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An integrated magnetic sensor is designed and tested that utilizes the negatively charged nitrogen vacancy centers (NVC) in diamond as a magnetic field‐sensitive quantum material, which is accessed and readout solely optically. The compact sensor device features a side length of 10 mm and includes a small HPHT diamond slab, light‐emitting diode (LED) for excitation, and integrated photodiodes. A microwave‐free approach is used. With the device, DC sensitivity to magnetic fields of 49 nA mT−1 in the range of 5–50 mT is achieved. The sensor device is also capable of detecting very small magnetic fields: Magnetic field dependencies at very low flux densities in the μT range (zero‐magnetic field) show a characteristic fluorescence behavior revealing a sensitivity of 4.8 pA μT−1. Additionally, a ray‐tracing model is applied, to identify loss mechanisms in the setup. Using this device, an ultracompact, reliable, and industry‐ready package is made available for sensor developments in industry and academia. [ABSTRACT FROM AUTHOR]

Owing to its unique optical and spin properties, the nitrogen‐vacancy (NV) center holds the promise of a diamond‐based room‐temperature scalable quantum computer, but the numerous technical and physical issues are not yet overcome, especially the poor N to NV conversion. The NV and other color centers are, however, successfully used as multitasking quantum sensors, and open new routes in quantum sensing technologies. Most recently, several breakthroughs and demonstrations were achieved, shedding a new light on the feasibility of a NV‐based quantum computer. Herein, the recently developed method of charge‐assisted single defect engineering is reviewed. With a controlled charging of the involved species, it modifies the diffusion or kinetics of defect formation and acts as a catalyzer of the NV creation while hindering the formation of competing and perturbing defects such as divacancies or NVH. Very high NV creation yields up to 75% are obtained and the method is suitable to other impurity‐vacancy defects. Furthermore, it has positive consequences on the charge state stability and coherence time of the NV centers, which is as well discussed. Together with the possibility to nowadays deterministically implant single ions, this powerful method brings the scalability of NV qubits closer. [ABSTRACT FROM AUTHOR]

The nanometer-scale engineering of single nitrogen-vacancy (NV) centres in diamond can be obtained by low-energy (keV) nitrogen implantation with limited straggling. However, shallow NV centres (a few nanometres deep) generally have inferior overall properties than deeply implanted or deep native NV centres, due to the surface proximity. It has already been shown that the spin coherence time of shallow NVs is improved by overgrowth of a thin diamond layer. However the influence of the overgrowth on the survival, the optical properties and the charge state of the centres has not been studied in detail. In this article, we have overgrown three diamond samples (containing NV centres implanted at different depths) using different procedures. We show the successful overgrowth of a pattern of very shallow (2 nm) implanted NV centres using an optimised overgrowth process. Furthermore, the charge state of ensembles and single NV centres was found to be shifted from NV0 to NV− and stabilised in the negative charge state after overgrowth. The combination of low-energy high-resolution ion implantation and high-purity chemical vapour deposition (CVD) overgrowth procedures opens the way towards the fabrication of scalable and efficient quantum devices based on single defects in diamond. Left: implanted pattern of very shallow NV centres (depth ∼2 nm) using a pierced AFM tip. Right: same pattern after CVD overgrowth of a 4 μm-thick diamond layer. [ABSTRACT FROM AUTHOR]

The control and stabilisation of the charge state of nitrogen-vacancy centres in diamond is an important issue for the achievement of reliable processing of spin-based quantum information. The effect of phosphorous and boron doping of diamond on the charge state of nitrogen-vacancy (NV) centres is shown here. Ensembles of NV centres are produced at a depth of 60 nm in ultrapure diamond by implantation of nitrogen ions. Overlapping with the NV ensembles, donor and acceptor doped regions of different doping levels are prepared by ion implantation of phosphorus and boron followed by annealing in vacuum at 1500 °C. We show how the charge state of NV centres is controlled by the presence of phosphorous or boron atoms in their neighbourhood. For the lowest doping level, spectral measurements on the ensemble of NV centres reveal a higher amount of NV0 in the case of boron and a higher amount of NV− in the case of phosphorus, as compared with undoped regions. This behaviour is strengthened when the doping level is increased. Interestingly, the charge state control of native silicon-vacancy centres is also evidenced. Finally, we discuss the role of the surface termination of diamond on the average charge state of the NV ensemble (still dominant even at a depth of 60 nm) and confirm that the surface 2D-hole-gas (H-termination) can be compensated by nitrogen itself. [ABSTRACT FROM AUTHOR]

The creation of nitrogen-vacancy (NV) centres in diamond is nowadays well controlled using nitrogen implantation and annealing. Although the high-resolution placement of NV centres has been demonstrated using either collimation through pierced tips of an atomic force microscope (AFM) or masks with apertures made by electron beam lithography, a targeted implantation into pre-defined structures in diamond may not be achieved using these techniques. We show that a beam of nitrogen ions can be focused to approximately 100 nm using focused ion beam (FIB) technology. The nitrogen ion beam is produced using an electron cyclotron resonance (ECR) plasma source. Combined with a scanning electron microscope, the nitrogen-FIB offers new possibilities for the targeted creation of single defects in diamond. This maskless technology is suitable for example for the creation of optical centres in the cavities of photonic crystals or in diamond tips for scanning magnetometry. [ABSTRACT FROM AUTHOR]

A cost‐effective approach to provide diamond platelets containing nitrogen vacancy center ensembles (NVs) in the range of ppm is investigated. Industry‐type high‐pressure–high‐temperature‐diamond type 1b containing a high number of interstitial nitrogen in the range of several tens of ppm are used and small diamond platelets (size ≈1 × 1 mm2, thickness ≈300 μm) are prepared by laser cutting and polishing. The nitrogen is converted into NV by means of high‐energy electron irradiation of 10 MeV and annealing at 900 °C. Variations in the irradiation dose between 0.5E18 1/cm2 and 2E18 1/cm2 result in different densities of NV. The diamond platelets are analyzed with regard to their nitrogen concentration and photoluminescence as well as optically detected magnetic resonance is used to investigate the usability for a NV‐based magnetometer. A method to calculate the ratio of negatively to neutrally charged NV (NV−/NV0) is proposed that uses the photoluminescence intensities of the spectrum at 575 and 638 nm, namely, the zero‐phonon lines of NV− and NV0. [ABSTRACT FROM AUTHOR]

Investigation of Ion Channeling and Scattering for Single-Ion Implantation with High Spatial Resolution A nanoaperture defined by drilling in a hollow pyramidal atomic force microscope (AFM) tip is used to produce precise nitrogen vacancy (NV) center nanostructures in diamond by low energy nitrogen implantation. In article number 1900528 by Nicole Raatz and co-workers, both effects are studied using iradina, crystal-trim and corresponding experiments. [Extracted from the article]