Abstract A nitrogen vacancy (NV) center in diamond is a promising platform for the study of quantum sensing and quantum many-body physics. It is essential for such study to realize a system in which NV centers interact with one another. This requires the fabrication of highly concentrated NV centers, as the centers must exist within a few nanometers of one another. Only a few such samples have been fabricated, because the required irradiation of several-MV electron beams over long periods makes such sample preparation difficult. Here, highly concentrated NV ensembles ([NV] = 8.5 × 1018 cm-3) were created by narrowing the electron beam of a transmission electron microscope to generate large amounts of vacancies in highly concentrated nitrogen-doped CVD diamond ([N] = 8 × 1020 cm-3). This result reduces the difficulty of producing high-concentration NV ensembles and is expected to promote the development of many-body quantum physics.
Abstract A nitrogen vacancy (NV) center in diamond is a promising platform for the study of quantum sensing and quantum many-body physics. It is essential for such study to realize a system in which NV centers interact with one another. This requires the fabrication of highly concentrated NV centers, as the centers must exist within a few nanometers of one another. Only a few such samples have been fabricated, because the required irradiation of several-MV electron beams over long periods makes such sample preparation difficult. Here, highly concentrated NV ensembles ([NV] = 8.5 × 1018 cm-3) were created by narrowing the electron beam of a transmission electron microscope to generate large amounts of vacancies in highly concentrated nitrogen-doped CVD diamond ([N] = 8 × 1020 cm-3). This result reduces the difficulty of producing high-concentration NV ensembles and is expected to promote the development of many-body quantum physics.
The studies of many-body dynamics of interacting spin ensembles, as well as quantum sensing in solid state systems, are often limited by the need for high spin concentrations, along with efficient decoupling of the spin ensemble from its environment. In particular, for an ensemble of nitrogen-vacancy (NV) centers in diamond, high conversion efficiencies between nitrogen (P1) defects and NV centers are essential while maintaining long coherence times of an NV ensemble. In this work, we study the effect of electron irradiation on the conversion efficiency and the coherence time of various types of diamond samples with different initial nitrogen concentrations. The samples were irradiated using a 200 keV transmission electron microscope. Our study reveals that the efficiency of NV creation strongly depends on the initial conversion efficiency and on the initial nitrogen concentration. The irradiation of the examined samples exhibits an order of magnitude improvement in the NV concentration (up to ∼1011 NV/cm2), without degradation in their coherence time of ∼180 μs. We address the potential of this technique toward the study of many-body physics of NV ensembles and the creation of non-classical spin states for quantum sensing.
Abstract The nitrogen-vacancy (NV) center in diamond is a promising quantum system for magnetometry applications exhibiting optical readout of minute energy shifts in its spin sub-levels. Key material requirements for NV ensembles are a high NV − concentration, a long spin coherence time and a stable charge state. However, these are interdependent and can be difficult to optimize during diamond growth and subsequent NV creation. In this work, we systematically investigate the NV center formation and properties in bulk chemical vapor deposition (CVD) diamond. The nitrogen flow during growth is varied by over four orders of magnitude, resulting in a broad range of single substitutional nitrogen concentrations of 0.2–20 parts per million. For a fixed nitrogen concentration, we optimize electron-irradiation fluences with two different accelerated electron energies, and we study defect formation via optical characterizations. We discuss a general approach to determine the optimal irradiation conditions, for which an enhanced NV concentration and an optimum of NV charge states can both be satisfied. We achieve spin–spin coherence times T 2 ranging from 45.5 to 549 μ s for CVD diamonds containing 168 to 1 parts per billion NV − centers, respectively. This study shows a pathway to engineer properties of NV-doped CVD diamonds for improved sensitivity.
We systematically investigate the NV center creation and properties in bulk chemical vapor deposition (CVD) diamond, throughout growth, electron-beam irradiation, and annealing steps. We study diamond series grown with a varying nitrogen flow over 4 orders of magnitude, resulting in a broad range of single substitutional nitrogen (P1 center) densities from 0.2 to 20 ppm. We investigate in-situ P1 and NV creations, as well as NV charge states distributions. As the next step, we optimize electron-irradiation fluences for a fixed nitrogen concentration, with two different accelerated electron energies. We bring up a general approach to determine the optimal irradiation conditions, and discuss criteria for P1 to NV conversion ratios in the context of stable NV charge states. Through all these optimizations, we enhance the NV- concentration remarkably in our CVD diamond samples, without sacrificing their Hahn-echo coherence time T2. We achieve NV concentrations from 1 to 168 ppb with T2 from 549 to 45.5 µs respectively. This study shows a pathway to engineer targeted, optimized properties of NV-ensembles in bulk CVD diamonds for improved sensitivity.
We report the formation of perfectly aligned, high-density, shallow nitrogen vacancy (NV) centers on the (111) surface of a diamond. The study involved step-flow growth with a high flux of nitrogen during chemical vapor deposition (CVD) growth, which resulted in the formation of a highly concentrated (>1019 cm−3) nitrogen layer approximately 10 nm away from the substrate surface. Photon counts obtained from the NV centers indicated the presence of 6.1 × 1015–3.1 × 1016 cm−3 NV centers, which suggested the formation of an ensemble of NV centers. The optically detected magnetic resonance (ODMR) spectrum confirmed perfect alignment (more than 99%) for all the samples fabricated by step-flow growth via CVD. Perfectly aligned shallow ensemble NV centers indicated a high Rabi contrast of approximately 30% which is comparable to the values reported for a single NV center. Nanoscale nuclear magnetic resonance demonstrated surface-sensitive nuclear spin detection and provided a confirmation of the NV centers' depth. Single NV center approximation indicated that the depth of the NV centers was approximately 9–10.7 nm from the surface with error of less than ±0.8 nm. Thus, a route for material control of shallow NV centers has been developed by step-flow growth using a CVD system. Our finding pioneers on the atomic level control of NV center alignment for large area quantum magnetometry.
Diamond color centers such as the nitrogen-vacancy (NV) center have been extensively studied as a popular platform that enables quantum sensing and computing applications. For highly sensitive sensing NV ensembles have significantly stronger signals than individual NV centers and can create strong light fields, which are also essentially required by novel concepts that need a large sensing volume, such as cavity coupling and readout, laser threshold magnetometry and multi-pass geometries. On top of strong signals, low optical material losses are the other key consideration for these techniques, by means of low optical absorption of signal light and low birefringence of the diamond crystal. In this work, we study systematically the behavior of absorption in the NV emission range around 700nm and birefringence with increasing nitrogen- and NV-doping, as well as their behavior during NV creation via diamond growth, electron beam irradiation and annealing treatments. Absorption correlates with increased nitrogen-doping yet single substitutional nitrogen atoms (Ns0 or P1 centers) do not seem to be the direct absorber. The high nitrogen doping level in the growth leads to high absorption in the whole UV-Vis range, which is the main contributors to the high absorption at 700 nm. When treating the diamond for an enhanced NV concentration, ‘over irradiating’ the diamond with too high fluence is harmful in the sense of creating neutral vacancies that increase absorption at the wavelength range of interest. Opposite to the absorption, birefringence reduces with increasing nitrogen doping and shows better homogeneity. After-growth treatments show a minor and if any a positive (i.e. reducing) influence on diamond birefringence. Multiple crystal defect concentrations and their changes are identified via absorption spectroscopy during the material processing steps and thus we identify potential causes of absorption and birefringence. From this we suggest strategies to fabricate CVD diamonds with high NV density yet low absorption and low birefringence
Applications of nitrogen-vacancy (NV) centers in diamond in quantum technology have attracted considerable attention in recent years. Deterministic generation of ensembles of NV centers can advance the research on quantum sensing, many-body quantum systems, multipartite entanglement, and so on. Here we report the complete process of controlled generation of NV centers in diamond as well as their characterization: growing diamond films through chemical vapor deposition (CVD), ion implantation, and spectroscopic characterization of the defect centers using a confocal microscope. A microwave-assisted CVD setup is presented which we constructed for the preparation of single-crystalline homoepitaxial diamond films. The films were prepared with minimized nitrogen concentration, which is confirmed through photoluminescence measurements. We demonstrate an in situ ultrahigh vacuum (UHV) implantation and heating process for creation of NV centers using a novel experimental setup. For the first time hot implantation has been shown which prevents surface charging effects. We do not observe graphitization due to UHV heating. By optimizing the implantation parameters it has been possible to implant NV centers in a precise way. We present large area mapping of the samples to determine the distribution of the centers and describe the characterization of the centers by spectroscopic techniques. Reducing the decoherence caused by environmental noise is of primary importance for many applications in quantum technology. We demonstrate improvement on coherence time T2 of the NV spins by suppression of their interaction with the surrounding spin bath using robust dynamical decoupling sequences.