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Papers - Itoh, Kohei

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Imaging Topological Spin Structures Using Light-Polarization and Magnetic Microscopy

T. Lenz, G. Chatzidrosos, Z. Wang, L. Bougas, Y. Dumeige, A. Wickenbrock, N. Kerber, J. Zázvorka, F. Kammerbauer, M. Kläui, Z. Kazi, K.-M. C. Fu, K. M. Itoh, H. Watanabe, and D. Budker

Phys. Lev. Appl. 15 024040 2021.02

Research paper (scientific journal), Joint Work, Accepted

Exchange Coupling in a Linear Chain of Three Quantum-Dot Spin Qubits in Silicon

K. W. Chan, H. Sahasrabudhe, W. Huang, Y. Wang, H. C. Yang, M. Veldhorst, J. C. C. Hwang, F. A. Mohiyaddin, F.E. Hudson, K. M. Itoh, A. Saraiva, A. Morello, A. Laucht, R. Rahman, and A. S. Dzurak

Nano Lett. 21 1517 - 1522 2021.01

Research paper (scientific journal), Joint Work, Accepted

Conditional Quantum Operation of Two Exchange-Coupled Single-Donor Spin Qubits in a MOS-Compatible Silicon Device

M. T. Ma̧dzik, A. Laucht, F. E. Hudson, A. M. Jakob, B. C. Johnson, D. N. Jamieson, K. M. Itoh, A. S. Dzurak, and A. Morello

Nature Communications 12 181 2021.01

Research paper (scientific journal), Joint Work, Accepted

Pauli Blockade in Silicon Quantum Dots with Spin-Orbit Control

A. E. Seedhouse, T. Tanttu, R. C. C. Leon, R. Zhao, K. Y. Tan, B. Hensen, F. E. Hudson, K. M. Itoh, J. Yoneda, C. H. Hwan, A. Morello, A. Laucht, N. Coppersmith, A. Saraiva, and A. S. Dzurak

PRX Quantum 2 010303 2021.01

Research paper (scientific journal), Joint Work, Accepted

Detection and Control of Single Proton Spins in a Thin Layer of Diamond Grown by Chemical Vapor Deposition

K. Sasaki, H. Watanabe, H. Sumiya, K. M. Itoh, and E. Abe

Appl. Phys. Lett. 117 114002 2020.09

Research paper (scientific journal), Joint Work, Accepted

Effect of Fluorine on the Suppression of Boron Diffusion in Pre-Amorphized Silicon

R. Kiga, M. Uematsu, and K. M. Itoh

J. Appl. Phys. 128 105701 2020.09

Research paper (scientific journal), Joint Work, Accepted

Controllable Freezing of the Nuclear Spin Bath in a Single-Atom Spin Qubit

M. T. Madzik, T. D. Ladd, F. E. Hudson, K. M. Itoh, A. M. Jakob, B. C. Johnson, J. C. McCallum, D. N. Jamieson, A. S. Dzural, A. Laucht, and A. Morello

Science Advances 6 442 2020.07

Research paper (scientific journal), Joint Work, Accepted

Spin Coherence and Depths of Single Nitrogen-Vacancy Centers Created by Ion Implantation into Diamond via Screening Masks

S. Ishizu, K. Sasaki, D. Misonou, T. Teraji, K. M. Itoh, and E, Abe

J. Appl. Phys. 127 244502 2020.06

Research paper (scientific journal), Joint Work, Accepted

Operation of a Silicon Quantum Processor Unit Cell above One Kelvin

C. H. Yang, R. C. C. Leon, J. C. C. Hwang, A. Saraiva, T. Tanttu, W. Huang, L. J. Camirand, K. W. Chan, K. Y. Tan, F. E. Hudson, K. M. Itoh, A. Morello, M. P.-Ladrière, A. Laucht, and A. S. Dzurak

Nature (Nature) 580 ( 7803 ) 350 - 354 2020.04

Research paper (scientific journal), Joint Work, Accepted, ISSN 00280836

© 2020, The Author(s), under exclusive licence to Springer Nature Limited. Quantum computers are expected to outperform conventional computers in several important applications, from molecular simulation to search algorithms, once they can be scaled up to large numbers—typically millions—of quantum bits (qubits)1–3. For most solid-state qubit technologies—for example, those using superconducting circuits or semiconductor spins—scaling poses a considerable challenge because every additional qubit increases the heat generated, whereas the cooling power of dilution refrigerators is severely limited at their operating temperature (less than 100 millikelvin)4–6. Here we demonstrate the operation of a scalable silicon quantum processor unit cell comprising two qubits confined to quantum dots at about 1.5 kelvin. We achieve this by isolating the quantum dots from the electron reservoir, and then initializing and reading the qubits solely via tunnelling of electrons between the two quantum dots7–9. We coherently control the qubits using electrically driven spin resonance10,11 in isotopically enriched silicon1228Si, attaining single-qubit gate fidelities of 98.6 per cent and a coherence time of 2 microseconds during ‘hot’ operation, comparable to those of spin qubits in natural silicon at millikelvin temperatures13–16. Furthermore, we show that the unit cell can be operated at magnetic fields as low as 0.1 tesla, corresponding to a qubit control frequency of 3.5 gigahertz, where the qubit energy is well below the thermal energy. The unit cell constitutes the core building block of a full-scale silicon quantum computer and satisfies layout constraints required by error-correction architectures8,17. Our work indicates that a spin-based quantum computer could be operated at increased temperatures in a simple pumped 4He system (which provides cooling power orders of magnitude higher than that of dilution refrigerators), thus potentially enabling the integration of classical control electronics with the qubit array18,19.

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Coherent Electrical Control of a Single High-Spin Nucleus in Silicon

S. Asaad, V. Mourik, B. Joecker, M. A. I. Johnson, A. D. Baczewski, H. R. Firgau, M. T. Mądzik, V. Schmitt, J. J. Pla, F. E. Hudson, K. M. Itoh, J. C. McCallum, A. S. Dzurak, A. Laucht, and A. Morello

Nature (Nature) 579 ( 7798 ) 205 - 209 2020.03

Research paper (scientific journal), Joint Work, Accepted, ISSN 00280836

© 2020, This is a U.S. government work and not under copyright protection in the U.S.; foreign copyright protection may apply. Nuclear spins are highly coherent quantum objects. In large ensembles, their control and detection via magnetic resonance is widely exploited, for example, in chemistry, medicine, materials science and mining. Nuclear spins also featured in early proposals for solid-state quantum computers1 and demonstrations of quantum search2 and factoring3 algorithms. Scaling up such concepts requires controlling individual nuclei, which can be detected when coupled to an electron4–6. However, the need to address the nuclei via oscillating magnetic fields complicates their integration in multi-spin nanoscale devices, because the field cannot be localized or screened. Control via electric fields would resolve this problem, but previous methods7–9 relied on transducing electric signals into magnetic fields via the electron–nuclear hyperfine interaction, which severely affects nuclear coherence. Here we demonstrate the coherent quantum control of a single 123Sb (spin-7/2) nucleus using localized electric fields produced within a silicon nanoelectronic device. The method exploits an idea proposed in 196110 but not previously realized experimentally with a single nucleus. Our results are quantitatively supported by a microscopic theoretical model that reveals how the purely electrical modulation of the nuclear electric quadrupole interaction results in coherent nuclear spin transitions that are uniquely addressable owing to lattice strain. The spin dephasing time, 0.1 seconds, is orders of magnitude longer than those obtained by methods that require a coupled electron spin to achieve electrical driving. These results show that high-spin quadrupolar nuclei could be deployed as chaotic models, strain sensors and hybrid spin-mechanical quantum systems using all-electrical controls. Integrating electrically controllable nuclei with quantum dots11,12 could pave the way to scalable, nuclear- and electron-spin-based quantum computers in silicon that operate without the need for oscillating magnetic fields.

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Coherent Spin Control of S-, P-, D- and F-Electrons in a Silicon Quantum Dot

R. C. C. Leon, C. H. Yang, J. C. C. Hwang, J. C. Lemyre, T. Tanttu, W. Huang, K.W. Chan, K. Y. Tan, F. E. Hudson, K. M. Itoh, A. Morello, A. Laucht, M. Pioro-Ladrière, A. Saraiva, and A. S. Dzurak

Nature Communications 11 ( 1 ) 797 2020.02

Research paper (scientific journal), Joint Work, Accepted

© 2020, The Author(s). Once the periodic properties of elements were unveiled, chemical behaviour could be understood in terms of the valence of atoms. Ideally, this rationale would extend to quantum dots, and quantum computation could be performed by merely controlling the outer-shell electrons of dot-based qubits. Imperfections in semiconductor materials disrupt this analogy, so real devices seldom display a systematic many-electron arrangement. We demonstrate here an electrostatically confined quantum dot that reveals a well defined shell structure. We observe four shells (31 electrons) with multiplicities given by spin and valley degrees of freedom. Various fillings containing a single valence electron—namely 1, 5, 13 and 25 electrons—are found to be potential qubits. An integrated micromagnet allows us to perform electrically-driven spin resonance (EDSR), leading to faster Rabi rotations and higher fidelity single qubit gates at higher shell states. We investigate the impact of orbital excitations on single qubits as a function of the dot deformation and exploit it for faster qubit control.

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Construction and Operation of a Tabletop System for Nanoscale Magnetometry with Single Nitrogen-Vacancy Centers in Diamond

D. Misonou, K. Sasaki, S. Ishizu, Y. Monnai, K. M. Itoh, and E. Abe

AIP Advances (AIP Advances) 10 ( 2 ) 025206 2020.02

Research paper (scientific journal), Joint Work, Accepted

© 2020 Author(s). A single nitrogen-vacancy (NV) center in diamond is a prime candidate for a solid-state quantum magnetometer capable of detecting single nuclear spins with prospective application to nuclear magnetic resonance (NMR) at the nanoscale. Nonetheless, an NV magnetometer is still less accessible to many chemists and biologists as its experimental setup and operational principle are starkly different from those of conventional NMR. Here, we design, construct, and operate a compact tabletop-sized system for quantum sensing with a single NV center, built primarily from commercially available optical components and electronics. We show that our setup can implement state-of-the-art quantum sensing protocols that enable the detection of single 13C nuclear spins in diamond and the characterization of their interaction parameters, as well as the detection of a small ensemble of proton nuclear spins on the diamond surface. This article provides extensive discussions on the details of the setup and the experimental procedures, and our system will be reproducible by those who have not worked on the NV centers previously.

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Oxidation-Enhanced Si Self-Diffusion in Isotopically Modulated Silicon Nanopillars

R. Kiga, S. Hayashi, S. Miyamoto, Y. Shimizu, Y. Nagai, T. Endoh, and K. M. Itoh

J. Appl. Phys. 127 045704 2020.01

Research paper (scientific journal), Joint Work, Accepted

Single-Spin Qubits in Isotopically Enriched Silicon at Low Magnetic Field

R. Zhao, T. Tanttu, K. Y. Tan, B. Hensen, K. W. Chan, J. C. C. Hwang, R. C. C. Leon, C. H. Yang, W. Gilbert, F. E. Hudson, K. M. Itoh, A. A. Kiselev, T. D. Ladd, A. Morello, A. Laucht, and A. S. Dzurak

Nature Communications (Nature Communications) 10 ( 1 ) 5500 2019.12

Research paper (scientific journal), Joint Work, Accepted

© 2019, The Author(s). Single-electron spin qubits employ magnetic fields on the order of 1 Tesla or above to enable quantum state readout via spin-dependent-tunnelling. This requires demanding microwave engineering for coherent spin resonance control, which limits the prospects for large scale multi-qubit systems. Alternatively, singlet-triplet readout enables high-fidelity spin-state measurements in much lower magnetic fields, without the need for reservoirs. Here, we demonstrate low-field operation of metal-oxide-silicon quantum dot qubits by combining coherent single-spin control with high-fidelity, single-shot, Pauli-spin-blockade-based ST readout. We discover that the qubits decohere faster at low magnetic fields with T2Rabi=18.6 μs and T2*=1.4 μs at 150 mT. Their coherence is limited by spin flips of residual 29Si nuclei in the isotopically enriched 28Si host material, which occur more frequently at lower fields. Our finding indicates that new trade-offs will be required to ensure the frequency stabilization of spin qubits, and highlights the importance of isotopic enrichment of device substrates for the realization of a scalable silicon-based quantum processor.

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Fidelity Benchmarks for Two-Qubit Gates in Silicon

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

Nature (Nature) 569 ( 7757 ) 532 - 536 2019.05

Research paper (scientific journal), Joint Work, Accepted, ISSN 00280836

© 2019, The Author(s), under exclusive licence to Springer Nature Limited. Universal quantum computation will require qubit technology based on a scalable platform1, together with quantum error correction protocols that place strict limits on the maximum infidelities for one- and two-qubit gate operations2,3. Although various qubit systems have shown high fidelities at the one-qubit level4–10, the only solid-state qubits manufactured using standard lithographic techniques that have demonstrated two-qubit fidelities near the fault-tolerance threshold6 have been in superconductor systems. Silicon-based quantum dot qubits are also amenable to large-scale fabrication and can achieve high single-qubit gate fidelities (exceeding 99.9 per cent) using isotopically enriched silicon11,12. Two-qubit gates have now been demonstrated in a number of systems13–15, but as yet an accurate assessment of their fidelities using Clifford-based randomized benchmarking, which uses sequences of randomly chosen gates to measure the error, has not been achieved. Here, for qubits encoded on the electron spin states of gate-defined quantum dots, we demonstrate Bell state tomography with fidelities ranging from 80 to 89 per cent, and two-qubit randomized benchmarking with an average Clifford gate fidelity of 94.7 per cent and an average controlled-rotation fidelity of 98 per cent. These fidelities are found to be limited by the relatively long gate times used here compared with the decoherence times of the qubits. Silicon qubit designs employing fast gate operations with high Rabi frequencies16,17, together with advanced pulsing techniques18, should therefore enable much higher fidelities in the near future.

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Electron Spin Relaxation of Single Phosphorus Donors in Metal-Oxide-Semiconductor Nanoscale Devices

S. B. Tenberg, S. Asaad, M. T. Madzik, M. A. I. Johnson, B. Joecker, A. Laucht, F. E. Hudson, K. M. Itoh, A. M. Jakob, B. C. Johnson, D. N. Jamieson, J. C. McCallum, A. S. Dzurak, R. Joynt, and A. Morello

Phys. Rev. B (Physical Review B) 99 ( 20 ) 205306 2019.05

Research paper (scientific journal), Joint Work, Accepted, ISSN 24699950

© 2019 American Physical Society. We analyze the electron spin relaxation rate 1/T1 of individual ion-implanted P31 donors in a large set of metal-oxide-semiconductor (MOS) silicon nanoscale devices, with the aim of identifying spin relaxation mechanisms peculiar to the environment of the spins. The measurements are conducted at low temperatures (T≈100 mK) as a function of external magnetic field B0 and donor electrochemical potential μD. We observe a magnetic field dependence of the form 1/T1B05 for B03 T, corresponding to the phonon-induced relaxation typical of donors in the bulk. However, the relaxation rate varies by up to two orders of magnitude between different devices. We attribute these differences to variations in lattice strain at the location of the donor. For B03T, the relaxation rate changes to 1/T1B0 for two devices. This is consistent with relaxation induced by evanescent-wave Johnson noise created by the metal structures fabricated above the donors. At such low fields, where T1>1s, we also observe and quantify the spurious increase of 1/T1 when the electrochemical potential of the spin excited state |↑) comes in proximity to empty states in the charge reservoir, leading to spin-dependent tunneling that resets the spin to |↓). These results provide precious insights into the microscopic phenomena that affect spin relaxation in MOS nanoscale devices, and provide strategies for engineering spin qubits with improved spin lifetimes.

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Controlling Spin-Orbit Interactions in Silicon Quantum Dots Using Magnetic Field Direction

5. T. Tanttu, B. Hensen, K. W. Chan, C. H. Yang, W. Huang, M. Fogarty, F. Hudson, K. M. Itoh, D. Culcer, A. Laucht, A. Morello, and A. Dzurak

Phys. Rev. X (Physical Review X) 9 ( 2 ) 021028 2019.05

Research paper (scientific journal), Joint Work, Accepted

© 2019 authors. Published by the American Physical Society. Published by the American Physical Society under the terms of the »https://creativecommons.org/licenses/by/4.0/» Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. Silicon quantum dots are considered an excellent platform for spin qubits, partly due to their weak spin-orbit interaction. However, the sharp interfaces in the heterostructures induce a small but significant spin-orbit interaction that degrades the performance of the qubits or, when understood and controlled, could be used as a powerful resource. To understand how to control this interaction, we build a detailed profile of the spin-orbit interaction of a silicon metal-oxide-semiconductor double quantum-dot system. We probe the derivative of the Stark shift, g-factor and g-factor difference for two single-electron quantum-dot qubits as a function of external magnetic field and find that they are dominated by spin-orbit interactions originating from the vector potential, consistent with recent theoretical predictions. Conversely, by populating the double dot with two electrons, we probe the mixing of singlet and spin-polarized triplet states during electron tunneling, which we conclude is dominated by momentum-term spin-orbit interactions that vary from 1.85 MHz up to 27.5 MHz depending on the magnetic field orientation. Finally, we exploit the tunability of the derivative of the Stark shift of one of the dots to reduce its sensitivity to electric noise and observe an 80% increase in T2∗. We conclude that the tuning of the spin-orbit interaction will be crucial for scalable quantum computing in silicon and that the optimal setting will depend on the exact mode of qubit operations used.

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Wide-Field Magnetic Imaging of Sub-50 nm Ferromagnetic Nanoparticles for Time-Resolved Bio-Mechanical Orientation Measurements

Z. Kazi, I. Shelby, N. Brunell, H. Watanabe, K. M. Itoh, P. Wiggins,and K.-M. Fu

2019 Conference on Lasers and Electro-Optics, CLEO 2019 - Proceedings (2019 Conference on Lasers and Electro-Optics, CLEO 2019 - Proceedings) 2019.05

Research paper (international conference proceedings), Joint Work

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Silicon Qubit Fidelities Approaching Incoherent Noise Limits via Pulse Engineering

C. H. Yang, K. W. Chan, R. Harper, W. Huang, T. Evans, J. C. C. Hwang, B. Hensen, A. Laucht, T. Tanttu, F. E. Hudson, S. T. Flammia, K. M. Itoh, A. Morello, S. D. Bartlett, and A. S. Dzurak

Nature Electronics (Nature Electronics) 2 ( 4 ) 151 - 158 2019.04

Research paper (scientific journal), Joint Work, Accepted

© 2019, The Author(s), under exclusive licence to Springer Nature Limited. Spin qubits created from gate-defined silicon metal–oxide–semiconductor quantum dots are a promising architecture for quantum computation. The high single qubit fidelities possible in these systems, combined with quantum error correcting codes, could potentially offer a route to fault-tolerant quantum computing. To achieve fault tolerance, however, gate error rates must be reduced to below a certain threshold and, in general, correlated errors must be removed. Here we show that pulse engineering techniques can be used to reduce the average Clifford gate error rates for silicon quantum dot spin qubits down to 0.043%. This represents a factor of three improvement over state-of-the-art silicon quantum dot devices and extends the randomized benchmarking coherence time to 9.4 ms. By including tomographically complete measurements in our randomized benchmarking, we infer a higher-order feature of the noise called the unitarity, which measures the coherence of noise. This, in turn, allows us to theoretically predict that average gate error rates as low as 0.026% may be achievable with further pulse improvements. These spin qubit fidelities are ultimately limited by incoherent noise, which we attribute to charge noise from the silicon device structure or the environment.

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Scalable Quantum Computing with Ion-Implanted Dopant Atoms in Silicon

A. Morello, G. Tosi, F. A. Mohiyaddin, V. Schmitt, V. Mourik, T. Botzem, A. Laucht J. J. Pla, S. Tenberg, R. Savytskyy, M. Madzik, F. Hudson, A. S. Dzurak, K. M. Itoh, A. M. Jakob, B. C. Johnson, J. C. McCallum, and D. M. Jamieson

Technical Digest - International Electron Devices Meeting, IEDM (Technical Digest - International Electron Devices Meeting, IEDM) 2018-December 6.2.1 - 6.2.4 2019.01

Joint Work, ISSN 9781728119878

© 2018 IEEE. We present a scalable strategy to manufacture quantum computer devices, by encoding quantum information in the combined electron-nuclear spin state of individual ion-implanted phosphorus dopant atoms in silicon. Our strategy allows a typical pitch between quantum bits of order 200 nm, and retains compatibility with the standard fabrication processes adopted in classical CMOS nanoelectronic devices. We theoretically predict fast and high-fidelity quantum logic operations, and present preliminary experimental progress towards the realization of a 'flip-flop' qubit system.

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