Measurement device and method

Abstract

To provide a measurement device and method capable of achieving higher sensitivity.SOLUTION: A high frequency magnetic field generator applies a microwave to a magnetic resonance member where an electron spin quantum state is varied corresponding to a measured AC field, and which can perform electron spin quantum operation with the microwave. The high frequency power source causes the high frequency magnetic field generator to generate the microwave. A light emission device emits excitation light to be radiated to the magnetic resonance member. A measurement control part controls the high frequency power source and the light emission device for applying the microwave and the excitation light to the magnetic resonance member at a prescribed measurement sequence. Especially, the measurement control part applies a pulse sequence of the microwave based on Hahn echo pulse sequence or dynamic decoupling to the magnetic resonance member. At the time, an inverse (1 / fLOCK) of a spin lock frequency of the pulse sequence of the above-mentioned microwave is different from a cycle (1 / fAC) of the measured AC field.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a measurement device and a measurement method. [Background technology]

[0002] One magnetic field measurement device performs magnetic measurements using optically detected magnetic resonance (ODMR), which utilizes the electron spin resonance of a sensing element such as a diamond structure having nitrogen and lattice defects (NV centers). In ODMR, a static magnetic field is applied to a magnetic resonance element such as a diamond having an NV center, in addition to the magnetic field to be measured, and laser light (excitation light for initialization and measurement) and microwaves are applied in a predetermined sequence, and the amount of fluorescent light emitted from the magnetic resonance element is detected, and the magnetic flux density of the magnetic field to be measured is derived based on the amount of light (see, for example, Patent Document 1).

[0003] For example, when the measured magnetic field is an AC magnetic field, a Hahn echo (spin echo) pulse sequence is used. In this Hahn echo pulse sequence, (a) excitation light is applied to the NV center, (b) a first π / 2 microwave pulse is applied to the NV center at a phase of 0° of the measured magnetic field, (c) a π microwave pulse is applied to the NV center at a phase of 180° of the measured magnetic field, (d) a second π / 2 microwave pulse is applied to the NV center at a phase of 360° of the measured magnetic field, (e) excitation light is applied to the NV center to measure the amount of light emitted by the NV center, and (f) the magnetic flux density is derived based on the measured amount of light emitted. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 2019-138772 Summary of the Invention [Problem to be solved by the invention]

[0005] As mentioned above, when the magnetic field to be measured is an AC magnetic field, Hahn echo (spin echo) pulse sequences and dynamic decoupling are generally used. In these methods, the spin of the NV center is inverted with a π pulse, thereby increasing the phase amount in which the effect of the magnetic field accumulates and improving sensitivity. However, it is desirable to achieve even higher sensitivity.

[0006] The present invention has been made in view of the above problems, and has as its object to provide a measuring device and a measuring method that can achieve higher sensitivity. [Means for solving the problem]

[0007] The measurement device according to the present invention includes a magnetic resonance element whose electron spin quantum state changes in response to a measured AC field and whose electron spin quantum state can be manipulated by microwaves, a radio-frequency magnetic field generator that manipulates the electron spin quantum state of the magnetic resonance element using the microwaves, a radio-frequency power supply that causes the radio-frequency magnetic field generator to generate microwaves, a light-emitting device that emits excitation light to be irradiated onto the magnetic resonance element, a light-receiving device that receives fluorescence emitted by the magnetic resonance element in response to the excitation light and generates a detection signal corresponding to the intensity of the fluorescence, a measurement controller that controls the radio-frequency power supply and the light-emitting device to apply the microwaves and excitation light to the magnetic resonance element in a predetermined measurement sequence, and a measurement processor that derives a measurement value based on the detection signal. The measurement controller applies a Hahn echo pulse sequence or a microwave pulse sequence based on dynamic decoupling to the magnetic resonance element. The reciprocal of the spin-locking frequency of the microwave pulse sequence is different from the period of the measured AC field.

[0008] The measurement method according to the present invention (a) performs electron spin quantum manipulation of a magnetic resonance component, the electron spin quantum state of which changes in response to a measured AC field and which can be manipulated by microwaves, using the microwaves in accordance with a predetermined measurement sequence, while irradiating the magnetic resonance component with excitation light to be irradiated thereon; (b) receives fluorescence emitted by the magnetic resonance component in response to the excitation light and generates a detection signal corresponding to the intensity of the fluorescence; and (c) derives a measurement value based on the detection signal. In the measurement sequence, a Hahn echo pulse sequence or a microwave pulse sequence based on dynamic decoupling is applied to the magnetic resonance component. The reciprocal of the spin locking frequency of the microwave pulse sequence is different from the period of the measured AC field. [Effects of the Invention]

[0009] According to the present invention, a measuring device and a measuring method that can achieve higher sensitivity are provided. [Brief explanation of the drawings]

[0010] [Figure 1] FIG. 1 is a block diagram showing the configuration of a measurement device according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a diagram showing an example of a measurement sequence according to the first embodiment. [Figure 3] FIG. 3 is a diagram illustrating the relationship between the spin lock frequency fLOCK and the frequency fAC of the AC field to be measured, and the maximum value max|dS / dB| of the derivative (dS / dB) of the detection signal intensity S with respect to the magnetic flux density B of the AC field to be measured. [Figure 4] FIG. 4 is a diagram illustrating the distribution of the detected signal strength S (relative value) with respect to the frequency fAC and phase shift of the AC field to be measured. [Figure 5] FIG. 5 is a diagram illustrating the maximum slope value max|dS / dB| with respect to the frequency fAC of the AC field to be measured according to the first embodiment. [Figure 6] FIG. 6 is a diagram illustrating sampling of the detection signal in the second embodiment. [Figure 7] FIG. 7 is a diagram illustrating a detection signal that appears in the observable band in the second embodiment. [Figure 8] FIG. 8 is a diagram illustrating a case where a band corresponding to a range from half the sampling frequency fs (fs / 2) to the sampling frequency fs is attenuated in the filter processing. [Figure 9] FIG. 9 is a diagram illustrating a case where a band corresponding to a range from 0 to half the sampling frequency (fs / 2) is attenuated in a filter process. [Figure 10] FIG. 10 is a diagram illustrating a measurement sequence (dynamic decoupling) according to the third embodiment. [Figure 11] FIG. 11 is a diagram illustrating the maximum gradient value max|dS / dB| with respect to the frequency fAC of the AC field to be measured according to the third embodiment. [Figure 12] FIG. 12 is a diagram showing an example of a measurement sequence according to the fourth embodiment. [Figure 13] FIG. 13 is a diagram illustrating the sensitivity corresponding to the frequency fAC of the AC field to be measured according to the fourth embodiment. [Figure 14] FIG. 14 is a diagram illustrating the first detection value, the second detection value, and the measurement value according to the fourth embodiment. [Figure 15] FIG. 15 is a diagram (1 / 2) illustrating the maximum gradient max|dS / dB| with respect to the frequency fAC of the AC field to be measured in the fourth embodiment. [Figure 16] FIG. 16 is a diagram (2 / 2) illustrating the maximum gradient max|dS / dB| with respect to the frequency fAC of the AC field to be measured in the fourth embodiment. [Figure 17] FIG. 17 is a diagram (1 / 2) illustrating the maximum gradient value max|dS / dB| with respect to the frequency fAC of the AC field to be measured in the fifth embodiment. [Figure 18] FIG. 18 is a diagram (2 / 2) illustrating the maximum gradient max|dS / dB| with respect to the frequency fAC of the AC field to be measured in the fifth embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0011] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0012] Embodiment 1

[0013] 1 is a block diagram showing the configuration of a measurement device according to embodiment 1 of the present invention. The measurement device shown in Fig. 1 includes a sensor unit 10, a high-frequency power supply 11, a light-emitting device 12, and a light-receiving device 13.

[0014] The sensor unit 10 detects a measured field (e.g., a magnetic field such as the strength and direction of the magnetic field) at a predetermined position (e.g., on or above the surface of an object to be inspected). The measured field may be an AC field of a single frequency or an AC field of a predetermined period having multiple frequency components.

[0015] In this embodiment, the sensor unit 10 includes a magnetic resonance member 1, a high-frequency magnetic field generator 2, and a magnet 3, and detects the field to be measured by ODMR.

[0016] The magnetic resonance component 1 has a crystalline structure, and the electron spin quantum state changes in response to the field to be measured (here, the magnetic field), and the electron spin quantum state can be manipulated (based on Rabi oscillation) by microwaves with a frequency corresponding to the alignment direction of defects and impurities in the crystal lattice. In other words, the magnetic resonance component 1 is placed at the position where the magnetic field is to be measured.

[0017] In this embodiment, the magnetic resonance component 1 is a photodetector magnetic resonance component having a plurality (i.e., an ensemble) of specific color centers, each of which has an energy level that can be Zeeman split and can take multiple orientations with different energy level shift widths during Zeeman splitting.

[0018] Here, the magnetic resonance component 1 is a component such as diamond that contains multiple NV (Nitrogen Vacancy) centers as a single type of specific color center. In the case of an NV center, the ground state is a triplet state of mso = 0, +1, -1, and the mso = +1 level and the mso = -1 level are Zeeman split. When the NV center transitions from the excited state of mso = +1 and mso = -1 to the ground state, a certain proportion of the NV centers emit fluorescence, while the remaining proportion of the NV centers transition from the excited state (mso = +1 or mso = -1) to the ground state (mso = 0) without radiation.

[0019] The color center included in the magnetic resonance member 1 may be a color center other than the NV center.

[0020] The high frequency magnetic field generator 2 applies microwaves to the magnetic resonance member 1 to perform electron spin quantum manipulation in the magnetic resonance member 1. The high frequency power supply 11 generates a current of the microwaves and conducts it through the high frequency magnetic field generator 2, causing the high frequency magnetic field generator 2 to generate microwaves.

[0021] For example, the high-frequency magnetic field generator 2 is a plate-shaped coil that includes a substantially circular coil portion that emits microwaves and terminal portions that extend from both ends of the coil portion and are fixed to a substrate. The coil portion conducts two parallel currents at both end surfaces at a predetermined interval so as to sandwich the magnetic resonance component 1, thereby emitting the microwaves described above. Here, although the coil portion is a plate-shaped coil, microwave current flows through the end surfaces of the coil portion due to the skin effect, forming two currents. As a result, microwaves of spatially uniform intensity are applied to the magnetic resonance component 1.

[0022] In the case of NV centers, color centers are formed in diamond crystals by defects (vacancies) (V) and nitrogen (N) as impurities. There are four possible positions for adjacent nitrogen (N) relative to the defects (vacancies) (V) in the diamond crystal (i.e., the orientation of the vacancy-nitrogen pair). The sublevels (i.e., the energy levels from the ground state) after Zeeman splitting corresponding to each of these orientations are different. Therefore, in the characteristics of the fluorescence intensity after Zeeman splitting by a static magnetic field versus microwave frequency, four different dip frequency pairs (fi+, fi-) appear corresponding to each orientation i (i = 1, 2, 3, 4). Here, the microwave frequency (wavelength) described above is set to correspond to one of these four dip frequency pairs.

[0023] The magnet 3 applies a static magnetic field (DC magnetic field) to the magnetic resonance member 1, and Zeeman-splits the energy levels of a plurality of specific color centers (here, a plurality of NV centers) in the magnetic resonance member 1. Here, the magnet 3 is a ring-shaped permanent magnet, such as a ferrite magnet, an alnico magnet, or a samarium-cobalt magnet.

[0024] In this embodiment, the direction of application of the static magnetic field is the same as the direction of application of the magnetic field to be measured, and application of the static magnetic field enhances the change in fluorescence intensity at the dip frequency, thereby increasing sensitivity.

[0025] Furthermore, in this embodiment, the magnetic resonance member 1 includes a plurality of color centers (here, NV centers) capable of electron spin quantum manipulation by microwaves, and the magnet 3 applies a substantially uniform static magnetic field to a predetermined region (excitation light irradiation region) of the magnetic resonance member 1. For example, the static magnetic field is applied so that the difference or ratio between the maximum and minimum values ​​of the static magnetic field strength in the predetermined region is equal to or less than a predetermined value.

[0026] Furthermore, in the magnetic resonance member 1, the crystals of the magnetic resonance member 1 are formed and the orientation of the magnetic resonance member 1 is set so that the arrangement direction of the above-mentioned defects and impurities approximately coincides with the direction of the above-mentioned static magnetic field (and the direction of the applied magnetic field).

[0027] Furthermore, in this embodiment, an optical system is provided from the light-emitting device 12 to the magnetic resonance component 1 in order to irradiate the magnetic resonance component 1 with excitation light, and an optical system is provided from the magnetic resonance component 1 to the light-receiving device 13 in order to detect fluorescence from the magnetic resonance component 1.

[0028] The light-emitting device 12 includes a laser diode or the like as a light source, which emits laser light of a predetermined wavelength as excitation light to be irradiated onto the magnetic resonance component 1. The light-receiving device 13 includes a photodiode, a phototransistor, or the like as a light-receiving element, which receives fluorescence emitted by the magnetic resonance component 1 in response to the excitation light, and generates a fluorescence sensor signal PL corresponding to the intensity of the fluorescence. This fluorescence is focused toward the light-receiving device 13 by an optical system such as a compound parabolic concentrator (CPC).

[0029] The light receiving device 13 includes a light receiving element that generates an electrical signal corresponding to the incident light by the photoelectric effect, receives the fluorescence emitted by the magnetic resonance component 1 in response to the excitation light, and generates a detection signal corresponding to the intensity of the fluorescence. The light receiving device 13 may include a signal processing unit that performs predetermined signal processing on the electrical signal output from the light receiving element to generate a detection signal, or the electrical signal output from the light receiving element may be used as the detection signal.

[0030] For example, the signal processing may involve common mode rejection using a reference signal based on a reference light branched from the excitation light.

[0031] Furthermore, the measuring device shown in FIG. 1 includes an analog-to-digital converter 21 that digitizes the detection signal, and a processing unit 31 that controls the measuring device and performs signal processing.

[0032] The analog-to-digital converter 21 samples and digitizes the detection signal at a predetermined sampling frequency fs, and outputs the digitized detection signal to the arithmetic processing device 31 .

[0033] The arithmetic processing device 31 includes, for example, a computer, and executes a signal processing program on the computer to operate as various processing units. In this embodiment, the arithmetic processing device 31 causes the computer to operate as a measurement control unit 41 and a measurement processing unit 42, and also includes a non-volatile storage device 43.

[0034] A signal processing program is stored in the storage device 43, and the computer is equipped with a CPU (Central Processing Unit), ROM (Read Only Memory), RAM (Random Access Memory), etc., and operates as a measurement control unit 41 and a measurement processing unit 42 by loading the signal processing program into the RAM and executing it on the CPU.

[0035] The measurement control unit 41 (a) controls the high-frequency power supply 11 and the light-emitting device 12 to apply microwaves and excitation light to the magnetic resonance member 1 in a predetermined measurement sequence, and (b) acquires the detection signals digitized as described above, stores them in RAM or the storage device 43, and causes the measurement processing unit 42 to derive measurement values ​​of the AC field to be measured. The measurement processing unit 42 derives the measurement values ​​based on the digitized detection signals.

[0036] However, in the case of a conventional Hahn echo pulse sequence (spin echo pulse sequence) or conventional dynamic decoupling, the reciprocal of the spin lock frequency of the microwave pulse sequence, 1 / f LOCK ) with the period (1 / f AC ) of the spin lock frequency of the microwave pulse sequence in the measurement sequence. LOCK ) is the period of the AC field to be measured (1 / f AC ) where f LOCK is the spin lock frequency, and f ACis the frequency of the AC field to be measured.

[0037] Fig. 2 is a diagram showing an example of a measurement sequence. Fig. 2 shows the timing of microwave pulses with respect to the AC magnetic field to be measured and the timing of excitation light irradiation (twice, for initialization and measurement) in the measurement sequence of embodiment 1. As shown in Fig. 2, for each measurement, fluorescence is detected during the excitation light irradiation period.

[0038] In particular, the measurement control unit 41 applies a Hahn echo pulse sequence or a microwave pulse sequence based on dynamic decoupling to the magnetic resonance component 1. At this time, the reciprocal of the spin lock frequency (1 / f LOCK ) is the period (1 / f AC ) In the first embodiment, a microwave pulse sequence based on a Hahn echo sequence (spin echo pulse sequence) is applied to the magnetic resonance component 1.

[0039] The reciprocal of the spin lock frequency (1 / f LOCK ) is the time length from the end of the first π / 2 pulse to the beginning of the second π / 2 pulse, as shown in FIG. 2, for example. In the first embodiment, the measurement control unit 41 applies a microwave pulse sequence based on the Hahn echo pulse sequence to the magnetic resonance component 1 in the measurement sequence. However, the reciprocal of the spin lock frequency (1 / f LOCK ) is the period (1 / f AC ) shorter.

[0040] Figure 3 shows the spin lock frequency f LOCK and the frequency f of the AC field to be measured AC 10 is a diagram illustrating the relationship between the intensity S of the detection signal and the maximum value max|dS / dB| of the derivative (dS / dB) of the intensity S of the detection signal with respect to the magnetic flux density B of the AC field to be measured.

[0041] As shown in Figure 3, the strength of the detected signal S is determined by B, f AC, and f LOCK is a function of f AC and f LOCK In the equation shown in Fig. 3, γ is the gyromagnetic ratio (a constant), and φ0 is the phase shift between the microwave pulse sequence and the AC field to be measured.

[0042] Here, as shown in Figure 3, for example, dS / dB represents the slope, and the larger dS / dB is, the higher the sensitivity is. Therefore, under the condition where max|dS / dB| is maximum, f AC and f LOCK is preferably set.

[0043] Figure 4 shows the frequency f AC 4 is a diagram illustrating the distribution of the detected signal strength S (relative value) with respect to the frequency f of the AC field to be measured in the first embodiment. In FIG. 4, the detected signal strength S (relative value) is represented by contour lines. AC 10 is a diagram illustrating the maximum gradient max|dS / dB| with respect to the

[0044] For example, as shown in FIG. 4, the detected signal strength S varies depending on the magnitude of the phase shift between the AC field to be measured and the measurement sequence. For example, as shown in FIGS. 4 and 5, the maximum value of the detected signal strength S is f AC is f LOCK If it is the same as f AC is f LOCK It should be noted that Figure 5 shows the results for f without considering the phase shift. AC The maximum slope max|dS / dB| at each value is shown.

[0045] In other words, the maximum value (max|dS / dB|) of the differential (dS / dB) of the intensity S of the detected signal with respect to the magnetic flux density B of the AC field to be measured is the spin lock frequency f LOCK is the frequency of the AC field to be measured, f AC The spin lock frequency f LOCK and the wave number f of the AC field to be measured ACThe frequency of the AC field to be measured is set as f AC is preferably set at (or near) the peak frequency of the characteristic curve in FIG.

[0046] Also, the frequency of the AC field to be measured, f AC If there is a possibility that fluctuations or deviations of a certain width may occur in the characteristic curve, a measurement band of a certain width is set that includes the peak frequency of the characteristic curve in Fig. 5. By setting the measurement band in this way, it is possible to perform measurements under conditions that provide a good maximum slope (max|dS / dB|) (i.e., sensitivity).

[0047] Next, the operation of the measurement device according to the first embodiment will be described.

[0048] The sensor unit 10 is placed at a measurement position of the AC field to be measured (here, an AC magnetic field). Note that the sensor unit 10 may be scanned to perform measurements at a plurality of measurement positions.

[0049] The measurement control unit 41 executes measurement sequences successively, for example, as shown in FIG. 2, and each measurement sequence (f AC Higher f LOCK In the Hahn echo sequence, light emitting device 12 is caused to emit excitation light and high frequency magnetic field generator 2 is caused to emit microwaves.

[0050] As a result, during the irradiation period of the excitation light during measurement, a detection signal is obtained by the light receiving device 13, and the detection signal is sampled and digitized by the analog-to-digital converter 21 to be continuously generated.

[0051] Upon receiving this detection signal, the measurement processing unit 42 derives a measurement value of the AC field to be measured from the detection signal using an existing method.

[0052] As described above, according to the first embodiment, the radio-frequency magnetic field generator 2 applies microwaves to the magnetic resonance member 1, whose electron spin quantum state changes in response to the AC field to be measured and whose electron spin quantum state can be manipulated by microwaves. The radio-frequency power supply 11 causes the radio-frequency magnetic field generator 2 to generate microwaves. The light-emitting device 12 emits excitation light to be irradiated onto the magnetic resonance member 1. The measurement control unit 41 controls the radio-frequency power supply and the light-emitting device to apply microwaves and excitation light to the magnetic resonance member 1 in a predetermined measurement sequence. In particular, the measurement control unit 41 applies a microwave pulse sequence based on a Hahn echo pulse sequence (or dynamic decoupling) to the magnetic resonance member 1. In this case, the reciprocal of the spin-locking frequency of the microwave pulse sequence is different from the period of the AC field to be measured.

[0053] This allows the measurement of the AC field to be measured with higher sensitivity than with a conventional Hahn echo sequence (or conventional dynamic decoupling).

[0054] Embodiment 2

[0055] Fig. 6 is a diagram illustrating sampling of a detection signal in embodiment 2. In embodiment 2, for example, as shown in Fig. 6, the analog-to-digital converter 21 samples and digitizes the detection signal at a predetermined sampling frequency fs under the undersampling condition, and outputs the digitized detection signal to the calculation processing device 31. Due to the undersampling condition, in embodiment 2, the observable band based on the detection signal is a band from 0 to fs / 2.

[0056] FIG. 7 is a diagram illustrating the detection signal that appears in the observable band in the second embodiment. For example, as shown in FIG. 7, if the detection signal contains unnecessary components in addition to the components of the AC field to be measured, the unnecessary components may enter the observable band due to aliasing. Therefore, in order to attenuate such unnecessary components, in the second embodiment, a filter process is performed on the detection signal to attenuate bands other than a predetermined measurement band. This measurement band is set according to the sampling frequency fs. Note that this filter process may be performed by an analog circuit on the detection signal as an analog signal, or by a digital signal processor or the above-mentioned measurement processing unit 42 on the detection signal as a digital signal.

[0057] 8 is a diagram illustrating a case where the band corresponding to the range from half the sampling frequency fs (fs / 2) to the sampling frequency fs is attenuated in the above-mentioned filtering process. For example, the spin lock frequency f is attenuated so that the above-mentioned measurement band corresponds to the range from 0 to half the sampling frequency fs and is a band including the peak frequency at which the maximum value (max|dS / dB|) of the derivative of the intensity of the detection signal with respect to the magnetic flux density of the AC field to be measured is reached. LOCK In this case, aliasing is suppressed, and as shown in Figure 8, for example, the measurement band is set to the range between a frequency that is an integer (n-1) times the sampling frequency fs ((n-1)fs) and a frequency that is an integer (n-1) times the sampling frequency fs plus half the sampling frequency fs ((n-1)fs+fs / 2), which allows detection signals to be detected with good sensitivity in the observable band.

[0058] 9 is a diagram illustrating a case where the band corresponding to the range from 0 to half the sampling frequency (fs / 2) is attenuated in the above-mentioned filtering process. For example, the spin lock frequency f is attenuated so that the above-mentioned measurement band corresponds to the range from half the sampling frequency fs to the sampling frequency fs and includes the peak frequency at which the derivative of the intensity of the detection signal with respect to the magnetic flux density of the AC field to be measured is maximized. LOCKIn this case, assuming that aliasing is utilized, the measurement band is set in the range between the frequency obtained by adding half the sampling frequency fs to an integer (n-1) multiple of the sampling frequency fs ((n-1)fs+fs / 2) and the frequency obtained by an integer multiple of the sampling frequency fs (nfs), as shown in Figure 9, thereby enabling detection signals to be detected with good sensitivity in the observable band. Note that in this case, due to aliasing, the detection signals are detected at frequencies that are symmetrical with respect to (n-1 / 2) × fs.

[0059] The other configurations and operations of the measurement device according to the second embodiment are the same as those of the first embodiment, and therefore the description thereof will be omitted.

[0060] As described above, according to the second embodiment, the unnecessary components are suppressed in the measurement band with good sensitivity by the above-mentioned filtering process.

[0061] Embodiment 3

[0062] Fig. 10 is a diagram illustrating a measurement sequence (dynamic decoupling) in the third embodiment. In the third embodiment, dynamic decoupling is used as the measurement sequence, for example, as shown in Fig. 10. Examples of dynamic decoupling include XY8-k and CPMG (Carr-Purcell-Meiboom-Gill).

[0063] In this measurement sequence, the measurement control unit 41 applies a microwave pulse sequence based on dynamic decoupling to the magnetic resonance component 1. However, the reciprocal of the spin lock frequency (1 / f LOCK ) is the period (1 / f AC ) is longer than the reciprocal of the spin lock frequency (1 / f LOCK) is the time length from the center of the first π pulse to the center of the last π pulse among three consecutive π pulses in the N π pulses in the pulse sequence, for example, as shown in FIG.

[0064] FIG. 11 shows the frequency f AC 10 is a diagram illustrating the maximum gradient max|dS / dB| with respect to the

[0065] In the case of dynamic decoupling, for example, as shown in Figure 11, the frequency f AC The maximum slope (max|dS / dB|) characteristic for the π pulse number N changes depending on the spin lock frequency f LOCK Therefore, the frequency f of the AC field to be measured AC is the spin lock frequency f LOCK It is set higher than the inverse of the spin lock frequency of the microwave pulse sequence (1 / f LOCK ) is the period (1 / f AC ) is set longer.

[0066] The other configurations and operations of the measurement device according to the third embodiment are the same as those of the first or second embodiment, and therefore a description thereof will be omitted.

[0067] Embodiment 4

[0068] FIG. 12 is a diagram showing an example of a measurement sequence in the fourth embodiment. In the fourth embodiment, for example, as shown in FIG. 12, the measurement control unit 41 controls the high-frequency power supply 11 and the light-emitting device 12 to apply microwaves and excitation light to the magnetic resonance member 1 in a first measurement sequence (first half sequence) and also applies microwaves and excitation light to the magnetic resonance member 1 in a second measurement sequence (second half sequence). The first measurement sequence and the second measurement sequence are the same as those in the first embodiment. However, the phase of the final microwave pulse in the second measurement sequence is inverted relative to the phase of the final microwave pulse in the first measurement sequence. In the fourth embodiment, the measurement control unit 41 applies a microwave pulse sequence based on a Hahn echo pulse sequence to the magnetic resonance member 1 in each of the first measurement sequence and the second measurement sequence. Here, the first and second measurement sequences are consecutive. Note that in the first embodiment, the final microwave pulse in the second measurement sequence has the same phase as the final microwave pulse in the first measurement sequence.

[0069] Here, for the final π / 2 pulse in the microwave pulse sequence, the final pulse in the first sequence rotates the spin state by π / 2 (counterclockwise) around the positive direction of the y-axis on the Bloch sphere, and the final pulse in the second sequence rotates the spin state by π / 2 (counterclockwise) around the negative direction of the y-axis on the Bloch sphere. As a result, the rotation angles of the spin states at the end of the pulse sequence differ by 180 degrees, so the positive and negative of the detected values ​​are reversed. Note that in the case shown in FIG. 12, the final pulses in the first and second sequences rotate the spin state around the y-axis, but instead, they may rotate the spin state around the x-axis (in opposite directions to each other).

[0070] The measurement processing unit 42 (a) acquires the detection signals of the first measurement sequence and the detection signals of the second measurement sequence, (b) derives the detection values ​​of the measured AC field (i.e., the first detection value and the second detection value, which are the measurement values ​​for each measurement sequence) based on those detection signals using an existing method, and (c) derives the difference between the first detection value and the second detection value as the measurement value of the measured AC field.

[0071] FIG. 13 shows the frequency f of the AC field to be measured in the fourth embodiment. AC 14 is a diagram illustrating the sensitivity corresponding to the frequency f of the AC field to be measured in the fourth embodiment. FIG. 14 is a diagram illustrating the first detected value, the second detected value, and the measurement value in the fourth embodiment. FIG. 14 shows the waveform when measurements are continuously and repeatedly performed (first and second measurement sequences). FIG. 15 and FIG. 16 are diagrams illustrating the sensitivity corresponding to the frequency f of the AC field to be measured in the fourth embodiment. AC 15 is a diagram illustrating the maximum slope value max|dS / dB| with respect to dS / dB. Note that in Fig. 15, the sampling frequency fs is set to 9 kHz, and in Fig. 16, the sampling frequency fs is set to 6 kHz. In Figs. 15 and 16, the case of embodiment 1 (i.e., the case where one measurement value is obtained in one measurement sequence) is referred to as single sequence, and the case of embodiment 4 (i.e., the case where one measurement value is obtained in two measurement sequences) is referred to as double sequence.

[0072] In the fourth embodiment, the phase of the final pulse of the microwave in the second measurement sequence is inverted relative to the phase of the final pulse of the microwave in the first measurement sequence, so that the frequency f AC is approximately an integer multiple of the sampling frequency fs, the phase of the AC field to be measured relative to the microwave pulse sequence is approximately in phase between the first and second sequences as shown in FIG. 13, and the positive and negative signs of the detected values ​​are reversed, so that the amplitude of the measured value (difference between detected values) is approximately twice the amplitude of each detected value as shown in FIGS. 14, 15 and 16.

[0073] On the other hand, the frequency of the AC field to be measured, f ACis approximately a half-integer multiple of the sampling frequency fs, the phase of the AC field to be measured relative to the microwave pulse sequence is approximately opposite in phase between the first and second sequences, as shown in FIG. 13, and the positive and negative signs of the detected values ​​are reversed, as shown in FIGS. 15 and 16, so the measured value (difference between the detected values) approaches zero.

[0074] Therefore, the sensitivity (maximum slope max|dS / dB|) is the frequency f AC The spin lock frequency f LOCK The sensitivity is higher than when the frequency of the AC field to be measured is set to f AC is set within the measurement band adjacent to the maximum peak frequency (27 kHz in FIG. 15, 24 kHz in FIG. 16).

[0075] In this case, if the detection signal is digitized under undersampling conditions as in embodiment 2, the frequency of the maximum peak in the observable band (0 to fs / 4) will correspond to 0 Hz in the observable band, so the measurement band (for example, measurement band #1 and measurement band #2 in Figures 15 and 16) is set so as not to include the maximum peak frequency.

[0076] In addition, in the case of Figure 15 (i.e., when the sampling frequency fs is 9 kHz), the maximum peak frequency in the double sequence (the magnetic field frequency f AC ) coincides with the peak frequency in the single sequence, but even if the maximum peak frequency in the double sequence does not coincide with the peak frequency in the single sequence due to factors such as the sampling frequency fs, by appropriately setting the measurement band as described above, the magnetic field frequency f AC is the spin lock frequency f LOCKThe magnetic field is measured with a higher maximum slope max|dS / dB| (i.e., sensitivity) than the maximum slope max|dS / dB| when the frequency characteristic matches the maximum slope max|dS / dB|. For example, as shown in Figure 16, even if the peak frequency of 27 kHz in the single sequence is located in the notch portion of the frequency characteristic in the double sequence, the magnetic field can be measured with the high sensitivity as described above by setting the measurement band adjacent to the maximum peak frequency of 24 kHz.

[0077] On the other hand, if a desired measurement band is already known, the sampling frequency fs can be set so that the maximum peak frequency is located within or adjacent to that measurement band, thereby enabling magnetic field measurements to be performed with the high sensitivity described above.

[0078] The other configurations and operations of the measurement device according to the fourth embodiment are the same as those of any of the other embodiments, and therefore a description thereof will be omitted.

[0079] As described above, in the fourth embodiment, the amplitude of the measured value is increased, and therefore the magnetic field is measured with good sensitivity. Furthermore, since the difference between the two detected values ​​of the first and second sequences is derived as described above, the in-phase noise components contained in the two detected values ​​are suppressed.

[0080] Embodiment 5.

[0081] In the fifth embodiment, the measurement control unit 41 applies a microwave pulse sequence based on dynamic decoupling, such as that shown in FIG. 10, to the magnetic resonance component 1 in each of the first and second measurement sequences. However, as in the fourth embodiment, the phase of the final microwave pulse in the second measurement sequence is inverted relative to the phase of the final microwave pulse in the first measurement sequence. Here, the first and second measurement sequences are continuous. Note that, in the third embodiment, the final microwave pulse in the second measurement sequence has the same phase as the final microwave pulse in the first measurement sequence.

[0082] As in the third embodiment, the reciprocal of the spin lock frequency of the microwave pulse sequence (1 / f LOCK ) is the period (1 / f AC ) is longer than the reciprocal of the spin lock frequency (1 / f LOCK ) is the time length from the center of the first π pulse to the center of the last π pulse among three consecutive π pulses in the N π pulses in each of the first and second pulse sequences.

[0083] 17 and 18 show the frequency f AC 18 is a diagram illustrating the maximum value of the gradient max|dS / dB| with respect to π pulse number N, sampling frequency fs is 9 kHz, and spin lock frequency f LOCK 17 and 18, the case of embodiment 3 (i.e., when one measurement value is obtained in one measurement sequence) is referred to as single sequence, and the case of embodiment 5 (i.e., when one measurement value is obtained in two measurement sequences) is referred to as double sequence.

[0084] In the case of dynamic decoupling, the frequency f of the AC field to be measured AC 17 and 18, for example, when the peak frequency is the spin lock frequency f LOCK Therefore, the frequency f of the AC field to be measured AC is the spin lock frequency f LOCK It is set higher than the inverse of the spin lock frequency of the microwave pulse sequence (1 / f LOCK ) is the period (1 / f AC ) is set longer.

[0085] The other configurations and operations of the measurement device according to the fifth embodiment are the same as those of the fourth embodiment, and therefore the description thereof will be omitted.

[0086] It should be noted that various changes and modifications to the above-described embodiments will be apparent to those skilled in the art. Such changes and modifications may be made without departing from the spirit and scope of the subject matter and without diminishing its intended advantages. In other words, it is intended that such changes and modifications be included within the scope of the claims. [Industrial Applicability]

[0087] The present invention is applicable to, for example, a measurement device that uses optically detected magnetic resonance. [Explanation of symbols]

[0088] 1 Magnetic resonance component 2. High frequency magnetic field generator 3. Magnets 11 High frequency power supply 12 Light-emitting device 13 Light receiving device 41 Measurement control section 42 Measurement processing section

Claims

1. a magnetic resonance member whose electron spin quantum state changes in response to a measured AC field and which is capable of quantum manipulation of electron spins using microwaves; a high frequency magnetic field generator for performing quantum manipulation of electron spins in the magnetic resonance member using the microwaves; a high frequency power source that causes the high frequency magnetic field generator to generate the microwaves; a light emitting device that emits excitation light to be irradiated onto the magnetic resonance member; a light receiving device that receives fluorescence emitted by the magnetic resonance member in response to the excitation light and generates a detection signal corresponding to the intensity of the fluorescence; a measurement control unit that controls the high-frequency power supply and the light-emitting device to apply the microwave and the excitation light to the magnetic resonance member in a predetermined measurement sequence; a measurement processing unit that derives a measurement value based on the detection signal, the measurement control unit applies the microwave pulse sequence based on a Hahn echo pulse sequence or dynamic decoupling to the magnetic resonance element; the inverse of the spin lock frequency of the microwave pulse sequence is different from the period of the AC field to be measured; A measuring device characterized by:

2. a magnetic resonance component whose electron spin quantum state changes in response to a measured AC field and whose electron spin quantum state can be controlled by microwaves is subjected to electron spin quantum control by the microwaves in accordance with a predetermined measurement sequence, and excitation light to be irradiated onto the magnetic resonance component is emitted; receiving fluorescence emitted by the magnetic resonance member in response to the excitation light and generating a detection signal corresponding to the intensity of the fluorescence; deriving a measurement value based on the detection signal; In the measurement sequence, a Hahn echo pulse sequence or a microwave pulse sequence based on dynamic decoupling is applied to the magnetic resonance element; the inverse of the spin lock frequency of the microwave pulse sequence is different from the period of the AC field to be measured; A measurement method characterized by:

3. 3. The measurement method according to claim 2, wherein the reciprocal of the spin lock frequency and the period of the AC field to be measured are set so that the maximum value of the derivative of the intensity of the detection signal with respect to the magnetic flux density of the AC field to be measured is larger when the reciprocal of the spin lock frequency of the microwave pulse sequence coincides with the period of the AC field to be measured.

4. applying a microwave pulse sequence based on a Hahn echo pulse sequence to the magnetic resonance element in the measurement sequence; the reciprocal of the spin lock frequency of the microwave pulse sequence is shorter than the period of the AC field to be measured; The measuring method according to claim 2 or 3, characterized by:

5. applying a microwave pulse sequence based on dynamic decoupling to the magnetic resonance element in the measurement sequence; the reciprocal of the spin lock frequency of the microwave pulse sequence is longer than the period of the AC field to be measured; The measuring method according to claim 2 or 3, characterized by:

6. sampling the detection signal at a sampling frequency that satisfies an undersampling condition; deriving measurements based on the sampled detection signals; The detection signal is subjected to a filter process that attenuates bands other than a predetermined measurement band; the measurement band corresponds to the spin lock frequency; the spin lock frequency is set so that the measurement band corresponds to a range from 0 to half the sampling frequency and is a band including a peak frequency at which the derivative of the intensity of the detection signal with respect to the magnetic flux density of the AC field to be measured is maximum; The measuring method according to claim 2 or 3, characterized by:

7. sampling the detection signal at a sampling frequency that satisfies an undersampling condition; deriving measurements based on the sampled detection signals; The detection signal is subjected to a filter process that attenuates bands other than a predetermined measurement band; the measurement band corresponds to the spin lock frequency; the spin lock frequency is set so that the measurement band corresponds to a range from half the sampling frequency to the sampling frequency and is a band including a peak frequency at which the derivative of the intensity of the detection signal with respect to the magnetic flux density of the AC field to be measured is maximum; The measuring method according to claim 2 or 3, characterized by:

8. controlling the high frequency power supply and the light emitting device to apply the microwave and the excitation light to the magnetic resonance member in a first measurement sequence and to apply the microwave and the excitation light to the magnetic resonance member in a second measurement sequence; the phase of the final pulse of the microwave in the second measurement sequence is inverted relative to the phase of the final pulse of the microwave in the first measurement sequence; deriving a first detection value based on the detection signals of the first measurement sequence and deriving a second detection value based on the detection signals of the second measurement sequence; deriving a difference between the first detection value and the second detection value as the measurement value; The measuring method according to claim 2 or 3, characterized by:

9. sampling the detection signal at a sampling frequency that satisfies an undersampling condition; deriving measurements based on the sampled detection signals; The detection signal is subjected to a filter process that attenuates bands other than a predetermined measurement band; the sampling frequency is set so that a maximum peak frequency for a maximum value of a derivative of the intensity of the detection signal with respect to the magnetic flux density of the AC field to be measured is located within the measurement band or adjacent to the measurement band; The measuring method according to claim 8,

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