arXiv subjects

Takeshi Ohshima

Publications and source records attributed to Takeshi Ohshima.

89 records · Page 5Linked to original sources

arXiv2018

Loop-gap Microwave Resonator for Hybrid Quantum Systems

We designed a loop-gap microwave resonator for applications of spin-based hybrid quantum systems, and tested it with impurity spins in diamond. Strong coupling with ensembles of nitrogen-vacancy (NV) centers and substitutional nitrogen (P1) centers was observed. These results show that loop-gap resonators are viable in the prospect of spin-based hybrid quantum systems, especially for an ensemble quantum memory or a quantum transducer.

quant-ph↗

arXiv2018

Effects of high energy electron irradiation on quantum emitters in hexagonal boron nitride

Hexagonal Boron Nitride (hBN) mono and multilayers are promising hosts for room temperature single photon emitters (SPEs). In this work we explore high energy (~ MeV) electron irradiation as a means to generate stable SPEs in hBN. We investigate four types of exfoliated hBN flakes - namely, high purity multilayers, isotopically pure hBN, carbon rich hBN multilayers and monolayered material - and find that electron irradiation increases emitter concentrations dramatically in all samples. Furthermore, the engineered emitters are located throughout hBN flakes (not only at flake edges or grain boundaries), and do not require activation by high temperature annealing of the host material after electron exposure. Our results provide important insights into controlled formation of hBN SPEs and may aid in identification of their crystallographic origin.

cond-mat.mtrl-sci↗

arXiv2018

Quantum properties of dichroic silicon vacancies in silicon carbide

The controlled generation and manipulation of atom-like defects in solids has a wide range of applications in quantum technology. Although various defect centres have displayed promise as either quantum sensors, single photon emitters or light-matter interfaces, the search for an ideal defect with multi-functional ability remains open. In this spirit, we investigate here the optical and spin properties of the V1 defect centre, one of the silicon vacancy defects in the 4H polytype of silicon carbide (SiC). The V1 centre in 4H-SiC features two well-distinguishable sharp optical transitions and a unique S=3/2 electronic spin, which holds promise to implement a robust spin-photon interface. Here, we investigate the V1 defect at low temperatures using optical excitation and magnetic resonance techniques. The measurements, which are performed on ensemble, as well as on single centres, prove that this centre combines coherent optical emission, with up to 40% of the radiation emitted into the zero-phonon line (ZPL), a strong optical spin signal and long spin coherence time. These results single out the V1 defect in SiC as a promising system for spin-based quantum technologies.

quant-ph↗

arXiv2017

Stark Tuning and Electrical Charge State Control of Single Divacancies in Silicon Carbide

Neutrally charged divacancies in silicon carbide (SiC) are paramagnetic color centers whose long coherence times and near-telecom operating wavelengths make them promising for scalable quantum communication technologies compatible with existing fiber optic networks. However, local strain inhomogeneity can randomly perturb their optical transition frequencies, which degrades the indistinguishability of photons emitted from separate defects, and hinders their coupling to optical cavities. Here we show that electric fields can be used to tune the optical transition frequencies of single neutral divacancy defects in 4H-SiC over a range of several GHz via the DC Stark effect. The same technique can also control the charge state of the defect on microsecond timescales, which we use to stabilize unstable or non-neutral divacancies into their neutral charge state. Using fluorescence-based charge state detection, we show both 975 nm and 1130 nm excitation can prepare its neutral charge state with near unity efficiency.

quant-ph↗

arXiv2017

Identification of Si-vacancy related room temperature qubits in 4H silicon carbide

Identification of microscopic configuration of point defects acting as quantum bits is a key step in the advance of quantum information processing and sensing. Among the numerous candidates, silicon vacancy related centers in silicon carbide (SiC) have shown remarkable properties owing to their particular spin-3/2 ground and excited states. Although, these centers were observed decades ago, still two competing models, the isolated negatively charged silicon vacancy and the complex of negatively charged silicon vacancy and neutral carbon vacancy [Phys. Rev. Lett.\ \textbf{115}, 247602 (2015)] are argued as an origin. By means of high precision first principles calculations and high resolution electron spin resonance measurements, we here unambiguously identify the Si-vacancy related qubits in hexagonal SiC as isolated negatively charged silicon vacancies. Moreover, we identify the Si-vacancy qubit configurations that provide room temperature optical readout.

cond-mat.mtrl-sci↗

arXiv2017

Nanomechanical sensing using spins in diamond

Nanomechanical sensors and quantum nanosensors are two rapidly developing technologies that have diverse interdisciplinary applications in biological and chemical analysis and microscopy. For example, nanomechanical sensors based upon nanoelectromechanical systems (NEMS) have demonstrated chip-scale mass spectrometry capable of detecting single macromolecules, such as proteins. Quantum nanosensors based upon electron spins of negatively-charged nitrogen-vacancy (NV) centers in diamond have demonstrated diverse modes of nanometrology, including single molecule magnetic resonance spectroscopy. Here, we report the first step towards combining these two complementary technologies in the form of diamond nanomechanical structures containing NV centers. We establish the principles for nanomechanical sensing using such nano-spin-mechanical sensors (NSMS) and assess their potential for mass spectrometry and force microscopy. We predict that NSMS are able to provide unprecedented AC force images of cellular biomechanics and to, not only detect the mass of a single macromolecule, but also image its distribution. When combined with the other nanometrology modes of the NV center, NSMS potentially offer unparalleled analytical power at the nanoscale.

quant-ph↗

arXiv2017

Scalable Quantum Photonics with Single Color Centers in Silicon Carbide

Silicon carbide is a promising platform for single photon sources, quantum bits (qubits) and nanoscale sensors based on individual color centers. Towards this goal, we develop a scalable array of nanopillars incorporating single silicon vacancy centers in 4H-SiC, readily available for efficient interfacing with free-space objective and lensed-fibers. A commercially obtained substrate is irradiated with 2 MeV electron beams to create vacancies. Subsequent lithographic process forms 800 nm tall nanopillars with 400-1,400 nm diameters. We obtain high collection efficiency, up to 22 kcounts/s optical saturation rates from a single silicon vacancy center, while preserving the single photon emission and the optically induced electron-spin polarization properties. Our study demonstrates silicon carbide as a readily available platform for scalable quantum photonics architecture relying on single photon sources and qubits.

physics.optics↗

arXiv2017

Isolated spin qubits in SiC with a high-fidelity infrared spin-to-photon interface

The divacancies in SiC are a family of paramagnetic defects that show promise for quantum communication technologies due to their long-lived electron spin coherence and their optical addressability at near-telecom wavelengths. Nonetheless, a mechanism for high-fidelity spin-to-photon conversion, which is a crucial prerequisite for such technologies, has not yet been demonstrated. Here we demonstrate a high-fidelity spin-to-photon interface in isolated divacancies in epitaxial films of 3C-SiC and 4H-SiC. Our data show that divacancies in 4H-SiC have minimal undesirable spin-mixing, and that the optical linewidths in our current sample are already similar to those of recent remote entanglement demonstrations in other systems. Moreover, we find that 3C-SiC divacancies have millisecond Hahn-echo spin coherence time, which is among the longest measured in a naturally isotopic solid. The presence of defects with these properties in a commercial semiconductor that can be heteroepitaxially grown as a thin film on shows promise for future quantum networks based on SiC defects.

quant-ph↗

arXiv2016

Vector magnetometry using silicon vacancies in 4H-SiC at ambient conditions

Point defects in solids promise precise measurements of various quantities. Especially magnetic field sensing using the spin of point defects has been of great interest recently. When optical readout of spin states is used, point defects achieve optical magnetic imaging with high spatial resolution at ambient conditions. Here, we demonstrate that genuine optical vector magnetometry can be realized using the silicon vacancy in SiC, which has an uncommon S=3/2 spin. To this end, we develop and experimentally test sensing protocols based on a reference field approach combined with multi frequency spin excitation. Our works suggest that the silicon vacancy in an industry-friendly platform, SiC, has potential for various magnetometry applications at ambient conditions.

cond-mat.mes-hall↗

arXiv2016

Remote Nanodiamond Magnetometry

Optical fibres have transformed the way people interact with the world and now permeate many areas of science. Optical fibres are traditionally thought of as insensitive to magnetic fields, however many application areas from mining to biomedicine would benefit from fibre-based remote magnetometry devices. In this work, we realise such a device by embedding nanoscale magnetic sensors into tellurite glass fibres. Remote magnetometry is performed on magnetically active defect centres in nanodiamonds embedded into the glass matrix. Standard optical magnetometry techniques are applied to initialize and detect local magnetic field changes with a measured sensitivity of 26 micron Tesla/square root(Hz). Our approach utilizes straight-forward optical excitation, simple focusing elements, and low power components. We demonstrate remote magnetometry by direct reporting of the magnetic ground states of nitrogen-vacancy defect centres in the optical fibres. In addition, we present and describe theoretically an all-optical technique that is ideally suited to remote fibre-based sensing. The implications of our results broaden the applications of optical fibres, which now have the potential to underpin a new generation of medical magneto-endoscopes and remote mining sensors.

physics.optics↗

arXiv2015

Single Spin Optically Detected Magnetic Resonance with E-Band Microwave Resonators

Magnetic resonance with ensembles of electron spins is nowadays performed in frequency ranges up to 240 GHz and in corresponding magnetic fields of up to 10 T. However, experiments with single electron and nuclear spins so far only reach into frequency ranges of several 10 GHz, where existing coplanar waveguide structures for microwave (MW) delivery are compatible with single spin readout techniques (e.g. electrical or optical readout). Here, we explore the frequency range up to 90 GHz, respectively magnetic fields of up to $\approx 3\,$T for single spin magnetic resonance in conjunction with optical spin readout. To this end, we develop MW resonators with optical single spin access. In our case, rectangular E-band waveguides guarantee low-loss supply of microwaves to the resonators. Three dimensional cavities, as well as coplanar waveguide resonators enhance MW fields by spatial and spectral confinement with a MW efficiency of $1.36\,\mathrm{mT/\sqrt{W}}$. We utilize single NV centers as hosts for optically accessible spins, and show, that their properties regarding optical spin readout known from smaller fields (<0.65 T) are retained up to fields of 3 T. In addition, we demonstrate coherent control of single nuclear spins under these conditions. Furthermore, our results extend the applicable magnetic field range of a single spin magnetic field sensor. Regarding spin based quantum registers, high fields lead to a purer product basis of electron and nuclear spins, which promises improved spin lifetimes. For example, during continuous single-shot readout the $^{14}$N nuclear spin shows second-long longitudinal relaxation times.

quant-ph↗

arXiv2014

Nanodiamond in tellurite glass Part II: practical nanodiamond-doped fibers

Tellurite glass fibers with embedded nanodiamond are attractive materials for quantum photonics applications. Reducing the loss of these fibers in the 600-800 nm wavelength range of nanodiamond fluorescence is essential to exploit the unique properties of nanodiamond in the new hybrid material. The first part of this study reported the origin of loss in nanodiamond-doped glass and impact of glass fabrication conditions. Here, we report the fabrication of nanodiamond-doped tellurite fibers with significantly reduced loss in the visible through further understanding of the impact of glass fabrication conditions on the interaction of the glass melt with the embedded nanodiamond. We fabricated tellurite fibers containing nanodiamond in concentrations up to 0.7 ppm-weight, while reducing the loss by more than an order of magnitude down to 10 dB/m at 600-800 nm.

physics.optics↗

arXiv2014

Coherent control of single spins in silicon carbide at room temperature

Spins in solids are cornerstone elements of quantum spintronics. Leading contenders such as defects in diamond, or individual phosphorous dopants in silicon have shown spectacular progress but either miss established nanotechnology or an efficient spin-photon interface. Silicon carbide (SiC) combines the strength of both systems: It has a large bandgap with deep defects and benefits from mature fabrication techniques. Here we report the characterization of photoluminescence and optical spin polarization from single silicon vacancies in SiC, and demonstrate that single spins can be addressed at room temperature. We show coherent control of a single defect spin and find long spin coherence time under ambient conditions. Our study provides evidence that SiC is a promising system for atomic-scale spintronics and quantum technology.

cond-mat.mes-hall↗

arXiv2014

Isolated electron spins in silicon carbide with millisecond-coherence times

The elimination of defects from SiC has facilitated its move to the forefront of the optoelectronics and power-electronics industries. Nonetheless, because the electronic states of SiC defects can have sharp optical and spin transitions, they are increasingly recognized as a valuable resource for quantum-information and nanoscale-sensing applications. Here, we show that individual electron spin states in highly purified monocrystalline 4H-SiC can be isolated and coherently controlled. Bound to neutral divacancy defects, these states exhibit exceptionally long ensemble Hahn-echo spin coherence, exceeding 1 ms. Coherent control of single spins in a material amenable to advanced growth and microfabrication techniques is an exciting route to wafer-scale quantum technologies.

cond-mat.mes-hall↗

arXiv2014

Tracking individual nanodiamonds in Drosophila melanogaster embryos

Tracking the dynamics of fluorescent nanoparticles during embryonic development allows insights into the physical state of the embryo and, potentially, molecular processes governing developmental mechanisms. In this work, we investigate the motion of individual fluorescent nanodiamonds micro-injected into Drosophila melanogaster embryos prior to cellularisation. Fluorescence correlation spectroscopy and wide-field imaging techniques are applied to individual fluorescent nanodiamonds in blastoderm cells during stage 5 of development to a depth of ~40 μm. The majority of nanodiamonds in the blastoderm cells during cellularisation exhibit free diffusion with an average diffusion coefficient of (6 $\pm$ 3) x 10$^{-3}$ μm$^2$/s, (mean $\pm$ SD). Driven motion in the blastoderm cells was also observed with an average velocity of 0.13 $\pm$ 0.10 μm/s (mean $\pm$ SD) μm/s and an average applied force of 0.07 $\pm$ 0.05 pN (mean $\pm$ SD). Nanodiamonds in the periplasm between the nuclei and yolk were also found to undergo free diffusion with a significantly larger diffusion coefficient of (63 $\pm$ 35) x10$^{-3}$ μm$^2$/s (mean $\pm$ SD). Driven motion in this region exhibited similar average velocities and applied forces compared to the blastoderm cells indicating the transport dynamics in the two cytoplasmic regions are analogous.

physics.bio-ph↗

arXiv2013

Strongly Coupled Diamond Spin Qubits by Molecular Nitrogen Implantation

Ionized nitrogen molecules ($^{15}$N$_{2}^+$) are used as efficient point sources for creating NV$^-$ pairs in diamond with nanoscale spatial separation and up to 55 kHz magnetic coupling strength. Co-implantation of $^{12}$C$^+$ increased the yield of pairs, and a $^{13}$C-depleted diamond allowed 0.65 ms coherence times to be obtained. Further coupling to a third dark spin provided a strongly coupled three spin register. These results mark an important step towards realization of multi-qubit systems and scalable NV$^-$ quantum registers.

quant-ph↗

arXiv2013

Detection of atomic spin labels in a lipid bi-layer using a single-spin nanodiamond probe

Magnetic field fluctuations arising from fundamental spins are ubiquitous in nanoscale biology, and are a rich source of information about the processes that generate them. However, the ability to detect the few spins involved without averaging over large ensembles has remained elusive. Here we demonstrate the detection of gadolinium spin labels in an artificial cell membrane under ambient conditions using a single-spin nanodiamond sensor. Changes in the spin relaxation time of the sensor located in the lipid bilayer were optically detected and found to be sensitive to near-individual proximal gadolinium atomic labels. The detection of such small numbers of spins in a model biological setting, with projected detection times of one second, opens a new pathway for in-situ nanoscale detection of dynamical processes in biology.

physics.bio-ph↗