JP2022165005A - Vacancy defect forming method, diamond producing method, and diamond - Google Patents

Abstract

To form high-density vacancy defects in diamond.SOLUTION: The present invention discloses a method for forming vacancy defects inside diamond, the method including the steps of: shaping a pulse wave form of laser having a transparent wavelength with respect to an absorption wavelength of diamond to compensate for temporal dispersion on a phase of pulse light of laser; and emitting the pulse light of laser subjected to dispersion compensation into the diamond plural times.SELECTED DRAWING: Figure 5

Description

The present invention relates to a method of forming vacancy defects in diamond, a method of producing diamond having vacancy defects, and a diamond with vacancy defects formed therein.

Due to its excellent optical, electrical, and thermal properties, diamond is expected to be applied to optical elements, electronic devices, and the like. Particularly in recent years, attention has been focused on nitrogen-vacancy centers called NV centers (nitrogen vacancy centers) existing inside diamond. The NV center consists of pairs of nitrogen impurities inside diamond and vacancy defects adjacent thereto, and exhibits a magnetic property called electron spin when electrons are trapped in the vacancies. The electron spin in the NV center has a long coherence time even at room temperature, and its spin state can be controlled and detected at room temperature. Applications such as sensors are expected.

Non-Patent Documents 1 and 2 listed below are examples of conventional reports on the formation of NV centers in diamond.

V. V. Kononenko, I. I. Vlasov, E. V. Zavedeev, A. A. Khomich, and V. I. Konov, “Correlation between surface etching and NV center generation in laser-irradiated diamond”, Appl. Phys. A 124, 226 (2018). https://doi. org/10.1007/s00339-018-1646-x V. V. Kononenko, I. I. Vlasov, V. M. Gololobov, T. V. Kononenko, T. A. Semenov, A. A. Khomich, V. A. Shershulin, V. S. Krivobok, and V. I. Konov, “Nitrogen-vacancy defects in diamond produced by femtosecond laser nanoablation technique”, Applied Physics Letters 111, 081101 ( 2017). https://doi.org/10.1063/1.4993751

An ensemble NV center, which is a collection of many NV centers, is important for applications to quantum computing. Ensemble NV centers have advantages such as improved quantum sensor performance due to increased signal strength. Moreover, if an ensemble NV center is a collection of NV centers with four different orientations, such an ensemble NV center can utilize the difference in the Zeeman splitting width due to the difference in orientation to obtain the three-dimensional vector component of the magnetic field has the advantage of being able to determine

Therefore, in application to quantum sensors, it is effective to form a large number of NV centers (ensemble NV centers) in diamond to increase the concentration of NV centers in order to improve the measurement sensitivity of the sensor. However, the concentration of the ^{NV center} produced ^by laser irradiation has not been ^{quantitatively} evaluated so far. There have been no previous reports of the formation of NV centers at concentrations of ³ or higher. In order to apply NV centers of diamond to quantum sensors and the like, there is a demand for a method of forming NV centers with a concentration high enough to be applied to quantum sensors and the like.

An object of the present invention is to form a high concentration of vacancy defects in diamond.

The present invention for achieving the above object includes, for example, the following aspects.
(Section 1)
A method for forming vacancy defects inside a diamond, comprising:
shaping a pulse waveform of a laser having a wavelength transparent to the absorption wavelength of the diamond to compensate for temporal dispersion in phase of the pulsed light of the laser;
a step of condensing and irradiating the pulsed light of the laser, the dispersion of which is compensated for, into the interior of the diamond a plurality of times;
method including.
(Section 2)
Item 2. The method according to item 1, wherein the number of the pulsed lights condensed and irradiated to the inside of the diamond is 5×10 ⁷ or more.
(Section 3)
Item 3. The method according to Item 2, wherein the number of the pulsed lights condensed and irradiated to the inside of the diamond is 2.5×10 ⁸ or more.
(Section 4)
the laser pulse energy is in the range of 60 nJ to 200 nJ;
Item 4. The method according to any one of Items 1 to 3, wherein the pulse width of the laser is 40 femtoseconds or less.
(Section 5)
5. The method of clause 4, wherein the laser pulse energy is in the range of 150 nJ to 200 nJ.
(Section 6)
In the step of compensating for dispersion, the pulsed light is phase-modulated to form a first sub-pulse light composed of a first polarization component and a second sub-pulse light composed of a second polarization component crossing the first polarization component. 6. The method according to any one of clauses 1 to 5, wherein a time delay is generated between the subpulse light of 2.
(Section 7)
preparing a diamond;
Forming vacancy defects inside the diamond by the method of any one of Items 1 to 6;
A method of making a diamond, comprising:
(Section 8)
A diamond in which the concentration of vacancy defects formed therein is 1×10 ¹⁵ cm ⁻³ or more.
(Section 9)
Item 9. The diamond according to Item 8, wherein the concentration of the vacancy defects is 3×10 ¹⁵ cm ⁻³ or more.
(Section 10)
Item 10. The diamond according to item 9, wherein the concentration of the vacancy defects is 1×10 ¹⁶ cm ⁻³ or more.

According to the present invention, a high concentration of vacancy defects can be formed in diamond.

It is a figure showing a typical composition of an optical system used when performing a vacancy defect formation method concerning one embodiment of the present invention. It is an example of a time waveform of pulsed light output by a laser. 2 is a diagram showing a schematic configuration of a pulse shaper shown in FIG. 1; FIG. FIG. 4 is a diagram showing a schematic configuration when setting dispersion compensation of pulsed light to a pulse shaper; FIG. 10 is a diagram for explaining the verification results according to the example, and is a graph showing changes in density of NV centers with respect to the number of pulsed lights for each pulse energy. FIG. 3 is a diagram for explaining verification results according to an example, where (a) is a pulse sequence by the Hahn echo method based on the optical detection magnetic resonance (ODMR) method used for measuring the transverse relaxation time T2, and ( _b ) is a pulse sequence; ˜(e) are measured signals by the Hahn echo method.

Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. In the following description and drawings, the same reference numerals denote the same or similar components, and redundant description of the same or similar components will be omitted.

According to a first aspect of the present invention, a method is provided for forming vacancy defects inside diamond. A method according to one embodiment comprises:
shaping a laser pulse waveform having a wavelength transparent to the absorption wavelength of diamond to compensate for temporal dispersion in phase of the pulsed light of the laser;
a step of concentrating and irradiating the inside of the diamond with pulsed light of a dispersion-compensated laser multiple times;
including.

In the method according to one embodiment, the number of pulsed lights focused on the inside of the diamond is 5×10 ⁷ or more. Preferably, the number of pulsed lights focused on the inside of the diamond is 2.5×10 ⁸ or more.

In one embodiment, the laser pulse energy is in the range of 60 nJ to 200 nJ and the laser pulse width is 40 femtoseconds or less. More preferably, the pulse energy of the laser ranges from 150 nJ to 200 nJ.

In one embodiment, in the step of compensating for dispersion, the pulsed light is phase-modulated to form a first sub-pulse light having a first polarization component and a second sub-pulse light that crosses the first polarization component. A time delay is generated with the second sub-pulse light composed of polarized light components.

According to a second aspect of the invention, a method of making diamond is provided. A manufacturing method according to one embodiment includes:
preparing a diamond;
forming vacancy defects inside diamond by the method provided by the first aspect of the present invention;
including.

According to a third aspect of the invention, a diamond is provided. A diamond according to one embodiment has a concentration of vacancy defects formed therein of 1×10 ¹⁵ cm ⁻³ or more. Preferably, the concentration of vacancy defects is 3×10 ¹⁵ cm ⁻³ or more. More preferably, the concentration of vacancy defects is 1×10 ¹⁶ cm ⁻³ or more.

In the examples of the present invention, which will be described later, even if the number of pulsed lights irradiated on the diamond sample was increased to 5×10 ⁵ to 5×10 ⁸ to form the NV centers, the lateral relaxation of the formed NV centers did not occur. Time _T2 does not vary significantly within the range of about 1.6±0.2 microseconds to about 2.4±0.2 microseconds, and diamond graphitization is suppressed.

[Optical system]
FIG. 1 is a diagram showing a schematic configuration of an optical system used when executing a vacancy defect formation method according to an embodiment of the present invention.

The optical system 10 includes a laser 1 used as a light source for modifying the sample 9, a pulse shaper 2 for shaping the pulse waveform of the laser light, and condensed irradiation of the pulsed light with the shaped waveform inside the sample 9. It mainly includes an objective lens 3 for A pulsed light Lp emitted from a laser 1 is shaped into a pulse shape by a pulse shaper 2 to control the pulse width, condensed by an objective lens 3, and irradiated to a predetermined depth inside a sample 9. FIG. The sample 9 is modified by irradiation with laser light. The traveling direction of the pulsed light Lp emitted from the laser 1 is appropriately adjusted by the total reflection mirror 4 .

The optical system 10 can further comprise a dichroic mirror 5 and a photodetector 6 such as an avalanche photodiode as a configuration for observing the modified sample 9 . The optical system for irradiating the sample 9 with the pulsed light Lp output from the laser 1 through the pulse shaper 2 and the optical system for observing the reflected light from the sample 9 through the photodetector 6 form a confocal optical system. there is Such an optical system 10 can be constructed using, for example, a confocal fluorescence microscope. It should be noted that the optical system 10 need not include the dichroic mirror 5 and the photodetector 6 when modifying the inside of the sample 9, and need not constitute a confocal optical system.

FIG. 2 is an example of the time waveform of the pulsed light Lp output by the laser, and an example of the intensity autocorrelation waveform. The vertical axis in FIG. 2 indicates the normalized light intensity. Unless otherwise specified in the description below in this specification, the pulse width is a value after time waveform shaping by the pulse shaper 2,
Pulse width = full width at half maximum (FWHM) of intensity autocorrelation waveform/1.5426
Means the value calculated by It is assumed that the waveform of the pulse is sech ² type.

Synthetic diamond is used for sample 9 in this embodiment. In this embodiment, the sample 9 is, for example, a type Ib HPHT single crystal synthetic diamond having a high concentration of nitrogen impurities, and illustratively, the nitrogen concentration of the synthetic diamond used for the sample 9 is about 33 ppm. The sample 9 is placed on a three-axis stage (not shown), and the area (XY plane) on which the sample 9 is irradiated with the laser light and the position of the sample 9 along the irradiation axis of the laser light ( Z axis) are adjustable. The irradiation of the sample 9 with laser light can be performed in the atmosphere at room temperature. Illustratively, room temperature means a temperature range of about 1°C to 30°C, including a normal temperature range of about 15°C to 25°C, but is not limited to these temperature ranges.

The laser 1 outputs pulsed light Lp with a pulse width on the order of femtoseconds. The pulsed light Lp output by the laser 1 has a transparent wavelength with respect to the absorption wavelength of the sample 9 . As a result, the laser 1 modifies the sample 9 in the vicinity of the focal point of the laser by nonlinear absorption, enabling spatially selective position control of the sample 9 including the depth direction. The fact that the pulsed light Lp has a transparent wavelength with respect to the absorption wavelength of the sample 9 means that even if the sample 9 is irradiated with the pulsed light Lp, spectral lines appear in the absorption spectrum of the sample 9 in the wavelength band of the pulsed light Lp. It means that it is a wavelength band that does not exist. The energy of the pulsed light Lp with which the sample 9 is irradiated is nonlinearly absorbed by the crystal lattice of the sample 9 . In this embodiment, the pulsed light Lp is linearly polarized, and the laser 1 is a regenerative amplification titanium sapphire laser that outputs pulsed light with a center wavelength of about 800 nm.

In this embodiment, the laser pulse energy is preferably in the range of about 60 nJ to 200 nJ and the pulse width is about 40 femtoseconds. As will be described later, the pulse width of the laser can be shaped by the pulse shaper 2, and this pulse width of about 40 femtoseconds in the example is the value after temporal waveform shaping by the pulse shaper 2. FIG. In this embodiment, the repetition frequency for outputting pulsed light is approximately 250 kHz.

In this embodiment, the sample 9 is irradiated with laser light for a longer time than conventional (for example, about 1 second). The time for irradiating the sample 9 with laser light is from about 2 seconds to about 5000 seconds. That is, in this embodiment, the laser 1 outputs a plurality of pulsed lights Lp of about 5×10 ⁵ to about 1.25×10 ⁹ .

（式１）に示す多項式中、パルスの波形に寄与する項は二次関数以上の項である。よって、（式１）中のａ_２の値を変更することにより、パルス幅を制御することができる。パルス整形器２は、後述する空間光変調器２７と回折格子による分散素子２５とにより、（式１）に記載されている二次の位相の項を制御することによって、照射レーザーパルスの時間波形を変化させて、パルス幅を調整する。パルス整形器２は、レーザーのパルス幅を約４０フェムト秒以下に整形することができる。 A pulse shaper 2 shapes the pulse waveform of the laser light to control the pulse width. The phase φ of the pulsed light can be approximated by a polynomial by Taylor expansion.

In the polynomial shown in (Equation 1), terms that contribute to the waveform of the pulse are quadratic or higher terms. Therefore, the pulse width can be controlled by changing the value of _a2 in (Equation 1). The pulse shaper 2 controls the second-order phase term described in (Equation 1) by means of a spatial light modulator 27 and a dispersive element 25 consisting of a diffraction grating, which will be described later, so that the time waveform of the irradiation laser pulse is to adjust the pulse width. A pulse shaper 2 can shape the pulse width of the laser to about 40 femtoseconds or less.

The objective lens 3 collects and irradiates the inside of the sample 9 with the pulsed light after the time waveform shaping. In this embodiment, the objective lens 3 has a magnification of about 50 (numerical aperture NA=0.80) and focuses to a depth of about 15 μm from the surface of the sample 9 .

[Pulse shaper and dispersion compensation]
• Pulse Shaper FIG. 3 is a diagram showing a schematic configuration of the pulse shaper shown in FIG. The pulse shaper 2 includes a polarization controller 21, mirrors 22, 23, 24, a dispersive element 25, a condensing element 26, and a spatial light modulator (SLM) 27. FIG. The pulse shaper 2 modulates the phase of the pulsed light Lp for each wavelength by passing the input pulsed light Lp through the dispersive element 25 and the spatial light modulator 27 in that order.

The pulse shaper 2 phase-modulates the pulsed light Lp output from the laser 1 to produce a first sub-pulse light composed of a first polarization component and a second polarization component crossing the first polarization component. A time delay is generated between the second sub-pulse light consisting of

The polarization controller 21 is an optical element that is optically coupled to the laser 1 and rotates the plane of polarization of the input pulsed light Lp. The polarization control unit 21 is composed of a wavelength plate such as a λ/2 plate, a polarizing element, and the like. Thereby, the pulsed light Lp includes a first polarization component along the first polarization direction and a second polarization component along a second polarization direction that intersects the first polarization direction. In one embodiment, the first polarization direction and the second polarization direction are orthogonal.

The mirrors 22 , 23 , 24 are optical elements that direct the traveling direction of the input pulsed light Lp toward the dispersive element 25 . The mirrors 22, 23, 24 are composed of total reflection mirrors, for example. Mirrors 22 , 23 , 24 can be omitted depending on the relative positional relationship with dispersive element 25 .

The dispersion element 25 is an optical element that disperses the pulsed light Lp for each wavelength. Dispersive element 25 is composed of, for example, a diffraction grating or a prism. Since the diffraction grating has a different diffraction angle for each wavelength, when the pulsed light Lp having wavelength components in a wide band is incident on the diffraction grating, the wavelength components are diffracted in different directions.

The condensing element 26 is an optical element that converges each wavelength component of the pulsed light Lp output from the dispersive element 25 while spreading to different positions on the spatial light modulator 27 . The condensing element 26 is configured by, for example, a cylindrical lens. The condensing element 26 has refractive power (lens power) in a plane including the direction of wavelength dispersion by the dispersion element 25, and does not have refractive power in a plane perpendicular to the direction of wavelength dispersion.

The spatial light modulator 27 is a phase modulation type spatial light modulator, and modulates the pulsed light Lp dispersed by the dispersive element 25 for each wavelength. In this embodiment, the spatial light modulator 27 is configured by a liquid crystal type (Liquid Crystal on Silicon: LCOS) spatial light modulator. The modulation surface of the spatial light modulator 27 includes a plurality of modulation regions corresponding to each of a plurality of wavelength components, and these modulation regions are arranged in the wavelength dispersion direction of the dispersive element 25 . When each wavelength component of the pulsed light Lp is input to the corresponding modulation area, it is modulated independently according to the modulation pattern of that modulation area.

The pulsed light Lp input to the spatial light modulator 27 is rotated with respect to the polarization direction in which the spatial light modulator 27 provides modulation as a result of the rotation of the polarization plane by the polarization controller 21 . As a result, among the polarization components of the pulsed light Lp, the polarization component along the polarization direction for which the spatial light modulator 27 provides modulation is modulated by the spatial light modulator 27, and the temporal waveform changes.

Dispersion Compensation FIG. 4 is a diagram showing a schematic configuration when setting dispersion compensation of pulsed light to a pulse shaper.

As shown in FIG. 4, when setting dispersion compensation of pulsed light to the pulse shaper, a condensing optical system 81 is installed after the optical system including the laser 1 and the pulse shaper 2 in the optical system shown in FIG. , the wavelength conversion element 82 and the spectroscope 83 are optically coupled. Dispersion compensation of pulsed light is set in the pulse shaper 2 by the control unit 84 .

The condensing optical system 81 is provided between the spatial light modulator 27 and the wavelength conversion element 82 and converges the pulsed light Lp toward the wavelength conversion element 82 .

The wavelength conversion element 82 changes the intensity spectrum of the emitted light according to the phase of the pulsed light Lp. A nonlinear optical crystal such as GaAs, GaP, ZnTe, KDP, BBO, BIBO, LiNbO ₃ , KTP, LBO, or CLBO can be used for the wavelength conversion element 82 . Several types of light are emitted from the wavelength conversion element 82, such as second harmonic, third harmonic, and higher harmonic waves. These several types of light emitted from the wavelength conversion element 82 can be separated by a wavelength filter.

The spectroscope 83 detects the intensity spectrum of the light emitted from the wavelength conversion element 82 by irradiating the wavelength conversion element 82 with the pulsed light Lp. The intensity spectrum of the detected light is output to control unit 84 as a detection signal.

The control unit 84 controls the polarization controller 21 and the spatial light modulator 27 based on the detection signal output from the spectroscope 83 . The control unit 84 is, for example, a computing device such as a general-purpose computer or a personal computer (PC). The control unit 84 changes the polarization direction of the pulsed light Lp by controlling the rotation angle of the plane of polarization in the polarization control section 21 . Also, the control unit 84 changes the temporal waveform of the pulsed light Lp by controlling the phase pattern of the spatial light modulator 27 .

In this embodiment, the pulse shaper 2 controls and compensates for the temporal dispersion regarding the phase of pulsed light based on the MIIPS (Multiphoton Intrapulse Interference Phase Scan) method. As a result, the phases of the pulsed light emitted from the laser 1 are aligned to generate a Fourier transform limit pulse with a further shortened laser pulse width.

In the MIIPS method, the pulsed light Lp is passed through a wavelength conversion element 82 such as a nonlinear optical crystal to generate second harmonics of the pulsed light Lp, and the phase dispersion is measured by a spectroscope 83. . Pulse shaper 2 generates a Fourier transform-limited pulse by compensating for its phase dispersion measured by spectrometer 83 . In this embodiment, the pulse shaper 2 compensates for phase dispersion and matches the phase of the pulsed light Lp by modulating the phase of the pulsed light Lp such that the intensity of the second harmonic is maximized. .

The measurement of phase dispersion using the wavelength conversion element 82, the spectroscope 83, and the control unit 84 and the setting of dispersion compensation for the pulse shaper 2 shown in FIG. 4 constitute the optical system 10 shown in FIG. It is enough to go once before.

Examples of the present invention are shown below to further clarify the features of the present invention.

In this example, the optical system according to the above-described embodiments of the present invention was configured using a confocal fluorescence microscope. Phase dispersion is measured using the wavelength conversion element, spectroscope and control unit described in the above embodiments, and dispersion compensation is set for the pulse shaper so as to generate Fourier transform limited pulses based on the MIIPS method. gone. An optical system with a pulse shaper with dispersion compensation settings was used to irradiate the diamond with pulsed light from the laser to form NV centers inside the diamond.

In this example, NV centers were formed inside diamond by the method of forming vacancy defects according to the above-described embodiments of the present invention. The formation of NV centers was performed with various combinations of laser irradiation time and pulse energy. The concentration of NV centers was estimated from measurements of the intensity of fluorescence emitted from NV centers. The intensity of fluorescence emitted from NV centers was measured using a photodiode.

In this example, two items were verified. In verification 1, it was verified whether or not the concentration of the formed NV center was improved as compared with the conventional reports. In verification 2, it was verified whether diamond was graphitized in the formed NV center.

<Verification 1>
Regarding the concentration of NV centers, the difference between the NV centers formed inside the diamond by the vacancy defect forming method according to this example and the NV centers formed on the surface or inside the diamond in the conventional report as a comparative example. made a comparison. A graph of the comparison results is shown in FIG.

Concentrations in comparative examples were estimated based on fluorescence intensity values described in previous reports. In estimating the concentrations of the comparative examples, conditions and values not described in the report were assumed. Two conventional reports cited as comparative examples are Non-Patent Documents 1 and 2 described above. Note that 1 ppm=1.76×10 ¹⁷ cm ⁻³ in the following description.

・Comparative example 1
As Comparative Example 1, the maximum value of fluorescence intensity reported in Non-Patent Document 1, which is about 2.3 (the number of pulsed lights is about 1.68×10 ⁷ ), was used to estimate the density of the NV center at 7.5. 2×10 ¹⁴ cm ⁻³ was obtained. In Non-Patent Document 1, NV centers are formed on the surface by surface ablation.

For Non-Patent Document 1, the concentration of NV centers was estimated as follows.
Nitrogen concentration of diamond sample: 0.5 ppm (calculated from absorption coefficient at 270 nm)
Fluorescence intensity (original PL signal) of non-irradiated portion of pulsed light: about 0.28
Maximum fluorescence intensity: about 2.3 (number of pulsed lights about 1.68×10 ⁷ )
Assuming that the NV concentration in the portion not irradiated with pulsed light was 0.1% with respect to the nitrogen concentration in the diamond sample, the maximum concentration in the portion irradiated with pulsed light was estimated to be 7.2×10 ¹⁴ cm ⁻³ .

・Comparative example 2
As Comparative Example 2, the maximum value of fluorescence intensity reported in Non-Patent Document 2, approximately 0.87 (the number of pulsed light is approximately 8.39×10 ⁴ ), was used to estimate the concentration of the NV center at 5.5. 4×10 ¹⁴ cm ⁻³ was obtained. In Non-Patent Document 2, NV centers are formed on the surface by surface ablation.

Regarding non-patent document 2, the concentration of NV centers was estimated as follows.
Nitrogen concentration of diamond sample: 0.5 ppm (calculated from absorption coefficient at 270 nm)
Fluorescence intensity (Original PL signal) of non-irradiated portion of pulsed light: about 0.14
Maximum value of fluorescence intensity: about 0.87 (number of pulsed lights about 8.39×10 ⁴ )
Assuming that the NV concentration in the pulsed light unirradiated portion was 0.1% with respect to the nitrogen concentration in the diamond sample, the maximum concentration in the pulsed light irradiated portion was estimated to be 5.4×10 ¹⁴ cm ⁻³ .

FIG. 5 is a diagram for explaining the verification results according to the example, and is a graph showing changes in density of NV centers with respect to the number of pulsed lights for each pulse energy. The data of the four types of line graphs plotted in the figure using four different types of symbols are the measured values of the concentration of the NV centers formed inside the diamond by the vacancy defect formation method according to this example. The data plotted in the figure using two different enclosing symbols are estimated values of the concentration of the NV center according to the comparative example.

Based on the graph shown in FIG. 5, which compares the concentrations of the NV centers, the laser light irradiation time and pulse energy conditions for forming high-concentration NV centers were examined. The concentration of the NV center targeted for formation was set to about 10 ¹⁵ cm ⁻³ to 10 ¹⁶ cm ⁻³ , which is the concentration that can be expected to increase the sensitivity of the quantum sensor.

First, an overview of the measurement results according to this example will be reported. In this example, as the number of pulses of light applied to the diamond sample increased, the concentration of NV centers initially increased and then saturated or slightly decreased. After that, the number of ^{pulsed lights} to be irradiated was increased to obtain measurement data. It increased again from ∼4×10 ¹⁵ cm ⁻³ . Further, the number of ^pulsed lights to be irradiated was increased to obtain measurement data. A maximum value of about 3×10 ¹⁶ cm ⁻³ was obtained. The NV centers were formed without annealing the diamond after irradiating the diamond sample with laser pulse light.

In this measurement result, it is speculated that the behavior that the concentration of the NV center saturates or decreases with an increase in the number of pulsed lights can be interpreted from the viewpoint of competition between the formation and disappearance of the NV center. was done.

The measurement result of the concentration of the NV center according to the present example and the estimated value of the concentration of the NV center according to Comparative Examples 1 and 2 were compared. The results of the study were as follows.

According to this example, a diamond sample having a NV center concentration of about 1×10 ¹⁵ cm ⁻³ was obtained by irradiating a diamond sample with about 2.5×10 ⁶ light pulses at a pulse energy of about 60 nJ. was taken. The concentration value obtained is higher than any estimated value of the concentration of the NV center shown in Comparative Examples 1 and 2, and is about 10 ¹⁵ which is the lower limit of the target value of the concentration at which high sensitivity can be expected in the quantum sensor. had achieved When the pulse energy is about 100 nJ, about 150 nJ, and about 200 nJ, the NV center concentration is about 1×10 ¹⁵ cm ⁻³ or more by irradiating about 1.25×10 ⁶ pulsed light. got a diamond.

According to this example, by irradiating a diamond sample with about 5×10 ⁷ pulsed light, a diamond having an NV center concentration of about 3×10 ¹⁵ cm ⁻³ or higher was obtained. This concentration of NV centers was obtained at any pulse energy. The obtained concentration value was the concentration when the once saturated NV center concentration began to increase again. This number of pulsed light irradiations was the number of pulsed light irradiations that was not achieved in either of Comparative Examples 1 and 2. The concentration value obtained is higher than any estimated value of the concentration of the NV center shown in Comparative Examples 1 and 2, and is about 10 ¹⁵ which is the lower limit of the target value of the concentration at which high sensitivity can be expected in the quantum sensor. had achieved

According to this example, by irradiating a diamond sample with about 2.5×10 ⁸ pulsed light, a diamond having an NV center concentration of about 1×10 ¹⁶ cm ⁻³ or more was obtained. This concentration of NV centers was obtained at any pulse energy. This number of pulsed light irradiations was the number of pulsed light irradiations that was not achieved in either of Comparative Examples 1 and 2. The obtained concentration value is higher than any estimated value of the concentration of the NV center shown in Comparative Examples 1 and 2, and achieves the target concentration of about 10 ¹⁶ that can be expected to increase the sensitivity of the quantum sensor. Was.

According to this example, by irradiating a diamond sample with up to about 5×10 ⁸ pulsed light at a pulse energy of about 150 nJ or about 200 nJ, the concentration of NV centers is increased up to about 3×10 ¹⁶ cm ⁻³ . A diamond was obtained. This number of pulsed light irradiations was not achieved in either of Comparative Examples 1 and 2, and the density values obtained were not achieved in either of Comparative Examples 1 and 2. concentration.

<Verification 2>
It was verified whether or not the diamond was graphitized with respect to the NV center formed inside the diamond by the vacancy defect forming method according to the present example.

Verification was performed by measuring the transverse relaxation _time T2 of the NV center by a known Optically Detected Magnetic Resonance (ODMR) method. This transverse relaxation _time T2 decreases if the diamond is graphitized during the formation of NV centers in the diamond.

For verification, a plurality of diamond samples were used in which NV centers were formed by varying the concentration, that is, the number of pulsed lights to be irradiated, between about 5×10 ⁵ and about 5×10 ⁸ . The pulse energy of the laser applied to the diamond sample was about 150 nJ.

FIG. 6 is a diagram for explaining the verification results according to the example, (a) is a pulse sequence by the Hahn echo method based on the optical detection magnetic resonance (ODMR) method used for measuring the transverse relaxation _time T2. , (b) to (e) are measured signals by the Hahn echo method.

As shown in the measurement signals of (b) to (e), even if the number of pulsed lights irradiated to the diamond sample is increased to 5×10 ⁵ to 5×10 ⁸ to form NV centers, no NV centers are formed. _The transverse relaxation time T2 of the NV center does not vary significantly within the range of about 1.6±0.2 μs to about 2.4±0.2 μs, and furthermore, the pristine diamond sample _The transverse relaxation time T2 of the NV centers contained in is about 1.6±0.2 μs, which is almost the same value. From this, it was confirmed that graphitization of diamond, which may occur when NV centers are formed, is suppressed by the vacancy defect formation method according to the present example.

When the number of pulsed lights irradiated on the diamond sample was increased to 7.5×10 ⁸ or more, the concentration of the NV centers decreased. It was confirmed that the diamond sample was graphitized by clearly turning black in the vicinity.

In addition, while increasing the number of pulsed lights irradiated to the diamond sample, the number of pulsed lights for which graphitization of the diamond sample was confirmed was confirmed. When the pulse energy was about 60 nJ, it was confirmed that the diamond sample was graphitized when about 1.75×10 ⁹ pulsed lights were irradiated. In the case of 25×10 ⁹ diamond samples, no graphitization was confirmed.

Similarly, when the pulse energy is about 100 nJ, it was confirmed that the diamond sample was graphitized when about 5×10 ⁹ pulsed lights were irradiated. In the case of 0.5×10 ⁸ , no graphitization of the diamond sample was confirmed. When the pulse energy is about 200 nJ, it was confirmed that the diamond sample was graphitized when about 1×10 ⁹ pulsed lights were irradiated. In the case of 10 ⁸ , no graphitization of the diamond sample was confirmed.

As described above, according to the present invention, high-concentration NV centers can be formed in diamond. Conventionally, it was not easy to form NV centers in diamond without graphitizing diamond, and it was difficult to form NV centers in diamond at a high concentration. According to the present invention, the concentration of the NV centers to be formed is a high concentration of about 10 ¹⁵ cm ⁻³ to 10 ¹⁶ cm ⁻³ , which is a concentration that can be expected to increase the sensitivity of the quantum sensor. Graphitization of diamond is also suppressed.

Further, according to the present invention, NV centers can be formed in diamond without annealing the diamond after irradiating the diamond with laser pulse light. Elimination of the annealing step makes it possible to employ low-temperature processes in the industrial fabrication of quantum sensor elements containing NV centers, enabling quantum sensor elements to be fabricated at room temperature in air. .

[Other forms]
Although the present invention has been described in terms of specific embodiments, the present invention is not limited to the embodiments described above.

In the above-described embodiment, diamond is used as the sample 9, and nitrogen-vacancy centers called NV centers are formed inside the diamond as color centers, but the color centers formed inside the diamond are limited to NV centers. not. Instead of NV centers, silicon-vacancy centers or germanium-vacancy centers may be formed inside the diamond.

In the above-described embodiment, the pulse width of the pulsed light Lp generated by the laser 1 and the pulse shaper 2 has a temporal order of femtoseconds. Pulse widths are not limited to the temporal order of femtoseconds. As long as a high concentration of NV centers can be preferentially formed inside the diamond, a pulse width having a temporal order such as femtosecond (10 ⁻¹⁵ seconds) or less, such as attosecond (10 ⁻¹⁸ seconds), is used. A laser can be directed at the diamond.

The concentration of nitrogen impurities contained in sample 9 is not limited to the concentrations exemplified in the above embodiments. For example, in quantum sensor applications, the concentration of nitrogen impurities contained in the synthetic diamond may be less than about 33 ppm (e.g., less than about 1 ppm) as exemplified above, and the synthetic diamond used is not limited to type Ib, but type IIa. may be

1 laser (light source)
2 pulse shaper 3 objective lens 4 total reflection mirror 5 dichroic mirror 6 photodetector (photodiode)
9 sample 10 optical system 21 polarization controller (wave plate)
22, 23, 24 mirror (total reflection mirror)
25 dispersive element (diffraction grating)
26 Condensing element (cylindrical lens)
27 Spatial Light Modulator (LCOS-SLM)
81 condensing optical system 82 wavelength conversion element (nonlinear optical crystal)
83 spectroscope 84 control unit Lp pulsed light

Claims (10)

A method for forming vacancy defects inside a diamond, comprising:
shaping a pulse waveform of a laser having a wavelength transparent to the absorption wavelength of the diamond to compensate for temporal dispersion in phase of the pulsed light of the laser;
a step of condensing and irradiating the pulsed light of the laser, the dispersion of which is compensated for, into the interior of the diamond a plurality of times;
method including. 2. The method according to claim 1, wherein the number of said pulsed lights condensed and irradiated into said diamond is 5*10< ⁷ > or more. 3. The method according to claim 2, wherein the number of said pulsed lights condensed and irradiated inside said diamond is 2.5*10< ⁸ > or more. the laser pulse energy is in the range of 60 nJ to 200 nJ;
A method according to any one of claims 1 to 3, wherein the pulse width of said laser is 40 femtoseconds or less. 5. The method of claim 4, wherein the laser pulse energy is in the range of 150 nJ to 200 nJ. In the step of compensating for dispersion, the pulsed light is phase-modulated to form a first sub-pulse light consisting of a first polarization component and a second sub-pulse light consisting of a second polarization component crossing the first polarization component. 6. A method according to any one of claims 1 to 5, wherein a time delay is created between the two sub-pulses of light. preparing a diamond;
forming vacancy defects inside the diamond by the method of any one of claims 1 to 6;
A method of making a diamond, comprising: A diamond in which the concentration of vacancy defects formed therein is 1×10 ¹⁵ cm ⁻³ or more. 9. The diamond according to claim 8, wherein the vacancy defect concentration is 3×10 ¹⁵ cm ⁻³ or more. 10. The diamond according to claim 9, wherein the vacancy defect concentration is 1×10 ¹⁶ cm ⁻³ or more.

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