arXiv subjects

Norio Tokuda

Publications and source records attributed to Norio Tokuda.

6 recordsLinked to original sources

arXiv2026

Radiation tolerance of a diamond radiation detector for space use

We present a study of the radiation tolerance of two types of diamond radiation detectors for space use. We plan to launch a 3U-size CubeSat, KSAT3-X, developed by Kanazawa University in 2027. The KSAT3-X mission is aimed to observe inflows and outflows of charged particles such as electrons and protons, particularly in the 10 - 40 keV energy range, in the Earth's magnetosphere. As the mission instrument, we have developed two diamond radiation detectors. The first is composed of a microwave plasma chemical vapor deposition (MPCVD) diamond fabricated by Element Six, and the second is based on a MPCVD diamond produced in-house at Kanazawa University. We irradiate both diamonds with 100 MeV protons and evaluate their spectroscopic performance as an indicator of radiation tolerance using characteristic X-rays from radioisotope sources. We find no significant degradation in their spectroscopic performance up to at least the 10-year equivalent irradiation under the orbital environments of KSAT3-X. We additionally irradiate the Element Six diamond with 100 MeV protons up to the 100-year equivalent. As a result, no significant degradation in the spectroscopic performance is observed. These results indicate that the two diamond radiation detectors have sufficiently high radiation tolerance. We also discuss possible physical origins of the observed difference in the spectroscopic performance between the two detectors.

astro-ph.IM↗

arXiv2023

Frequency-tunable magnetic field sensing using continuous-wave optically detected magnetic resonance with nitrogen-vacancy centers in diamond

The nitrogen-vacancy (NV) center is a promising candidate to realize practical quantum sensors with high sensitivity and high spatial resolution, even at room temperature and atmospheric pressure. In conventional high-frequency AC magnetometry with NV centers, the setup requires a pulse sequence with an appropriate time synchronization and strong microwave power. To avoid these practical difficulties, AC magnetic field sensing using continuous-wave opticallydetected magnetic resonance (CW-ODMR) was recently demonstrated. That previous study utilized radio frequency (RF) dressed states generated by the coherent interaction between the electron spin of the NV center and the RF wave. However, the drawback of this method is that the detectable frequency of the AC magnetic fields is fixed. Here, we propose and demonstrate frequency-tunable magnetic field sensing based on CW-ODMR. In the new sensing scheme, we obtain RF double-dressed states by irradiation with a RF field at two different frequencies. One creates the RF dressed states and changes the frequency of the target AC field. The other is a target AC field that induces a change in the CW-ODMR spectrum by generating the RF double-dressed states through coherent interaction with the RF dressed states. The sensitivity of our method is estimated to be comparable to or even higher than that of the conventional method based on a RF field with a single frequency. The estimated bandwidth is 7.45 MHz, higher than that of the conventional method using the RF dressed states. Our frequency-tunable magnetic field sensor based on CW-ODMR paves the way for new applications in diamond devices.

quant-ph↗

arXiv2023

Electron-spin double resonance of nitrogen-vacancy centers in diamond under strong driving field

The nitrogen-vacancy (NV) center in diamond has been the focus of research efforts because of its suitability for use in applications such as quantum sensing and quantum simulations. Recently, the electron-spin double resonance (ESDR) of NV centers has been exploited for detecting radio-frequency (RF) fields with continuous-wave optically detected magnetic resonance. However, the characteristic phenomenon of ESDR under a strong RF field remains to be fully elucidated. In this study, we theoretically and experimentally analyzed the ESDR spectra under strong RF fields by adopting the Floquet theory. Our analytical and numerical calculations could reproduce the ESDR spectra obtained by measuring the spin-dependent photoluminescence under the continuous application of microwaves and an RF field for a DC bias magnetic field perpendicular to the NV axis. We found that anticrossing structures that appear under a strong RF field are induced by the generation of RF-dressed states owing to the two-RF-photon resonances. Moreover, we found that $2n$-RF-photon resonances were allowed by an unintentional DC bias magnetic field parallel to the NV axis. These results should help in the realization of precise MHz-range AC magnetometry with a wide dynamic range beyond the rotating wave approximation regime as well as Floquet engineering in open quantum systems.

quant-ph↗

arXiv2022

n-Type diamond synthesized with tert-butylphosphine for long spin coherence times of perfectly aligned NV centers

The longest spin coherence times for nitrogen-vacancy (NV) centers at room temperature have been achieved in phosphorus-doped n-type diamond. However, difficulty controlling impurity incorporation and the utilization of highly toxic phosphine gas in the chemical vapor deposition (CVD) technique pose problems for the growth of n-type diamond. In the present study, n-type diamond samples were synthesized by CVD using tert-butylphosphine, which is much less toxic than phosphine. The unintentional incorporation of nitrogen was found to be suppressed by incrementally increasing the gas flow rates of H2 and CH$_4$. Hall measurements confirmed n-type conduction in three measured samples prepared under different growth conditions. The highest measured Hall mobility at room temperature was 422 cm$^2$/(Vs). In the sample with the lowest nitrogen concentration, the spin coherence time ($T_2$) increased to 1.62 $\pm$ 0.10 ms. Optically detected magnetic resonance spectra indicated that all of the measured NV centers were aligned along the [111] direction. This study provides appropriate CVD conditions for growing phosphorus-doped n-type diamond with perfectly aligned NV centers exhibiting long spin coherence times, which is important for the production of quantum diamond devices.

cond-mat.mtrl-sci↗

arXiv2018

Quantitative relevance of substitutional impurities to carrier dynamics in diamond

We have quantified substitutional impurity concentrations in synthetic diamond crystals down to sub parts-per-billion levels. The capture lifetimes of electrons and excitons injected by photoexcitation were compared for several samples with different impurity concentrations. Based on the assessed impurity concentrations, we have determined the capture cross section of electrons to boron impurity, sA=1.3x10^-14 cm2, and that of excitons to nitrogen impurity, sD^ex=3.1x10^-14 cm2. The general tendency of the mobility values for different carrier species is successfully reproduced by including carrier scattering by impurities and by excitons.

cond-mat.mtrl-sci↗

arXiv2014

Atomistic mechanism of perfect alignment of nitrogen-vacancy centers in diamond

Nitrogen-vacancy (NV) centers in diamond have attracted a great deal of attention because of their possible use in information processing and electromagnetic sensing technologies. We examined theatomistic generation mechanism for the NV defect aligned in the [111] direction of C(111) substrates. We found that N is incorporated in the C bilayers during the lateral growth arising from a sequence of kink propagation along the step edge down to [-1,-1,2]. As a result, the atomic configuration with the N-atom lone-pair pointing in the [111] direction is formed, which causes preferential alignment of NVs. Our model is consistent with recent experimental data for perfect NV alignment in C(111) substrates.

cond-mat.mtrl-sci↗