論文 - 伊藤　公平

Wide-field magnetic imaging of sub-50 nm ferromagnetic nanoparticles for time-resolved bio-mechanical orientation measurements

Kazi Z., Shelby I., Brunelle N., Watanabe H., Itoh K., Wiggins P., Fu K.

Optics InfoBase Conference Papers （Optics InfoBase Conference Papers）  Part F127-CLEO_AT 2019 2019年

ISSN  9781943580576

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© 2019 The Author(s) We image the stray magnetic field of commercial chemically functionalized ferromagnetic cobalt nanoparticles using optically detected magnetic resonance of a near-surface ensemble of nitrogen vacancy centers in diamond.

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Fabrication of Ge MOS with Low Interface Trap Density by ALD of Al2O3 on Epitaxially Grown Ge

R. Matsuoka, E. Shigesawa, S. Miyamoto, K. Sawano, and K. M. Itoh

Semicond. Sci. Technol. 34   014004 2018年12月

研究論文（学術雑誌）, 共著, 査読有り

Three-Dimensional Localization Spectroscopy of Individual Nuclear Spin with Sub-Angstrom Resolution

J. Zopes, K. S. Cujia, K. Sasaki, J. M. Boss, K. M. Itoh, and C. L. Degen

Nature Communications （Nature Communications）  9 （ 1 ） 4678 2018年12月

研究論文（学術雑誌）, 共著, 査読有り

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© 2018, The Author(s). Nuclear magnetic resonance (NMR) spectroscopy is a powerful method for analyzing the chemical composition and molecular structure of materials. At the nanometer scale, NMR has the prospect of mapping the atomic-scale structure of individual molecules, provided a method that can sensitively detect single nuclei and measure inter-atomic distances. Here, we report on precise localization spectroscopy experiments of individual 13C nuclear spins near the central electronic sensor spin of a nitrogen-vacancy (NV) center in a diamond chip. By detecting the nuclear free precession signals in rapidly switchable external magnetic fields, we retrieve the three-dimensional spatial coordinates of the nuclear spins with sub-Angstrom resolution and for distances beyond 10 Å. We further show that the Fermi contact contribution can be constrained by measuring the nuclear g-factor enhancement. The presented method will be useful for mapping atomic positions in single molecules, an ambitious yet important goal of nanoscale nuclear magnetic resonance spectroscopy.

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Coherent control of solid state nuclear spin nano-ensembles

Unden T., Tomek N., Weggler T., Frank F., London P., Zopes J., Degen C., Raatz N., Meijer J., Watanabe H., Itoh K.M., Plenio M.B., Naydenov B., Jelezko F.

npj Quantum Information （npj Quantum Information）  4 （ 1 ）  2018年12月

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© 2018, The Author(s). Detecting and controlling nuclear spin nano-ensembles is crucial for the further development of nuclear magnetic resonance (NMR) spectroscopy and for the emerging solid state quantum technology. Here we present the fabrication of a ≈1 nanometre thick diamond layer consisting of 13C nuclear spins doped with nitrogen-vacancy centres (NV) embedded in a spin-free 12C crystal matrix. A single NV in the vicinity of the layer is used for polarization of the 13C spins and the readout of their magnetization. We demonstrate a method for coherent control of few tens of nuclear spins by using radio frequency pulses, and show the basic coherent control experiments, Rabi oscillations and Ramsey spectroscopy, though any NMR pulse sequence can be implemented. The results shown here present an important step towards the realization of a nuclear spin based quantum simulator.

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Study on Al2O3/Ge Interface Formed by ALD Directly on Epitaxial Ge

E. Shigesawa, R. Matsuoka, M. Fukumoto, R. Sano, K. M. Itoh, H. Nohira, and K. Sawano

Sci. Technol. 33   124020 2018年11月

研究論文（学術雑誌）, 共著, 査読有り

Assessment of a Silicon Quantum Dot Spin Qubit Environment via Noise Spectroscopy

K. W. Chen, W. Huang, C. H. Yang, J. C. C. Hwang, B. Hensen, T. Tanttu, F. E. Hudson, K. M. Itoh, A. Laucht, A. Morello, A. S. Dzurak

Phys. Rev. Applied （Physical Review Applied）  10 （ 4 ） 044017 2018年10月

研究論文（学術雑誌）, 共著, 査読有り

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© 2018 American Physical Society. Preserving coherence long enough to perform meaningful calculations is one of the major challenges on the pathway to large-scale quantum-computer implementations. Noise coupled in from the environment is the main factor contributing to decoherence but can be mitigated via engineering design and control solutions. However, this is possible only after acquisition of a thorough understanding of the dominant noise sources and their spectrum. In the work reported here, we use a silicon quantum dot spin qubit as a metrological device to study the noise environment experienced by the qubit. We compare the sensitivity of this qubit to electrical noise with that of an implanted silicon-donor qubit in the same environment and measurement setup. Our results show that, as expected, a quantum dot spin qubit is more sensitive to electrical noise than a donor spin qubit due to the larger Stark shift, and the noise-spectroscopy data show pronounced charge-noise contributions at intermediate frequencies (2-20 kHz).

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Coherent Control via Weak Measurements in 31P Single-Atom Electron and Nuclear Spin Qubits

J. T. Muhonen, J. P. Dehollain, A. Laucht, S. Simmons, R. Kalra, F. E. Hudson, A. S. Dzurak, A. Morello, D. N. Jamieson, J. C. McCallum, and K. M. Itoh

Phys. Rev. B （Physical Review B）  98 （ 15 ） 155201 2018年10月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  24699950

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© 2018 American Physical Society. The understanding of weak measurements and interaction-free measurements has greatly expanded the conceptual and experimental toolbox to explore the quantum world. Here we demonstrate single-shot variable-strength weak measurements of the electron and nuclear spin states of a P31 single-atom donor in silicon. We first show how the partial collapse of the nuclear spin due to measurement can be used to coherently rotate the spin to a desired pure state. We explicitly demonstrate that phase coherence is preserved with high fidelity throughout multiple sequential single-shot weak measurements and that the partial state collapse can be reversed. Second, we use the relation between measurement strength and perturbation of the nuclear state as a physical meter to extract the tunnel rates between the P31 donor and a nearby electron reservoir from data conditioned on observing no tunneling events. Our experiments open avenues to measurement-based state preparation, steering and feedback protocols for spin systems in the solid state, and highlight the fundamental connection between information gain and state modification in quantum mechanics.

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Determination of the position of a single nuclear spin from free nuclear precessions detected by a solid-state quantum sensor

K. Sasaki, K. M. Itoh, and E. Abe

Phys. Rev. B （Physical Review B）  98 （ 12 ） 121405 2018年09月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  24699950

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© 2018 American Physical Society. We report on a nanoscale quantum sensing protocol which tracks a free precession of a single nuclear spin and is capable of estimating an azimuthal angle - a parameter which standard multipulse protocols cannot determine - of the target nucleus. Our protocol combines pulsed dynamic nuclear polarization, a phase-controlled radio-frequency pulse, and a multipulse ac sensing sequence with a modified readout pulse. Using a single nitrogen-vacancy center as a solid-state quantum sensor, we experimentally demonstrate this protocol on a single C13 nuclear spin in diamond and uniquely determine the lattice site of the target nucleus. Our result paves the way for magnetic resonance imaging at the single-molecular level.

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Fabrication of Arrays of Tapered Silicon Micro-/Nano-Pillars by Metal-Assisted Chemical Etching and Anisotropic Wet Etching

K. Yamada, M. Yamada, H. Maki, and K. M. Itoh

Nanotechnology （Nanotechnology）  29 （ 28 ） 28LT01 2018年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  09574484

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© 2018 IOP Publishing Ltd. Fabrication of a 2D square lattice array of intentionally tapered micro-/nano-silicon pillars by metal-assisted chemical etching (MACE) of silicon wafers is reported. The pillars are square rod shaped with the cross-sections in the range 0.2, 0.2-0.9, 0.9 μm2 and heights 3-7 μm. The spacing between pillars in the 2D square lattice was controlled between 0.5 and 3.0 μm. While the pillars after MACE had the high aspect ratio ∼1:5, subsequent anisotropic wet etching in potassium hydroxide solution led to 80°-89.5° tapers with smooth sidewalls. The resulting taper angle showed the relation with geometry of pillar structures; the spacing 0.5-3.0 μm led to the tapering angle 89.5°-80° for 3 and 5 μm tall pillars but 7 μm tall pillars showed no dependency between the tapering angle and the inter-pillar spacing. Such an array of silicon tapered-rods with smooth sidewalls is expected to be applicable as a mold in nanoimprinting applications.

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73Ge-NMR study on magnetic fluctuations of ferromagnetic superconductor UGe<inf>2</inf>

Y. Noma, H. Kotegawa, T. Kubo, H. Tou, H. Harima, Y. Haga, E. Yamamoto, Y. Onuki, K. M. Itoh, E. E. Haller, A. Nakamura, Y. Homma, F. Honda, and D. Aoki

Physica B: Condensed Matter （Physica B: Condensed Matter）  536   543 - 545 2018年05月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  09214526

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© 2017 We report 73Ge-NMR measurement on the ferromagnetic superconductor UGe2 at ambient pressure. The observed NMR spectrum supports that the electric field gradient at three inequivalent Ge sites is correctly deduced by a LDA calculation. The temperature dependences of the nuclear spin lattice relaxation rate 1/T1 for H0⊥a (easy axis) and H0∥a were obtained for the oriented sample. The contrasting behavior in 1/T1 for H0⊥a and H0∥a reveals that the magnetic fluctuation of UGe2 is highly anisotropic.

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Electron spin resonance identification di-carbon-related centers in irradiated silicon

S. Hayashi, H. Saito, K. M. Itoh, M. P. Vlasenko, and L. S. Vlasenko

J. Appl. Phys. （Journal of Applied Physics）  123 （ 16 ）  2018年04月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  00218979

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© 2018 Author(s). A previously unreported electron spin resonance (ESR) spectrum was found in γ-ray irradiated silicon by the detection of the change in microwave photoconductivity arising from spin-dependent recombination (SDR). In the specially prepared silicon crystals doped by 13C isotope, a well resolved hyperfine structure of SDR-ESR lines due to the interaction between electrons and two equivalent carbon atoms having nuclear spin I = 1/2 was observed. The Si-KU4 spectrum is described by spin Hamiltonian for spin S = 1 and of g and D tensors of orthorhombic symmetry with principal values g1 = 2.008, g2 = 2.002, and g3 =2.007; and D1 = ± 103 MHz, D2 = 170 MHz, and D3 = ± 67 MHz where axes 1, 2, and 3 are parallel to the [11-0], [110], and [001] crystal axes, respectively. The hyperfine splitting arising from 13C nuclei is about 0.35 mT. A possible microstructure of the detect leading to the Si-KU4 spectrum is discussed.

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Electron spin resonance study of surface and oxide interface spin-triplet centers on (100) silicon wafers

H. Saito, S. Hayashi, Y. Kusano, K. M. Itoh, M. P. Vlasenko, and L. S. Vlasenko

J. Appl. Phys. 123 （ 16 ） 161582 2018年04月

研究論文（学術雑誌）, 査読有り,  ISSN  00218979

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© 2018 Author(s). Electron spin resonance (ESR) spectra of surface and interface recombination centers recently observed on (001) silicon wafers, labeled Pm and KU1, were studied using spin dependent microwave photoconductivity. Both ESR spectra, having the orthorhombic symmetry and spins S = 1/2 and S = 1 for Pm and KU1, respectively, were observed in the commercially available surface oxidized (001)-Si wafers. Systematic studies on annealing and oxidation conditions for the Pm and KU1 formation conclude that both ESR spectra arise from the same center that contains the interaction between the two nearest Si dangling bonds on the (001) Si surface.

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Anisotropic Magnetic Fluctuations in Ferromagnetic Supweconductor UGe2: 73Ge-NQR Study at Ambient Pressure

Y. Noma, H. Kotegawa, T. Kubo, H. Tou, H. Harima, Y. Haga, E. Yamamoto, Y. Onuki, K. M. Itoh, E. E. Haller, A. Nakamura, Y. Homma, R. Honda, and D. Aoki

J. Phys. Soc. Jpn. 87   033704 2018年02月

研究論文（学術雑誌）, 共著, 査読有り

Defects for quantum information processing in silicon

Abe E., Itoh K.M.

Defects in Advanced Electronic Materials and Novel Low Dimensional Structures （Defects in Advanced Electronic Materials and Novel Low Dimensional Structures）     241 - 263 2018年01月

ISSN  9780081020548

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© 2018 Elsevier Ltd. All rights reserved. In this chapter, we discuss defects in silicon, primarily focusing on phosphorus donors, from the viewpoint of quantum information processing. We start with a historical perspective on our understanding of the limits to information processing. In doing so, we illuminate why we are so excited about the recent experimental challenges to realize silicon-based quantum computers. After reviewing the spin physics of donors in silicon, we discuss the coherence properties of donor electron and nuclear spins, and evaluate their feasibilities as carriers of quantum information, quantum bits. Recent developments in coherent control of single donor spins in silicon nanoelectronic devices are then outlined.

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Anisotropic magnetic fluctuations in ferromagnetic superconductor UGe<inf>2</inf>:⁷³Ge-NQR study at ambient pressure

Noma Y., Kotegawa H., Kubo T., Tou H., Harima H., Haga Y., Yamamoto E., Ōnuki Y., Itoh K., Haller E., Nakamura A., Homma Y., Honda F., Aoki D.

Journal of the Physical Society of Japan （Journal of the Physical Society of Japan）  87 （ 3 ）  2018年

ISSN  00319015

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© 2018 The Physical Society of Japan. We report a 73Ge nuclear quadrupole resonance reinvestigation of the ferromagnetic (FM) superconductor UGe2 at ambient pressure. Careful measurement and analysis of the paramagnetic (PM) spectrum taking into account the calculated electric field gradient (EFG) resulted in modification of the previously reported site assignments for three inequivalent Ge sites. The crossover anomaly at Tx in the FM state is not clearly seen in the temperature dependence of the static internal field at the Ge site, whereas it appears in the nuclear spin–lattice relaxation rate, 1/T1. A remarkable site dependence of 1/T1 is observed among the inequivalent Ge sites, where the directions of the principal axes of the EFG are different. This result reveals that the magnetic fluctuation of UGe2 is highly anisotropic, which is consistent with the presence of Ising magnetic fluctuations in the PM state.

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High-Resolution Quantum Sensing with Shaped Control Pulses

J. Zopes, K. Sasaki, K. S. Cujia, J. M. Boss, K. Chang, T. F. Segawa, K. M. Itoh, and C. L. Degen

Phys. Rev. Lett. 119   260510 2017年12月

研究論文（学術雑誌）, 共著, 査読有り

A quantum-dot spin qubit with coherence limited by charge noise and fidelity higher than 99.9%

J. Yoneda, K. Takeda, T. Otsuka, T. Nakajima, M. R. Delbecq, G. Allison, T. Honda, T. Kodera, S. Oda, Y. Hoshi, N. Usami, K. M. Itoh, and S. Tarucha

Nature Nanotechnology （Nature Nanotechnology）  13 （ 2 ） 102 - 106 2017年12月

研究論文（学術雑誌）, 共著, 査読有り,  ISSN  17483387

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© 2017 The Author(s). The isolation of qubits from noise sources, such as surrounding nuclear spins and spin-electric susceptibility 1-4, has enabled extensions of quantum coherence times in recent pivotal advances towards the concrete implementation of spin-based quantum computation. In fact, the possibility of achieving enhanced quantum coherence has been substantially doubted for nanostructures due to the characteristic high degree of background charge fluctuations 5-7 . Still, a sizeable spin-electric coupling will be needed in realistic multiple-qubit systems to address single-spin and spin-spin manipulations 8-10. Here, we realize a single-electron spin qubit with an isotopically enriched phase coherence time (20 μs) 11,12 and fast electrical control speed (up to 30 MHz) mediated by extrinsic spin-electric coupling. Using rapid spin rotations, we reveal that the free-evolution dephasing is caused by charge noise - rather than conventional magnetic noise - as highlighted by a 1/f spectrum extended over seven decades of frequency. The qubit exhibits superior performance with single-qubit gate fidelities exceeding 99.9% on average, offering a promising route to large-scale spin-qubit systems with fault-tolerant controllability.

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Coherent Rabi Dynamics of a Superradiant Spin Ensemble in a Microwave Cavity

B. C. Rose, A. M. Tyryshkin, H. Riemann, N. V. Abrosimov, P. Becker, H.-J. Pohl, M. L. W. Thewalt, K. M. Itoh, and S. A. Lyon

Phys. Rev. X 7   031002 2017年07月

研究論文（学術雑誌）, 共著, 査読有り

Multiple-Quantum Transitions and Charge-Induced Decoherence of Donor Nuclear Spins in Silicon

D. P. Franke, M. P. D. Pfluger, K. M. Itoh, and M. S. Brandt

Phys. Rev. Lett. 118   246401 2017年06月

研究論文（学術雑誌）, 共著, 査読有り

Nitrogen-Vacancy Centers Created by N+ Ion Implantation Through Screening SiO2 Layers on Diamond

K. Ito, H. Saito, K. Sasaki, H. Watanabe, T. Teraji, K. M. Itoh, and E. Abe

Appl. Phys. Lett. 110   213105 2017年05月

研究論文（学術雑誌）, 共著, 査読有り