We experimentally demonstrate quantum enhanced resolution in confocal fluorescence microscopy exploiting the nonclassical photon statistics of single nitrogen-vacancy color centers in diamond. By developing a general model of superresolution based on the direct sampling of the kth-order autocorrelation function of the photoluminescence signal, we show the possibility to resolve, in principle, arbitrarily close emitting centers. DOI: 10.1103/PhysRevLett.113.143602 PACS numbers: 42.50.-p, 42.30.Va, 42.50.Ar, 42.50.St In the last decade, measurement techniques enhanced by using peculiar properties of quantum light [1,2] have been successfully demonstrated in several remarkable real application scenarios, for example, interferometric measurements aimed to reveal gravitational waves and the quantum gravity effect [3,4], biological particle tracking [5], phase contrast microscopy [6], and imaging [7,8]. Very recently, a novel technique to beat the diffraction limit in microscopy that relies on the antibunching behavior of photons emitted by single fluophores has been proposed [9], and realized in wide field microscopy [10] by using an EMCCD camera.The maximum obtainable imaging resolution in classical far-field fluorescence microscopy, according to the Abbe diffraction limit, is R ≃ 0.61λ=NA, where λ is the wavelength of the light and NA is the numerical aperture of the objective. This restricts the current capability of precisely measuring the position of very small objects such as single photon emitters (color centers, quantum dots, etc.) [11][12][13][14][15][16][17][18][19], limiting their potential exploitation in the frame quantum technology [20,21]. In general, the research of methods to obtain a microscopy resolution below the diffraction limit is a topic of the utmost interest [22][23][24][25][26][27][28][29] that could provide dramatic improvement in the observation of several systems spanning from quantum dots [30] to living cells [31][32][33][34]. As a notable example, in several entanglement-related experiments using strongly coupled single photon emitters it is of the utmost importance to measure their positions with the highest spatial resolution [35]. In principle, this limitation can be overcome by recently developed microscopy techniques such as stimulated emission depletion (STED) and ground state depletion (GSD) [36,37]. Nevertheless, even if they have been demonstrated effectively able to provide superresolved imaging in many specific applications, among which are color centers in diamond [38], they are characterized by rather specific experimental requirements (dual laser excitation system, availability of luminescence quenching mechanisms by stimulated emission, nontrivial shaping of the quenching beam, high power). Furthermore, these techniques are not suitable in applications in which the fluorescence is not optically induced [39,40], so that new methods are required for those applications.Inspired by the works in [9], in this Letter we develop a comprehensive theory of superresolution ima...

We report on the systematic characterization of conductive micro-channels fabricated in single-crystal diamond with direct ion microbeam writing. Focused high-energy (∼MeV) helium ions are employed to selectively convert diamond with micrometric spatial accuracy to a stable graphitic phase upon thermal annealing, due to the induced structural damage occurring at the end-of-range. A variable-thickness mask allows the accurate modulation of the depth at which the microchannels are formed, from several µm deep up to the very surface of the sample. By means of cross-sectional transmission electron microscopy (TEM), we demonstrate that the technique allows the direct writing of amorphous (and graphitic, upon suitable thermal annealing) microstructures extending within the insulating diamond matrix in the three spatial directions, and in particular, that buried channels embedded in a highly insulating matrix emerge and electrically connect to the sample surface at specific locations. Moreover, by means of electrical characterization at both 2 room temperature and variable temperature, we investigate the conductivity and the charge-transport mechanisms of microchannels obtained by implantation at different ion fluences and after subsequent thermal processes, demonstrating that upon high-temperature annealing, the channels implanted above a critical damage density convert into a stable graphitic phase. These structures have significant impact for different applications, such as compact ionizing radiation detectors, dosimeters, bio-sensors and more generally diamond-based devices with buried three-dimensional all-carbon electrodes.

We report on the systematic characterization of photoluminescence (PL) lifetimes in NV − and NV 0 centers in 2-MeV H + -implanted type Ib diamond samples by means of a time-correlated single-photon counting (TCSPC) microscopy technique. A dipole-dipole resonant energy transfer model was applied to interpret the experimental results, allowing a quantitative correlation of the concentration of both native (single substitutional nitrogen atoms) and ion-induced (isolated vacancies) PL-quenching defects with the measured PL lifetimes. The TCSPC measurements were carried out in both frontal (i.e., laser beam probing the main sample surface along the same normal direction of the previously implanted ions) and lateral (i.e., laser beam probing the lateral sample surface orthogonally with respect to the same ion implantation direction) geometries. In particular, the latter geometry allowed a direct probing of the centers lifetime along the strongly nonuniform damage profiles of MeV ions in the crystal. The extrapolation of empirical quasiexponential decay parameters allowed the systematic estimation of the mean quantum efficiency of the centers as a function of intrinsic and ion-induced defect concentration, which is of direct relevance for the current studies on the use of diamond color centers for photonic applications.

Single-photon sources are a fundamental element for developing quantum technologies, and sources based on colour centres in diamonds are among the most promising candidates. The well-known nitrogen vacancy centres are characterized by several limitations, and thus few other defects have recently been considered. In the present work, we characterize, in detail, native efficient single colour centres emitting in the near infra-red (λ = 740-780 nm) in both standard IIa single-crystal and electronic-grade polycrystalline commercial chemical vapour deposited (CVD) diamond samples. In the former case, a hightemperature (T > 1000°C) annealing process in vacuum is necessary to induce the formation/activation of luminescent centres with good emission properties, while in the latter case the annealing process has marginally beneficial effects on the number and performance of native centres in commercially available samples. Although displaying significant variability in several photo-physical properties (emission wavelength, emission rate instabilities, saturation behaviours), these centres generally display appealing photophysical properties for Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. applications as single photon sources: short lifetimes (0.7-3 ns), high emission rates (∼50-500 × 10 3 photons s −1 ) and strongly (>95%) polarized light. The native centres are tentatively attributed to impurities incorporated in the diamond crystal during the CVD growth of high-quality type-IIa samples, and offer promising perspectives in diamond-based photonics.Single photon sources represent a key element for developing quantum technologies [1][2][3][4]. Diamond offers a promising platform for the implementation of single-photon-emitter architectures, due to the vast range of available luminescent defects [5,6] with suitable emission properties that can be allocated in a broadly transparent crystal structure. The nitrogenvacancy (NV − ) complex has established a prominent role as a single photon emitter in several pioneering works [7-9], due to its ubiquity, quantum efficiency and well-understood electronic transition structure [10]. In the last decade, single NV − emitters were successfully employed to implement quantum cryptography schemes [11][12][13][14] as well as more fundamental demonstrations of quantum complementarity and entanglement [15][16][17][18]. At the same time, the research in diamond-based single-photon sources has broadened to new types of defects, with the goal of overcoming some inherent limitations in the NV − centre, namely its strong phonon coupling, relatively long lifetime and charge-state blinking. In particular, the identification of centres emitting in the near-infrared (NIR) offers the perspective of combining diamond colour centres with Si-based photodetectors in the spectral range where they are maximally efficient...

Focused MeV ion beams with micrometric resolution are suitable tools for the direct writing of conductive graphitic channels buried in an insulating diamond bulk, as already demonstrated for different device applications. In this work we apply this fabrication method to the electrical excitation of color centers in diamond, demonstrating the potential of electrical stimulation in diamond-based single-photon sources. Differently from optically-stimulated light emission from color centers in diamond, electroluminescence (EL) requires a high current flowing in the diamond subgap states between the electrodes. With this purpose, buried graphitic electrode pairs, 10 μm spaced, were fabricated in the bulk of a single-crystal diamond sample using a 6 MeV C microbeam. The electrical characterization of the structure showed a significant current injection above an effective voltage threshold of 150 V, which enabled the stimulation of a stable EL emission. The EL imaging allowed to identify the electroluminescent regions and the residual vacancy distribution associated with the fabrication technique. Measurements evidenced isolated electroluminescent spots where non-classical light emission in the 560–700 nm spectral range was observed. The spectral and auto-correlation features of the EL emission were investigated to qualify the non-classical properties of the color centers.

The purpose of this work was to investigate: (1) the differences in temperament and character between 49 women with migraine and 49 controls using the Temperament and Character Inventory (TCI), and (2) the extent to which these differences were related to migraine or to the presence of comorbid depression. The migraine patients scored significantly higher than the controls in two temperament dimensions—Harm Avoidance (HA) and Persistence (P)—and significantly lower in one character dimension—Self-Directedness (SDir) (Student’s t ). After multiple logistic regression, the TCI P and HA dimensions were significantly associated with the presence of migraine. The HA dimension was also related to the presence of depression. Our results show that in migraine the higher HA score could be partly associated to comorbid depression while the high P dimension seems to be solely related to the presence of migraine.

An accurate control of the optical properties of single crystal diamond during microfabrication processes such as ion implantation plays a crucial role in the engineering of integrated photonic devices. In this work we present a systematic study of the variation of both real and imaginary parts of the refractive index of single crystal diamond, when damaged with 2 and 3 MeV protons at low-medium fluences (range: 10 15 -10 17 cm 2 ). After implanting in 125 × 125 μm 2 areas with a scanning ion microbeam, the variation of optical pathlength of the implanted regions was measured with laser interferometric microscopy, while their optical transmission was studied using a spectrometric set-up with micrometric spatial resolution. On the basis of a model taking into account the strongly non-uniform damage profile in the bulk sample, the variation of the complex refractive index as a function of damage density was evaluated. ©2012 Optical Society of America

In the present work we report about a parallel-processing ion beam fabrication technique whereby high-density sub-superficial graphitic microstructures can be created in diamond. Ion beam implantation is an effective tool for the structural modification of diamond: in particular ion-damaged diamond can be converted into graphite, therefore obtaining an electrically conductive phase embedded in an optically transparent and highly insulating matrix.The proposed fabrication process consists in the combination of Deep Ion Beam Lithography (DIBL) and Focused Ion Beam (FIB) milling. FIB micromachining is employed to define micro-apertures in the contact masks consisting of thin (<10 µm) deposited metal layers through which ions are implanted in the sample. A prototypical single-cell biosensor was realized with 2 the above described technique. The biosensor has 16 independent electrodes converging inside a circular area of 20 µm diameter (typical neuroendocrine cells size) for the simultaneous recording of amperometric signals.