As a potential candidate for quantum computation and metrology, the nitrogen vacancy (NV) center in diamond presents both challenges and opportunities resulting from charge-state conversion. By utilizing different lasers for the photon-induced charge-state conversion, we achieved subdiffraction charge-state manipulation. The charge-state depletion (CSD) microscopy resolution was improved to 4.1 nm by optimizing the laser pulse sequences. Subsequently, the electron spin-state dynamics of adjacent NV centers were selectively detected via the CSD. The experimental results demonstrated that the CSD can improve the spatial resolution of the measurement of NV centers for nanoscale sensing and quantum information. Keywords: charge state; NV center; photon ionization; super-resolution microscopy INTRODUCTION Because of the stable fluorescence and long coherence time of its spin state, the negatively charged nitrogen vacancy (NV 2 ) center in diamond has been studied extensively over the past decade. This defect has the potential to be used for quantum computation, 1-4 nanoscale metrology 5-8 and biological imaging. [9][10][11] To further extend the study of the interaction between a multi-NV center and the nanoscale sensing with the NV center, it is necessary to detect and control the NV center spin-state dynamics with high spatial resolution. 7,12-14 Therefore, many optical super-resolution microscopy techniques have been developed to detect single NV centers. [13][14][15][16][17] Among these methods, stimulated emission depletion (STED) microscopy 12,18-20 is one of the most promising. This method utilizes a doughnut-shaped laser to produce the position-dependent stimulated emission, which changes the fluorescence signal. With STED, the electron spin resonance signals of NV centers have been detected with a resolution lower than the diffraction limit. 12,21,22 A new super-resolution microscopy technique was recently developed by Han et al. 15 The authors replaced the stimulated excitation of STED with the dark-state pumping of NV centers. The dark state was later proven to be the neutral charge NV center (NV 0 ) by other groups. [23][24][25] The charge-state conversion results in a change of the local field in diamond 26 and the spectral diffusion of the NV center. 24,27 For high-fidelity quantum manipulation, the charge state should be well controlled. 28 Based on the mechanism of charge-state conversion and super-resolution microscopy, 25,29,30 we demonstrated the optical manipulation of the charge state of an NV center with subdiffraction resolution. By changing the duration and power of laser

A quantum measurement method based on the quantum nature of anti-bunching photon emission has been developed to detect single particles without the restriction of the diffraction limit. By simultaneously counting the single-photon and two-photon signals with fluorescence microscopy, the images of nearby Nitrogen-Vacancy centers in diamond at a distance of 8.5 ± 2.4 nm have been successfully reconstructed. Also their axes information was optically obtained. This quantum statistical imaging technique, with a simple experimental setup, can also be easily generalized in the measuring and distinguishing of other physical properties with any overlapping, which shows high potential in future image and study of coupled quantum systems for quantum information techniques.PACS numbers: 06.30. Bp,42.30.Wb The measurement of physical quantities is not only a major goal but also an active impulsion for scientific research. Especially, the imaging of nearby particles is important for modern science [1,2]. The precision with which two nearby particles can be resolved is classically restricted by the optical diffraction limit. Imaging methods that used distinguishing information based on the photons emitted from different particles have been proposed to achieve precision beyond the diffraction limit [3][4][5][6][7][8][9]. When the emitted photons have the same properties, distinguishing nearby particles which are separated by distances much less than the diffraction limit is difficult.Recently, phenomena from quantum mechanics have been used to improve the measurement and applied to some special purposes which cannot be performed by classical method. Such quantum techniques are being applied to enhance the precision of measurements beyond the classical limit [10,11]. However, many quantum-based protocols to improve the measurement used the quantum entanglement. They are fragile because of quantum decoherence [12][13][14]. For practical purpose, stable quantum phenomena should be applied in the measurement. There are proposals to enhance the imaging resolution based on the quantum statistics [9,15]. Here, we have developed a quantum statistical imaging (QSI) method to detect single particles without the restriction of the diffraction limit. In the quantum regime, the situation for particles imaging is different because each particle emits only one photon and shows the single-photon antibunching effect [16]. By detecting the photon coincident counts, the particles can be imaged and resolved even when they are almost completely overlapping and the emitted photons are identical. Here, Nitrogenvacancy center (NVC) in diamond was used in this experimental demonstration. Single NVC has shown its good quality as a single-photon source [17,18]. When two NVCs are close to each other, i.e., within tens of nanometers, the strong dipoledipole interaction can be applied in quantum information techniques [19,20]. Diamond nano-crystals with NVCs have been successfully used to image biological processes [21,22]. The ability to image and disti...

A theoretical study of free space coupling to high-Q whispering gallery modes both in circular and deformed microcavities are presented. In the case of a circular cavity, both analytical solutions and asymptotic formulas are derived. The coupling efficiencies at different coupling regimes for cylinder incoming wave are discussed, and the maximum efficiency is estimated for the practical Gaussian beam excitation. In the case of a deformed cavity, the coupling efficiency can be higher if the excitation beam can match the intrinsic emission well and the radiation loss can be tuned by adjusting the degree of deformation. Employing an abstract model of slightly deformed cavity, we found that the asymmetric and peak like line shapes instead of the Lorentz-shape dip are universal in transmission spectra due to multi-mode interference, and the coupling efficiency can not be estimated from the absolute depth of the dip. Our results provide guidelines for free space coupling in experiments, suggesting that the high-Q ARCs can be efficiently excited through free space which will stimulate further experiments and applications of WGMs based on free space coupling.

Nitrogen-vacancy defect color centers are created in a high purity single crystal diamond by nitrogen-ion implantation. Both optical spectrum and optically detected magnetic resonance are measured for these artificial quantum emitters. Moreover, with a suitable mask, a lattice composed of nitrogen-vacancy centers is fabricated. Rabi oscillation driven by micro-waves is carried out to show the quality of the ion implantation and potential in quantum manipulation. Along with compatible standard lithography, such an implantation technique shows high potential in future to make structures with nitrogen-vacancy centers for diamond photonics and integrated photonic quantum chip.

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The coupled negatively charged nitrogen-vacancy (NV − ) center system is a promising candidate for scalable quantum information techniques. In this work, ionized nitrogen molecules are implanted into bulk diamond to generate coupled NV − center pairs. The two-photon autocorrelation measurement and optically detected magnetic resonance measurement are carried out to confirm the production of the NV − center pair. Also, both 1.3 𝜇s decoherence time and 4.9 kHz magnetic coupling strength of the NV − center pair are measured by controlling and detecting the spin states. Along with nanoscale manipulation and detection methods, such coupled NV − centers through short distance dipole-dipole interaction would show high potential in scalable quantum information processes.