arXiv subjects

Tokuyuki Teraji

Publications and source records attributed to Tokuyuki Teraji.

At least 19 recordsLinked to original sources

arXiv2026

Efficient creation of shallow NV$^-$ ensembles by high-angle ion implantation

Negatively charged nitrogen-vacancy (NV$^-$) centers located a few nanometers below the diamond surface are key quantum defects for nanoscale sensing of external spins. However, the creation of shallow NV$^-$ centers with high yield remains a materials challenge. Here, we demonstrate that high-angle ion implantation enhances the creation efficiency of shallow NV$^-$ centers. By implanting $^{15}$N ions at angles exceeding 60$^\circ$, we achieve high NV$^-$ yields approaching 10% with effective NV$^-$ depths below 10 nm. These yields are significantly higher than those typically reported for shallow NV$^-$ creation. The enhanced NV$^-$ yield is consistent with an increased vacancy-to-nitrogen ratio in the near-surface region, which is expected to promote NV formation during annealing. The created NV$^-$ ensembles show coherence properties comparable to those of single shallow NV$^-$ centers at similar depths, and allow detection of nuclear spins in van der Waals materials attached to the diamond surface. Our results establish geometric control of ion implantation as a simple and broadly applicable approach to engineer shallow vacancy-related quantum defects.

quant-ph↗

arXiv2026

Vacancy-mediated nitrogen diffusion and aggregation via high-fluence electron beam irradiation in HPHT synthesized diamond crystal

The negatively charged nitrogen vacancy (NV-) center in diamond is a promising point defect for highly sensitive quantum sensing. The formation of high-density NV- centers is essential for improving sensitivity. We performed room-temperature electron beam irradiation (EBI) and annealing on nitrogen-doped high-pressure high-temperature diamond crystals, aiming to convert all substitutional nitrogen into NV structures by increasing EBI fluence. While the Ns0 to NV0 and NV- conversion process dominated at low EBI fluences, in a high-fluence region, NV0 and NV- center and Ns0 and Ns+ concentrations decreased with increasing EBI fluence, indicating the formation of unknown nitrogen-related defects such as the H3 center, which is a nitrogen and vacancy aggregation defect. Although H3 centers were observed at high EBI fluence, their annealing temperature of 1375 +- 25 °C was lower than the typically reported temperatures over 1600 °C. We attribute this low-temperature formation to vacancy-mediated nitrogen diffusion and aggregation.

cond-mat.mtrl-sci↗

arXiv2026

A Highly Sensitive Diamond NV Magnetometer Using Ramsey Interferometry with a Short Sensor-to-Sample Distance

In this study, we developed a diamond quantum magnetometer based on Ramsey interferometry with a short sensor-to-sample distance. Conventional biomagnetic sensors with ensemble nitrogen-vacancy centers using continuous-wave optically detected magnetic resonance and Ramsey methods typically rely on watt-level lasers to achieve high sensitivity, resulting in thermal issues. In contrast, by employing the light-trapping diamond waveguide technique in a high-pressure and high-temperature diamond sample treated with electron beam irradiation, we obtained a high photon conversion efficiency of 9.5%, enabling us to simultaneously achieve a high sensitivity of 2.93(7) pT/Hz^1/2 in the 100-400 Hz frequency range and a minimal temperature increase of only approximately 13 K at a low laser power of 210 mW. Using a dry phantom designed to mimic magnetoencephalography signals, we measured a weak magnetic field of 77.7(2) pT without signal averaging at a sensor-to-sample distance of 2.5 mm. This short-distance measurement prevents severe spatial signal attenuation, yielding a high signal-to-noise ratio. The development here is crucial for practical biomagnetic applications based on Ramsey interferometry.

quant-ph↗

arXiv2026

Direct imaging of stress tensor around single dislocation in diamond

Dislocations are fundamental crystal defects whose stress fields govern a wide range of material properties. The analytical form of the stress tensor around single dislocation was established by elasticity theory more than 80 years ago and has provided a theoretical basis for evaluating essential characteristics of dislocations. However, direct experimental verification has long remained out of reach because it has been difficult to measure the components of the stress tensor with conventional methods. Here, we present the experimental visualization of the stress tensor around single dislocation in diamond. Using quantum sensors based on nitrogen-vacancy (NV) centers, we mapped the shear components ($σ_{xy}$, $σ_{yz}$, $σ_{zx}$) together with the trace of the stress tensor ($σ_{xx}+σ_{yy}+σ_{zz}$) around single 45° dislocation. The observed distributions exhibited good agreement with predictions from elasticity theory, thus providing experimental validation of this theoretical framework.

cond-mat.mtrl-sci↗

arXiv2025

Multichannel highly sensitive diamond quantum magnetometer

We demonstrate a highly sensitive real-time magnetometry method at two measurement points. This magnetometry method is based on the frequency-division multiplexing of continuous-wave optically detected magnetic resonance. We use two ensembles of nitrogen-vacancy (NV) centers separated by 3.6 mm to measure a magnetic field. A different bias field is applied to the two NV ensembles to resolve the resonance peak for each ensemble in the frequency space and enables the multiplexed magnetometry at the two points. The sensitivities achieved at the measurement points are $21~\mathrm{pT/\sqrt{Hz}}$ and $22~\mathrm{pT/\sqrt{Hz}}$. The proposed magnetometry method can be expanded to include more measurement points and shorter spacing. The capability of real-time measurement at numerous points with short spacing and high sensitivity is beneficial for various applications, including biomagnetic sensing, geophysical research, and material science.

quant-ph↗

arXiv2025

High-Fidelity Electron Spin Gates for Scaling Diamond Quantum Register

Diamond is a promising platform for quantum information processing as it can host highly coherent qubits that could allow for the construction of large quantum registers. A prerequisite for such devices is a coherent interaction between nitrogen vacancy (NV) electron spins. Entanglement between dipolar-coupled NV spin pairs has been demonstrated, but with a limited entanglement fidelity and its error sources have not been characterized. Here, we design and implement a robust, easy to implement entangling gate between NV spins in diamond and quantify the influence of multiple error sources on the gate performance. Experimentally, we demonstrate a record gate fidelity of $F=(96.0 \pm 2.5)$ % under ambient conditions. Our identification of the dominant errors paves the way towards NV-NV gates beyond the error correction threshold.

quant-ph↗

arXiv2024

Performance Evaluation of a Diamond Quantum Magnetometer for Biomagnetic Sensing: A Phantom Study

We employ a dry-type phantom to evaluate the performance of a diamond quantum magnetometer with a high sensitivity of about $6~\mathrm{pT/\sqrt{Hz}}$ from the viewpoint of practical measurement in biomagnetic sensing. The dry phantom is supposed to represent an equivalent current dipole (ECD) generated by brain activity, emulating an encephalomagnetic field. The spatial resolution of the magnetometer is evaluated to be sufficiently higher than the length of the variation in the encephalomagnetic field distribution. The minimum detectable ECD moment is evaluated to be 0.2 nA m by averaging about 8000 measurements for a standoff distance of 2.4 mm from the ECD. We also discuss the feasibility of detecting an ECD in the measurement of an encephalomagnetic field in humans. We conclude that it is feasible to detect an encephalomagnetic field from a shallow cortex area such as the primary somatosensory cortex.

physics.ins-det↗

arXiv2023

Optical-power-dependent splitting of magnetic resonance in nitrogen-vacancy centers in diamond

Nitrogen-vacancy (NV) centers in diamonds are a powerful tool for accurate magnetic field measurements. The key is precisely estimating the field-dependent splitting width of the optically detected magnetic resonance (ODMR) spectra of the NV centers. In this study, we investigate the optical power dependence of the ODMR spectra using NV ensemble in nanodiamonds (NDs) and a single-crystal bulk diamond. We find that the splitting width exponentially decays and is saturated as the optical power increases. Comparison between NDs and a bulk sample shows that while the decay amplitude is sample-dependent, the optical power at which the decay saturates is almost sample-independent. We propose that this unexpected phenomenon is an intrinsic property of the NV center due to non-axisymmetry deformation or impurities. Our finding indicates that diamonds with less deformation are advantageous for accurate magnetic field measurements.

cond-mat.mes-hall↗

arXiv2023

Demonstration of geometric diabatic control of quantum states

Geometric effects can play a pivotal role in streamlining quantum manipulation. We demonstrate a geometric diabatic control, that is, perfect tunneling between spin states in a diamond by a quadratic sweep of a driving field. The field sweep speed for the perfect tunneling is determined by the geometric amplitude factor and can be tuned arbitrarily. Our results are obtained by testing a quadratic version of Berry's twisted Landau-Zener model. This geometric tuning is robust over a wide parameter range. Our work provides a basis for quantum control in various systems, including condensed matter physics, quantum computation, and nuclear magnetic resonance.

quant-ph↗

arXiv2023

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.

quant-ph↗

arXiv2021

Millimetre-scale magnetocardiography of living rats using a solid-state quantum sensor

A key challenge in cardiology is the non-invasive imaging of electric current propagation occurring in the cardiovascular system at an intra-cardiac scale. A promising approach for directly mapping the current dynamics is to monitor the associated stray magnetic field. However, in this magnetic field approach, the spatial resolution deteriorates significantly as the standoff distance between the target and the sensor increases. Existing sensors usually remain relatively far from the target and provide only centimetre-scale resolution because their operating temperature is not biocompatible. Here we demonstrate millimetre-scale magnetocardiography of living rats using a solid-state quantum sensor based on nitrogen-vacancy centres in diamond. The essence of the method is a millimetre proximity from the sensor to heart surface, which enhances the cardiac magnetic field to greater than nanoteslas and allows the mapping of these signals with intra-cardiac resolution. From the acquired magnetic images, we also estimate the source electric current vector, flowing from the right atria base via the Purkinje fibre bundle to the left ventricular apex. Our results establish the solid-state quantum sensor's capability to probe cardiac magnetic signals from mammalian animals and reveal their intra-cardiac electrodynamics. This technique will enable the study of the origin and progression of myriad cardiac arrhythmias including flutter, fibrillation, and tachycardia.

physics.med-ph↗

arXiv2020

Effect of deep-defect excitation on mechanical energy dissipation of single-crystal diamond

The ultra-wide bandgap of diamond distinguishes it from other semiconductors, in that all known defects have deep energy levels that are inactive at room temperature. Here, we present the effect of deep defects on the mechanical energy dissipation of single-crystal diamond experimentally and theoretically up to 973 K. Energy dissipation is found to increase with temperature and exhibits local maxima due to the interaction between phonons and deep defects activated at specific temperatures. A two-level model with deep energies is proposed to well explain the energy dissipation at elevated temperatures. It is evident that the removal of boron impurities can substantially increase the quality factor of room-temperature diamond mechanical resonators. The deep-energy nature of nitrogen bestows single-crystal diamond with outstanding low-intrinsic energy dissipation in mechanical resonators at room temperature or above.

physics.app-ph↗

arXiv2020

Spin coherence and depths of single nitrogen-vacancy centers created by ion implantation into diamond via screening masks

We characterize single nitrogen-vacancy (NV) centers created by 10-keV N+ ion implantation into diamond via thin SiO$_2$ layers working as screening masks. Despite the relatively high acceleration energy compared with standard ones (< 5 keV) used to create near-surface NV centers, the screening masks modify the distribution of N$^+$ ions to be peaked at the diamond surface [Ito et al., Appl. Phys. Lett. 110, 213105 (2017)]. We examine the relation between coherence times of the NV electronic spins and their depths, demonstrating that a large portion of NV centers are located within 10 nm from the surface, consistent with Monte Carlo simulations. The effect of the surface on the NV spin coherence time is evaluated through noise spectroscopy, surface topography, and X-ray photoelectron spectroscopy.

quant-ph↗

arXiv2018

On-chip self-sensing enhancing actuation for MEMS/NEMS with large efficiency

The implementation of on-chip MEMS/NEMS transducers for arbitrary resonators is difficult due to a number of difficulties such as material choice, large dissipation, restriction in high frequency, low sensitivity, poor reliability, and poor integrability. We show a universal on-chip transduction scheme, which can be adapted to any MEMS/NEMS resonator. We achieve all electrical, on-chip MEMS/NEMS for any resonator.

physics.app-ph↗

arXiv2017

Photoluminescence excitation spectroscopy of SiV$^{-}$ and GeV$^{-}$ color center in diamond

Color centers in diamond are important quantum emitters for a broad range of applications ranging from quantum sensing to quantum optics. Understanding the internal energy level structure is of fundamental importance for future applications. We experimentally investigate the level structure of an ensemble of few negatively charged silicon-vacancy (SiV$^{-}$) and germanium-vacancy (GeV$^{-}$) centers in bulk diamond at room temperature by photoluminescence (PL) and excitation (PLE) spectroscopy over a broad wavelength range from 460 nm to 650 nm and perform power-dependent saturation measurements. For SiV$^{-}$ our experimental results confirm the presence of a higher energy transition at ~ 2.31 eV. By comparison with detailed theoretical simulations of the imaginary dielectric function we interpret the transition as a dipole-allowed transition from $^{2}E_{g}$-state to $^{2}A_{2u}$-state where the corresponding $a_{2u}$-level lies deeply inside the diamond valence band. Therefore, the transition is broadened by the diamond band. At higher excitation power of 10 mW we indicate signs of a parity-conserving transition at ~2.03 eV supported by saturation measurements. For GeV$^{-}$ we demonstrate that the PLE spectrum is in good agreement with the mirror image of the PL spectrum of the zero-phonon line (ZPL). Experimentally we do not observe a higher lying energy level up to a transition wavelength of 460 nm. The observed PL spectra are identical, independent of excitation wavelength, suggesting a rapid decay to $^{2}E_{u}$ excited state and followed by optical transition to $^{2}E_{g}$ ground state. Our investigations convey important insights for future quantum optics and quantum sensing experiments based on SiV$^{-}$ center and GeV$^{-}$ center in diamond.

cond-mat.mtrl-sci↗

arXiv2017

Nitrogen-vacancy centers created by N$^+$ ion implantation through screening SiO$_2$ layers on diamond

We report on an ion implantation technique utilizing a screening mask made of SiO$_2$ to control both the depth profile and the dose. By appropriately selecting the thickness of the screening layer, this method fully suppresses the ion channeling, brings the location of the highest NV density to the surface, and effectively reduces the dose by more than three orders of magnitude. With a standard ion implantation system operating at the energy of 10 keV and the dose of 10$^{11}$ cm$^2$ and without an additional etching process, we create single NV centers close to the surface with coherence times of a few tens of $μ$s.

cond-mat.mtrl-sci↗

arXiv2017

Protecting a diamond quantum memory by charge state control

In recent years, solid-state spin systems have emerged as promising candidates for quantum information processing (QIP). Prominent examples are the Nitrogen-Vacancy (NV) center in diamond, phosphorous dopants in silicon (Si:P), rare-earth ions in solids and V$_{\text{Si}}$-centers in Silicon-carbide (SiC). The Si:P system has demonstrated, that by eliminating the electron spin of the dopant, its nuclear spins can yield exceedingly long spin coherence times. For NV centers, however, a proper charge state for storage of nuclear spin qubit coherence has not been identified yet. Here, we identify and characterize the positively charged NV center as an electron-spin-less and optically inactive state by utilizing the nuclear spin qubit as a probe. We control the electronic charge and spin utilizing nanometer scale gate electrodes. We achieve a lengthening of the nuclear spin coherence times by a factor of 20. Surprisingly, the new charge state allows switching the optical response of single nodes facilitating full individual addressability.

quant-ph↗

arXiv2016

Polarization- and frequency-tunable microwave circuit for selective excitation of nitrogen-vacancy spins in diamond

We report on a planar microwave resonator providing arbitrarily polarized oscillating magnetic fields that enable selective excitation of the electronic spins of nitrogen-vacancy (NV) centers in diamond. The polarization plane is parallel to the surface of diamond, which makes the resonator fully compatible with (111)-oriented diamond. The field distribution is spatially uniform in a circular area with a diameter of 4 mm, and a near-perfect circular polarization is achieved. We also demonstrate that the original resonance frequency of 2.8 GHz can be varied in the range of 2-3.2 GHz by introducing varactor diodes that serve as variable capacitors.

cond-mat.mes-hall↗