KR102274933B1 - Diamond nitrogen vacancy center magnetic field sensor - Google Patents

Abstract

The present invention relates to a method for improving the sensitivity in a diamond nitrogen vacancy magnetic field sensor, a diamond nitrogen-vacancy center (DNV) sensor is a cylindrical or prismatic mirror, which is provided inside one side of the mirror A first filter, a diamond, a hemispherical lens, a second filter and a photodetector attached to the mirror from one side opposite to the mirror, wherein the first filter, the diamond and the hemispherical lens are bonded with the diamond in the center, The first filter is a filter that does not pass a wavelength band of photons emitted while the diamond nitrogen-vacancy center returns from an excited state to a ground state, and the hemispherical lens may have a refractive index close to that of the diamond, Accordingly, by increasing the fluorescence emitted out of the diamond, the amount detected by the photodetector can be increased to increase the measurement sensitivity of the magnetic field sensor.

Description

DIAMOND NITROGEN VACANCY CENTER MAGNETIC FIELD SENSOR

Various embodiments relate to methods for improving sensitivity in a diamond nitrogen vacancies magnetic field sensor.

Diamond crystals are made up of carbon atoms, but lattice defects occur when carbon atoms are replaced by other types of atoms. One of them is a nitrogen-vacancy center, in which one carbon atom is replaced by a nitrogen atom and the neighboring carbon atom is removed, leaving a vacant space.

Nitrogen-vacancies present in diamond generate fluorescence in a wavelength band of 600 nm or more when irradiated with a laser of 532 nm wavelength. When an external magnetic field exists in the axial direction of nitrogen-vacancies in diamond _{, the superposition of nitrogen-vacancy spin quantum (m s} =+1, -1) states disappears due to the Zeeman effect, and the nitrogen-vacancy spin becomes a spin state. It has two resonance frequencies corresponding to the spin transition between (m _s =0) and the spin state (m _s =+1) or between the spin state (m _s =0) and the spin state (m _{s =-1).} . The difference between the two resonant frequencies is proportional to the magnitude of the external magnetic field. Therefore, if a microwave that is frequency-modulated close to the resonance frequency of the nitrogen-vacancy spin is applied to the nitrogen-vacancy site, each spin transition can be induced independently, and the external magnetic field from the change in the frequency at which fluorescence caused by the spin transition is generated. change can be detected.

The fluorescence generated by the nitrogen-vacancies can be measured by a photodetector or a photodiode. When the nitrogen-vacancies center is excited with a 532 nm laser of the same power, the more the fluorescence generated by the nitrogen-vacancies is captured, the greater the signal strength measured by the photodiode increases the signal-to-noise ratio, thereby improving the measurement sensitivity. have.

In order for the fluorescence light generated by nitrogen-vacancies to reach the photodiode, it must first pass through the interface between the diamond and the external medium (air) and come out of the diamond. However, in order for fluorescent light to pass through the interface, it must be incident within the angle of total reflection, but due to the difference in refractive index between the external medium and diamond, the angle of total reflection is quite small, so only a small part of the fluorescent light generated from the nitrogen-vacancy center can be measured by the photodiode. There is a problem that the sensitivity may be weak.

In order to solve the above problem and improve the measurement sensitivity in the photodiode, the present invention proposes a DNV magnetic field sensor that allows more fluorescent light to escape out of the diamond by increasing the total reflection angle to be measured by the photodiode.

The technical problems to be achieved in this document are not limited to the technical problems mentioned above, and other technical problems not mentioned can be clearly understood by those of ordinary skill in the art to which the present invention belongs from the description below. There will be.

According to various embodiments of the present disclosure, the diamond nitrogen-vacancy center (DNV) sensor is a cylindrical or prismatic mirror, a first filter provided inside one side of the mirror, a diamond, a hemispherical lens, and a second filter and a photodetector attached to the mirror from one side opposite to the mirror, wherein the first filter, the diamond and the hemispherical lens are bonded with the diamond in the center, and the first filter is the diamond nitrogen- The vacancy center is a filter that does not pass a wavelength band of photons emitted while returning from an excited state to a ground state, and the hemispherical lens may have a refractive index close to that of the diamond.

According to various embodiments of the present disclosure, a diamond nitrogen-vacancy center (DNV) sensor system is configured to excite the above-described DNV sensor and the diamond nitrogen-vacancy center of the DNV sensor from a ground state to an excited state. a light source for injecting light and the spin in the ground state of the diamond of the DNV sensor status (m _s = 0) of nitrogen-nitrogen of the spin state of vacancy center (m _s = + 1) - vacancy center or spin states (m _s = A microwave source that excites the nitrogen-vacancy center of -1) may be included.

According to various embodiments, more fluorescence emitted from the nitrogen-vacancy center in the diamond may be emitted out of the diamond.

According to various embodiments, the measurement sensitivity of the magnetic field sensor may be increased by increasing the amount detected by the photodetector by increasing the fluorescence emitted out of the diamond.

Effects obtainable in the present disclosure are not limited to the above-mentioned effects, and other effects not mentioned may be clearly understood by those of ordinary skill in the art to which the present disclosure belongs from the description below. will be.

1A is a diagram illustrating an energy level diagram of a diamond nitrogen-vacancy center.
1B is a diagram illustrating an example of an ODMR spectrum.
2 is a schematic diagram of a sensor system using diamond nitrogen-vacancies (DNV).
3 is a diagram illustrating an example in which photons are emitted into the air in diamond.
4 is a diagram illustrating an example of photon emission from diamond processed into a trapezoidal shape.
5 is a diagram illustrating an example of photon emission when a high refractive index hemispherical lens is bonded to diamond.
6 is a diagram illustrating an example of photon emission when a high refractive index hemispherical lens and a filter are bonded to a diamond processed in a trapezoidal shape.
7 is a diagram illustrating a DNV sensor structure according to various embodiments of the present disclosure;
In connection with the description of the drawings, the same or similar reference numerals may be used for the same or similar components.

Hereinafter, various embodiments will be described in detail with reference to the accompanying drawings.

1A is a diagram illustrating an energy level diagram of a diamond nitrogen-vacancy center.

Referring to FIG. 1A , the nitrogen-vacancy center has three spin states: a spin state (m _s =0), a spin state symmetric to each other (m _s =+1), and a spin state (m _s =-1). It has a ground state 110 that is a triplet. In the absence of a magnetic field, by spin-spin interaction, the spin state (m _s =+1) and the spin state (m _s =-1) are in the _{same energy state away from the spin state (m s} =0) by a certain energy level. do. In the absence of a magnetic field _{, the energy level of the spin state (m s} =0) is separated from the energy level of the spin state (m _s =+1) and the spin state (m _s =-1) by an energy of approximately 2.87 GHz.

When an external magnetic field is applied in the ground state, the energy of the spin state (m _s =+1) and the spin state (m _s =-1), which have the same energy, have separate energy levels in proportion to the size of the applied external magnetic field. do.

The nitrogen-vacancy center of the ground state 110 is excited to the excited state 120 when green light is irradiated. The green light may be light having a wavelength of 637 nm or less, but preferably light having a wavelength of 532 nm. At this time, each spin state of the nitrogen-vacancy center is excited while maintaining each spin state.

The nitrogen-vacancy center of the excited state 120 returns to the ground state 110, some of which return to the ground state 110 while emitting photons of red light (eg, 600 nm or more and 900 nm or less) (141), and some It returns to the ground state 110 through the singlet 130 ( 143 ), and returns to the ground state 9110 without emitting red light when passing through the singlet 130 .

The nitrogen-vacancy center of the spin state (m _s = 0) of the excited state 120 returns to the ground state 110 while emitting a photon of red light. On the other hand, _{most of the nitrogen-vacancy centers of the spin state (m s} =+1) and the spin state (m _s =-1) of the excited state 120 return to the ground state 110 through the singlet 130 , When it returns, it returns to the spin state (m _s =0) rather than the original spin state. Therefore, when green light is irradiated, the spin state of the nitrogen-vacancy center is determined as the _{spin state (m s = 0), which is the spin ground state after a certain period of time.}

로 결정될 수 있다. 여기서

는 전자 스핀 자기회전 비율이고, B는 자기장의 세기일 수 있다.Meanwhile, in a spin state (m _s =0), between a spin state (m _s =0) and a spin state (m _s =+1) or between a spin state (m _s =0) and a spin state (m _s =-1) When a microwave corresponding to the energy difference is applied, the transition from the spin state (m _s =0) of the ground state 110 to the spin state (m _s =+1) or the spin state (m _s =-1) is induced. Here, the energy difference (first energy difference) between the spin state (m _s =0) and the spin state (m _s =+1) and the energy between the spin state (m _s =0) and the spin state (m _s =-1) The spacing of the difference (second energy difference) may be determined by an external magnetic field applied to the nitrogen-vacancy center. For example, the first energy difference minus the second energy difference =

can be determined as here

is the electron spin magnetic rotation rate, and B may be the strength of the magnetic field.

When green light is applied to the nitrogen-vacancy center of the ground state 110, the excited state 120 is excited, and the spin state (m _s =+1) and the spin state (m _s =-1) of the excited state 120 are obtained. The nitrogen-vacancy center returns to the ground state 110 without emitting red light through 143 in FIG. 1 .

Therefore, if an optically-detected magnetic resonance (ODMR) spectrum that records the change in the amount of emitted light using a photodiode while changing the wavelength of the applied microwave is recorded, the spin state (m _s = 0) and the spin state (m _s) =+1), and a portion with a low light intensity in two frequency bands corresponding to the energy difference between the _{spin state (m s} =0) and the spin state (m _{s =-1) can be observed.}

1B is a diagram illustrating an example of an ODMR spectrum.

Referring to Figure 1b, the ODMR spectrum shows the _{energy difference (163) between the spin state (m s} =0) and the spin state (m _s =+1) or the spin state (m _s =0) and the spin state (m _s =-) 1) The amount of light measured in the two frequency bands corresponding to the energy difference 161 is low. When a microwave in a band other than the corresponding frequency band is applied, the spin state (ms=0) of the ground state 110 _{is not excited into a spin state (m s} =+1) or a spin state (m _s =-1), but spins It remains in the state (ms=0). And when excited to the excited state 120 by green light, the nitrogen-vacancy center remaining in the spin state (ms=0) returns to the ground state 110 while emitting photons of red light along the path 141 of FIG. 1A. . Conversely, when microwaves of the corresponding frequency band are applied, the spin state (ms=0) of the ground state 110 _{is excited into a spin state (m s} =+1) or a spin state (m _s =-1), and again in green light. After being excited to the excited state 120 by the polarizer, it returns to the ground state 110 without emitting a photon of red light through the path 143 of FIG. 1A , so that the amount of light measured by the photodiode is reduced. Therefore, measuring the ODMR spectrum shows the _{energy difference (163) between the spin state (m s} =0) and the spin state (m _s =+1) and the spin state (m _s =0) and the spin state (m _s =-1). The amount of light measured in the two frequency bands corresponding to the energy difference between them is low. And the difference between these two frequency bands is proportional to the strength of the magnetic field at the center of the diamond nitrogen-vacancy. Thus, the diamond nitrogen-vacancies can be used to detect the magnetic field present.

2 is a schematic diagram of a sensor system 200 using diamond nitrogen-vacancies (DNV).

Referring to FIG. 2 , the DNV sensor system 200 emits through a diamond 230 having a nitrogen-vacancy center, an excitation light source 220 for providing optical excitation energy to the diamond 230 , and a microwave antenna 221 . It may include a microwave source 210 , a filter 240 , and a photodetector 250 providing microwaves.

The microwave source 210 provides microwaves emitted through the microwave antenna 221 , and according to an embodiment, the microwave antenna 221 may be disposed around the diamond 230 rather than in front of the diamond 230 . have. As shown in FIG. 1B , the microwave source 210 may provide microwaves of various frequency bands. The frequency band of the microwave provided by the microwave source 210 is the _{energy difference 163 between the spin state (m s} =0) and the spin state (m _s =+1) in the ground state 110 or the spin state (m _s = 0) and the _{energy difference 161 between the spin state (m s} =-1), spin the nitrogen-vacancy center _{in the spin state (m s} = 0) from the ground state 110 shown in Fig. 1a. It can be excited to a state (m _s =+1) or a spin state (m _{s =-1).}

The light source 220 may be a laser and may emit green light (eg, light having a wavelength of 532 nm). The light incident on the diamond 230 by the light source 220 excites the nitrogen-vacancy center in the ground state 110 to the excited state 120 . As shown in FIG. 1A, the nitrogen-vacancy center in the spin state (m _s = 0) in the nitrogen-vacancy center excited to the excited state 120 returns to the ground state while emitting a photon of red light (141), and the spin Most of the nitrogen-vacancy centers in the state (m _s =+1) or the spin state (m _{s =-1) return to the spin state (m s} =0) while passing through the singlet 130 . The red light emitted while returning from the excited state 120 to the ground state 110 may be detected by the photodetector 250 through the filter 240 .

Filter 240 may pass red light and block lights having other wavelengths, including green light generated by light source 220 .

The photodetector 250 may detect a photon that has passed through the filter 240 , and may acquire an ODMR spectrum based on the intensity of fluorescence detected by the photodetector 250 . And as shown in FIG. 1b, two frequency bands applied from the microwave source 210 are obtained when the intensity of fluorescence in the ODMR spectrum is small, and the strength of the magnetic field can be inferred based on the difference between the two frequency bands. have.

In this case, a light guide for guiding photons emitted from the diamond 230 toward the filter 240 may be provided between the diamond 230 and the filter 240 .

In order to increase the magnetic field measurement sensitivity in the sensor system 200 shown in FIG. 2 , photons emitted while returning from the excited state 120 to the ground state 110 at the nitrogen-vacancy center in the diamond exit the diamond 230 and light Detector 250 should be reached.

3 is a diagram illustrating an example in which photons are emitted into the air in diamond.

Referring to FIG. 3 , when a photon is emitted while returning from the excited state 120 to the ground state 110 at the nitrogen-vacancy center in the diamond 310 , the emitted photon travels in an arbitrary direction. And when the boundary of the diamond 310 is met, if the angle of incidence is not within a certain angle, it is totally reflected and returned to the diamond 310 again. If the refractive index of diamond is 2.4 and the refractive index of air outside the diamond is 1, when the incident angle is greater than 24.6 degrees, the photons are not emitted out of the diamond 310 and come back inside. Thus, only a small fraction of the emitted photons can be emitted out of diamond 310 . Detection sensitivity in the actual sensor system 200 may be low.

The present invention proposes various methods to overcome the situation as shown in FIG. 3 and to allow more photons to be emitted to the diamond 310 .

4 is a diagram illustrating an example of photon emission from a diamond 410 processed in a trapezoidal shape.

Referring to FIG. 4 , when the diamond 410 is processed in a trapezoidal shape, even if the photon is not emitted outside the diamond 410 when it first meets the surface, it meets the side surface and is reflected from the inside, so that the photon is finally emitted out of the diamond 410 . It shows that it can be released. Accordingly, the trapezoidal diamond 410 may emit more photons than the rectangular diamond 310 .

FIG. 5 is a diagram illustrating an example of photon emission when a high refractive index hemispherical lens 510 is bonded to a diamond 310 .

Referring to FIG. 5 , when a high refractive index hemispherical lens (for example, a refractive index of 2.0 or more) 510 is attached to one surface of the diamond 310, when the incident angle is less than 56.5 degrees, a photon is transferred from the diamond 31 to the hemispherical lens 510. can be emitted. In addition, almost all of the photons emitted by the hemispherical lens 510 may be emitted into the air as shown in FIG. 5 . Accordingly, by bonding the hemispherical lens 510 having a high refractive index to the diamond 310 , the amount of photons emitted from the diamond can be increased.

6 is a diagram illustrating an example of photon emission when a high refractive index hemispherical lens 630 and a filter 610 are bonded to a diamond 620 processed in a trapezoidal shape.

Referring to FIG. 6 , as described with reference to FIGS. 4 and 5 , photons having a more shape than that of a diamond having a simple rectangular shape may be emitted to the outside of the diamond 620 . In addition, the filter 610 may be attached to the surface opposite to the surface to which the high refractive index hemispherical lens 630 is attached. The filter 610 may have a characteristic that does not pass a wavelength band (eg, a red light frequency band) of a photon emitted from the diamond 620 . Then, when a photon emitted in an arbitrary direction from the center of the diamond nitrogen-vacancy meets the filter 610 , it is reflected without passing through and may be emitted toward the high refractive index hemispherical lens 630 .

As such, the amount of emitted photons is increased by adding a hemispherical lens to the conventional square diamond, adding a filter, and processing into a trapezoidal shape, and as a result, as the amount of photons obtained from the photodetector increases, the sensitivity of the sensor is increased. can improve

7 is a diagram illustrating a structure of a DNV sensor 700 according to various embodiments of the present disclosure.

The DNV sensor 700 according to various embodiments applies a method for increasing the amount of photons emitted from the diamond shown in FIG. 6 .

Referring to FIG. 7 , the DNV sensor 700 is bonded to a diamond 620 , a hemispherical lens 630 bonded to the diamond 620 , and a surface opposite to the surface to which the hemispherical lens 630 of the diamond 620 is bonded. It may include a first filter 610 , a mirror 740 having a cylindrical or prismatic shape, a second filter 750 , and a photodetector 760 .

Here, a first filter 610 , a diamond 620 , and a hemispherical lens 630 are provided at one end inside the cylindrical or prismatic mirror 740 , and the other end of the cylindrical or prismatic mirror 740 . A second filter 750 and a photodetector 760 may be provided. Accordingly, the mirror 740 may reflect the photon emitted from the diamond 620 and perform a guide function such that the photon passes through the second filter 750 and reaches the photo detector 760 .

The first filter 610 sets the photon to be reflected when the photon emitted from the diamond goes out to the opposite side of the surface to which the hemispherical lens 630 is bonded, so that the photon returns to the diamond and is emitted toward the hemispherical lens 630 . can be performed. For example, the first filter 610 may not pass photons having a wavelength corresponding to red light.

The second filter 750 passes only photons having a wavelength corresponding to the red light emitted from the diamond and transmits them to the photodetector 760, and the DNV sensor 700 by the light source (eg, the light source 220 in FIG. 2). Photons having a wavelength corresponding to the green light and other wavelengths other than the green light may be prevented from passing through.

The microwave source 210 and the light source 220 of the sensor system shown in FIG. 2 are disposed outside the diamond 620 of the cylindrical or prismatic mirror 740 to provide microwave and excitation energy to the diamond 620 . can do.

As a result of optical simulation, it was confirmed that 31.32% of the light emitted from the diamond nitrogen-vacancy center reached the photodetector when the DNV sensor shown in FIG. 7 was used. On the other hand, in the structure using the conventional flat diamond, it was confirmed that only 8.83% reached the photodetector. Therefore, the DNV sensor proposed in the present invention can capture more than 3.5 times more light than the conventional sensor, and as a result, the sensitivity of the sensor can be further improved.

According to various embodiments, the diamond nitrogen-vacancy center (DNV) sensor is a cylindrical or prismatic mirror, a first filter provided inside one side of the mirror, a diamond, a hemispherical lens, the mirror of a second filter and a photodetector attached to the mirror from the opposite side, wherein the first filter, the diamond and the hemispherical lens are joined with the diamond in the center, and the first filter is the diamond nitrogen-vacancy center A filter that does not pass a wavelength band of photons emitted while returning from an excited state to a ground state, and the hemispherical lens may have a refractive index close to that of the diamond.

According to various embodiments, the diamond may be processed into a trapezoidal plate shape.

According to various embodiments, the first filter may pass light of a wavelength of 532 nm, reflect light of a wavelength range of 630 nm to 900 nm, and the second filter may pass only light of a wavelength range of 630 nm to 900 nm.

According to various embodiments, the hemispherical lens may be made of a material having a refractive index of 2.0 or more.

According to various embodiments, the diamond surface bonded to the hemispherical lens may be polished to minimize interface properties.

According to various embodiments, the diamond nitrogen-vacancy center (DNV) sensor system comprises a DNV sensor according to any one of claims 1 to 5, and a diamond nitrogen-vacancy center of the DNV sensor in a ground state. A light source injecting light to excite to an excited state (eg, the light source 220 in FIG. 2 ) and the nitrogen-vacancy center of the spin state (m _{s = 0) in the ground state of the diamond of the DNV sensor are set to the spin state (m)} A microwave source (eg, the microwave source 210 of FIG. 2 ) that excites a nitrogen-vacancy center of _s =+1) or a nitrogen-vacancy center of a spin state (m _{s =-1) may be included.}

As described above, the present invention proposes various methods for improving the sensitivity of a photodetector in a DNV sensor. The methods proposed in the present invention allow more photons to be emitted out of the diamond as the diamond nitrogen-vacancy center returns from the excited state 120 to the ground state 110 . This allows more photons to reach the photodetector, improving the sensitivity of the DNV sensor.

Claims (6)

In a diamond nitrogen-vacancy center (DNV) sensor,
cylindrical or prismatic mirrors;
a first filter, diamond, hemispherical lens provided inside one side of the mirror;
A second filter and a photodetector attached to the mirror from one side opposite to the mirror,
The first filter, the diamond and the hemispherical lens are bonded with the diamond in the center,
The first filter is a filter that does not pass a wavelength band of photons emitted while the diamond nitrogen-vacancy center returns from an excited state to a ground state,
The hemispherical lens is a DNV sensor having a refractive index close to that of the diamond.
According to claim 1,
The diamond is processed into a trapezoidal plate shape, DNV sensor.
According to claim 1,
The first filter passes light of a wavelength of 532 nm and reflects light of a wavelength region of 630 to 900 nm,
The second filter passes only light in a wavelength region of 630 to 900 nm, a DNV sensor.
According to claim 1,
The hemispherical lens is made of a material having a refractive index of 2.0 or more, DNV sensor.
According to claim 1,
The surface of the diamond bonded to the hemispherical lens is polished to minimize the interface properties, DNV sensor.
In a diamond nitrogen-vacancy center (DNV) sensor system,
DNV sensor according to any one of claims 1 to 5;
a light source injecting light to excite the diamond nitrogen-vacancy center of the DNV sensor from a ground state to an excited state; and
In the ground state of the diamond of the DNV sensor _{, the nitrogen-vacancy center in the spin state (m s} =0) is replaced by the nitrogen-vacancy center in the spin state (m _s =+1) or the nitrogen-vacancy center in the spin state (m _s =-1) A DNV sensor system comprising a microwave source that excites the center of the void.

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