Diamond quantum sensor

Abstract

The diamond quantum sensor according to the present invention senses a magnetic field by simultaneously irradiating two kinds of microwaves having different frequencies, and if the frequency difference between the two kinds of microwaves is set as [Delta] f, the [Delta] f is within any one of 0.2 MHz < = [Delta] f < = 3.0 MHz and 3.8 MHz < = [Delta] f < = 5.4 MHz. [Delta] f may be within any one of 0.2 MHz < = [Delta] f < = 0.8 MHz, 1.8 MHz < = [Delta] f < = 2.8 MHz, and 4.0 MHz < = [Delta] f < = 4.8 MHz.

Description

Technical Field

[0001] This invention relates to a diamond quantum sensor. Background Technology

[0002] Japanese Patent No. 6616342 discloses a magnetic field detection device that is made of diamond with nitrogen vacancy (NV) centers, and that the electron spins in the NV centers interact with the magnetic field being measured. The magnetic field detection device of Japanese Patent No. 6616342 irradiates the detection element with microwaves having resonant frequencies of NV centers in four directions. Summary of the Invention

[0003] To improve the magnetic field sensitivity of the detection element, it is necessary to increase the slope of the spectrum at the NV center in one direction. While increasing microwave power is known, issues arise regarding the specifications of the microwave source or its power consumption.

[0004] This invention was made to solve this problem, and its purpose is to provide a diamond quantum sensor that can improve sensitivity.

[0005] One aspect of the present invention involves a diamond quantum sensor that simultaneously irradiates two microwaves of different frequencies to sense a magnetic field. If the frequency difference between the two microwaves is defined as Δf, then Δf is within any one of the ranges of 0.2MHz ≤ Δf ≤ 3.0MHz and 3.8MHz ≤ Δf ≤ 5.4MHz.

[0006] In the diamond quantum sensor, if the frequency difference between the two microwaves is set as Δf, then Δf can be within any of the following ranges: 0.2MHz≤Δf≤0.8MHz, 1.8MHz≤Δf≤2.8MHz, and 4.0MHz≤Δf≤4.8MHz.

[0007] This invention provides a diamond quantum sensor with improved sensitivity. Attached Figure Description

[0008] Hereinafter, with reference to the accompanying drawings, the features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described, in which the same reference numerals denote the same elements, and wherein:

[0009] Figure 1 This is a block diagram illustrating the diamond quantum sensor involved in the comparative example.

[0010] Figure 2A This is a graph illustrating the photodetector magnetic resonance spectrum detected by the diamond quantum sensor involved in the comparative example. The horizontal axis represents the frequency of the microwave, and the vertical axis represents the luminescence intensity derived from the signal intensity.

[0011] Figure 2B This is a graph illustrating the relationship between microwave power and slope improvement ratio in the diamond quantum sensor involved in the comparative example. The horizontal axis represents microwave power, and the vertical axis represents slope improvement ratio.

[0012] Figure 3 This is a block diagram illustrating the diamond quantum sensor according to Embodiment 1.

[0013] Figure 4 This is a graph illustrating the microwave power and microwave frequency difference used for measurement in the diamond quantum sensor according to Embodiment 1, as well as the slope and slope improvement ratio of the measured spectrum.

[0014] Figure 5A This is a bar chart illustrating the slope improvement ratios of Comparative Examples 1, 2, and 3. The horizontal axis represents Comparative Examples 1, 2, and 3, and the vertical axis represents the slope of the spectra in Comparative Examples 2 and 3 when the slope of the spectrum in Comparative Example 1 is set to 1, which is taken as the slope improvement ratio.

[0015] Figure 5B This is a bar chart illustrating the slope improvement ratios of Comparative Example 1, Comparative Example 2, Example 2, Example 11, and Example 21. The horizontal axis represents Comparative Example 1, Comparative Example 2, Example 2, Example 11, and Example 21, and the vertical axis represents the slope of the spectra in Comparative Example 2, Example 2, Example 11, and Example 21 when the slope of the spectrum in Comparative Example 1 is set to 1, as the slope improvement ratio.

[0016] Figure 6 This is a graph illustrating the slope improvement effect when the diamond quantum sensor according to Embodiment 1 is irradiated with two microwaves of different frequencies. The horizontal axis represents the frequency difference Δf between the two microwaves, and the vertical axis represents the slope improvement ratio. Detailed Implementation

[0017] Hereinafter, the specific structure of this embodiment will be described with reference to the accompanying drawings. The following description illustrates preferred embodiments of the present invention, but the scope of the present invention is not limited to these embodiments. Furthermore, not all structures described in this embodiment are necessarily necessary as means of solving the problem. For clarity, the following descriptions and drawings have been appropriately omitted and simplified. In the drawings, the same components are labeled with the same symbols, and repeated descriptions have been omitted as necessary.

[0018] <Summary of Implementation Methods>

[0019] The diamond quantum sensor of this embodiment improves magnetic field sensitivity by increasing the slope of the optically detected magnetic resonance spectrum. Specifically, the diamond quantum sensor of this embodiment senses the magnetic field by simultaneously irradiating two microwaves of different frequencies to visualize the optically detected magnetic resonance phenomenon. Furthermore, by limiting the frequency difference between them within a specific range, the slope of the spectrum is increased. Thus, by using two microwaves, the diamond quantum sensor of this embodiment can achieve a greater spectral slope with the same power than when using only one microwave, thereby improving the sensitivity of magnetic field detection.

[0020] Before describing the diamond quantum sensor of this embodiment in detail, a comparative example using microwaves will be described. Then, the problems discovered by the inventors of the diamond quantum sensor of the comparative example will be described. Then, the diamond quantum sensor of this embodiment will be described in comparison with the comparative example. Thus, the diamond quantum sensor of this embodiment will be more clearly defined.

[0021] <Comparative Example>

[0022] Figure 1 This is a block diagram illustrating the diamond quantum sensor 101 involved in the comparative example. For example... Figure 1 As shown, the diamond quantum sensor 101 includes an excitation light optical system 10, a microwave generator 21, a diamond 30, a photodetector 40, a voltmeter 50, and a processing unit 60.

[0023] The excitation optical system 10 illuminates the diamond 30 with excitation light 11. The excitation optical system 10 may include a light source for generating the excitation light 11. The excitation optical system 10 may include optical components for focusing the excitation light 11 onto the diamond 30.

[0024] Microwave generator 21 generates microwaves 23. Microwave generator 21 irradiates the diamond 30 with the generated microwaves 23. Microwave generator 21 generates microwaves 23 with frequency f1. Microwave generator 21 varies the frequency f1 within a specified range.

[0025] The diamond 30 has an NV center. For example, the diamond 30 may have an NV center as described in Japanese Patent No. 6,616,342. The diamond 30, when irradiated with excitation light 11, emits a predetermined light.

[0026] The photodetector 40 detects the intensity of the light emitted from the diamond 30. The photodetector 40 outputs the detected light intensity to a voltmeter.

[0027] The voltmeter 50 converts the light intensity into a signal strength such as a voltage value. The voltmeter 50 outputs the converted signal strength to the processing unit 60.

[0028] The processing unit 60 derives the photodetector magnetic resonance spectrum based on the relationship between frequency f1 and signal intensity. The processing unit 60 is, for example, an information processing device such as a personal computer (PC).

[0029] Figure 2A This is a graph illustrating the photodetector magnetic resonance spectrum detected by the diamond quantum sensor 101 involved in the comparative example. The horizontal axis represents the frequency f1 of the microwave 23, and the vertical axis represents the luminescence intensity derived from the signal intensity. The processing unit 60 calculates the magnetic field sensitivity based on the photodetector magnetic resonance spectrum. Specifically, the magnetic field sensitivity is determined by the slope of the photodetector magnetic resonance spectrum and the stability (time variation) of the signal intensity. The slope of the photodetector magnetic resonance spectrum is obtained, for example, by differentiating the photodetector magnetic resonance spectrum with respect to the frequency. The processing unit 60 can use the maximum value of the slope as the slope of the photodetector magnetic resonance spectrum. The stability of the signal intensity is determined by the deviation range of the time variation of the signal intensity at a fixed frequency. The magnetic field sensitivity can be derived from the following equation (1).

[0030] Magnetic field sensitivity = signal intensity stability / spectral slope (1)

[0031] Here, the magnetic field sensitivity is the lower limit of the detectable magnetic field strength, and therefore preferably small. Therefore, it is preferable to increase the slope of the spectrum. It has been found that increasing the power of the microwave 23 irradiated for detecting magnetic resonance phenomena via optical imaging increases the slope of the spectrum.

[0032] Figure 2B This is a graph illustrating the relationship between the power of microwave 23 and the slope improvement ratio in the diamond quantum sensor 101 involved in the comparative example. The horizontal axis represents the power of microwave 23, and the vertical axis represents the slope improvement ratio. Here, the slope improvement ratio represents the slope of the spectrum relative to the slope of the spectrum when the slope of the spectrum at a specified power of microwave 23 is set to 1.

[0033] like Figure 2B As shown, if the power of microwave 23 is increased, the slope improvement ratio also increases. In the comparative example diamond quantum sensor 101, in order to improve the magnetic field sensitivity, a countermeasure is taken to increase the power of the irradiated microwave 23, so as to increase the slope of the above spectrum.

[0034] <The Problem Discovered by the Inventor>

[0035] However, the improvement in the power of microwave 23 and the slope of the spectrum is disproportionate. The improvement diminishes as the power of microwave 23 increases. For example, even if the power of microwave 23 is doubled, the improvement in the slope of the spectrum is only 1.2 times. That is, the effect of increasing the power of microwave 23 is limited. Furthermore, from the perspective of the specifications of the microwave source or the power consumption required in the diamond quantum sensor 101, the power of the microwave 23 that can be irradiated has a certain upper limit. Therefore, the slope of the spectrum, and consequently, the magnetic field sensitivity, also has an upper limit.

[0036] The reason why the improvement in the spectral slope deteriorates with increasing the power of microwave 23 is unclear, but it is believed to be due to an upper limit on the amount of microwave 23 that can be absorbed on the material (diamond 30) side. It is unclear whether the absorption of microwave 23 can be increased on the material side. Furthermore, the control parameters for microwave 23 are only the power of microwave 23 and the frequency f1 of microwave 23. The frequency f1 of microwave 23 is set to the point where the slope of the photodetector magnetic resonance spectrum is the largest. Therefore, the only parameter that can be substantially controlled is the power of microwave 23, thus leading to the aforementioned problem.

[0037] As can be seen from the above, in order to further improve the high sensitivity of the diamond quantum sensor 101, the goal is to improve the spectral slope without relying on the same irradiation power of microwave 23 or by increasing the power of microwave 23.

[0038] <Implementation Method 1>

[0039] Next, the diamond quantum sensor according to this embodiment will be described. In order to solve the above-mentioned problems, the diamond quantum sensor of this embodiment senses a magnetic field by simultaneously irradiating two microwaves of different frequencies. Figure 3 This is a block diagram illustrating the diamond quantum sensor D according to Embodiment 1. Figure 3 As shown, the diamond quantum sensor D includes an excitation optical system 10, a microwave generator 21, a microwave generator 22, a diamond 30, a photodetector 40, a voltmeter 50, and a processing unit 60. Compared with the comparative example diamond quantum sensor 101, the diamond quantum sensor D of this embodiment also includes a microwave generator 22.

[0040] Microwave generator 21 generates microwaves 23. Microwave generator 21 irradiates the diamond 30 with the generated microwaves 23. On the other hand, microwave generator 22 generates microwaves 24. Microwave generator 22 irradiates the diamond 30 with the generated microwaves 24. Alternatively, microwave generators 21 and 22 can be integrated. An integrated microwave generator can generate both microwaves 23 and 24.

[0041] Microwave generators 21 and 22 generate two types of microwaves 23 and 24 with different frequencies. For example, microwave generator 21 generates microwave 23 with frequency f1. Microwave generator 22 generates microwave 24 with frequency f2. Microwave generators 21 and 22 simultaneously irradiate diamond 30 with two types of microwaves 23 and 24 with different frequencies. The frequency difference between microwave 23 (frequency f1) and microwave 24 (frequency f2) is called Δf. Therefore, the frequency difference Δf is given by the following equation (2).

[0042] Δf = f2 - f1 (2)

[0043] Microwave generators 21 and 22, while maintaining a frequency difference Δf, cause frequencies f1 and f2 to vary within a specified range.

[0044] The processing unit 60 derives the photodetector magnetic resonance spectrum based on the relationship between frequencies f1, f2, and the frequency difference Δf with the signal intensity. Furthermore, the processing unit 60 calculates the slope of the spectrum and the slope improvement ratio. The slope of the spectrum can be obtained by differentiating the spectrum with frequency f1 or f2 as the horizontal axis.

[0045] Figure 4 This is a graph illustrating the microwave power and frequency difference used for measurement in the diamond quantum sensor D according to Embodiment 1, as well as the slope and slope improvement ratio of the measured spectrum. Figure 4 The diagram also shows the microwave power used for measurement in the diamond quantum sensor 101 of the comparative example, as well as the slope of the measured spectrum and the slope improvement ratio. Microwave power 1 represents the power of microwave 23, and microwave power 2 represents the power of microwave 24.

[0046] like Figure 4 As shown, in Examples 1 to 30 using the diamond quantum sensor D, the microwave power 1 and microwave power 2 used for measurement are 2 mW. Therefore, in Examples 1 to 30, the total microwave power 1 and microwave power 2 is 4 mW. On the other hand, in Comparative Example 1 using the diamond quantum sensor 101, the microwave power 1 is 2 mW, and in Comparative Example 2 it is 4 mW. Comparative Example 3 is an example using the diamond quantum sensor D, but it is an example where the frequency difference is 0.

[0047] exist Figure 4 In the table, the slope improvement ratio (relative to Comparative Example 1) indicates the magnitude of the slope when the slope of Comparative Example 1 is set to 1. The slope improvement ratio (relative to Comparative Example 2) indicates the magnitude of the slope when the slope of Comparative Example 2 is set to 1. Cases with a slope improvement ratio of 1 or higher are marked as valid and shown in gray.

[0048] like Figure 4As shown, Examples 1 to 30 of this embodiment simultaneously irradiate two microwaves 23 and 24 with different frequencies. However, to improve the slope improvement ratio, simultaneous irradiation of only two microwaves 23 and 24 with different frequencies is insufficient. Instead, it was found that the slope improvement ratio of the spectrum sometimes decreases (deteriorates). The reason for this is not yet clear. It is believed that some kind of interference occurs between the microwaves 23 and 24 from the two microwave generators 21 and 22, resulting in a loss.

[0049] In Comparative Example 1, microwave 23 was irradiated with the same power (2mW) as each of the microwaves in microwaves 23 and 24. Figure 4 As shown, the principle is not yet clear, but when the frequency difference Δf between the two microwaves 23 and 24 is set to the following ranges A1 and A2, the slope improvement ratio of the spectrum can be improved compared with Comparative Example 1.

[0050] Range A1: 0.2MHz ≤ Δf ≤ 3.0MHz

[0051] Range A2: 3.8MHz ≤ Δf ≤ 5.4MHz

[0052] Furthermore, in Comparative Example 2, a microwave 23 was irradiated with the same power (4mW) as the combined power of microwaves 23 and 24. When the frequency difference Δf between the two microwaves 23 and 24 was set to the range B1 to B3, the slope improvement ratio of the spectrum was improved compared to Comparative Example 2.

[0053] Range B1: 0.2MHz ≤ Δf ≤ 0.8MHz

[0054] Range B2: 1.8MHz ≤ Δf ≤ 2.8MHz

[0055] Range B3: 4.0MHz ≤ Δf ≤ 4.8MHz

[0056] Figure 5A This is a bar chart illustrating the slope improvement ratios of Comparative Examples 1, 2, and 3. The horizontal axis represents Comparative Examples 1, 2, and 3. The vertical axis represents the slope improvement ratios of the spectra in Comparative Examples 2 and 3 when the slope of the spectrum in Comparative Example 1 is set to 1. Figure 5A As shown, compared to Comparative Example 1, where the power of microwave 23 is 2mW, Comparative Example 2, where the power of microwave 23 is 4mW, achieves a slope improvement ratio of 1.2 times. However, Comparative Example 3, where two microwaves 23 and 24 are simultaneously irradiated with a combined power of 4mW, fails to improve the slope improvement ratio. Thus, it can be seen that simultaneously irradiating only two microwaves 23 and 24 is insufficient. The reason is not yet clear, but it is believed that some kind of interference occurs between microwaves 23 and 24 from the two microwave generators 21 and 22, resulting in a loss.

[0057] Figure 5B This is a bar chart illustrating the slope improvement ratios of Comparative Example 1, Comparative Example 2, Example 2, Example 11, and Example 21. The horizontal axis represents Comparative Example 1, Comparative Example 2, Example 2, Example 11, and Example 21. The vertical axis represents the slope improvement ratio of the spectra in Comparative Example 2, Example 2, Example 11, and Example 21 when the slope of the spectrum in Comparative Example 1 is set to 1. Figure 5B As shown, by setting the frequency difference Δf in any one of the ranges A1 and A2 or any one of the ranges B1 to B3, the slope of the spectrum can be improved compared to Comparative Example 1 and Comparative Example 2, which were irradiated with microwave 23.

[0058] Figure 6 This is a graph illustrating the slope improvement effect when the diamond quantum sensor D according to Embodiment 1 is irradiated with two microwaves 23 and 24 with different frequencies f1 and f2. The horizontal axis represents the frequency difference Δf between the two microwaves 23 and 24. The vertical axis represents the slope improvement ratio. The slope improvement ratio is set to 1 for Comparative Example 2, which is irradiated with only one type of microwave 23 at 4mW.

[0059] like Figure 6 As shown, by setting the frequency difference Δf within any of the ranges B1 to B3, the slope improvement effect of the spectrum can be improved compared to Comparative Example 2, which was irradiated with microwave 23. When the frequency Δf is outside the ranges B1 to B3, the slope improvement of the spectrum is smaller compared to Comparative Example 2. The reason for this is not yet clear, but it is believed that some kind of interference occurred between the microwaves 23 and 24 from the two microwave generators 21 and 22, resulting in a loss.

[0060] According to this embodiment, by using two microwaves 23 and 24 with different frequencies, the slope of the spectrum can be made greater with the same power than when using only one microwave. Therefore, a diamond quantum sensor D with improved sensitivity can be provided.

[0061] Furthermore, the present invention is not limited to the embodiments described above, and appropriate modifications can be made without departing from the spirit of the invention. For example, structures combining the structures of Embodiment 1 and Comparative Examples 1 to 3 are also included in the technical concept of the embodiments. Moreover, the following sensing method using the diamond quantum sensor D is also included in the technical concept of the embodiments.

[0062] A sensing method is disclosed in which a magnetic field is sensed by simultaneously irradiating two microwaves of different frequencies. In this sensing method, if the frequency difference between the two microwaves is defined as Δf, a diamond quantum sensor is used that is within the range of 0.2MHz≤Δf≤3.0MHz or 3.8MHz≤Δf≤5.4MHz.

Claims

1. A diamond quantum sensor, characterized in that, Simultaneous irradiation with two microwaves of different frequencies to sense the magnetic field. If the frequency difference between the two microwaves is denoted as Δf, then Δf in 0.2MHz≤Δf≤3.0MHz 3.8MHz≤Δf≤5.4MHz Within any range of the above.

2. The diamond quantum sensor according to claim 1, characterized in that, If the frequency difference between the two microwaves is denoted as Δf, then Δf in 0.2MHz≤Δf≤0.8MHz 1.8MHz≤Δf≤2.8MHz 4.0MHz≤Δf≤4.8MHz Within any range of the above.

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