Butsuri
Online ISSN : 2423-8872
Print ISSN : 0029-0181
ISSN-L : 0029-0181
Volume 78, Issue 6
Displaying 1-18 of 18 articles from this issue
Preface
Contents
Overview Articles
Researches
  • Kotaro Shimizu, Shun Okumura, Yasuyuki Kato, Yukitoshi Motome
    Article type: Researches
    2023 Volume 78 Issue 6 Pages 314-319
    Published: July 05, 2023
    Released on J-STAGE: June 05, 2023
    JOURNAL FREE ACCESS

    Moiré is an interference fringe generated by a superposition of waves. Here, we extend this idea to superpositions of spin density waves in magnets. By using an analogy with moiré in optics, we have studied the effects of three control parameters: amplitudes, twist angles, and phases of superposed spin waves. We clarified that the changes in these parameters bring about various topological spin textures and the emergent electromagnetic field. Our results would pave a way for future studies of investigating and controlling novel magnetic and electronic states through the spin moiré picture.

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  • Tomohiro Abe, Takashi Toma
    Article type: Researches
    2023 Volume 78 Issue 6 Pages 320-325
    Published: July 05, 2023
    Released on J-STAGE: June 05, 2023
    JOURNAL FREE ACCESS

    Thermal production mechanism for dark matter is attractive. Such thermal dark matter is being explored by various ways. Direct detection experiments utilize scattering events between dark matter particle and nuclei under the ground. However, no dark matter signal is found so far despite its high experimental sensitivity. As a result, the direct detection experiments impose a severe upper bound on the interaction strength between thermal dark matter and ordinary matter particles. In this article, we show that a pseudo-Nambu–Goldstone boson as a thermal dark matter candidate can naturally evade this severe bound. This is because the scattering amplitude is suppressed by small momentum transfer while the annihilation cross section determining the relic abundance is not suppressed. Furthermore, we also point out that early kinetic decoupling of dark matter is induced if the dark matter mass is close to resonances. This effect can give a correction to the calculation of coupling strength between dark matter and ordinary matter particles. Therefore, it will be testable via precise measurements of the Higgs coupling.

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  • Kenta Takeda, Akito Noiri, Seigo Tarucha
    Article type: Researches
    2023 Volume 78 Issue 6 Pages 326-331
    Published: July 05, 2023
    Released on J-STAGE: June 05, 2023
    JOURNAL FREE ACCESS

    Quantum information is fragile and prone to errors such as decoherence. To overcome the problem and realize reliable quantum computing, quantum error correction (QEC) is an essential technology. The QEC is viable only when the fidelities of basic quantum operations are above a certain value, known as the fault-tolerance threshold. Therefore, realizing a scalable, high-fidelity qubit system is key to implementing a practical quantum computer. Silicon-based semiconductor qubits offer great potential for quantum computation due to their small footprint, long coherence time, and potential scalability enabled by mature nanofabrication technologies. Here we introduce our recent materials and technical developments to improve our silicon-based spin qubits. We demonstrate a universal quantum gate set with fidelities above the 99% threshold for surface code, a three-qubit Toffoli-like gate, and a basic quantum error-correcting code. These results establish the fundamental operations of silicon-based spin qubits and pave the way toward large-scale semiconductor quantum computing.

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