C hyperfine interactions in the ground state of the negatively charged nitrogen vacancy ͑NV − ͒ center have been investigated using electron-paramagnetic-resonance spectroscopy. The previously published parameters for the 14 N hyperfine interaction do not produce a satisfactory fit to the experimental NV − electron-paramagnetic-resonance data. The small anisotropic component of the NV − hyperfine interaction can be explained from dipolar interaction between the nitrogen nucleus and the unpaired-electron probability density localized on the three carbon atoms neighboring the vacancy. Optical spin polarization of the NV − ground state was used to enhance the electron-paramagnetic-resonance sensitivity enabling detailed study of the hyperfine interaction with 13 C neighbors. The data confirmed the identification of three equivalent carbon nearest neighbors but indicated the next largest 13 C interaction is with six, rather than as previously assumed three, equivalent neighboring carbon atoms.

Engineering coherent systems is a central goal of quantum science. Color centers in diamond are a promising approach, with the potential to combine the coherence of atoms with the scalability of a solid-state platform. We report a color center that shows insensitivity to environmental decoherence caused by phonons and electric field noise: the neutral charge state of silicon vacancy (SiV). Through careful materials engineering, we achieved >80% conversion of implanted silicon to SiV SiV exhibits spin-lattice relaxation times approaching 1 minute and coherence times approaching 1 second. Its optical properties are very favorable, with ~90% of its emission into the zero-phonon line and near-transform-limited optical linewidths. These combined properties make SiV a promising defect for quantum network applications.

No abstract

No abstract

The negatively charged nitrogen-vacancy (NV  ) center in diamond is an attractive candidate for applications that range from magnetometry to quantum information processing. Here we show that only a fraction of the nitrogen (typically < 0.5 %) incorporated during homoepitaxial diamond growth by Chemical Vapor Deposition (CVD) is in the form of undecorated NV  centers. Furthermore, studies on CVD diamond grown on   110 oriented substrates show a near 100% preferential orientation of NV  centers along only the   111 and   111 directions, rather than the four possible orientations. The results indicate that NV centers grow in as units, as the diamond is deposited, rather than by migration and association of their components. The NV unit of the NVH  is similarly preferentially oriented, but it is not possible to determine whether this defect was formed by H capture at a preferentially aligned NV center or as a complete unit. Reducing the number of NV orientations from 4 orientations to 2 orientations should lead to increased optically-detected magnetic resonance contrast and thus improved magnetic sensitivity in ensemble-based magnetometry.

The zero-phonon line (ZPL) at 1.68 eV has been attributed to the negatively charged silicon split-vacancy center in diamond, (Si-V) − , and has been extensively characterized in the literature. Computational studies have predicted the existence of the neutral charge state of the center, (Si-V) 0 , and it has been experimentally observed using electron paramagnetic resonance (EPR). However, the optical spectrum associated with (Si-V) 0 has not yet been conclusively identified. In this paper the 1.31 eV band visible in luminescence and absorption is attributed to (Si-V) 0 using an approach which combines optical absorption and EPR measurements. The intensities of both 1.68 eV and 1.31 eV bands are found to increase in deliberately Si-doped chemical vapor deposition (CVD) grown diamond, and also after electron irradiation and annealing, suggesting the involvement of both Si and a vacancy in the centers. The 1.31 eV ZPL is unambiguously associated to Si by its shift to a lower energy when the dominant Si isotope is changed from 28 Si to 29 Si. Charge transfer between (Si-V) − and (Si-V) 0 induced via ultraviolet photoexcitation or heating in the dark allows calibration factors relating the integrated absorption coefficient of their respective ZPLs to the defect concentration to be determined. Preferential orientation of (Si-V) 0 centers in CVD diamond grown on {110}-oriented diamond substrates is observed by EPR. The (Si-V) 0 centers are shown to grow predominantly into CVD diamond as complete units, rather than by the migration of mobile vacancies to substitutional Si (Si S ) atoms. Corrections for the preferential alignment of trigonal centers for quantitative analysis of optical spectra are proposed and the effect is used to reveal that the 1.31 eV ZPL arises from a transition between the 3 A 2g ground state and 3 A 1u excited state of (Si-V) 0 . A simple rate equation model explains the production of (Si-V) 0 upon irradiation and annealing of Si-doped CVD diamond. In as-grown Si-doped diamond the (Si-V) defects only account for a fraction of the total silicon present; the majority being incorporated as Si S . The data show that both Si S and (Si-V) are effective traps for mobile vacancies.

The silicon-vacancy center in diamond offers attractive opportunities in quantum photonics due to its favorable optical properties and optically addressable electronic spin. Here, we combine both to achieve all-optical coherent control of its spin states. We utilize this method to explore spin dephasing effects in an impurity-rich sample beyond the limit of phonon-induced decoherence: Employing Ramsey and Hahn-echo techniques at temperatures down to 40 mK we identify resonant coupling to a substitutional nitrogen spin bath as limiting decoherence source for the electron spin.

Near-surface nitrogen-vacancy (NV) centers in diamond have been successfully employed as atomic-sized magnetic field sensors for external spins over the last years. A key challenge is still to develop a method to bring NV centers at nanometer proximity to the diamond surface while preserving their optical and spin properties. To that aim we present a method of controlled diamond etching with nanometric precision using an oxygen inductively coupled plasma (ICP) process. Importantly, no traces of plasma-induced damages to the etched surface could be detected by X-ray photoelectron spectroscopy (XPS) and confocal photoluminescence microscopy techniques. In addition, by profiling the depth of NV centers created by 5.0 keV of nitrogen implantation energy, no plasma-induced quenching in their fluorescence could be observed. Moreover, the developed etching process allowed even the channeling tail in their depth distribution to be resolved. Furthermore, treating a 12 C isotopically purified diamond revealed a threefold increase in T2 times for NV centers with < 4 nm of depth (measured by NMR signal from protons at the diamond surface) in comparison to the initial oxygen-terminated surface.Keywords: diamond plasma etching, shallow NV centers, surface damage, spin coherence timesThe negatively-charged nitrogen-vacancy (NV) center in diamond has attracted increasing attention due to its outstanding properties. It is an atomic-sized, bright and stable single photon source[1] with relatively long coherence times, ranging milliseconds in isotopically purified single crystal diamond layers [2,3]. Additionally, its electron spin can be coherently manipulated by microwave and readout optically at room temperature. In the recent years the use of near-surface (shallow) NV centers as sensors to detect external nuclear [4][5][6] and electronic [7,8] spins have been successfully demonstrated. However, since the signal detection relies on the relatively weak dipolar coupling to the targeted external spins, decaying proportional to r −3 (with r being the distance between the targeted and sensor spins), NV centers must be located close to the diamond surface (< 5 nm) [4,5].Up to now, the engineering of near-surface NV centers has relied mostly on low-energy nitrogen implantation [9] or epitaxial growth of high quality nitrogen-doped CVD diamond followed by electron[10] or ion irradiation [11]. Furthermore, NV centers can be brought closer to the diamond surface by post-treatments such as thermal oxidation [12,13] and etching in plasma [13][14][15].A major drawback for thermal oxidation is the uncertainty in the resulting etching rate and infeasibility of selective etching. Overcoming these issues, plasma processes are widely employed, providing a smooth and uniform method to selectively etch diamond. In particular for reactive ion etching (RIE) processes, the pres- * Corresponding author: a.denisenko@physik.uni-stuttgart.de ence of a bias between the plasma source and the sample leads to ion bombardment on the diamond surface. This resu...