Long Rayleigh length confocal microscope: A fast evaluation tool for obtaining quantum properties of color centers

Color centers in wide band-gap semiconductors, which have superior quantum properties even at room temperature and atmospheric pressure, have been actively applied to quantum sensing devices. Characterization of the quantum properties of the color centers in the semiconductor materials and ensuring that these properties are uniform over a wide area are key issues for developing quantum sensing devices based on color center. In this article, we will describe the principle and performance of a newly developed confocal microscope system with a long Rayleigh length (LRCFM). This system can characterize a wider area faster than the confocal microscope systems commonly used for color center evaluation

Charge stability of shallow single nitrogen-vacancy centers in lightly boron-doped diamond

Nitrogen vacancy (NV) centers in diamond must be in a stable negatively charged state for their application to quantum sensing and quantum information processing. In this study, we investigated the charge-state stability of single NV centers in lightly boron-doped diamond ([B] ≈ 1 × 1015 cm−3). Photoluminescence and optically detected magnetic resonance measurements indicated that single NV centers near the diamond surface are negatively charged despite the presence of boron acceptors. This unique phenomenon can be explained by charge transfer between the NV centers and their local environment under laser excitation. This study provides a new perspective on the charge stability of single NV centers in lightly doped diamond and insights for further development of high-performance diamond quantum devices

Evaluation of NV centers in bulk diamond formed by electron beam irradiation

IntroductionNegatively charged nitrogen-vacancy (NV-) center in diamond is known as quantum sensor, can be used to measure small changes in physical quantities, such as magnetic field and temperature. To enhance the sensitivity of the quantum sensor, increasing NV- and decreasing neutral charge state NV0 in diamonds are needed since NV0 does not act as quantum sensor. The electron irradiation is a good method to create high concentration of NV centers. The high energy electrons create vacancies in diamond. Annealing allows the vacancies to move and to be trapped by substitutional nitrogen (P1 centers), forming NV centers. In this study, we irradiate diamonds containing different initial P1 concentrations with electrons and evaluate the fluence dependence of the charge state and the amount of created NV centers, for the purpose of determining appropriate fluence to form NV centers efficiently. MethodThe commercial diamonds synthesized by High Pressure and High Temperature (HPHT) were used. 2 MeV electrons were irradiated with fluences up to 3×1018 cm-2 at room temperature. Then, the samples were annealed at 1000℃ for 2 hours to create NV centers. The concentration of P1 (number of electron spins) was measured by Electron Spin Resonance (ESR). The initial concentration of P1 was in the range from 50 ppm to 100 ppm. The ratio of NV- to NV0 was evaluated from photoluminescence (PL) spectrum. All these measurements were performed at room temperature. Results & DiscussionThe concentration of P1 decreased with increasing fluence. In contrast, total amount of NV centers increased with increasing fluence and only NV- was detected when the fluence of 3×1018 cm-2. The result suggests that remained P1 centers act as electron donor, and provide electron to NV0. Further irradiation with higher fluence will be needed to achieve the adequate one to maximize NV- concentration for diamonds remaining the charge state only in NV-.3rd IFQM

Equilibrium charge state of NV centers in diamond

電子線照射を用いればダイヤモンド中のNV（窒素・空孔）センターを高濃度に作成することができる。2 MeV電子線によって導入した原子空孔と窒素不純物（P1センター）を熱処理によって結合させてNVセンターを形成し、NVセンターの電荷状態やその総量を調べた。特にP1センター濃度とNVセンターの濃度比から電荷状態について化学平衡式を用いて議論し、その平衡点を決定している

Diamond crystal growth aiming at quantum magnetic sensor application

The diamond NV center is expected to be applied to high-sensitivity quantum magnetic sensors. The excellent spin characteristics are derived from the physical properties of diamond as a high-temperature material, and it has already been reported that the spin coherence time at room temperature exceeds 2 ms. In order to improve the sensitivity, it is indispensable to improve the crystalline quality and appropriately form the NV centers. In this talk, we will focus on the research conducted at NIMS regarding diamond crystal growth for the purpose of quantum magnetic sensor application.NIMS WEE

Nitrogen concentration control in diamond growth for NV center formation

Diamond growth is a key technology for the developing quantum sensing device using NV centers. Desired concentration of NV centers varies from 1ppb to 10ppm depending on the type of quantum sensing devices. Then, precise control of nitrogen concentration in wide doping range is requested for diamond growth. Carbon isotope control is another important issue of diamond growth to prolong the spin coherent time. Here, research activity of diamond growth in National Institute for Materials Science (NIMS) by chemical vapor deposition (CVD) and high-pressure and high-temperature (HPHT) will be introduced focusing on the NV center formation.3rd IFQM

Exploring NV center formation condition for high Econv and charge-state ratio of NV- and NV0 centers

The study on NV center formation condition for high Econv and charge-state ratio of NV- and NV0 centersThe 4th International Forum on Quantum Metrology and Sensin

Optimal amount of vacancy in diamond for negative-charge stability of NV centers at various nitrogen concentration

we consider the total amount of NV center in diamond as an indicator of amount of vacancy assuming all vacancies created in diamond were coupled with nitrogen during the consecutive annealing. In this study, we investigate the dependence of the negative-charge stability of NV centers, [NV-]/[NV0] ratio, on the percentage of vacancies to nitrogen, [NVT]/[P1] ratio. Our result indicates that the negative-charge stability is realized at [NVT]/[P1] < 0.2 except for the case in which [NV-] is compatible to residual [B].3rd IFQM

Long Rayleigh length confocal microscope: A fast evaluation tool for obtaining quantum propensities of color centers

Color centers in wide band-gap semiconductors, which have superior quantum properties even at room temperature and atmospheric pressure, have been actively applied to quantum sensing devices. Characterization of the quantum properties of the color centers in the semiconductor materials and ensuring that these properties are uniform over a wide area are key issues for developing quantum sensing devices based on color center. In this article, we will describe the principle and performance of a newly developed confocal microscope system with a long Rayleigh length (LRCFM). This system can characterize a wider area faster than the confocal microscope systems commonly used for color center evaluation