KR102765079B1 - Solid-state qubit imaging apparatus - Google Patents

Abstract

An imaging device according to the present embodiment includes a microsphere positioned on a defect located within a sample and providing a single photon and a quantum spin; an optical system providing light to the microsphere and imaging the defect through the microsphere; and a signal processing unit receiving light formed at the defect and converting it into a corresponding electrical signal.

Description

SOLID-STATE QUBIT IMAGING APPARATUS

The present technology relates to imaging devices.

Point defects in crystals provide important building blocks for quantum applications. Since defect qubits are manipulated optically, efficient optical interfaces are important.

Optically active point defects in crystals, such as nitrogen vacancy in diamond or silicon vacancy centers, are attracting attention as candidates for implementing quantum technologies on semiconductor platforms. These defects can provide spins with long-term coherence of single photons and up to 1 ms at room temperature. Recently, it has become increasingly important to address multiple adjacent defects beyond single defects.

Many previous studies have demonstrated scalable quantum systems that enable multi-qubit registers, superradiant emission from multiple resonant emitters, and wide-field imaging of magnetic or electric fields. Therefore, the importance of optical interfaces with high resolution and high signal-to-noise ratio is increasing to optically isolate multiple adjacent defects. However, conventional optical microscopes have difficulty in addressing defects in bulk crystals due to diffraction-limited spatial resolution and background fluorescence from the crystal, substrate, nearby defects, and the sample substrate.

There have been many efforts to improve the light extraction efficiency by fabricating micro/nanophotonic structures such as nanowires, nanobeams, bullseyes, and solid immersion lenses. These structures dramatically increased the brightness of a single defect by more than an order of magnitude and enhanced the radiative recombination rate by the Purcell effect.

However, these approaches require sophisticated fabrication processes for high-hardness materials such as diamond, and nanoscale devices often deteriorate the coherence of optical and spin qubits. In addition, precise spatial control of patterns or defects is required to couple defects with photonic structures in the maximum optical mode.

To improve the spatial resolution, various super-resolution techniques such as near-field probes, plasmon gratings, stimulated emission depletion microscopy, and Fourier magnetic imaging can be used. Although these techniques have brought about significant improvements in the spatial resolution below 10 nm, they suffer from limited imaging depth, low optical throughput, non-radiative losses, and require coupling with complex optical systems such as depletion beams or gradient magnetic fields. Therefore, it remains a challenge to isolate closely spaced defects with high spatial resolution and high signal-to-noise ratio, and conventional confocal fluorescence microscopy for high-refractive-index determinations has limited photon collection efficiency and spatial resolution.

An imaging device according to the present embodiment includes: a microsphere positioned on a sample and arranged on a target; an optical system providing light to the microsphere and imaging the target through the microsphere; and a signal processing unit receiving light formed at the target and converting it into a corresponding electrical signal.

According to one aspect of the present invention, the microspheres are made of a material having a difference in refractive index between the microspheres and an external environment of the microspheres of 1.3 to 1.7.

According to one aspect of the present invention, the microspheres are made of one of barium titanate (BaTiO3), fused silica, or lime glass.

In one aspect of the present embodiment, the target is a solid qubit.

In one aspect of the present invention, the solid qubit comprises a quantum dot, a two-dimensional material, and a solid point defect.

According to one aspect of the present invention, the solid point defect is any one of a SiC point defect, a HBN point defect, and a point defect located in diamond.

According to one aspect of the present invention, a point defect located within the diamond provides a single photon and a quantum spin.

According to one aspect of the present embodiment, the imaging device images a virtual image formed under the sample.

According to one aspect of the present invention, the microspheres are immersed in an immersion oil having a lower refractive index than the refractive index of the microspheres.

According to one aspect of the present embodiment, the imaging device further includes a light source providing the light, a light receiving unit receiving the light provided from the defect and converting it into a corresponding electrical signal, and a signal processing unit processing the electrical signal.

According to one aspect of the present embodiment, the light source is a continuous wave laser, and the light receiving unit includes an avalanche photodiode.

In one aspect of the present invention, the imaging device further comprises optical tweezers for positioning the microspheres on the defect, wherein the optical tweezers comprise a laser light source.

In one aspect of the present invention, the optical system is a confocal microscope.

Herein, we demonstrate high-resolution, high-contrast imaging of defects in diamond using microsphere-assisted confocal microscopy. The microspheres provide an excellent optical interface to point defects with a spatial resolution of up to λ/5 and a magnified virtual image that improves the optical signal-to-noise ratio by a factor of four. These features enable individual optical access to single photons and single spins of multiple defects that are not spatially separable in conventional confocal microscopy, with high signal contrast compared to prior art.

In addition, the combined optical tweezers also demonstrate the possibility of positioning or scanning microspheres. This approach does not require complex fabrication and additional optical systems, but uses simple off-the-shelf micro-optics. Due to these unique advantages of microspheres, our approach can provide an efficient way to image and isolate closely spaced defects with higher resolution and sensitivity.

The dielectric microspheres of the present invention offer unique advantages over conventional fabrication-based photonic structures and super-resolution techniques. First, the microspheres are off-the-shelf optical elements with a wide range of material and size choices, and can be coupled to defects via simple dispersion. Furthermore, coupled optical tweezers can capture and move the microspheres for position control of the microspheres, coupling to defects, and wide-field scanning of the defects. In addition, super-resolution imaging beyond the diffraction limit is possible by sub-diffraction-limited illumination and long-distance propagation of evanescent waves.

Microspheres form virtual or real images far from the actual sample surface. The spatially varied images separate the defect signal from the optical background noise present near the sample surface. This capability of high-resolution, high-contrast optical imaging allows optical separation of single photons and single spins, which are not spatially separated in conventional confocal microscopy. Thus, along with the simplicity of fabrication, microspheres provide a relocatable and efficient optical interface for solid-state single photon emitters.

FIG. 1(a) is a schematic drawing showing an imaging device (10) according to the present embodiment imaging a defect using light provided by a light source (300), and FIG. 1(b) is a schematic drawing showing an imaging device (10) according to the present embodiment placing a microsphere (100) on a defect using laser light provided from an optical tweezers (400).
Figure 2 is a schematic diagram of a microsphere-assisted imaging device having a virtual image beneath the sample surface.
Figure 3 is a confocal image scanned vertically of a defect with microspheres, with dotted lines indicating the microsphere, sample surface, and virtual image planes.
Figure 4(a) shows xy-scanned confocal images of microspheres in different perpendicular planes: z = 0 μm (sample surface) and Figure 4(b) at z = - 12 μm (virtual plane). The color bar represents photoluminescence (PL) intensity in kcounts per second.
Figure 4(c) is a schematic representation of the optical phenomenon of the microspheres that magnifies the image and couples the evanescent field, and Figure 4(d) is a numerical simulation of the incident plane wave toward the 20 μm-sized microspheres of the sample. The logarithmic color map of intensity || ² illustrates the photonic nanojet effect that tightly focuses the incident wave on the bottom of the microsphere.
FIG. 5(a) is a drawing showing a confocal fluorescence image of a conventional microsphere-assisted microscope, FIG. 5(b) is a drawing showing the results of lateral scanning in the same xy scan range at = 0 (excluding microspheres) and = -12 μm (including microspheres). The enlarged image in FIG. 5(b) corresponds to the area indicated by the orange dotted box in (a). FIG. 5(c) is a drawing showing the magnification factor measured at another virtual image plane of the microsphere-assisted microscope, where the solid line represents the calculated magnification (z). FIG. 5(d) is a drawing comparing the signal-to-noise ratio with (red) and without (black) microspheres, where the yellow circles in FIG. 5(a,b) indicate single defects used for the comparison in FIG. 5(d).
Fig. 6(a) is a diagram showing a conventional confocal image (a,b) of a defect in a microsphere-assisted microscope according to the present embodiment. The virtual image at z = -13 μm in Fig. 6(b) is rescaled in magnification for comparison with the conventional confocal image of Fig. 6(a). The defects indicated by S, D and T in Fig. 6(a) represent single and spatially non-separated double and triple defects. These defects are clearly distinguished in Fig. 6(b) and are indicated as (D1-2) and (T1-3). Fig. 6(c) shows cross-sectional intensity profiles of the defect S obtained by the conventional confocal microscope (black dots) and the microsphere-assisted microscope at different z positions of z = -13 μm (red dots) and z = -17 μm (blue dots), and the solid line is a line fitted by a Gaussian function. Figure 6(d) is a plot showing the spatial resolution and normalized intensity of a single defect S according to the z-position of the virtual image, where the green dashed horizontal line represents the diffraction limit of the conventional microscope. Figures 6(e, f) are plots showing the intensity profiles of two adjacent defects D in Figure 6(a) and D1-2 in Figure 6(b), respectively. The data in Figures 6(e) and 6(f) were fitted with a single and two-part Gaussian function, respectively. Figure 6(g) shows the maximum peak of the merged defect D, and Figure 6(h) shows the second-order photon correlation curves measured at each peak of the separated defects D1 and D2. The red line is fitted with the g ⁽²⁾ (τ) curve.
Figures 7(a) and 7(b) are diagrams showing the optically detected magnetic resonance spectra of a single defect without and with microspheres, respectively. Figure 6(c) shows two defects that are not spatially separated in the conventional confocal microscope and a defect that is spatially separated in the microsphere-assisted microscope, and shows the ODMR spectra with a magnetic field of about 50 G for (d) 1 and (e) 2. The inset images show confocal mapping images of the same defect in the conventional and microsphere-assisted microscopes, and the scale bar in the confocal maps represents 200 nm.

Hereinafter, an imaging device (10) according to the present embodiment will be described with reference to the attached drawings. FIG. 1(a) is a drawing schematically illustrating an imaging device (10) according to the present embodiment that images a target using light provided by a light source (300), and FIG. 1(b) is a drawing schematically illustrating an imaging device (10) according to the present embodiment that places microspheres (100) on a target using laser light provided by an optical tweezers (400). Referring to FIG. 1(a), light provided by a light source (300) is provided to an optical system (200) through a beam splitter (BS). In one embodiment, the light source (300) may provide continuous wave laser light of a 532 nm band. In addition, the optical system (200) may be a confocal microscope.

In an illustrated embodiment, the target being imaged is a solid-state cubit. In one embodiment, the solid qubit can be a quantum dot, a two-dimensional material, a solid point defect, etc., and the solid point defect can be any one of a SiC point defect, a HBN point defect, and a point defect located in diamond.

In addition, as an example, the point defect may be a nitrogen vacancy defect, a silicon vacancy defect, or a silicon carbide (SiC) point defect located in diamond, which allows independent access of a single photon and a single spin of the defect, but for the sake of easy and concise explanation, the target is described below as a nitrogen vacancy defect in diamond. However, this is only to facilitate the explanation of the present embodiment and is not intended to limit the scope of the present invention.

Light provided through the optical system (200) can be provided to microspheres (100) placed on a defect of a sample. The light is provided to the defect of the sample through the microspheres (100), and the defect forms and provides light having a larger wavelength than the light provided by the light source (300). The optical system (200) collects the light formed by the defect, obtains a virtual image formed under the sample therefrom, and provides the obtained image to a fiber coupler.

As described later, the sample and microspheres (100) can be immersed in immersion oil, and the imaging device (10) can perform imaging while the sample and microspheres (100) are immersed.

The light receiving unit receives light corresponding to the virtual image through an avalanche photodiode (APD), forms a corresponding electrical signal, and provides it to a signal processing device such as an FPGA or PC.

In one embodiment, the imaging device (10) may further include an RF generator, which generates microwaves having a frequency that resonates with the electron spin state in the diamond point defects and irradiates the microwaves onto the sample, thereby controlling the spin state of electrons in the NV point defects of the diamond.

Fig. 1(b) is a drawing illustrating a process of performing optical tweezing. Referring to Fig. 1(b), the optical tweezers (400) include a laser light source, and light provided from the optical tweezers (400) is provided to the microspheres (100) through a fiber coupler and an optical system (200).

The microsphere (100) moves on the surface of the sample according to the light provided by the optical tweezers (400), and when the microsphere (100) is positioned on a defect of the sample, the optical tweezers (400) stop providing the laser. In this way, the microsphere (100) is placed on the defect of the sample.

The present invention relates to a high-resolution, high-contrast optical interface for defects based on hybrid integration of dielectric micro-optics. A diamond sample containing point defects that generate nitrogen-vacancy (NV) color centers randomly distributed within 100 nm from the surface with a density of 1–2 μm ^-2 by implanting N ₂ ions into the diamond was prepared. Barium titanate (BaTiO ₃ ) glass microspheres (100) were dispersed on the diamond sample for microsphere-assisted confocal fluorescence microscopy imaging. The BaTiO ₃ microspheres (100) have a high refractive index (n ~ 1.9-2.1) and a diameter of 10–20 μm.

Spheres (100) with high refractive index are more advantageous for defect imaging in diamond (n~2.42) than low refractive index microspheres such as soda-lime glass (n~1.51) and polystyrene (n~1.59).

In one embodiment, the refractive index of the microspheres is selected by considering the refractive index of the external environment of the microspheres. When barium titanate (BaTiO ₃ ) glass microspheres (100) having a high refractive index, as in the present embodiment, are used, immersion oil can be used. For example, in the present embodiment, the refractive index of the microspheres is set so that the refractive index of the microspheres/refractive index of the external environment in relation to the immersion oil has a value of approximately 1.3 to 1.7. As another example, by using fused silica or lime glass, enlarged virtual image imaging can be performed without immersion oil.

The microspheres (100) and the diamond sample can minimize total internal reflection at the interface. The refractive index contrast between the microspheres (100) and the environment plays an important role in the image because it determines the propagation of light through the microspheres. A small (large) refractive index contrast with the environment forms a virtual image (real image) below (above) the sample. In order to reduce the refractive index contrast with the environment while maintaining the advantage of the high refractive index microspheres, the microspheres (100) were immersed in immersion oil (n=1.518). From this, the super-resolution imaging function can be brought to the virtual image plane. Furthermore, the small refractive index contrast between the microspheres and the immersion oil reduces the scattering force at the interface and enables the capture of the high refractive index microspheres using optical tweezers.

A confocal microscope setup at room temperature was used for fluorescence imaging. The sample was excited with a 532 nm continuous wave (CW) laser and the fluorescence was collected from the sample with an oil immersion objective (NA=1.4). The excitation laser was band-filtered from the collected fluorescence signal using a dichroic mirror, and the fluorescence signal was spatially filtered using a 50 μm pinhole and two lenses, followed by a fiber-coupled silicon single-photon avalanche photodiode (Excelitas, SPCM-AQRH).

Figure 2 is a schematic diagram of a microsphere-assisted microscope for imaging defects in diamond. When high-refractive index microspheres are immersed in a liquid (n~1.518), a virtual image of the defect is formed beneath the sample surface. The sample is scanned vertically to determine the image plane with and without the microsphere (100) lens.

A confocal map outside the microsphere (100) illustrated in FIG. 3 shows fluorescence from defects near z = 0 on the diamond surface, while defects beneath the microsphere form artifacts in the lower plane near z = -12 μm.

Figures 4(a) and 4(b) show x-y lateral maps at two different image planes, z = 0 and z = -12 μm. The virtual image in Figure 4(b) prominently shows the defects with improved contrast and resolution at the sample surface outside the microspheres.

The improvement in image quality is related to the optical phenomenon of the microspheres. As illustrated in Fig. 4(c), the microspheres (100) act as spherical lenses to create a magnified virtual image. The magnification depends on the size of the sphere, the optical index contrast, and the distance from the microspheres to the defect. Furthermore, the microspheres enhance the spatial resolution beyond the diffraction limit in conventional confocal microscopes.

As illustrated in Fig. 4(c), the microspheres (100) couple high-frequency evanescent waves to far-field emission within the gap (λ/2) between the microspheres and the surface. This near-field emission enhances both light extraction and spatial resolution, which occurs near a contact area that is approximately 1/4 the size of the sphere.

Figure 4(d) shows the results of a finite-difference time-domain simulation of a || ² profile of a microsphere cross-section with a diameter of 20 μm. Figure 4(d) shows a sub-diffraction-limited illumination, so-called photonic nanojet. The dielectric microspheres (100) cause constructive interference between the diffracted waves. In the simulation, the microspheres focused the incident wave to a local point with a beam waist of 232 nm for an illumination wavelength of 532 nm.

For quantitative analysis, images of the same defect with and without microspheres are directly compared. This comparison is possible because the microspheres can be repositioned as described below. Figures 5(a) and 5(b) are lateral confocal maps without and with microspheres (100), respectively. At the same stage scan range, the microspheres (100) show an artifact that is magnified by almost a factor of two. The magnification (M) of the artifacts is determined from the unmagnified confocal image without the microspheres.

Figure 5(c) shows the experimentally measured magnification (M) as a function of depth. The magnification increases from 1.9 to 2.5 in the range = -9 to -15 μm. The magnification of a spherical lens system can be approximated using geometrical optics. Taking spherical aberration into account, the microsphere has a focal length f(x) which is given by the following mathematical expression 1.

[Mathematical formula 1]

(x: transverse distance from the optical axis, R is the radius of the microsphere, =1.38 is the refractive index ratio between microspheres and oil)

The microspheres (100) are placed at a distance ( ) to form an illusion. The magnification is , where δ is the defect depth on the sample surface. According to the above equation, when R = 10 μm, δ = 100 nm, and x = 1 μm, the virtual plane can be calculated as M = 2.28 at d _v = -13 μm. Based on the observed virtual plane, the magnification is can be expressed as follows. The theoretically calculated result is consistent with the experimentally observed result shown in Fig. 5(c).

In terms of brightness, the high-index spheres couple evanescent waves near the diamond surface to free space. Numerical simulations have calculated that the extraction efficiency of the dipole under the microspheres (100) is improved by a factor of two. In unillustrated experimental examples, a brightness enhancement of up to 40% was observed by comparing the saturation intensity of the same defect with and without the microspheres.

The discrepancy between simulations and observations is attributed to the narrow spatial window of the microspheres for maximum brightness. Simulations show that maximum enhancement occurs within about 1 μm directly beneath the sphere (see Figure S2 in the Supporting Information). This window can be widened further by increasing the size of the microspheres.

Although the enhancement in brightness is modest, the microspheres enable a significant increase in the signal-to-noise ratio by substantially reducing the background fluorescence in the artifacts compared to the sample surface. Achieving a high signal-to-noise ratio is important in semiconductor qubit systems, as the signal must be controlled from a single photon. However, using high optical excitation powers in the vicinity of 1 mW typically generates unwanted background fluorescence from scattered photons and autofluorescence from environments such as immersion oil, hosting crystals, and nearby defects. As can be observed in Fig. 3, the background fluorescence is relatively darker inside the diamond where the artifacts are present compared to the region near the sample surface. Therefore, spatial separation of the artifacts away from the sample surface is useful for avoiding optical background noise. Fig. 4(a) compares the signal-to-noise ratio with and without the microspheres in the same single defect (yellow circles in Figs. 5(a) and 5(b)). The results show a significant improvement in the signal-to-noise ratio by an average of four times for the artifacts.

The fluorescence of single-atom defects can serve as a perfect point-spread function to measure the spatial resolution of the image. The scale of the virtual image is compensated by using M measured in Fig. 3c to determine the spatial resolution of the microscope using microspheres. In Fig. 4a and Fig. 4b, the defect groups D and T, which are not spatially resolved in the conventional microscope, are well resolved into isolated defects D1, D2 and T1, T3 in the microsphere-assisted microscope, respectively. These results clearly demonstrate the improved resolution in the microsphere-assisted microscope.

To compare the full width at half maximum (FWHM) of the point-spread function, a single defect marked as S in Fig. 6(a) and Fig. 6(b) is selected, and the cross-sectional intensity curve is plotted in Fig. 6(c). The FWHM of the fitted Gaussian function in the conventional microscope is about 280 nm. Considering the central wavelength of 700 nm for the broad spectrum (600–800 nm) of the N ₂ vacancy center, the value corresponds to a spatial resolution of ~λ/2.5, which is close to the Abbe diffraction limit /(2*NA), which is 1.4 for an NA oil immersion lens.

For the microscope using microspheres, the point-spread functions were measured at two different virtual planes at z = -13 and z = -17 μm, and the FWHM of 188 nm (λ/3.7) and 142 nm (λ/5) were achieved, respectively. Thus, the microscope using microspheres provides a spatial resolution beyond the diffraction limit in conventional microscopes.

Figure 6(d) shows the spatial resolution and intensity as a function of imaging depth from the surface. The microspheres form virtual images with the highest intensity around z = -12 to -13 μm. As the imaging plane goes further down, higher resolution is achieved but the intensity decreases. At z = -17 μm, a resolution of around λ/5 is achieved, but the intensity decreases to 20% of the maximum intensity. In addition, the intensity profile at z = -17 μm shows two shoulder peaks as shown in Figure 6(c). These peaks originate from the Airy disk pattern and become stronger as they pass through the focal plane dv = =13 μm.

The improved resolution and enhanced optical signal contrast allow for the examination of close-by defects that are not resolved by conventional microscopy. In Figures 6(e) and 6(f), conventional microscopy shows the intensity profile of defect group D as a combined single peak, whereas microsphere-assisted microscopy shows two separate peaks for defects D1 and D2 in Figure 6(b).

Each single quantum source ideally behaves as a single photon source, quantified by the antibunching dip, where g ⁽²⁾ (0) = 0. When multiple defects overlap spatially, the value where N is the number of quantum sources. To investigate the single-photon purity, the second-order photon-photon correlation g ⁽²⁾ (τ) is measured using the Hanbury Brown and Twiss measurements, and the following equation The data were fitted using , where τ _c is the time constant associated with the transition between the ground and excited states. For the single defect (S), both the conventional and microsphere-assisted microscopy show the expected low g ⁽²⁾ (0) values of 0.12 ± 0.07 and 0.09 ± 0.06, respectively.

Next, g ⁽²⁾ (τ) was measured for two adjacent defects. For defect group D, a histogram was recorded at the maximum intensity of the merged peak as shown in Fig. 6(g), and g ⁽²⁾ (0) = 0.3 ± 0.08 was obtained. This value is a marked increase compared to that of a single defect.

In contrast, for the spatially separated single defects D1 and D2 as illustrated in Fig. 6(h), the g ⁽²⁾ (0) values of the virtual single defects D1 and D2 remain low, at 0.13±0.06 and 0.16±0.06, respectively. This high single-photon purity indicates that the magnified high-resolution imaging can optically separate single photons from the emissions of adjacent defects.

It is also worth noting that the g ⁽²⁾ (0) value is still less than 0.5 for two spatially overlapped defects in conventional microscopes. The emission from two independent and identical quantum sources is expected to have g ⁽²⁾ (0)~0.5. However, even with two defects, the g value less than 0.5 can be obtained if the brightness of each emitter is not identical or if the measurement is spatially one-sided between the two defects. Moreover, such defects can blink transiently, so that they behave as if a single and two emitters are mixed under a given experimental condition. Although g ⁽²⁾ (0) < 0.5 is often used as a criterion for a single defect, our results suggest that in practice, g ⁽²⁾ (0) < 0.5 alone does not indicate a single quantum source. Therefore, the use of high-resolution imaging systems would be more advantageous in identifying single defects and in independently manipulating closely spaced defects.

Subsequently, microsphere-assisted microscopy is shown to improve the spin read-out contrast and to allow independent access to single spins in adjacent defects. The N ₂ vacancy center in diamond has a zero-field splitting of 2.87 GHz in the absence of an external magnetic field, which can be detected by optically detected magnetic resonance (ODMR) measurements.

Figures 7(a) and 7(b) show the ODMR spectra of the same single defect under the conventional microscope and the microsphere-assisted microscope. The single defect under the microsphere exhibits an ODMR contrast of 25 ± 0.9%, which is higher than the value of 15 ± 1.1% under the conventional microscope. This increase is believed to be due to the improved signal-to-noise ratio of the artifact.

To demonstrate that we can resolve single spins of merged defects at the conventional optical diffraction limit, we investigate the ODMR spectra of two closely spaced defects using two microscope setups. In the conventional microscope, the two defects are spatially overlapped, but by applying a randomly oriented magnetic field (~50 G) that breaks the degeneracy of S = 1, as shown in the inset of Fig. 7(c), we confirm the presence of two different spins.

Since the NV center in diamond has four possible spin configurations in the crystal, the two defects can have different amounts of Zeeman splitting depending on the applied magnetic field. As shown in Fig. 7(c), four peaks can be observed from the two defects in the ODMR spectrum. Each defect shows a splitting of δ ₁ = 50 MHz and δ ₂ = 118 MHz, respectively, centered at 2.87 GHz. In a conventional microscope, these defects are merged, so that each spin cannot be optically controlled.

However, using the microsphere-assisted confocal microscope according to the present embodiment, such defects are clearly separated, as shown in the inserted drawing in Fig. 7(d). The ODMR signal of each defect is recorded separately, as exemplified in Fig. 7(d) and Fig. 7(e). Unlike the previous four peaks due to the two non-separated defects, each ODMR spectrum shows only two separated peaks (defect 1: δ ₁ = ±55 MHz, defect 2: δ ₂ = ±120 MHz) due to each defect without crosstalk for different defects. The difference in δ _1,2 between the two setups is due to the variation of the magnet alignment during the measurement. Therefore, the microsphere-assisted imaging with improved spatial resolution and signal contrast enables independent access of single photons and single spins of defects that are not spatially separated in conventional microscopy.

Microsphere lenses have the advantage of being a repositionable optical interface. The position of the microspheres can be easily controlled by mechanical or optical forces. Optical tweezers (400) were combined to control the position of the microspheres. In general, high refractive index microspheres are difficult to capture using optical tweezers because of the large scattering force at the interface. However, the immersion oil lowers the optical index contrast between the microspheres and the environment, which allows the van der Waals force and scattering force to be overcome. Figures 6a and 6b illustrate the capture and reposition of individual microspheres with optical tweezers. It should be noted that the microspheres are attached to the substrate without a trapping laser, and the spheres remain in place even after several days of placement.

10: Imaging device 100: Microsphere
200: Optical system 300: Light source

Claims (13)

A microsphere positioned on a sample and arranged on a target, the target being a point defect within the diamond;
An optical system for providing light to the microspheres and imaging the target through the microspheres;
A signal processing unit that receives light formed from the target and converts it into a corresponding electrical signal; and
Further comprising an RF generator for generating and irradiating microwaves of a frequency that resonates with the electron spin state within the above diamond point defect,
An imaging device in which the above microwaves irradiated by the RF generator control the spin state of electrons within the point defects of the diamond. In the first paragraph,
The above microspheres are,
An imaging device made of a material having a difference in refractive index between the microsphere and the external environment of the microsphere of 1.3 to 1.7. In the first paragraph,
The above microspheres are
An imaging device made of one of barium titanate (BaTiO ₃ ), fused silica, or lime glass. delete delete delete In the first paragraph,
The point defect located within the above diamond is an imaging device that provides single photons and quantum spins. In the first paragraph,
The above imaging device,
An imaging device for imaging an image formed under the sample. In the first paragraph,
The above microspheres are,
An imaging device immersed in immersion oil having a lower refractive index than the refractive index of the above microspheres. In the first paragraph,
The above imaging device,
A light source providing the above light,
A light receiving unit that receives light provided from the above defect and converts it into a corresponding electrical signal; and
An imaging device further comprising a signal processing unit for processing the electrical signal. In Article 10,
The above light source is a continuous wave laser,
The above light-receiving unit is an imaging device including an avalanche photodiode. In the first paragraph,
The above imaging device,
Further comprising an optical tweezer for placing the microspheres on the defect,
The optical tweezers are imaging devices including a laser light source. In the first paragraph,
The above optical system is an imaging device that is a confocal microscope.