magnetic field strength estimation device] First, the magnetic field intensity estimation device used to estimate the magnetic field intensity will be briefly described with reference to Fig. 1. As shown in Fig. 1, the magnetic field intensity estimation device 1 mainly comprises an excitation light irradiation unit 2, a quantum sensor unit 3 in which diamond elements are arranged, a light detection unit 4, a control unit 5, a microwave source 6, and a voltmeter 7.

[0016] The excitation light irradiation unit 2 is a laser light source that generates excitation light to be irradiated onto the diamond element. The excitation light irradiation unit 2 is connected to the quantum sensor unit 3 by optical components such as optical fibers and lenses, and outputs green (e.g., 532 nm) excitation light to the quantum sensor unit 3. This excitation light irradiation unit 2 is electrically connected to the control unit 5, and operates based on control commands from the control unit 5.

[0017] The quantum sensor unit 3 has a single crystal diamond substrate on which diamond elements are arranged. The diamond element has a first color center, for example an NV center, and a second color center, for example an SiV center, and each emits fluorescence (in other words, emits light) when irradiated with excitation light. That is, inside the diamond element, a first color center formed by nitrogen impurities and vacancies, and a second color center formed by silicon impurities and vacancies are provided. These color centers each emit fluorescence when irradiated with excitation light. To distinguish between them, the fluorescence emitted from the first color center (i.e., the NV center) is referred to as the "first fluorescence" and the fluorescence emitted from the second color center (i.e., the SiV center) is referred to as the "second fluorescence" below.

[0018] The microwave source 6 is controlled by the control unit 5, and irradiates and sweeps a variable frequency microwave to the diamond element. The magnetic field shown in FIG. 1 is applied by a magnetic field source (not shown) to be estimated. That is, the magnetic field source applies an external magnetic field to the diamond element. The magnetic field strength is the strength of the external magnetic field applied by the magnetic field source to the diamond element.

[0019] The light detection unit 4 is connected to the quantum sensor unit 3 by optical components such as optical fibers and lenses, and is configured to have a spectrometer that measures (in other words, acquires) the spectra of the first and second fluorescence emitted from the diamond element. The light detection unit 4 outputs the acquired fluorescence spectrum (e.g., fluorescence intensity-microwave frequency) to the control unit 5.

[0020] The control unit 5 is configured, for example, by a microcomputer that combines a CPU (Central processing unit) that executes calculations, a ROM (Read only memory) as a secondary storage device that records programs for the calculations, and a RAM (Random access memory) as a temporary storage device that saves the calculation progress and temporary control variables, and by executing the stored programs, it controls each component that makes up the magnetic field strength estimation device 1 and performs various calculations related to the estimation of magnetic field strength.

[0021] For example, the control unit 5 is electrically connected to the excitation light irradiation unit 2, microwave source 6, and voltmeter 7, and controls the operation timing, output, operation time, etc. of each of these. The control unit 5 also estimates the magnetic field strength based on the output result from the light detection unit 4. For example, the control unit 5 calculates the amount of position change and the amount of temperature change (described later) based on the fluorescence spectrum acquired by the light detection unit 4.

[0022] [Method of estimating magnetic field strength using one peak] The method for estimating magnetic field strength according to the present embodiment is characterized in that the magnetic field strength is estimated using one peak in the fluorescence spectrum. Hereinafter, the method for estimating magnetic field strength using one peak will be described with reference to FIG.

[0023] Figure 2 is a diagram for explaining the estimation of magnetic field strength using one peak. In Figure 2, the horizontal axis indicates the frequency of the microwave irradiated to the diamond element, and the vertical axis indicates the acquired fluorescence intensity (arbitrary unit). In Figure 2, the solid line indicates the fluorescence spectrum when a magnetic field is applied, and the dashed line indicates the fluorescence spectrum when a magnetic field is not applied.

[0024] As shown in FIG. 2, when a microwave having a frequency of 2.8 to 2.9 GHz is swept, a point where the fluorescence intensity drops occurs due to optically detected magnetic resonance (ODMR), and multiple peaks indicating the point of drop in intensity (the "valley" part in FIG. 2) appear. For example, only one of these peaks (for example, the highest peak) can be picked up and used to examine the change in the spectrum when a magnetic field is applied and when a magnetic field is not applied. That is, when a magnetic field is applied, the spectrum moves compared to when a magnetic field is not applied, so by focusing on the amount of change in the position of the peak (also called the amount of shift or movement), it is possible to estimate the strength of the applied magnetic field by examining the amount of change in the position of the peak due to the application of a magnetic field.

[0025] More specifically, the magnetic field strength can be calculated using the formula ΔB=Δf / γ. In this formula, ΔB is the strength of the applied magnetic field (i.e., the strength of the magnetic field to be estimated), Δf is the amount of change in the position of the peak, and γ is the gyromagnetic ratio of the electron spin (e.g., 28 GHz / T). In the example shown in FIG. 2, the amount of change in the position of the peak Δf between when a magnetic field is applied and when a magnetic field is not applied is about 18 MHz, so the magnetic field strength ΔB=18(MHz) / 28(GHz / T)=0.6 mT. In this way, the magnetic field strength can be estimated using only one peak.

[0026] However, as described above, the amount of change in the position of the peak includes components caused by temperature change as well as components caused by the application of a magnetic field. Therefore, in order to improve the accuracy of estimating the magnetic field strength, it is necessary to eliminate the components caused by temperature change, in other words, to eliminate the effect of temperature on the position change.

[0027] Therefore, as a result of extensive research, the inventors of the present application discovered that the effect of temperature on position change can be eliminated by using the following estimation method, and thus completed the present invention.

[0028] [Estimation method according to this embodiment] The method for estimating magnetic field strength according to this embodiment is a method for irradiating a diamond element having a first color center and a second color center with excitation light and sweeping microwaves, acquiring the spectrum of fluorescence emitted from the diamond element, and estimating magnetic field strength based on the acquired spectrum. This estimation method includes a position change amount calculation step of calculating the position change amount of the peak in the case of magnetic field application to the diamond element and in the case of no magnetic field application using one peak of the spectrum of the first fluorescence emitted from the first color center, a temperature change amount calculation step of calculating the temperature change amount of the peak in the case of magnetic field application to the diamond element and in the case of no magnetic field application using one peak of the spectrum of the second fluorescence emitted from the second color center, a correction step of correcting the position change amount using the calculated temperature change amount, and an estimation step of estimating the magnetic field strength in the case of magnetic field application based on the position change amount after correction.

[0029] First, the position change amount calculation step and the temperature change amount calculation step will be described with reference to Fig. 3. Note that the position change amount calculation step and the temperature change amount calculation step may be performed in parallel, or either step may be performed first.

[0030] First, in a state where no magnetic field is applied to the diamond element, a diamond element having a first color center and a second color center is irradiated with excitation light and microwaves are swept, the fluorescence (first fluorescence and second fluorescence) emitted from the diamond element is detected, and the spectrum of the detected fluorescence is obtained. In this embodiment, the spectrum of the fluorescence obtained is a photoluminescence (PL) spectrum.

[0031] FIG. 3(a) is a diagram showing the spectrum of the acquired fluorescence, where the horizontal axis shows wavelength and the vertical axis shows PL fluorescence intensity (arbitrary units). The spectrum shown in FIG. 3(a) is a superposition of the first fluorescence emitted from the first color center and the second fluorescence emitted from the second color center. As shown in FIG. 3(a), in the spectrum of the superposition of fluorescence, the peak of the first fluorescence (indicated by "NV") and the peak of the second fluorescence (indicated by "SiV") are clearly separated.

[0032] Fig. 3(c) is a diagram showing the acquired OMDR spectrum of the first fluorescence emitted from the NV center, where the horizontal axis shows the swept microwave frequency and the vertical axis shows the intensity of the first fluorescence. Next, for example, the highest peak is picked up as one peak in the spectrum of the first fluorescence, and the frequency at the position of the peak is specified. Note that, although it is assumed here that the microwave is swept, this is not limiting, and a multi-point measurement method (for example, a method of restoring a peak using four points of fluorescence intensity and a Lorentz function, etc.) may also be used.

[0033] Next, in a state where a magnetic field is applied to the diamond element (i.e., when a magnetic field is applied), the diamond element is irradiated with excitation light and microwaves are swept to obtain the spectra of the first fluorescence and the second fluorescence emitted from the diamond element. Next, the highest peak of the OMDR spectrum of the obtained first fluorescence is picked up, and the frequency of the position of the peak is specified.

[0034] Next, for the frequencies in the identified peaks with and without magnetic field application, the magnetic field intensity estimation method using one peak described above is used to calculate the amount of change in peak position Δf.

[0035] Next, the highest peak of the second fluorescence shown in Fig. 3(a) is focused on, and the temperature change amount is calculated using the peak. Fig. 3(b) is a plot diagram showing the relationship between temperature and wavelength for SiV, which is prepared in advance, for example. A linear approximation equation between wavelength and temperature (for example, wavelength = 0.012 x temperature) can be obtained from the data plotted in Fig. 3(b). Then, the temperature T0 corresponding to the wavelength of the highest peak of the second fluorescence shown in Fig. 3(a) can be obtained using the linear approximation equation.

[0036] Next, the temperature T1 corresponding to the highest peak of the second fluorescence is obtained in the same manner using the PL spectrum of the fluorescence obtained with the magnetic field applied. Next, the temperature difference between the case with and without the magnetic field applied is calculated as ΔT=T1-T0. After that, the temperature change is calculated as temperature change=kΔT (k is the temperature coefficient of the NV center (-74.2 kHz / K)).

[0037] In the correction step, the position change is corrected using the calculated temperature change. Specifically, the temperature change calculated in the temperature change calculation step is subtracted from the peak position change Δf calculated in the position change calculation step. In other words, it is calculated as Δf-kΔT (※The high frequency side is positive).

[0038] In the estimation step following the correction step, the magnetic field strength is estimated as ΔB=(Δf-kΔT) / γ.

[0039] In the method for estimating magnetic field strength according to the present embodiment, one peak in the spectrum of the first fluorescence emitted from the first color center is used to calculate the amount of change in position of the peak, and one peak in the spectrum of the second fluorescence emitted from the second color center is used to calculate the amount of change in temperature of the peak. Then, the amount of change in position is corrected using the calculated amount of change in temperature, and the magnetic field strength is estimated based on the amount of change in position after the correction. In this way, the influence of temperature on the change in position can be eliminated, and the accuracy of the estimation of the magnetic field strength can be improved compared to the conventional method. In addition, since the magnetic field strength is estimated using one peak in the spectrum of the acquired first fluorescence, the sweep range of the microwave is smaller than in the conventional method using two peaks, and the time required to acquire the fluorescent spectrum can be shortened. As a result, the work time required for estimating the magnetic field strength can be shortened, and the workability can be improved.

[0040] In this embodiment, the SiV center is used as an example of the second color center. This is because the SiV center has a sharp and stable emission in response to excitation light, and the peak wavelength changes depending on the temperature. By using the SiV center in this way, a sharp fluorescence spectrum can be obtained, and the temperature dependency of the peak wavelength can be used to accurately calculate the temperature change amount. The second color center is not limited to the SiV center, and may be a group IV-vacancy complex other than carbon.

[0041] Furthermore, in the position change amount calculation step and temperature change amount calculation step, it is preferable to obtain the spectra of the first fluorescence and the second fluorescence within 300 seconds after irradiating the diamond element with excitation light while applying a magnetic field of 50 μT or less.

[0042] That is, the inventors of the present application used a single crystal diamond substrate of 5.0 mm long x 2.5 mm wide x 0.5 mm thick as a diamond element, and investigated the temperature change while irradiating the diamond element with a 0.2 mW laser. As a result, as shown in Figure 4, it was found that the temperature tends to increase up to an irradiation time of 300 seconds, and the temperature becomes stable after 300 seconds. Therefore, it was found that when the irradiation time is within 300 seconds, the effect of the laser irradiation on the temperature change (i.e., the wavelength change Δλ of the SiV center) is significant, and correction is required.

[0043] In this study, the maximum wavelength change (Δλ) was 0.23 MHz, so the experimental correction formula ΔT = Δλ / 0.012 gave a temperature change of ΔT = 19°C. The ODMR frequency shift (i.e., the peak position shift) was Δf = (-74.2 kHz / K) × ΔT = -1.4 MHz. The corresponding magnetic field strength was ΔB = Δf / γ = 1.4 (MHz) / 28 (GHz / T) = 50 μT.

[0044] From this result, it is considered that the amount of ODMR frequency shift due to temperature change is equivalent to 50 μT within 300 seconds after laser irradiation. Therefore, by acquiring the first and second fluorescence spectra within 300 seconds after irradiating the diamond element with excitation light while applying a magnetic field of 50 μT or less, the correction effect on the amount of change in peak position due to the amount of temperature change can be more effectively achieved.

[0045] Furthermore, in the position change amount calculation step and the temperature change amount calculation step, the lower limit value (T)×3.8×10 of the magnetic field strength for which the temperature change is to be estimated is set to 1 for the following reasons. 5 When the above is true, it is preferable to acquire spectra of the first and second fluorescent lights.

[0046] That is, as described above, the ODMR frequency shift due to temperature change (i.e., the temperature change) is calculated as kΔT = (-74.2kHz / K) × ΔT, and the ODMR frequency shift due to magnetic field application (i.e., the position change) is calculated as Δf = γΔB. If this temperature change is equal to or greater than the peak position change, at least the above-mentioned correction must be performed. If correction is desired when γΔB≦kΔT, then ΔT≧γΔB / k=ΔB×28(GHz / T) / 74.2(kHz / K)=ΔB×3.8×10 5 Here, ΔB is the lower limit (T) of the magnetic field strength to be estimated. When ΔB=50μT, ΔT=ΔB×3.8×10 5 = 50μT × 3.8 × 10 5 =19℃.

[0047] Therefore, the lower limit of the magnetic field strength for which the temperature change is estimated (T) × 3.8 × 10 5 By acquiring the spectra of the first fluorescent light and the second fluorescent light when the above conditions are met, it is possible to more effectively correct the amount of change in peak position due to the amount of temperature change.

[0048] The inventors of the present application carried out the following examples in order to verify the effects of the estimation method of the present embodiment.

[0049] [Example 1] In Example 1, the estimation method described in the embodiment was used and compared with the conventional method. Specifically, the highest peak of the acquired first fluorescence spectrum was picked up and the frequency corresponding to the peak was identified. The frequency was 2872.0MHz. Next, a magnetic field of 40μT was applied to the diamond element using an electromagnet, and the frequency corresponding to the highest peak in the detected ODMR spectrum was 2873.4MHz. This resulted in a peak position change Δf=2873.4MHz-2872.0MHz=1.4MHz. Then, when the magnetic field strength was estimated as in the conventional method, the result was ΔB=Δf / γ=1.4(MHz) / 28(GHz / T)=50μT. An error of 25% was observed for the magnetic field applied value of 40μT.

[0050] Next, the SiV central peak was picked up from the PL spectra acquired with and without a magnetic field applied, and the temperature change was investigated based on the peak position. As a result, it was found that the peak position shifted 0.02 nm to the lower wavelength side and the temperature dropped by about 2°C (i.e., ΔT = 2°C). From the temperature change of about 2°C, the temperature change amount = kΔT = (-74.2kHz / K) × 2°C = 148kHz was obtained.

[0051] When the peak position change was corrected for the temperature change, the result was Δf-kΔT = 1.4MHz-148kHz = 1252kHz. Then, when the magnetic field strength was estimated using the corrected position change, the result was ΔB = (Δf-kΔT) / γ = 1252(kHz) / 28(GHz / T) = 45μT. An error of 12.5% ​​was observed for the applied magnetic field value of 40μT.

[0052] In addition, the result was that the error could be halved by correcting the amount of change in the peak position with the amount of change in temperature, compared to the conventional method. This shows that the estimation accuracy of the magnetic field strength can be improved by using the estimation method of this embodiment.

[0053] [Example 2] In Example 2, first, as shown in FIG. 5(a), a diamond element was produced that contains a large amount of Si and has a layer in which the SiV center is dominant and a layer in which the NV center is dominant. More specifically, Si was added at a concentration of 1×10 16 cm -3 N ion implantation was performed on the surface 600 nm of diamond containing 19 cm -3These layers were subjected to heat treatment at 600 to 1500°C to form a layer containing many NV centers in the base material, which is a layer dominated by SiV centers. Next, an excitation laser was irradiated onto the diamond element, and the light emitted from the diamond element was collected by a lens, and adjustments were made to obtain light emission from these two layers. The PL spectrum obtained in this way was a superposition of light emission from SiV centers and light emission from NV centers, as shown in Figure 3(a) above.

[0054] Next, using the estimation method described in the embodiment, the temperature change amount was calculated using the peak of the PL spectrum of the fluorescence emitted from the SiV center, and the position change amount was calculated using one ODMR peak of the fluorescence emitted from the NV center. Note that here, two points, the peak position of the SiV center and the peak position of the NV center shown in Figure 3(a), may be used.

[0055] After that, the position change was corrected by the calculated temperature change, and the magnetic field strength was estimated based on the corrected position change. As a result, by correcting the position change by the temperature change, the noise, which was about 7 μT, was reduced to 2.5 μT.

[0056] [Example 3] In Example 3, similar to Example 2, a diamond element was fabricated having a layer containing a large amount of Si and dominated by SiV centers (shown as "Region 2" in Figure 5(b)) and a layer containing a large amount of NV centers (shown as "Region 1" in Figure 5(b)). Next, excitation light was irradiated onto the fabricated diamond element, and the PL spectrum of the fluorescence emitted from the diamond element was obtained. At this time, the focus was changed to obtain the PL spectra from Region 1 and Region 2.

[0057] Specifically, this was achieved by, for example, introducing a pinhole into the optical path and narrowing the depth-wise region where the focus was achieved (confocalization). In this way, the PL spectrum of the SiV center emission from region 2 was obtained, and then the PL spectrum of the NV center emission from region 1 was obtained. Figure 6 shows the obtained PL spectra. In Figure 6, the horizontal axis shows the wavelength, and the vertical axis shows the PL fluorescence intensity (arbitrary units). As shown in Figure 6, the emission from the NV center (shown as "Region 1" in Figure 6) and the emission from the SiV center (shown as "Region 2" in Figure 6) did not overlap, but were independent of each other.

[0058] Next, the estimation method described in the embodiment was used to calculate the temperature change amount using the peak of the PL spectrum emitted from the SiV center, and the position change amount was calculated using one ODMR peak of the fluorescence emitted from the NV center. After that, the position change amount was corrected by the calculated temperature change amount, and the magnetic field strength was estimated based on the corrected position change amount. As a result, the estimation accuracy of the magnetic field strength was improved by using the estimation method of this embodiment.

[0059] Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above-described embodiments, and various design modifications can be made without departing from the spirit of the present invention as described in the claims.

[0060] For example, in the above-mentioned embodiment, the diamond element having the first color center and the second color center is described as an example, but the diamond element only needs to have at least two different color centers, and may have three or more types of color centers.For example, in addition to the NV center and the SiV center, it may also have a GeV center.In this case, the temperature change amount is calculated using the SiV center and the GeV center, respectively, and the error of the temperature change amount is verified based on these calculation results, so that the accuracy of the correction using the temperature change amount can be further improved. [Explanation of symbols]

[0061] 1: magnetic field strength estimation device, 2: excitation light irradiation unit, 3: quantum sensor unit, 4: light detection unit, 5: control unit, 6: microwave source, 7: voltmeter

Claims

1. A method for estimating magnetic field strength, comprising irradiating a diamond element having at least a first color center and a second color center different from the first color center with excitation light and sweeping microwaves, acquiring a spectrum of fluorescence emitted from the diamond element, and estimating magnetic field strength based on the acquired spectrum, a position change amount calculation step of calculating the amount of change in the position of one peak in the spectrum of the first fluorescence emitted from the first color center when a magnetic field is applied to the diamond element and when a magnetic field is not applied; a temperature change calculation step of calculating the temperature change amount of one peak in the spectrum of the second fluorescence emitted from the second color center when a magnetic field is applied to the diamond element and when a magnetic field is not applied to the diamond element; a correction step of correcting the position change amount using the temperature change amount; an estimation step of estimating a magnetic field strength when a magnetic field is applied based on the corrected position change amount; A method for estimating magnetic field strength, comprising:

2. the first color center is a nitrogen-vacancy complex; the second color center is a non-carbon Group IV-vacancy complex; The method for estimating magnetic field strength according to claim 1 , wherein at least the spectrum of the second fluorescence is a photoluminescence spectrum.

3. A method for estimating magnetic field strength as described in claim 1 or 2, wherein in the position change calculation step and the temperature change calculation step, the spectra of the first fluorescence and the second fluorescence are obtained within 300 seconds after the diamond element is irradiated with the excitation light while a magnetic field of 50 μT or less is applied.

4. In the position change amount calculation step and the temperature change amount calculation step, the temperature change is calculated by calculating the lower limit value of the magnetic field strength to be estimated×3.8×10 ５ The method for estimating magnetic field intensity according to claim 1 or 2, further comprising acquiring spectra of the first fluorescence and the second fluorescence when the first fluorescence and the second fluorescence are greater than or equal to the first fluorescence.

Images