JP7384399B2 - Measuring device and method - Google Patents

Description

The present invention relates to a measuring device and a measuring method using a quantum sensor.

Complex defects called nitrogen-vacancy centers are sometimes found in the crystal structure of diamond. This nitrogen-vacancy center consists of a pair of a nitrogen atom that replaces a carbon atom in the crystal lattice, and a vacancy that is located adjacent to the nitrogen atom (without a carbon atom). It is also called the NV center (Nitrogen Vacancy center). In the crystal structure of diamond, in addition to NV centers, complex defects called silicon vacancy centers and germanium vacancy centers can be found. These complex defects containing NV centers are called color centers.

The NV center exhibits a magnetic property called electron spin in a state in which electrons are captured in vacancies (negatively charged state, hereinafter referred to as "NV ^- "). This NV ⁻ exhibits a longer transverse relaxation time (decoherence time, hereinafter referred to as “T ₂ ”) compared to a state in which no electrons are captured (neutral state, hereinafter referred to as “NV ⁰ ”). In other words, the NV ^- electron spin state is caused by the precession of individual spins after horizontally tilting the magnetization of the electron spins aligned in the vertical direction of the external magnetic field (hereinafter referred to as the "quantization axis"). As a result, the individual orientations shift, and it takes a long time for the transverse magnetization as a whole to disappear. Furthermore, NV ⁻ exhibits a long T ₂ value even at room temperature (approximately 300 K).

The electron spin state of NV ⁻ changes in response to an external magnetic field, and this electron spin state can be measured at room temperature, so diamond containing an NV center can be used as a material for a magnetic field sensor element.

For example, Patent Document 1 discloses a method of measuring an alternating magnetic field using an optically detected magnetic resonance (ODMR) method for electron spins in diamond. The NV center is excited by laser light, and a magnetic resonance signal (phase information) related to the spin state is detected by measuring changes in fluorescence intensity emitted from the NV center.

For example, Non-Patent Document 1 and Non-Patent Document 2 disclose an electrically detected magnetic resonance (EDMR) method for electron spins in diamond. The NV center is excited by laser light, and a photocurrent depending on the spin state is generated. This photocurrent is generated due to the difference in the lifetime of the excited state depending on the spin state. For example, a comb-shaped measurement electrode is arranged on the surface of the diamond including the NV center, and the change in photocurrent generated at the NV center by irradiation with excitation light is electrically measured through the measurement electrode. As a result, a magnetic resonance signal (phase information) related to the spin state is electrically detected.

In addition to sensors using diamond color centers, sensors used as magnetic field sensor elements include, for example, sensors using color centers in silicon carbide (SiC), and optically pumped atomic magnetometers. There are various types such as OPM), superconducting quantum interference device (SQUID), etc. These diamond color centers, silicon carbide color centers, optically pumped magnetometers, and superconducting quantum interferometers are called quantum sensors because they measure physical quantities using quantum effects.

Japanese Patent Application Publication No. 2017-75964

E. Bourgeois, et al., “Photoelectric detection of electron spin resonance of nitrogen-vacancy centers in diamond”, Nature Communications, Vol. 6, 8577 (2015). https://doi.org/10.1038/ncomms9577 F. M. Hrubesch, et al., “Efficient Electrical Spin Readout of NV- Centers in Diamond”, Physical. Review. Letters, Vol. 118, 037601 (2017). https://doi.org/10.1103/PhysRevLett.118.037601

In order to electrically detect a signal related to the spin state of the NV center, it is necessary to apply a bias voltage to the measurement electrode. However, there is a problem in that the spin state of the NV center is affected by the electric field generated by applying a bias voltage, and the sensitivity of the sensor is reduced.

The present invention aims to improve measurement sensitivity in measurements using quantum sensors.

The present invention for achieving the above object includes, for example, the following embodiments.
(Section 1)
A quantum sensor element whose spin state changes due to interaction with the measurement target,
a pair of measurement electrodes arranged with the quantum sensor element sandwiched therebetween;
an electromagnetic wave irradiation unit that irradiates the quantum sensor element with electromagnetic waves for manipulating the spin state of the quantum sensor element by magnetic resonance;
a physical quantity measurement unit that calculates the physical quantity of the measurement target based on the change in the spin state;
Equipped with
The measuring device, wherein the electric field strength applied to the quantum sensor element is greater than or equal to zero and less than 130 V/cm.
(Section 2)
Item 2. The measuring device according to Item 1, wherein the electric field strength is zero.
(Section 3)
The physical quantity measuring section includes:
a light irradiation unit that irradiates the quantum sensor element with light for initializing the spin state of the quantum sensor element;
a detection unit that detects a change in photocurrent generated in the quantum sensor element by the irradiation of the light as a change in the spin state through the measurement electrode;
Item 3. The measuring device according to Item 1 or 2, comprising:
(Section 4)
The physical quantity measuring section includes:
4. The measuring device according to item 3, further comprising a data processing unit that reads out phase information of the spin state from the detected change in the photocurrent and calculates the physical quantity based on the read phase information.
(Section 5)
5. The measuring device according to any one of Items 1 to 4, wherein the quantum sensor element is a sensor element having a color center.
(Section 6)
6. The measuring device according to item 5, wherein the color center is a complex of nitrogen (N) substituted with a carbon atom and a vacancy (V) adjacent to the nitrogen.
(Section 7)
7. The measuring device according to any one of Items 1 to 6, wherein the physical quantity measuring unit calculates at least one of a magnetic field, an electric field, a temperature, and a mechanical quantity as the physical quantity related to interaction with spin. .
(Section 8)
Applying an electric field with an intensity of zero or more and less than 130 V/cm to a quantum sensor element disposed between a pair of measurement electrodes whose spin state changes due to interaction with a measurement target;
irradiating the quantum sensor element with electromagnetic waves for manipulating the spin state of the quantum sensor element by magnetic resonance;
calculating a physical quantity of the measurement target based on the change in the spin state;
including measurement methods.
(Section 9)
The step of calculating the physical quantity includes:
irradiating the quantum sensor element with light for initializing the spin state of the quantum sensor element;
Detecting a change in photocurrent generated in the quantum sensor element by the irradiation of the light as a change in the spin state through the measurement electrode;
The measuring method according to item 8, comprising:
(Section 10)
The step of calculating the physical quantity includes:
10. The measuring method according to item 9, further comprising the step of reading phase information of the spin state from the detected change in the photocurrent and calculating the physical quantity based on the read phase information.

According to the present invention, measurement sensitivity can be improved in measurements using quantum sensors.

1 is a diagram schematically showing a general configuration of a measuring device 10 according to an embodiment of the present invention. 2 is a diagram schematically showing an example of a specific configuration of the measuring device 10 shown in FIG. 1. FIG. 3 is an enlarged view of a region R including the sensor element 1 on the diamond crystal 12 shown in FIG. 2. FIG. FIG. 2 is a diagram schematically showing the energy level of electrons at the NV ^- center of diamond. 3 is a flowchart showing the procedure of a measuring method according to an embodiment of the present invention. 2 is a graph showing the measurement results of magnetic resonance signals by electric detection magnetic resonance method in Example 1. 7 is a graph showing measurement results regarding the dependence of photocurrent on laser power in Example 2. FIG. FIG. 2 is a schematic diagram for explaining changes in energy level that electron spins at the center of NV undergo due to magnetic fields and electric fields.

Embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that in the following description and drawings, the same reference numerals indicate the same or similar components, and therefore, redundant description of the same or similar components will be omitted.

Note that in this specification, a physical quantity means a quantity whose dimensions are determined under a certain system in physics and which can be expressed as a multiple of a specified physical unit. Examples of physical quantities include, for example, magnetic fields, electric fields, temperature, and mechanical quantities (mechanical stress, pressure, etc.). The magnetic field, electric field, and mechanical quantities include physical quantities that do not change over time and physical quantities that repeatedly change direction over time. That is, the magnetic field includes a static magnetic field and an alternating magnetic field, the electric field includes a static electric field and an alternating electric field, and the mechanical quantity includes a static mechanical quantity and an alternating mechanical quantity.
[Key points of the invention]

In the present invention, by reducing the bias voltage applied to the measurement electrode as low as possible, the influence of the electric field felt by the spin state of the color center is reduced as much as possible. As a result, the influence of the electric field generated by applying a bias voltage on the spin state of the color center is reduced as much as possible, and improvement in measurement sensitivity is achieved. The bias voltage applied to the measurement electrode can preferably be approximately zero, more preferably zero.

As an example, a case will be exemplified in which a magnetic field sensor is constructed using an NV center in a diamond as a color center, and the intensity of a magnetic field generated from a measurement object is to be measured by electric detection magnetic resonance (EDMR) method. When electrically detecting magnetic resonance signals related to spin states by electrical detection magnetic resonance, a bias voltage is usually applied to the measurement electrodes. When a bias voltage is applied, an electric field is generated around the measurement electrode. The spin state of the NV center is affected by the interaction with the electric field when it senses the electric field.

Regarding this point, as will be explained with reference to FIG. 8, when the spin state at the center of the NV is affected by the electric field, the strength of the magnetic field of the measurement target will increase due to the influence of the electric field generated around the measurement electrode. There is a problem that the lower the value, the lower the sensitivity to Zeeman splitting, and the lower the measurement sensitivity.

FIG. 8 is a schematic diagram for explaining the change in energy level that the electron spin at the NV center undergoes due to the magnetic field and electric field. (A) shows a state where the influence of the electric field is large, and (B) shows a state where the influence of the electric field is small.

As shown in (A), in a state where the electric field strength is high and the influence of the electric field is large, the degree of splitting due to Zeeman splitting does not change much even if the strength of the magnetic field of the measurement target decreases. The magnitude of the energy level fluctuation Δω with respect to the change in magnetic field strength ΔB _z is also relatively small.

On the other hand, as shown in (B), when the strength of the electric field generated around the measurement electrode is low and the influence of the electric field is small, as the strength of the magnetic field of the measurement target decreases, the degree of splitting due to Zeeman splitting also decreases. Changes greatly. The magnitude of the energy level fluctuation Δω with respect to the change in magnetic field strength ΔB _z is also relatively large, and the sensitivity to the magnetic field is maintained well compared to the state shown in (A) where the influence of the electric field is large.

の下では、以下の式で表される。

The fact that the sensitivity of the magnetic field to be measured decreases due to the influence of the electric field can also be explained from the spin Hamiltonian H _gs . From the Hamiltonian H _gs , the change in the magnetic resonance frequency at the NV center due to the magnetic field B and the electric field E is determined under certain conditions.

is expressed by the following formula.

This equation shows that when the applied electric field is zero, the resonant frequency changes linearly with changes in magnetic field strength. On the other hand, when the applied electric field is stronger than the applied magnetic field, the resonant frequency hardly changes with changes in the magnetic field strength, indicating that the sensitivity of the magnetic field is degraded by the influence of the electric field.

According to the invention, the bias voltage applied to the measurement electrode is made as low as possible, thereby making the strength of the electric field generated around the measurement electrode as low as possible. As a result, the influence of the electric field felt by the spin state at the NV center is reduced as much as possible, and improvement in measurement sensitivity is achieved.
[Device configuration]

In one embodiment of the present invention, a case will be described in which the intensity of a magnetic field generated from a measurement target is measured as an example of a physical quantity to be measured.

FIG. 1 is a diagram schematically showing the general configuration of a measuring device 10 according to an embodiment of the present invention. FIG. 2 is a diagram schematically showing an example of a specific configuration of the measuring device 10 shown in FIG. 1. FIG. 3 is an enlarged view of the region R including the sensor element 1 on the diamond crystal 12 shown in FIG.

The measuring device 10 includes a sensor element 1, a pair of measurement electrodes 13 (13a, 13b), an electromagnetic wave irradiation section 2, and a physical quantity measurement section 3. In this embodiment, the sensor element 1 and the measurement electrode 13 are attached to the tip of the probe 11 of the measurement device 10.

The sensor element 1 is a quantum sensor element. In this embodiment, the sensor element 1 is a diamond crystal having a color center, and the NV center is used as the color center. The NV center is a complex (complex defect) of nitrogen (N) replacing a carbon atom and a vacancy (V) adjacent to the nitrogen. In this embodiment, the sensor element 1 is previously produced within a predetermined region on the diamond crystal 12 by a known method. For example, a plurality of sensor elements 1 on the order of approximately several thousand (concentration: ~1×10 ¹² /cm ⁻³ ) are generated within the region. In this embodiment, the sensor element 1 is the center of the ensemble NV.

The electron spin state of the sensor element 1 is changed by the interaction 8 with the measurement target 9. In this embodiment, the interaction 8 is an interaction due to a magnetic field. When the interaction 8 is due to a magnetic field, the electron spin state at the color center of the sensor element 1 will be in a state depending on the strength of the magnetic field generated from the measurement object 9.

A pair of measurement electrodes 13 (13a, 13b) are electrodes for detecting electrical changes occurring in the sensor element 1. A pair of measurement electrodes 13 are arranged with sensor element 1 in between. Illustratively, the minimum distance d of the gap between the pair of measurement electrodes 13a, 13b is about 2 μm. The measurement electrode 13 is formed on the diamond crystal 12 using a conductive metal, for example, by lithography technology.

In the configuration illustrated in FIG. 3, the sensor element 1 is arranged at a substantially central position between the pair of measurement electrodes 13a, 13b. In order to efficiently detect electrical changes occurring in the sensor element 1, the sensor element 1 is preferably offset from approximately the center between the pair of measurement electrodes 13a, 13b toward one of the measurement electrodes 13. It can be placed in any position.

The electromagnetic wave irradiation section 2 irradiates the sensor element 1 with electromagnetic waves for manipulating the electron spin state of the sensor element 1 by magnetic resonance. As an example, in this embodiment, the electromagnetic wave irradiation unit 2 includes a known microwave (MW) oscillator 21, a switch 22 that irradiates electromagnetic waves in a pulsed form, and an amplifier 23. Switch 22 and amplifier 23 can have any configuration. In this embodiment, the electromagnetic wave irradiation unit 2 irradiates the sensor element 1 with electromagnetic waves in a pulsed format for manipulating the electron spin state of the sensor element 1.

Various pulse sequences for causing magnetic resonance can be used as the pulse sequence of the electromagnetic waves that the electromagnetic wave irradiation section 2 irradiates the sensor element 1 with. For example, when sensing an alternating current magnetic field, the electromagnetic wave irradiation section 2 irradiates the sensor element 1 with electromagnetic waves in a pulse sequence based on the Hahn echo method of the spin echo method. Further, for example, when sensing a static magnetic field, the electromagnetic wave irradiation unit 2 irradiates the sensor element 1 with electromagnetic waves in a pulse sequence based on the Ramsey method of spin echo method.

The electromagnetic wave irradiation section 2 irradiates the sensor element 1 with electromagnetic waves through the antenna 14 for electromagnetic wave irradiation arranged near the sensor element 1 . The antenna 14 is formed on the diamond crystal 12 using a conductive metal, for example, by lithography technology.

The physical quantity measurement unit 3 calculates the physical quantity of the measurement object 9 based on the change in the electron spin state of the sensor element 1 after the change due to interaction with the measurement object 9 . In this embodiment, the physical quantity measurement unit 3 calculates the strength of the magnetic field generated from the measurement target 9. The physical quantity measurement section 3 includes a light irradiation section 31, a voltage application section 32, a detection section 33, and a data processing section 34.

The light irradiation unit 31 irradiates the sensor element 1 with light for initializing the electron spin state of the sensor element 1 . As an example, in this embodiment, the light irradiation unit 31 includes a light source 311, an acousto-optic modulator (AOM) 312, and an objective lens 313. The acousto-optic modulation element 312 and the objective lens 313 can have any configuration.

The light source 311 emits light for exciting and initializing the electron spin state of the sensor element 1 . The wavelength of the light emitted by the light source 311 is determined depending on the type of sensor element 1. In this embodiment, the light source 311 emits laser light with a wavelength of 532 nm (green). For example, various known laser generators can be used as the light source 311. In this embodiment, the light source 311 is a semiconductor laser that emits green laser light.

The objective lens 313 condenses the light emitted from the light source 311 and irradiates it onto the area on the diamond crystal 12 where the sensor element 1 is formed. Illustratively, the spot size of the laser beam focused on the diamond crystal 12 has a diameter of about 2 μm. As the spot size of the laser light decreases, the intensity of the laser light per unit area increases and the efficiency of the photocurrent generated in the diamond conductive band also increases.

In the configuration illustrated in FIG. 3, the laser beam spot is placed approximately at the center between the pair of measurement electrodes 13a and 13b so as to cover the area where the sensor element 1 on the diamond crystal 12 is generated. ing. Preferably, the spot of the laser beam can be placed at a position offset toward one of the measurement electrodes 13 from approximately the center between the pair of measurement electrodes 13a, 13b.

The voltage application unit 32 applies an electric field to the sensor element 1 through the measurement electrode 13 by applying a bias voltage between the pair of measurement electrodes 13 (13a, 13b). The electric field strength applied to the sensor element 1 is preferably approximately zero, more preferably zero. When the electric field strength is approximately zero, the electric field strength that the voltage application unit 32 applies to the sensor element 1 can be, for example, in the range of zero or more and less than 130 V/cm. When the electric field strength applied to the sensor element 1 is set to zero, the voltage application section 32 can be omitted.

The detection unit 33 detects a change in the photocurrent generated in the sensor element 1 as a change in the electron spin state of the sensor element 1. In this embodiment, the detection unit 33 converts the magnetic resonance signal into an electrical signal by detecting, through the measurement electrode 13, a change in photocurrent generated in the sensor element 1 due to light irradiation, based on a known electrical detection magnetic resonance method. Detect accurately. Illustratively, a known lock-in amplifier or ammeter can be used for the detection unit 33, for example.

The data processing unit 34 is connected to the detection unit 33 and reads phase information of the electron spin state of the sensor element 1 after interacting with the measurement target 9 from the change in the photocurrent detected by the detection unit 33. The physical quantity of the measurement object 9 is calculated based on the obtained phase information. In this embodiment, the data processing unit 34 calculates the strength of the magnetic field generated from the measurement target 9. For the data processing unit 34, for example, a known general-purpose computer or various information terminal devices such as a smartphone can be used.

The data processing section 34 may be configured to be integrated with the measuring device 10, or as illustrated, it may be provided outside the measuring device 10 and connected to the measuring device 10 via a network 99. You can.
[Measurement principle]

<Detection principle of magnetic resonance signals based on electric detection magnetic resonance method>
FIG. 4 is a diagram schematically showing the energy level of electrons at the NV ⁻ center of diamond. Referring to FIG. 4, the principle of detecting magnetic resonance signals based on the electric detection magnetic resonance method for electron spins in diamond will be described.

In this embodiment, the NV center of a diamond is used as the sensor element 1. The energy of the electron at the NV center is in the spin triplet (magnetic quantum number m _s = -1, 0, +1) state of |0> and |±1> in the ground state ³ A ₂ , and in the steady state at room temperature. , all levels are equally distributed in the ground state.

When |0> electrons in ground state ³ A ₂ are irradiated with laser light with a wavelength of 532 nm (green), they transition to excited state ³ E |0>, emitting red fluorescence PL, Ground state ³ A relaxes to |0> of ₂ . In the optical detection magnetic resonance (ODMR) method, magnetic resonance signals are detected as points where the red fluorescence intensity decreases.

|0> electrons in excited state ³ E can be further excited by green laser light irradiation before emitting fluorescent PL and relaxing to |0> in ground state ³ A ₂ . The excited electrons reach the diamond's conduction band, where a photocurrent is generated. In electrical detection magnetic resonance (EDMR), a magnetic resonance signal is detected as a change in this generated photocurrent.

Regarding the NV center of diamond, an electron in the excited state ³ E has a property that the relaxation process to the ground state ³ A ₂ is different depending on whether the spin is |0> or |±1>. Specifically, |0> electrons in the excited state ³ E emit fluorescence PL and relax to |0> in the ground state ³ A ₂ . On the other hand, the |±1> electron in the excited state ³ E transitions to the meta stable state ¹ E through a non-radiative process and returns to the ground state ³ A ₂ | without emitting fluorescence PL. Relax to 0>. By utilizing this property, when the NV center is continuously irradiated with green laser light, the spin state of the ground state ³ A ₂ is polarized to |0> (also referred to as initializing the NV center).

In such a state where the spin state of ground state ³ A ₂ is polarized to |0>, the spin state is polarized to |0>, so electrons can be transferred to the conductive band relatively efficiently. can be excited and a photocurrent is efficiently generated in the conductive band.

In this state, when microwaves (MW) with a resonance frequency of about 2.87 GHz are irradiated to the center of the NV, electron spin resonance (ESR) occurs, and the ground state ³ A ₂ , which is polarized to |0>, The spin state transitions to |±1> of the ground state ³ A ₂ . As mentioned above, the |±1> electron in the ground state ³ A ₂ transitions to the excited state ³ E |±1> by irradiation with green laser light, and then returns to the ground state ³ A ₂ through a non-radiative process. has the property of relaxing to |0>. Therefore, in the state where the spin is |±1> in the ground state ³ A ₂ , the generation efficiency of photocurrent generated in the conductive band is lower than in the state where the spin is |0>.

In this way, in the state where the spin is |0> in the ground state ³ A ₂ and the state where the spin is |±1>, the relaxation process to the ground state ³ A ₂ that occurs after being excited by laser light irradiation is It's different. Further, when magnetic resonance is generated, the ratio of the state in which the spin is |0> and the state in which the spin is |±1> in the ground state ³ A ₂ also changes. This change in proportion corresponds to magnetic resonance. Therefore, magnetic resonance signals can be electrically measured by measuring changes in the generated photocurrent.

<Method of calculating the physical quantity of the measurement target>
In the electrical detection magnetic resonance (EDMR) method, phase information (magnetic resonance signal) of the electron spin state of the sensor element 1 after interacting with the measurement target 9 is detected as a change in photocurrent. The detected phase information is in a state corresponding to the physical quantity of the measurement target. Therefore, by appropriately processing the phase information of the detected electron spin state after interaction, the physical quantity to be measured can be calculated. The physical quantity to be measured can be calculated based on the Hamiltonian of electron spin.

The Hamiltonian H _gs of electron spin is expressed by the following formula.

Here, μ _B is the Bohr magneton, g _e is the g-factor of the electron, and h is Planck's constant. Vector S is the electron spin. Vector B is the applied magnetic field. D _gs is the zero field splitting constant. S _x , S _y , and S _z are components of the electron spin S in the x, y, and z directions, respectively. d _gs ^⊥ is the electric dipole moment. E _x and E _y are the x- and y-direction components of the electric field, respectively.

は、ゼーマン効果による項であり、電子スピンが磁場センサとして機能することを意味している。 first term

is a term due to the Zeeman effect, which means that the electron spin functions as a magnetic field sensor.

は、電子スピンが温度センサおよび力学量（圧力）センサとして機能することを意味している。３番目の項

は、電子スピンが電場センサとして機能することを意味している。 The second and third terms are terms due to dipole interaction (ie, spin-spin interaction). second term

means that electron spin functions as a temperature sensor and a mechanical quantity (pressure) sensor. third term

means that the electron spin functions as an electric field sensor.

Therefore, the strength of the magnetic field can be calculated based on the first term. The temperature and the strength of the mechanical quantity can be calculated based on the second term. The strength of the electric field can be calculated based on the third term.
[Measurement procedure]

FIG. 5 is a flowchart showing the procedure of a measuring method according to an embodiment of the present invention. The procedure for sensing a magnetic field will be described with reference to FIGS. 5 and 2.

In the procedure illustrated below, it is assumed that the electron spin at the center of the NV interacts with the magnetic field of the measurement object 9 before and during the series of measurements. By allowing interaction for a sufficient period of time, the electron spin state at the NV center becomes a state that corresponds to the strength of the magnetic field.

In step S1, a low intensity electric field is applied to the sensor element 1. The sensor element 1 is arranged between a pair of measurement electrodes 13 (13a, 13b). The electric field is generated by applying a bias voltage between the pair of measurement electrodes 13 using the voltage application section 32. The generated electric field is applied to the sensor element 1 through the measurement electrode 13.

The low electric field strength applied to the sensor element 1 is preferably approximately zero, more preferably zero. When the electric field strength is approximately zero, the electric field strength that the voltage application unit 32 applies to the sensor element 1 can be, for example, in the range of zero or more and less than 130 V/cm. When the electric field strength applied to the sensor element 1 is set to zero, this step can be omitted.

In step S2, the electron spin at the color center (NV center) of the sensor element 1 is initialized by irradiating the sensor element 1 with laser light.

In step S3, the sensor element 1 is irradiated with electromagnetic waves for manipulating the electron spin state of the sensor element 1 by magnetic resonance. By manipulating the electron spin state of the sensor element 1 to cause magnetic resonance, the generation efficiency of the photocurrent generated in the sensor element 1 changes.

Electromagnetic waves for causing magnetic resonance are irradiated from the electromagnetic wave irradiation unit 2 to the sensor element 1 . The electromagnetic wave irradiation unit 2 irradiates electromagnetic waves in a pulse sequence according to the magnetic field of the measurement target. The electromagnetic wave irradiation unit 2 irradiates electromagnetic waves using a pulse sequence based on the Hahn echo method when measuring an alternating magnetic field, for example, and using a pulse sequence based on the Ramsey method when measuring a static magnetic field, for example.

In step S4, a change in photocurrent generated in the sensor element 1 is detected as a change in the electron spin state of the sensor element 1. Changes in photocurrent are electrically detected through the measurement electrode 13 using the detection unit 33 . The detected change in photocurrent is transmitted to the data processing unit 34 as a change in the electron spin state of the sensor element 1. The data processing unit 34 reads and records phase information (magnetic resonance signal) of the electron spin state of the sensor element 1 after interacting with the measurement target 9 from the change in the photocurrent detected by the detection unit 33.

In step S5, it is determined whether the series of measurement processes in steps S1 to S4 has been repeatedly executed a predetermined number of times. If the series of measurement processes has been repeatedly executed a predetermined number of times (Yes in step S5), the process in step S6 is performed, and if the series of measurement processes have not been repeatedly executed a predetermined number of times (No in step S5), steps S1 to S4 are performed. Executes a series of measurement processes. Illustratively, the number of times the series of measurement processes is repeatedly executed is approximately 500,000 times or more.

Note that when a series of measurement processes is repeatedly performed, the signal strength is integrated, so the S/N ratio of the signal improves as the number of times the measurement process is repeatedly performed increases.

In step S6, the strength of the magnetic field to be measured is calculated. The intensity of the magnetic field to be measured is calculated based on the change in the phase information (magnetic resonance signal) of the electron spin state of the sensor element 1, which is read from the change in the photocurrent detected in step S4. The phase information of the electron spin state of the sensor element 1 after the interaction detected by the detection unit 33 is in a state according to the magnetic field of the measurement object 9. Therefore, the strength of the magnetic field can be calculated by appropriately processing the phase information of the detected electron spin state after interaction. For example, the strength of the magnetic field of the measurement target 9 can be calculated by determining the probability that the electron spin state after interaction becomes the ground state. The intensity is calculated based on the term of the Hamiltonian H _gs of the electron spin due to the Zeeman effect.
[effect]

As described above, according to one embodiment of the present invention, measurement sensitivity can be improved in measurement using a quantum sensor. In this embodiment, in which the magnetic field sensor is configured to measure the strength of the magnetic field, the sensitivity of measuring the magnetic field can be improved, and the measurable strength of the magnetic field can be set smaller.

According to one embodiment of the present invention, by reducing the bias voltage applied to the measurement electrode 13 as low as possible, the influence of the electric field felt by the spin state of the sensor element 1 can be reduced as much as possible. Thereby, the influence on the spin state of the sensor element 1 due to the electric field generated by applying the bias voltage is reduced as much as possible, and improvement in measurement sensitivity is achieved.

According to one embodiment of the present invention, the magnetic resonance signal is electrically detected as a change in photocurrent by the electric detection magnetic resonance method, so that the measurement apparatus set can be configured as an electrical device. If a complete set of measurement equipment can be configured as an electrical device, it will be advantageous in terms of applications of the measurement equipment, such as integration and sophistication of devices, and development into next-generation quantum electronics is also expected.

When the color center of diamond or the color center of silicon carbide (SiC) is used for the sensor element 1, the measuring device 10 can be operated at room temperature (approximately 300 K) without using a cooling mechanism. A superconducting quantum interferometer (SQUID), known as an example of an advanced highly sensitive magnetic field sensor, requires a cooling mechanism, such as liquid nitrogen, to maintain its superconducting state. On the other hand, when the color center of diamond or the color center of silicon carbide (SiC) is used for the sensor element 1, the measuring device 10 does not need to be equipped with a cooling mechanism. It is advantageous compared to other advanced magnetic field sensors in that it is easy to install on vehicles (for example, on transportation equipment such as automobiles).
[Other forms]

Although the present invention has been described above using specific embodiments, the present invention is not limited to the above-described embodiments.

In the embodiment described above, a diamond crystal is used as the sensor element 1, and the NV center is used as the color center of the diamond, but the color center used is not limited to the NV center. Instead of NV centers, silicon-vacancy centers or germanium-vacancy centers can be used for the diamond color centers of the sensor element 1. Furthermore, the color center is not limited to the color center of a diamond crystal, and color centers of various crystals can be used for the sensor element 1.

In the embodiment described above, the color center of diamond is used for the sensor element 1, but the material used for the sensor element 1 is not limited to diamond. As long as it is possible to manipulate the electron spin state by irradiating the sensor element 1 with electromagnetic waves, the color center of silicon carbide (SiC), electrons and holes flowing in an organic semiconductor, PIN diode or Various quantum sensors such as electrons and holes in a PN diode can be used as the sensor element 1. As the organic semiconductor, for example, PPV (polyparaphenylene vinylene), fullerene, or a derivative thereof can be used. Spin is detected based on the electrical detection magnetic resonance (EDMR) method, which detects the magnetic resonance signals of the spins of electrons and holes flowing in organic semiconductors. Note that when electrons and holes flowing through an organic semiconductor, a PIN diode, and a PN diode are used as a quantum sensor element, initialization using laser light is not necessary.

In the embodiment described above, the sensor element 1 is an ensemble NV center generated on the order of several thousand within a predetermined region on the diamond crystal 12, but the sensor element 1 has only a single electron spin. A single NV center with .

In the embodiments described above, the physical quantity to be measured is a magnetic field (alternating magnetic field or static magnetic field), but the physical quantity to be measured is not limited to the magnetic field, but also electric fields, temperature, and mechanical quantities (mechanical stress, pressure, etc.). be able to. These physical quantities are physical quantities related to interaction with electron spin, and can be calculated based on the Hamiltonian of electron spin.

In the embodiment described above, the magnetic resonance signal is detected by the electric detection magnetic resonance method based on the magnetic properties of the electron spin of the NV center of the diamond. is not limited to electron spin. A magnetic resonance signal may be detected directly or indirectly by electric detection magnetic resonance method using nuclear spin instead of electron spin and based on the magnetic properties of the nuclear spin. Indirectly means, for example, using electromagnetic interaction (also called hyperfine interaction) between an atomic nucleus and an atomic electron.

In the embodiment described above, the pair of measurement electrodes 13 (13a, 13b) are arranged approximately symmetrically in order to detect electrical changes occurring in the sensor element 1, but the arrangement of the measurement electrodes used for detection is as follows. but not limited to. For example, by using the asymmetry of the diffusion current, electrical changes occurring in the sensor element 1 can be detected more efficiently. For example, when the arrangement of the measurement electrodes 13 is approximately symmetrical, the spot of the laser beam may be arranged at a position offset from the approximate center between the measurement electrodes 13 toward one of the measurement electrodes. Under zero bias voltage, the photocurrent propagates as a diffusion current, so it is preferable that the measurement electrode and the measurement point (the position of the laser beam spot) with respect to the measurement electrode be asymmetrical.

In the embodiment described above, after applying a low-strength electric field to the sensor element 1, the electron spin at the color center of the sensor element 1 is initialized. It is only necessary to apply the voltage to the sensor element 1 when detecting the voltage.

In the embodiment described above, the electron spins at the NV center interact with the magnetic field of the measurement object 9 before and during the measurement, but the timing at which the electron spins at the NV center interact with the magnetic field of the measurement object 9 is at this time. but not limited to. The electron spins at the NV center need only interact with the magnetic field of the measurement object 9 before or during magnetic resonance.

Examples of the present invention will be shown below to clarify the characteristics of the present invention.

In Example 1, it was confirmed that the magnetic resonance signal at the NV center of diamond could be electrically detected under zero bias voltage.

Detection of magnetic resonance signals was performed using a configuration similar to that of the measuring device according to the embodiment of the present invention shown in FIG. The magnetic resonance signal generated from the NV center by irradiation with electromagnetic waves for spin state manipulation was measured by electric detection magnetic resonance method. The bias voltage applied to the measurement electrode was set to zero. FIG. 6 shows the measurement results of magnetic resonance signals by electric detection magnetic resonance method. In the figure, (B) shows a magnetic resonance signal, and (A) shows the timing and period of irradiation of laser light and electromagnetic waves to the NV center. As shown in the measurement results in (B), it was confirmed that the magnetic resonance signal by the electric detection magnetic resonance method could be measured even under zero bias voltage.

In addition, in the measurement shown in Example 1, as shown in the irradiation timing in (A), the current change due to magnetic resonance (EDMR signal ΔI) is measured by the first laser irradiation, and the total photocurrent amount is measured by the second laser irradiation. Measuring I. This total photocurrent amount I corresponds to the photocurrent amount that does not include magnetic resonance signals. Next, by dividing the EDMR signal ΔI by the total photocurrent amount I, the value of the vertical axis of the magnetic resonance signal shown in the graph (B) is obtained.

In Example 2, the dependence of photocurrent on laser power was confirmed while changing the bias voltage applied to the center of the NV. The confirmation was performed using the same configuration as the measuring device according to the embodiment of the present invention shown in FIG. The photocurrent generated at the NV center by irradiation with excitation light was electrically measured through a measurement electrode. The power of the laser irradiated to the center of the NV was varied in the range of 0 mW to 8.8 mW. The bias voltage applied between the electrodes was varied stepwise in steps of 1 volt in the range from 8 V to 0 V until it reached zero. The minimum distance d of the gap between the electrodes was approximately 2 μm, and the electric field strength applied to the NV center ranged from 40 kV/cm to 0 V/cm. The measurement results are shown in FIG.

As shown in the measurement results in FIG. 7, it was confirmed that magnetic resonance signals by electric detection magnetic resonance method can be measured even under zero bias voltage. The measurement results of the magnetic resonance signals shown in FIG. 7 when the electric field strength applied to the NV center is 0 V/cm are different from the electric field strength applied to the NV center in the conventional technology (0.13 to 50 kV/cm). Even when compared to the measurement at , the measurement was performed under conditions where the applied electric field strength was lower.

1 Sensor element 2 Electromagnetic wave irradiation section 3 Physical quantity measurement section 8 Interaction 9 Measurement object 10 Measurement device 11 Probe 12 Crystal (diamond)
13 (13a, 13b) Measuring electrode 14 Antenna 21 Oscillator 22 Switch 23 Amplifier 31 Light irradiation section 32 Voltage application section 33 Detection section 34 Data processing section 99 Network 311 Light source 312 Acousto-optic modulation element 313 Objective lens

Claims (9)

A quantum sensor element whose spin state changes due to interaction with the measurement target,
a pair of measurement electrodes arranged with the quantum sensor element sandwiched therebetween;
an electromagnetic wave irradiation unit that irradiates the quantum sensor element with electromagnetic waves for manipulating the spin state of the quantum sensor element by magnetic resonance;
a physical quantity measurement unit that calculates the physical quantity of the measurement target based on the change in the spin state,
The measuring device, wherein the electric field strength applied to the quantum sensor element is zero . The physical quantity measuring section includes:
a light irradiation unit that irradiates the quantum sensor element with light for initializing the spin state of the quantum sensor element;
a detection unit that detects a change in photocurrent generated in the quantum sensor element by the irradiation of the light as a change in the spin state through the measurement electrode;
The measuring device according to claim 1 , comprising: The physical quantity measuring section includes:
The measuring device according to claim 2 , further comprising a data processing unit that reads out phase information of the spin state from the detected change in the photocurrent and calculates the physical quantity based on the read phase information. The measuring device according to any one of claims 1 to 3 , wherein the quantum sensor element is a sensor element having a color center. 5. The measuring device according to claim 4 , wherein the color center is a composite of nitrogen (N) replacing a carbon atom and a vacancy (V) adjacent to the nitrogen. The measurement according to any one of claims 1 to 5 , wherein the physical quantity measurement unit calculates at least one of a magnetic field, an electric field, a temperature, and a mechanical quantity as the physical quantity related to interaction with spin. Device. A quantum sensor element that is disposed between a pair of measurement electrodes and whose spin state changes due to interaction with a measurement target, and in which an electromagnetic wave for manipulating the spin state of the quantum sensor element by magnetic resonance is transmitted to the quantum sensor. a step of irradiating the element;
calculating a physical quantity of the measurement target based on the change in the spin state;
including ;
A measuring method , wherein the electric field strength applied to the quantum sensor element is zero . The step of calculating the physical quantity includes:
irradiating the quantum sensor element with light for initializing the spin state of the quantum sensor element;
Detecting a change in photocurrent generated in the quantum sensor element by the irradiation of the light as a change in the spin state through the measurement electrode;
The measuring method according to claim 7 , comprising: The step of calculating the physical quantity includes:
9. The measuring method according to claim 8 , further comprising the step of reading phase information of the spin state from the detected change in the photocurrent and calculating the physical quantity based on the read phase information.

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