JP7645491B2 - Detection device and electromagnetic wave detection method - Google Patents

Description

Application of Article 30, paragraph 2 of the Patent Act Publication by proceedings, publication date: September 27, 2020, publication address: http://www.ssdm.jp/2020/index.html Publication at an academic conference, conference name: "the 2020 International Conference on Solid State Devices and Materials", held date: September 29, 2020

The present invention relates to a detection device and an electromagnetic wave detection method.

There is a technology that visualizes the distribution of radio frequency (RF) signals and electromagnetic waves on the surface of an object or in a space distant from the object. Patent Document 1 shows an RF sensor system that has multiple magnetoresistive sensors, each of which generates an output voltage in response to an external magnetic field that changes over time, thereby visualizing the intensity distribution of electromagnetic waves. The intensity of electromagnetic waves is, for example, the amplitude of an electric field or a magnetic field.

JP 2009-014720 A

When electrically coupled magnetoresistive sensors are arranged and the intensity of electromagnetic waves is visualized using the output of each magnetoresistive sensor, as in the RF sensor system described in Patent Document 1, the spatial resolution and the number of pixels are limited by the size of the sensor and the number of sensors arranged between them. When the spatial resolution and the number of pixels are limited, it becomes difficult to visualize electromagnetic waves from a tiny object. Furthermore, when the object is tiny, the signal strength of the electromagnetic waves may be small, so in addition to the spatial resolution, it is necessary to increase the detection sensitivity. In addition, the effects of mutual interference between sensors and between the sensor and the object cannot be avoided, and the method of correcting the effects of mutual interference is complicated, and the measurement accuracy decreases. For these reasons, it has been difficult to visualize the intensity of electromagnetic waves with a high spatial resolution on the order of μm to mm.

The present invention aims to provide an electromagnetic wave detection device with high spatial resolution and high detection sensitivity.

The detection device according to one aspect of the present invention includes a diamond crystal having an NV center, an electromagnetic wave supply unit that supplies the diamond crystal with either a first electromagnetic wave having a magnetic field of a first amplitude or a second electromagnetic wave having a magnetic field of a second amplitude different from the first amplitude according to a predetermined supply sequence, a laser irradiation unit that irradiates the diamond crystal with a laser that excites the NV center, a light receiving element that receives a first fluorescence having a first intensity corresponding to the first amplitude of the first electromagnetic wave from the NV center excited by the laser and receives a second fluorescence having a second intensity corresponding to the second amplitude of the second electromagnetic wave from the NV center excited by the laser, and obtains a first received light signal based on the first fluorescence and a second received light signal based on the second fluorescence as received light signals, a detection signal generation unit that generates a first detection signal based on the first received light signal and a second detection signal based on the second received light signal as detection signals, and an image generation unit that generates a detection image showing the distribution of an external electromagnetic field incident on the diamond crystal based on the first detection signal and the second detection signal.

In the detection device of the above aspect, a first electromagnetic wave having a magnetic field of a first amplitude and a second electromagnetic wave having a magnetic field of a second amplitude are supplied to the NV center of the diamond crystal at different times.

The spins in the NV center to which the first electromagnetic wave is supplied undergo Rabi oscillations (first Rabi oscillations) having a first frequency corresponding to the first amplitude. The spins undergoing the first Rabi oscillations are strongly affected by an external electromagnetic field having a frequency close to the first frequency. The spins undergoing the first Rabi oscillations emit more fluorescence the closer the external electromagnetic field is to the first frequency.

The spins of the NV center to which the second electromagnetic wave is supplied undergo Rabi oscillations (second Rabi oscillations) having a second frequency corresponding to the second amplitude. Since the second amplitude is different from the first amplitude, the second frequency is different from the first frequency. If the second amplitude is greater than the first amplitude, the second frequency is higher than the first frequency.

Spins undergoing the second Rabi oscillation are strongly affected by external electromagnetic fields with frequencies close to the second frequency. Spins undergoing the second Rabi oscillation emit stronger fluorescence the closer the external electromagnetic field is to the second frequency.

The light receiving unit acquires a first light receiving signal based on the first electromagnetic wave and the external electromagnetic field, and a second light receiving signal based on the second electromagnetic wave and the external electromagnetic field, which are generated as a result of the laser irradiation unit exciting the NV center. The detection signal generating unit generates a first detection signal based on the first light receiving signal and a second detection signal based on the second light receiving signal.

The first detection signal is a signal indicating the intensity of an external electromagnetic field of a first frequency detected by the NV center to which the first electromagnetic wave is supplied. The second detection signal is a signal indicating the intensity of an external electromagnetic field of a second frequency detected by the NV center to which the second electromagnetic wave is supplied.

The image generating unit generates a detection image showing the distribution of the intensity of the external electromagnetic field incident on the diamond crystal based on the first detection signal and the second detection signal.

The first detection signal alone does not adequately image the distribution of the intensity of the external electromagnetic field. This is because, when the frequency of the external electromagnetic field is far from the first frequency, the first detection signal is hardly affected by the external electromagnetic field. Therefore, even if the first detection signal has a signal intensity that is spatially distributed in the diamond crystal, it is difficult to distinguish whether the distribution of the intensity is due to noise or a distribution that reflects the external electromagnetic field. This makes it difficult to adequately image the distribution of the intensity of the external electromagnetic field.

The detection device further acquires a second detection signal indicating the intensity of the external electromagnetic field at a second frequency different from the first frequency. The first detection signal and the second detection signal make it possible to calculate the intensity of the external electromagnetic field at each of the first and second frequencies. By using the first detection signal and the second detection signal as a basis, the influence of the intensity distribution of the external electromagnetic field caused by noise can be suppressed.

The detection device has high spatial resolution by using tiny structures called NV centers, and high detection sensitivity by using detection signals of external electromagnetic fields at different frequencies.

In the above aspect, the second amplitude is greater than the first amplitude, the electromagnetic wave supply unit supplies the diamond crystal with any one of the first electromagnetic wave, the second electromagnetic wave, or a third electromagnetic wave having a magnetic field with a third amplitude greater than the second amplitude according to the supply sequence, the light receiving unit receives a third fluorescence having a third intensity according to the third amplitude of the third electromagnetic wave from the NV center excited by the laser, and obtains a third received light signal based on the third fluorescence as the received light signal, the detection signal generating unit generates a third detection signal based on the third received light signal as the detection signal, the image generating unit calculates a background signal based on the third detection signal and the first detection signal, and the image generating unit may generate a detection image based on a signal obtained by removing the background signal from the second detection signal.

The detection signal generating unit calculates a background signal as noise based on the first detection signal and the third detection signal. The image generating unit can generate a detection image based on a signal obtained by removing the background signal from the second detection signal, thereby suppressing the influence of the intensity distribution of the external electromagnetic field caused by noise.

When the frequency of the second Rabi oscillation due to the second electromagnetic wave having a magnetic field of the second amplitude is close to the frequency of the external electromagnetic field, the second detection signal has a large value. Since the second amplitude is a magnetic field amplitude intermediate between the first amplitude and the third amplitude, the third frequency, which is the frequency of the third Rabi oscillation based on the first frequency and the third electromagnetic wave, has a value far from the frequency of the external electromagnetic field. Therefore, the values of the first detection signal and the third detection signal are smaller than the second detection signal. Therefore, when the intensities of the first detection signal, the second detection signal, and the third detection signal are plotted with frequency on the horizontal axis, the frequency plot has an extreme value based on the second detection signal.

The detection device detects and visualizes the external electromagnetic field with higher detection sensitivity by generating a detection image based on the second detection signal, which is an extreme value and from which background signals have been removed.

In the above aspect, the supply sequence includes a first supply sequence and a second supply sequence, and in the first supply sequence, the electromagnetic wave supply unit may supply to the diamond crystal a supply electromagnetic wave that sets the spin state of the NV center to a first spin state, supply to the diamond crystal a supply electromagnetic wave that has a magnetic field that oscillates in a first spin direction of the first spin state and sets the spin state to a second spin state, and supply to the diamond crystal a supply electromagnetic wave that sets the second spin state to a third spin state.

In addition, in the second supply sequence, the electromagnetic wave detection unit may supply to the diamond crystal a supply electromagnetic wave that sets the spin state to a first spin state, supply to the diamond crystal a supply electromagnetic wave having a magnetic field oscillating in the first spin direction that sets the spin state to a second spin state, and supply to the diamond crystal a supply electromagnetic wave that sets the second spin state to a fourth spin state having a spin direction opposite to the spin direction of the third spin state.

The light receiving unit may also acquire a third light receiving signal emitted from the NV center in the third spin state and a fourth light receiving signal emitted from the NV center in the fourth spin state, and the detection signal generating unit may generate a detection signal based on the difference between the third light receiving signal and the fourth light receiving signal.

By the first supply sequence and the second supply sequence, the light receiving unit can obtain two light receiving signals, the third light receiving signal and the fourth light receiving signal, based on the amplitude of the magnetic field of the supplied electromagnetic wave having a certain amplitude. The third light receiving signal and the fourth light receiving signal have opposite spin directions of the spin states on which they are based. The NV center in the second spin state is affected by the external electromagnetic field of the detection target and other noise. Since the direction of the noise is random, the noise can be canceled by taking the difference between the third light receiving signal and the fourth light receiving signal. Since the third spin state and the fourth spin state are opposite to each other, it is possible to extract the net effect of the external electromagnetic field on the second spin state by taking the difference between the third light receiving signal and the fourth light receiving signal.

In the above aspect, the electromagnetic wave supply unit may supply, in the second supply sequence, electromagnetic waves that have a phase that is 180 degrees different from the phase of the electromagnetic waves that cause the spin state in the first supply sequence to be the third spin state, and that cause the spin state to be the fourth spin state. This makes it possible to extract the net effect of the external electromagnetic field on the second spin state.

In the above embodiment, the diamond crystal may have a plurality of NV centers distributed inside the surface of the diamond crystal and within a range that occupies a predetermined volume in the diamond crystal. This makes it possible to detect an external electromagnetic field from a wider range of the electromagnetic wave detection target that emits the external electromagnetic field.

A fluorescence detection method according to another aspect of the present invention includes a fluorescence detection device supplying a supply electromagnetic wave, either a first electromagnetic wave having a magnetic field of a first amplitude or a second electromagnetic wave having a magnetic field of a second amplitude different from the first amplitude, to a diamond crystal having an NV center according to a predetermined supply sequence; irradiating the diamond crystal with a laser that excites the NV center; receiving a first fluorescence having a first intensity corresponding to the first amplitude of the first electromagnetic wave from the NV center excited by the laser, receiving a second fluorescence having a second intensity corresponding to the second amplitude of the second electromagnetic wave from the NV center excited by the laser; acquiring a first received signal based on the first fluorescence and a second received signal based on the second fluorescence as received signals; generating a first detection signal based on the first received signal and a second detection signal based on the second received signal as detection signals; and generating a detection image showing the distribution of the intensity of the external electromagnetic field incident on the diamond crystal based on the first detection signal and the second detection signal.

The present invention provides an electromagnetic wave detection device with high spatial resolution and high detection sensitivity.

FIG. 1 is a block diagram of a detection device according to an embodiment of the present invention. FIG. 2 is a diagram showing the arrangement of a diamond crystal, an antenna, and a sample according to the present embodiment. 1 is a diagram for explaining detection of an external electromagnetic field according to the present embodiment. FIG. FIG. 4 is a diagram illustrating an example of a first supply sequence according to the present embodiment. FIG. 11 is a diagram illustrating an example of a second supply sequence according to the embodiment. 10A to 10C are diagrams illustrating another example of the first supply sequence according to the embodiment. 13A to 13C are diagrams illustrating another example of the second supply sequence according to the embodiment. 5A and 5B are diagrams illustrating binning of detection signals according to the present embodiment. 10 is a flowchart for explaining a process for detecting an external electromagnetic field according to the present embodiment. 11 is a diagram for explaining the resonant frequency of the NV center according to the embodiment. FIG. 10 is a flowchart illustrating a detection image generation process according to the present embodiment. FIG. 2 is a plan view of an example of a sample according to the embodiment. FIG. 4 is a diagram for explaining fluorescence intensity according to the embodiment. FIG. 4 is a diagram for explaining an example of fluorescence intensity according to the embodiment. FIG. 4 is a diagram for explaining an example of a detection image according to the embodiment. FIG. 13 is a diagram for explaining an NV center.

A preferred embodiment of the present invention will be described with reference to the attached drawings. In each drawing, the same reference numerals are used to denote the same or similar configurations.

Figure 1 shows a block diagram of a detection device 10 according to this embodiment. The detection device 10 has a diamond crystal 101, an antenna unit 102, a control unit 103, a pulse generator 104, a laser irradiator 105, an imaging device 106, a local oscillator 107, an arbitrary waveform generator 108, a mixer 109, a switch 110, an amplifier 111, and a signal generator 112. The detection device 10 is used to detect an external electromagnetic field emitted by a sample S.

The diamond crystal 101 is placed very close to or in contact with the sample S. The diamond crystal 101 has an NV center, which will be described below.

Here, we will briefly explain the NV center. Figure 16 shows a structural diagram for explaining the structure of the NV center. The NV center is a complex defect formed by a nitrogen atom N at one of the lattice points of a diamond crystal composed of carbon atoms C and a vacancy V caused by the loss of a carbon atom adjacent to the nitrogen atom N. This complex defect can capture an electron e, as conceptually shown in Figure 16. The electron e has a quantum state (spin s). The NV center strongly absorbs light of a specific wavelength, for example, green laser light, and emits light of another specific wavelength, for example, red fluorescence. The intensity of the fluorescence from the NV center has the characteristic that it changes depending on the spin s of the electron e.

When light of a specific wavelength, for example a green laser, is incident on the diamond crystal 101, the NV center of the diamond crystal 101 emits light of another specific wavelength, for example red fluorescence. The shapes of the diamond crystal 101 and the antenna portion 102 will be described later.

The antenna part 102 is provided in contact with the diamond crystal 101. The diamond crystal 101 is sandwiched between the antenna part 102 and the sample S. The antenna part 102 transmits an electromagnetic wave (supplied electromagnetic wave) based on a radio frequency signal having a predetermined frequency and a selected amplitude, which is input through the amplifier 111, to the diamond crystal 101, thereby propagating the electromagnetic wave to the diamond crystal 101.

The control unit 103 is a control component connected to the pulse generator 104, the imaging device 106, the local oscillator 107, and the arbitrary waveform generator 108. The control unit 103 is a device that performs various controls for the detection of electromagnetic waves by the detection device 10. The physical configuration of the control unit 103 includes a CPU (Central Processing Unit) that performs the processes required for control, a RAM (Random Access Memory), a ROM (Read Only Memory), or a HDD (Hard Disk Drive) as a storage area, and a communication device that performs various communications.

The control unit 103 has, as its functional configuration, a memory unit 1031, a signal generation unit 1032, an electromagnetic wave supply control unit 1033, a light reception signal acquisition unit 1034, a detection signal generation unit 1035, and an image generation unit 1036. Each of these units is realized, for example, by using a memory area such as a RAM or ROM, or by the CPU executing a program stored in the memory area. For example, the program is stored in the memory unit 1031.

The memory unit 1031 is a memory area in which programs and information necessary for various processes in the control unit 103 are stored.

The signal generating unit 1032 controls the signal generator 112 described below, thereby controlling the supply of a radio frequency signal (RF signal) to the sample S. A "radio frequency signal" refers to a signal having a frequency band used for wireless communication. The radio frequency signal is supplied to the sample S via a wired connection. Note that the radio frequency signal may also be supplied to the sample S wirelessly.

The electromagnetic wave supply control unit 1033 controls the local oscillator 107 and the arbitrary waveform generator 108 to control the supply of electromagnetic waves to the antenna unit 102.

The light receiving signal acquisition unit 1034 acquires a light receiving signal based on the fluorescence from the NV center detected by the imaging device 106 from the imaging device 106.

The detection signal generating unit 1035 generates a detection signal based on the received light signal acquired by the received light signal acquiring unit 1034.

The image generating unit 1036 generates a detection image showing the intensity distribution of the external electromagnetic field emitted by the sample S to the outside based on the detection signal generated by the detection signal generating unit 1035.

The specific processing performed by each part of the control unit 103 will be described later.

The pulse generator 104 is connected to the control unit 103, the laser irradiator 105, the image capture device 106, the arbitrary waveform generator 108, and the switch 110. Based on the control of the control unit 103, the pulse generator 104 supplies a pulse signal having a predetermined pulse width (hereinafter also simply referred to as a "pulse") to the laser irradiator 105, the image capture device 106, the arbitrary waveform generator 108, and the switch 110.

The pulse generator 104 supplies a pulse for the RF signal supplied to the antenna unit 102 to the switch 110. The pulse generator 104 supplies an irradiation pulse to the laser irradiator 105, which controls the irradiation of the laser by the laser irradiator 105. The pulse generator 104 supplies an imaging pulse to the imaging device 106, which triggers the imaging timing by the imaging device 106. The pulse generator 104 supplies a waveform generation pulse to the arbitrary waveform generator 108, which controls signal generation by the arbitrary waveform generator 108. The pulse generator 104 supplies a switching control pulse to the switch 110, which controls the on/off switching of the switch 110.

The laser irradiator 105 irradiates laser light L having a frequency of . For example, the wavelength of the laser light L is 520 nm, and the laser light L is a green laser. The output of the laser light L is 7 mW, for example. Note that the wavelength and output of the laser light L are not limited to the above values, and may be any value that can excite the NV center of the diamond crystal 101.

The laser light L is irradiated onto the diamond crystal 101 through an optical system having a mirror 1051, a half mirror 1052, and an objective lens 1053. The laser irradiator 105, the mirror 1051, the half mirror 1052, and the objective lens 1053 can be collectively referred to as the laser irradiation unit.

The imaging device 106 receives the fluorescence PL emitted from the diamond crystal 101 irradiated with the laser light L. The fluorescence has a frequency and wavelength that results in red fluorescence, for example. The imaging device 106 receives the fluorescence PL emitted from the diamond crystal 101 through the objective lens 1053, the long wavelength filter 1061, and the imaging lens 1062. The long wavelength filter 1061 is a filter that transmits fluorescence with wavelengths longer than red. The imaging lens 1062 is a lens that adjusts the fluorescence so that it is suitable for reception by the imaging device 106.

The imaging device 106 is, for example, a CMOS camera having multiple light receiving elements. When a CMOS camera is used for the imaging device 106, the CMOS camera may be a cooled CMOS camera. The imaging device 106 generates a light receiving signal based on the incidence of fluorescent light on the light receiving element. The generated light receiving signal is transmitted to the light receiving signal acquisition unit 1034. The imaging device 106 and the light receiving signal acquisition unit 1034 can be collectively referred to as the light receiving unit. Note that the half mirror 1052 and the objective lens 1053 may be included in both the laser irradiation unit and the light receiving unit.

The local oscillator 107 is connected to the control unit 103 and the mixer 109. The local oscillator 107 generates an RF signal of a predetermined frequency based on a signal from the electromagnetic wave supply control unit 1033. The local oscillator 107 transmits the generated RF signal to the mixer 109.

The arbitrary waveform generator 108 supplies mutually orthogonal I and Q signals to the mixer 109 based on the waveform generation pulse from the pulse generator 104. The I and Q signals are signals with a phase difference of π/2.

The mixer 109 generates a pulsed RF signal based on the RF signal from the local oscillator 107 and the I and Q signals from the arbitrary waveform generator 108. The pulsed RF signal is sent to the switch 110.

The switch 110 is a switch that connects the mixer 109 and the amplifier 111 so that the pulsed RF signal from the mixer 109 is supplied to the antenna unit 102 through the amplifier 111 based on a switching control pulse from the pulse generator 104. The switch 110 is controlled to be on only when the mixer 109 is generating a pulsed RF signal.

The amplifier 111 amplifies the power of the pulsed RF signal. The amplifier 111 supplies the amplified pulsed RF signal to the antenna unit 102. The antenna unit 102, the control unit 103, the pulse generator 104, the local oscillator 107, the arbitrary waveform generator 108, the mixer 109, and the switch 110 can be collectively referred to as the electromagnetic wave supply unit.

The signal generator 112 supplies a predetermined radio frequency signal (RF signal) to the sample S based on the signal from the signal generating unit 1032. The RF signal generated by the signal generator 112 is a signal generated independently of the RF signal generated by the local oscillator 107. By supplying the RF signal to the sample S, an external electromagnetic field is generated by the sample S in the vicinity of the diamond crystal 101.

An outline of how the detection device 10 detects an external electromagnetic field is as follows. A pulsed RF signal is supplied to the antenna unit 102. The antenna unit 102 supplies electromagnetic waves to the diamond crystal 101 based on the pulsed RF signal. The supplied electromagnetic waves put the diamond crystal 101 in a state that enables it to detect the external electromagnetic field.

When an RF signal is supplied to the sample S, an external electromagnetic field is generated near the diamond crystal 101. The laser irradiator 105 irradiates the diamond crystal 101, which is affected by the external electromagnetic field, with laser light L. The diamond crystal 101 is excited by the laser light L and emits fluorescence PL. The fluorescence PL is input to the imaging device 106, and a received light signal is acquired by the received light signal acquisition unit 1034.

The control unit 103 is supplied with a pulse signal from a pulse generator 104. The timing of the supply of an RF signal to the antenna unit 102, the irradiation of laser light L by the laser irradiator 105, and the generation of a light receiving signal by the imaging device 106 are synchronized by this pulse signal.

The detection signal generating unit 1035 generates a detection signal based on the light receiving signal at a certain timing. The image generating unit 1036 generates a detection image showing the intensity distribution of the external electromagnetic field in the sample S based on the detection signal.

The structures of the diamond crystal 101, antenna portion 102, and sample S will be described with reference to Figure 2.

The diamond crystal 101 has a diamond crystal layer 201 and an NV central layer 202.

The diamond crystal layer 201 is a diamond crystal structure having a main surface parallel to the xy plane. The diamond crystal layer 201 is provided sandwiching the NV center layer 202. Since the diamond crystal 101 is separated by the NV center layer 202, for convenience, the diamond crystal layer 201 is referred to as a layer.

The NV center layer 202 is a layer containing multiple NV centers formed in the diamond crystal 101. The NV center layer 202 is formed in a predetermined range, for example, a range of about 10 nm, in the positive z-axis direction from the surface of the diamond crystal layer 201 facing the negative z-axis direction. The NV center layer 202 is inside the surface of the diamond crystal and is distributed in a range that occupies a predetermined volume in the diamond crystal.

A static magnetic field is applied to the NV center of the NV center layer 202 by permanent magnets 207a and 207b. The static magnetic field separates the degeneracy of the spin state of the NV center of the NV center layer 202, making it detectable by the detection device 10.

The antenna section 102 has a substrate 203 and an antenna 204. The substrate 203 is, for example, a mounting substrate formed from a resin material. The antenna 204 is a metal pattern formed in the substrate 203 parallel to the main surface of the diamond crystal 101. The antenna 204 can be made of, for example, gold. When a signal MW is input through the amplifier 111, the antenna 204 emits an electromagnetic wave to the diamond crystal 101.

Sample S has a substrate 205 and wiring 206. Substrate 205 has a main surface parallel to the main surface of diamond crystal 101. Substrate 205 is a mounting substrate formed of, for example, a resin material. Although sample S and diamond crystal 101 are shown in FIG. 2 as being in contact with each other, they may be separated by a small distance.

The wiring 206 is a metal wiring formed on the substrate 205. The material of the wiring 206 is, for example, a Ti/Au alloy. The wiring 206 is formed on the substrate 205 using photolithography.

A radio frequency signal, RF signal, is input to the wiring 206 via the signal generator 112. The RF signal causes the wiring 206 to emit an external electromagnetic field toward the outside.

Referring to Figure 3, we will explain an overview of how the detection device 10 detects an external electromagnetic field.

In the detection device 10, as process (A), an RF signal is supplied to the wiring 206. The wiring 206 emits an external electromagnetic field based on the RF signal.

In the next process (B), laser light L1 from the laser irradiator 105 is irradiated onto the diamond crystal 101, more specifically onto the NV center layer 202. The NV centers of the NV center layer 202 irradiated with the laser light L1 are initialized to have a predetermined spin state.

In process (C), a signal MW is input to the antenna 204, and an electromagnetic wave from the antenna 204 is supplied to the NV center layer 202. The supplied electromagnetic wave sets the NV center in the NV center layer 202 to a spin state capable of detecting a specified external electromagnetic field.

In process (D), the external electromagnetic field emitted by the wiring 206 affects the spin state of the NV centers in the NV center layer 202, so that the strength of the external electromagnetic field is reflected in the spin state of the NV centers in the NV center layer 202.

In process (E), laser light L2 from the laser irradiator 105 is irradiated onto the NV center layer 202. The laser light L2 is a laser light for reading out the spin state of the NV center in the NV center layer 202.

In process (F), fluorescence PL is emitted from the NV centers of the NV center layer 202 excited by the laser light L2. The fluorescence PL is detected by the imaging device 106 through the half mirror 1052.

Through the above process, the strength of the external electromagnetic field emitted by wiring 206 is detected.

The sequence of irradiating laser light by the laser irradiator 105 and supplying electromagnetic waves to the diamond crystal 101 by the antenna unit 102 will be described with reference to Figures 4 to 6.

Figure 4 shows the laser supply sequence LS, and the electromagnetic wave supply sequences MSx and MSy (first supply sequence). The laser supply sequence LS indicates that the laser irradiator 105 irradiates the diamond crystal 101 with laser light for a predetermined time τ.

By irradiating the laser light, the spin state of the NV center is initialized to the |0> state. The initialized spin direction points in the positive z-axis direction in a three-dimensional xyz rotating coordinate system.

The electromagnetic wave supply sequence MSx indicates that the antenna section 102 supplies to the diamond crystal 101 an electromagnetic wave (first electromagnetic wave) having a magnetic field of a predetermined amplitude A1 (first amplitude) and causing the spin state of the NV center in the NV center layer 202 to become a predetermined spin state. Specifically, in the above coordinate system, an electromagnetic wave is supplied that rotates the spin direction by 90 degrees in the positive x-axis direction. This electromagnetic wave is also called a π/2 pulse.

By supplying the first π/2 pulse in the electromagnetic wave supply sequence MSx, the initialized spin state becomes a predetermined spin state (first spin state).

By supplying the second π/2 pulse in the electromagnetic wave supply sequence MSx, the spin state based on the electromagnetic wave supply sequence MSy described below becomes a predetermined spin state (third spin state).

The electromagnetic wave supply sequence MSy indicates that the antenna section 102 supplies electromagnetic waves having a magnetic field of amplitude A1, which sets the spin state of the NV center in the NV center layer 202 to a predetermined spin state (second spin state), to the diamond crystal 101. The second spin state is a dressed state, which is a hybrid state of spin and electromagnetic wave, as shown in the following mathematical formula.

An energy gap Ω1 occurs between the dressed spins |+〉 and |-〉. The energy gap Ω1 is an energy gap that corresponds to the energy of an electromagnetic wave having a Rabi frequency proportional to the magnitude of the amplitude A1. The Rabi frequency is the frequency of the Rabi oscillation, which undergoes repeated transitions between energy states when irradiated with electromagnetic waves.

The spin is only affected by electromagnetic waves that have the same energy as the energy gap Ω1, that is, electromagnetic waves whose frequencies resonate with the energy gap Ω1. It is not affected by electromagnetic waves whose frequencies do not resonate with the energy gap Ω1.

After the electromagnetic wave is applied to the diamond crystal 101 for a predetermined time by the electromagnetic wave supply sequence MSy, a second π/2 pulse is supplied in the electromagnetic wave supply sequence MSx. This supply causes the spin state of the NV center to become a predetermined spin state (third spin state).

Figure 5 shows a laser supply sequence LS, and electromagnetic wave supply sequences MSx and MSy (second supply sequence). The second supply sequence differs from the first supply sequence in the second supply of electromagnetic waves in the electromagnetic wave supply sequence MSx. In the electromagnetic wave supply sequence MSx of the second supply sequence, an electromagnetic wave that rotates the spin direction by 90 degrees in the negative x-axis direction is supplied in the second supply of electromagnetic waves. This electromagnetic wave is also called a -π/2 pulse. By supplying a -π/2 pulse in the electromagnetic wave supply sequence MSx, the spin state based on the electromagnetic wave supply sequence MSy described below becomes a specified spin state (fourth spin state).

The third spin state and the fourth spin state include the influence of electromagnetic waves that resonate with the energy gap Ω in the second spin state, and the influence of other noise components. Of these, the influence of electromagnetic waves that resonate with the energy gap Ω is approximately the same in the third spin state and the fourth spin state, resulting in spin states with opposite positive and negative signs. In addition, the influence of noise is random in both the third spin state and the fourth spin state.

Since the third spin state and the fourth spin state are in opposite directions, it is possible to extract the net effect of the external electromagnetic field on the second spin state by taking the difference between the third spin state and the fourth spin state.

Figure 6 shows another example of the first supply sequence. The difference from the first supply sequence shown in Figure 4 is that the magnetic field in the electromagnetic wave supply sequences MSx and MSy has an amplitude A2 (second amplitude).

Amplitude A2 is greater than amplitude A1. As a result, in the second spin state, the energy gap Ω2 based on the electromagnetic wave of amplitude A2 (second electromagnetic wave) is greater than the energy gap Ω1 based on the electromagnetic wave of amplitude A1.

The energy gap Ω2 is affected by an external electromagnetic field of a higher frequency than the frequency of the external electromagnetic field corresponding to the energy gap Ω1. By changing the amplitude of the magnetic field, it is possible to change the frequency of the external electromagnetic field that can be detected using the energy gap in the second spin state. As a result, when the frequency of the external electromagnetic field is unknown, the detection device 10 can scan the amplitude of the magnetic field to scan the detection frequency to accommodate the unknown frequency of the external electromagnetic field.

Figure 7 shows a second supply sequence corresponding to the first supply sequence when the magnetic field has an amplitude A2.

The binning of the signal from the imaging device 106 by the image generating unit 1036 will be described with reference to FIG. 8. Fluorescence PL corresponding to the external electromagnetic field from the diamond crystal 101 enters the light receiving element 801 of the imaging device 106.

The light receiving element 801 has pixels 802 with a number of pixels, for example 528 x 512 pixels, that provides sufficient resolution to detect the intensity distribution of the external electromagnetic field generated by the sample S. If the size of the pixels 802 exceeds the analysis limit of the objective lens 1053, it becomes difficult for each pixel 802 to properly detect the fluorescence PL.

The image generating unit 1036 bins (combines) the detection signals corresponding to the signals from the pixels 802 of 16 x 16 pixels, so that the image 804 generated by the image generating unit 1036 is 33 x 32 pixels. This makes it possible to improve the signal-to-noise ratio and increase the dynamic range.

The process up to recording the detection signal by the detection device 10 will be described with reference to Figure 9.

In step S901, the control unit 103 causes the laser irradiator 105 to irradiate the diamond crystal 101 with laser light via the pulse generator 104.

In step S902, the light receiving signal acquisition unit 1034 acquires a signal indicating the fluorescence intensity from the NV center of the NV center layer 202 through the imaging device 106. The acquired fluorescence intensity is stored in the memory unit 1031.

In step S903, the electromagnetic wave supply control unit 1033 supplies electromagnetic waves of a certain frequency to the antenna unit 102.

In step S904, the control unit 103 causes the laser irradiator 105 to irradiate the diamond crystal 101 with laser light.

In step S905, the light receiving signal acquisition unit 1034 causes the imaging device 106 to acquire fluorescence from the NV center of the NV center layer 202, and acquires a signal indicating the fluorescence intensity. The acquired fluorescence intensity is stored in the memory unit 1031.

By repeating the above processes from step S901 to step S905, normalized fluorescence intensities that satisfy the following relationship for multiple frequencies are calculated: normalized fluorescence intensity = (fluorescence intensity with electromagnetic wave applied) / (fluorescence intensity without electromagnetic wave irradiation). An example of normalized fluorescence intensity is shown in FIG. 10.

In step S906, the electromagnetic wave supply control unit 1033 can select a frequency at which the normalized fluorescence intensity is small, that is, at which the NV center resonates with the laser light, thereby reducing the fluorescence intensity under the supply of electromagnetic waves. For example, the frequency f in FIG. 10 can be set as the resonant frequency.

In step S907, the signal generating unit 1032 supplies an RF signal to the sample S via the signal generator 112. This causes the sample S to generate an external electromagnetic field. The RF signal is, for example, a signal with a frequency of 15 MHz and a power of -30 dBm.

In step S908, the electromagnetic wave supply control unit 1033 selects the amplitude of the magnetic field of the electromagnetic wave that the antenna unit 102 supplies to the diamond crystal 101.

In step S909, the electromagnetic wave supply control unit 1033 supplies a signal having a frequency that is the resonant frequency and a selected amplitude to the diamond crystal 101 according to the first sequence. At this time, the laser irradiator 105 irradiates the laser according to the laser supply sequence.

In step S910, the control unit 103 causes the laser irradiator 105 to irradiate the diamond crystal 101 with laser light.

In step S911, the light receiving signal acquisition unit 1034 causes the imaging device 106 to acquire fluorescence having an intensity according to the selected amplitude. In step S912, the light receiving signal acquisition unit 1034 acquires and stores a light receiving signal SG1 (third light receiving signal) based on the acquired intensity.

In step S913, the electromagnetic wave supply control unit 1033 supplies a signal having a frequency that is the resonant frequency and a selected amplitude to the diamond crystal 101 in accordance with the second sequence. At this time, the laser irradiator 105 irradiates a laser in accordance with the laser supply sequence.

In step S914, the control unit 103 causes the laser irradiator 105 to irradiate the diamond crystal 101 with laser light.

In step S915, the light receiving signal acquisition unit 1034 causes the imaging device 106 to acquire fluorescence having an intensity according to the selected amplitude. In step S916, the light receiving signal acquisition unit 1034 acquires and stores a light receiving signal SG2 (fourth light receiving signal) based on the acquired intensity. Both the light receiving signal SG1 and the light receiving signal SG2 are light receiving signals (first light receiving signals) based on the intensity of fluorescence (first fluorescence) having an intensity (first intensity) according to the selected amplitude.

In step S917, the detection signal generating unit 1035 generates and stores a detection signal (first detection signal) corresponding to each pixel of the detection image generated by the image generating unit 1036 based on the light receiving signal SG1 and the light receiving signal SG2. Specifically, the detection signal generating unit 1035 calculates the detection signal by calculating the difference between the light receiving signal SG1 and the light receiving signal SG2 for each pixel.

Note that the processes from step S909 to step S917 may be repeated multiple times to reduce noise in the detection signal due to errors in the received light signal.

In step S918, the detection signal generation unit 1035 determines whether storage of the detection signal has been completed for the frequency range to be detected, which is determined in response to the external electromagnetic field.

If the detection signal is not stored over the frequency range to be detected, the process from step S908 is repeated. At this time, the electromagnetic wave supply control unit 1033 selects the amplitude of the magnetic field of the electromagnetic wave supplied by the antenna unit 102 to the diamond crystal 101 as a magnetic field having an amplitude greater than the amplitude of the magnetic field of the electromagnetic wave already supplied. This makes it possible to scan the amplitude, i.e., scan the frequency. The amplitude is, for example, an amplitude corresponding to the Rabi frequency from 10.2 MHz to 20.8 MHz.

By repeating the process from step S908, new light receiving signals SG1 and SG2 are repeatedly acquired as light receiving signals (second light receiving signals) based on the intensity of the fluorescence (second fluorescence) having an intensity (second intensity) according to the other selected amplitude. The detection signal generating unit 1035 generates and stores detection signals (second detection signals) corresponding to each pixel of the detection image generated by the image generating unit 1036 based on the new light receiving signals SG1 and SG2.

When the detection signal has been stored across the frequency range to be detected, the process ends.

The detection image generation process will be described with reference to Figures 11 to 15 along with an example of a detection image. Here, the description will be given assuming that all detection signal storage has been completed.

In step S1101, the image generation unit 1036 acquires a detection signal for each frequency in the frequency range to be detected for a pixel in the detection range.

For example, as shown in the plan view of sample S in FIG. 12, a wiring 206 with a width of 10 μm is provided on a substrate 205 with a size of 35 μm×35 μm. The detection device 10 has a detection range of 35 μm×35 μm on the substrate 205. The detected image is an image having the pixels 803 described in FIG. 8.

In step S1102, the image generation unit 1036 calculates the peak frequency at which the acquired detection signal has an extreme value.

For example, Figure 13 shows an example of detection signals at multiple frequencies for a pixel. The detection signals are plotted with frequency on the horizontal axis and normalized fluorescence intensity on the vertical axis.

Each frequency in FIG. 13 is based on the amplitude of the magnetic field of the electromagnetic wave supplied to the diamond crystal 101 by the electromagnetic wave supply control unit 1033. The normalized fluorescence intensity for the magnetic field amplitudes A1, A2, and A3 (third amplitude) are indicated by arrows in FIG. 13. The amplitudes increase in the order of A1, A2, and A3, and the corresponding Rabi frequencies also increase in this order.

In FIG. 13, the detection signal has an extreme value when the amplitude A2, i.e., the second frequency, is 15 MHz. Therefore, the image generating unit 1036 calculates 15 MHz as the peak frequency (second frequency). This frequency corresponds to the frequency (15 MHz) of the RF signal supplied to the sample S by the signal generating unit 1032 in step S907 of FIG. 9. This is because the NV center of the NV center layer 202, which is affected by the external electromagnetic field of 15 MHz, emits the strongest fluorescence when supplied with an electromagnetic wave having a magnetic field of amplitude A2.

In this way, by taking the extreme value of the detection signal, the image generation unit 1036 is able to calculate the frequency of the external electromagnetic field to be detected.

In step S1103, the image generating unit 1036 calculates a first frequency and a second frequency around the peak frequency based on the change in the slope of the detection signal. For example, the frequencies at which the absolute value of the slope of the detection signal becomes smaller than a predetermined value are set as the first frequency and the second frequency, respectively, to the frequencies corresponding to amplitude A1 and amplitude A3 in FIG. 13.

In step S1104, the image generating unit 1036 calculates a background signal based on the detection signal at the first frequency and the detection signal at the second frequency (third detection signal). Specifically, the image generating unit 1036 calculates an equation representing a straight line connecting a point indicating the normalized fluorescence intensity at the first frequency and a point indicating the normalized fluorescence intensity at the second frequency in FIG. 13. The image generating unit 1036 calculates the normalized fluorescence intensity when the frequency is the second frequency in the equation of the calculated straight line. The image generating unit 1036 regards this normalized fluorescence intensity as the background signal.

In step S1105, the image generation unit 1036 subtracts the background signal from the detection signal at the peak frequency.

In step S1106, the image generating unit 1036 stores the spin locking signal, which is the detection signal from which the background signal has been subtracted, in association with the pixel.

In step S1107, the image generation unit 1036 determines whether calculation of the spin locking signal has been completed for all pixels in the detection range.

If calculation of the spin locking signal has not been completed for all pixels in the detection range, the image generation unit 1036 repeats the processes from steps S1101 to S1106.

When calculation of the spin locking signal has been completed for all pixels in the detection range, in step S1108, the image generation unit 1036 generates a detection image based on the spin locking signal.

Figure 14 shows an example of the strength of the spin locking signal at each pixel across the x direction at a certain y direction position. As shown in Figure 14, the spin locking signal has a large value at a position corresponding to the end of the wiring 206 in Figure 12 in the x direction. In other words, it can be seen that at that position, the wiring 206 is emitting a strong external electromagnetic field, and that the frequency is 15 MHz.

Figure 15 shows an example of a detection image 1501 generated by the image generating unit 1036. The spin locking signal as shown in Figure 14 is calculated for each pixel in the y direction. Therefore, it is visualized that the spin locking signal has a large value at the position corresponding to the end of the wiring 206 in Figure 12 in the x direction.

Detection image 1501 is an image obtained by visualizing the electromagnetic waves emitted by wiring 206 based on the spin locking signal. Detection image 1501 visualizes the electromagnetic waves emitted by wiring 206 by scanning the Rabi frequency that excites diamond crystal 101.

The present embodiment has been described above. In the detection device 10, the spatial resolution is limited by the distance (approximately 10 nm) from the surface of the diamond crystal 101 to the NV center layer 202, making it possible to significantly improve the spatial resolution. In addition, the number of pixels in the detected image is not limited by the number of wirings. The inductance of the NV center is extremely small, and the effects of mutual interference between sensors and between the sensor and the target object can be avoided. Therefore, the detection device 10 can significantly improve the detection sensitivity of electromagnetic waves. By performing mathematical processing, the detection device 10 can also be applied to visualization of dielectric constant changes regardless of whether the material is transparent or opaque, and technology for estimating and visualizing the current path and distribution of electronic circuits.

The above-described embodiments are intended to facilitate understanding of the present invention, and are not intended to limit the present invention. The elements of the embodiments, as well as their arrangement, materials, conditions, shapes, sizes, etc., are not limited to those exemplified, and may be modified as appropriate.

10...detection device, 101...diamond crystal, 102...antenna unit, 204...antenna, 103...control unit, 104...pulse generator, 105...laser irradiator, 106...imaging device, 107...local oscillator, 108...arbitrary waveform generator, 109...mixer, 110...switch, 111...amplifier, 112...signal generator, S...sample, 201...diamond crystal layer, 202...NV center layer, 203, 205...substrate, 206...wiring, 1031...storage unit, 1032...signal generation unit, 1033...electromagnetic wave supply control unit, 1034...received light signal acquisition unit, 1035...detection signal generation unit, 1036...image generation unit

Claims (6)

A diamond crystal having NV centers;
an electromagnetic wave supply unit that supplies, in accordance with a predetermined supply sequence, to the diamond crystal, either a first electromagnetic wave having a magnetic field of a first amplitude or a second electromagnetic wave having a magnetic field of a second amplitude different from the first amplitude;
a laser irradiation unit that irradiates the diamond crystal with a laser that excites the NV center;
a light receiving unit having a light receiving element that receives a first fluorescence having a first intensity corresponding to the first amplitude of the first electromagnetic wave from the NV center excited by the laser and receives a second fluorescence having a second intensity corresponding to the second amplitude of the second electromagnetic wave from the NV center excited by the laser, and obtains a first light receiving signal based on the first fluorescence and a second light receiving signal based on the second fluorescence as light receiving signals;
a detection signal generating unit that generates, as detection signals, a first detection signal based on the first light receiving signal and a second detection signal based on the second light receiving signal;
and an image generating unit that generates a detection image showing the distribution of the intensity of the external electromagnetic field incident on the diamond crystal based on the first detection signal and the second detection signal. 2. The detection device according to claim 1,
the second amplitude is greater than the first amplitude;
the electromagnetic wave supplying unit supplies any one of the first electromagnetic wave, the second electromagnetic wave, and a third electromagnetic wave having a magnetic field of a third amplitude greater than the second amplitude to the diamond crystal in accordance with the supply sequence;
the light receiving unit receives a third fluorescence having a third intensity corresponding to the third amplitude of the third electromagnetic wave from the NV center excited by the laser, and obtains a third received light signal based on the third fluorescence as the received light signal;
The detection signal generating unit
generating a third detection signal based on a third light receiving signal as the detection signal;
The image generating unit calculates a background signal based on the first detection signal and the third detection signal,
The detection device generates the detection image based on a signal obtained by removing the background signal from the second detection signal. 3. The detection device according to claim 1 or 2,
the supply sequence includes a first supply sequence and a second supply sequence;
The electromagnetic wave supply unit includes:
In the first supply sequence,
supplying the supply electromagnetic wave to the diamond crystal such that the spin state of the NV center is a first spin state;
supplying to the diamond crystal an electromagnetic wave having a magnetic field oscillating in a first spin direction of the first spin state, the electromagnetic wave causing the spin state to become a second spin state;
supplying to the diamond crystal the supply electromagnetic wave that causes the second spin state to become a third spin state;
In the second supply sequence,
supplying the supply electromagnetic wave to the diamond crystal such that the spin state is the first spin state;
supplying to the diamond crystal an electromagnetic wave having a magnetic field oscillating in the first spin direction, which causes the spin state to become the second spin state;
supplying to the diamond crystal the supply electromagnetic wave that causes the second spin state to become a fourth spin state having a spin direction opposite to that of the third spin state;
the light receiving unit acquires a third light receiving signal emitted from the NV center in the third spin state and a fourth light receiving signal emitted from the NV center in the fourth spin state;
The detection device, wherein the detection signal generating unit generates the detection signal based on a difference between the third light receiving signal and the fourth light receiving signal. 4. The detection device according to claim 3,
The electromagnetic wave supply unit includes:
a detection device that supplies, in the second supply sequence, an electromagnetic wave having a phase that is 180 degrees different from a phase of the electromagnetic wave that sets the spin state to the third spin state in the first supply sequence, and sets the spin state to the fourth spin state. A detection device according to any one of claims 1 to 4,
A detection device, wherein the diamond crystal has a plurality of NV centers distributed within a surface of the diamond crystal and occupying a predetermined volume in the diamond crystal. 1. An electromagnetic wave detection method, comprising:
The detection device is
supplying, according to a predetermined supply sequence, either a first electromagnetic wave having a magnetic field of a first amplitude or a second electromagnetic wave having a magnetic field of a second amplitude different from the first amplitude, to a diamond crystal having NV centres;
irradiating the diamond crystal with a laser that excites the NV centers;
receiving a first fluorescence having a first intensity corresponding to the first amplitude of the first electromagnetic wave from the NV center excited by the laser, and receiving a second fluorescence having a second intensity corresponding to the second amplitude of the second electromagnetic wave from the NV center excited by the laser;
acquiring, as light receiving signals, a first light receiving signal based on the first fluorescence and a second light receiving signal based on the second fluorescence;
generating, as detection signals, a first detection signal based on the first light receiving signal and a second detection signal based on the second light receiving signal;
generating a detection image showing a distribution of intensity of an external electromagnetic field incident on the diamond crystal based on the first detection signal and the second detection signal.

Images