応用物理学輪講 I
5月16日
[注意事項]
発表の10日前までに　office[at]ap.t.u-tokyo.ac.jp　宛てに「氏名」「指導教員」「発表題目（英語）」「要旨（英語）」「発表言語（英語または日本語）」を送付して下さい。
発表日
2025年5月16日(金) 16：50～18：50

Aグループ

座長
本田　和大
指導
教員名
中村　泰信　教授
座長
本多　健亮
指導
教員名
芦原　聡　教授
発表者名 岩垣　貴祐
指導教員名 金澤　直也　准教授
発表題目（英語） A new class of insulators hosting emergent surface states 
要旨（英語） Surface states in solids—such as Rashba spin-split bands and topological insulator surfaces—exhibit various novel properties. While these phenomena typically require strong spin–orbit coupling (SOC) from heavy elements, it has recently become apparent that even materials composed of light elements, whose bulk bands are conventional band insulators, can support exotic surface states derives from the Zak phase. 

Recently, a closely related concept known as Obstructed Atomic Insulators (OAIs) has been proposed, in which Wannier charge centers are located at empty atomic sites. In this talk, we will introduce the concepts of the Zak phase and OAIs, review recent experimental and theoretical advances, and discuss high-throughput materials searches aimed at discovering such electronic phases.
発表言語 日本語
発表者名 植田　大雅
指導教員名 金澤　直也　准教授
発表題目（英語） Quantum phase control in van der Waals materials using ionic gating method
要旨（英語） Van der Waals (vdW) materials have attracted considerable attention as platforms for exploring quantum condensed matter phenomena such as superconductivity, magnetism, and topological phases, owing to their highly tunable layered structures. 
Various approaches to engineering the properties of vdW materials have been developed, including monolayer fabrication and heterostructure assembly. Among these, the ionic gating method has emerged as a powerful tool for quantum phase control, enabling dramatic modulation of carrier density as well as ion intercalation into the interlayer space. These processes have led to discoveries such as superconductor–insulator transitions and the tuning of magnetic anisotropy. 
In this presentation, I will provide an overview of the ionic gating technique, its mechanisms, representative applications, and recent advances.
発表言語 日本語
発表者名 岡村　圭太
指導教員名 香取　秀俊　教授・山口　敦史　委嘱准教授
発表題目（英語） Sympathetic Cooling of Triply Charged Th-229 Ions with Singly Charged Ca ions
要旨（英語） Nuclear clocks are a new type of clock based on the nuclear transition frequency. Unlike electronic transition frequencies used in the existing atomic clocks, nuclear transition frequencies are largely unaffected by external fields due to the shielding effect of the surrounding electrons, making them highly resistant to environmental perturbations. The transition between the nuclear ground state and nuclear excited state of Th-229 is a particularly promising candidate for such clocks, as it is the only known nuclear transition in the optical wavelength range. To make a nuclear clock based on trapped Th-229 ions we need to cool the ions to reduce the Doppler effect, which changes the resonance frequency of the nuclear transition due to ion motion. For this purpose, triply charged Th-229 (Th-2293+) ions are desirable because they possess cyclic electronic transitions required for laser cooling. However, direct laser cooling of Th-2293+ ions is challenging because of the weakness and complex hyperfine structures of the cooling transitions. To overcome this, we plan to sympathetically cool Th-2293+ ions with co-trapped Ca+ ions, which can be efficiently laser-cooled. This presentation will discuss the principles of sympathetic cooling and recent progress in the experiment of co-trapping of Th3+ and Ca+image.pngions.
発表言語 日本語
発表者名 川畑　光瑠
指導教員名 香取　秀俊　教授
発表題目（英語） Miniaturization of a cold atom source for a portable and high-precision optical lattice clock
要旨（英語） In optical lattice clocks based on alkaline-earth(-like) atoms, Zeeman slowers have traditionally been used to decelerate atoms sublimated from solid sources until they can be cooled and trapped by a magneto-optical trap (MOT). However, these Zeeman slowers are one of the main obstacles to miniaturization and portability. Meanwhile, from the perspective of clock precision, the dominant sources of systematic uncertainty in the clock frequency are the blackbody radiation (BBR) shift and, secondarily, the lattice-induced light shift. To suppress the BBR shift, previous approaches have transported the cold atoms into a BBR-shielded environment using a moving optical lattice. However, the moving lattice itself introduced additional frequency shifts, presenting a new source of frequency.

This study aims to realize a compact, portable, and high-precision optical lattice clock by combining two novel approaches: (1) laser cooling and trapping of atoms without using a Zeeman slower, and (2) magnetic guiding of atoms to the spectroscopy region to suppress frequency shifts caused by both BBR and the optical lattice itself. This strategy significantly establishes a foundation for future applications, such as high-sensitivity measurements of gravitational redshift, monitoring of crustal deformation, and tests of fundamental physical constants. In this presentation, we introduce the proposed configuration of the optical lattice clock and its theoretical basis, and report our experimental achievement of successfully cooling and trapping atoms using a MOT without a Zeeman slower.
発表言語 日本語

Bグループ

座長
政岡　凜太郎
指導
教員名
渡辺　悠樹　准教授
座長
三澤　遼
指導
教員名
Max Hirschberger 准教授
発表者名 押金　こよみ
指導教員名 齊藤　英治　教授
発表題目（英語） Machine learning using quantum systems  -Physical Extreme Learning-
要旨（英語）  A new class of non-von Neumann computing architectures is attracting attention, in which the intrinsic nonlinear responses of physical systems are utilized as information transducers. Among them, physical reservoir computing has emerged as a promising approach that leverages the nonlinear dynamics of physical media for feature transformation, followed by linear post-processing for learning. However, its reliance on transient responses and external wave excitations imposes practical limitations in terms of computation time and energy consumption.
 To overcome these challenges, this study focuses on the wave nature of electrons in solids. Electrons near the Fermi level inherently exist as coherent waves without requiring thermal excitation, and their quantum transport properties—arising from wave interference—have been extensively studied. In particular, the phenomenon known as universal conductance fluctuations (UCF), where conductance exhibits sample-specific and complex variations due to multi-path interference of electron wavefunctions, provides a direct and accessible means to probe such quantum interference electrically.
 Building on this, we propose a novel computing architecture that harnesses the naturally existing steady-state electron waves to realize immediate and energy-efficient mapping into a high-dimensional feature space.
 In this seminar, I will present the methodology, experimental setup, and preliminary evaluations of Physical Extreme Learning (PEL), highlighting its potential to bridge quantum phenomena and machine learning.
発表言語 日本語
発表者名 香川　巧
指導教員名 高橋　陽太郎　准教授
発表題目（英語） In-plane Kerr effect in EuCd2Sb2
要旨（英語）  Ordinary Hall effect requires out-of-plane magnetic field, but recently in-plane Hall effect induced by in-plane magnetic field has been reported. EuCd2Sb2 is one of the materials in which in-plane Hall effect is observed. This material is A-type antiferromagnet and has Weyl points near the Fermi level. 
 Magneto-optical Kerr effect is a change in a linear polarized light after reflection at the surface with Out-of-plane magnetic field or magnetization. This effect is connected to σ_xy(ω) as well as Hall effect σ_xy, so a lot of research has been done related to anomalous Hall effect, quantum anomalous Hall effect and so on. In this presentation, I will explain our experiment on in-plane Kerr effect in EuCd2Sb2 induced by in-plane magnetic field.
発表言語 日本語
発表者名 梶原　葵
指導教員名 求　幸年　教授
発表題目（英語） Spin current generation by skyrmions and merons
要旨（英語）  Spin current, a flow of spin angular momentum, functions as an energy-efficient information carrier in spintronic devices. Typically, spin current is generated via ferromagnets, where an electric current can acquire spin polarization. However, to further advance spintronics technology, alternative approaches beyond conventional ferromagnets are required. Topological spin textures, such as skyrmions, offer a potential new platform for spin current generation due to emergent electromagnetic fields arising from the Berry phase and their rich phase transitions induced by external stimuli. Despite these promising features, the potential of topological spin textures for spin current generation remains elusive. 
 Here we investigate spin current generation by two-dimensional topological spin textures. We calculated the spin conductivity for three types of topological spin textures: a skyrmion crystal (SkX) with out-of-plane magnetization, a magnetic bimeron crystal (BmX) with in-plane magnetization, and a meron crystal (MX) with zero net magnetization. Using linear response theory in a spin-charge coupled model, we show that these distinct spin textures generate spin currents with characteristic spin polarization directions. In the absence of spin–orbit coupling (SOC), SkX and BmX generate nonzero spin currents with spin polarization aligned with their magnetization, whereas MX does not generate spin current. By introducing SOC, BmX generates nonzero spin currents with multiple polarization directions, and MX exhibits pronounced out-of-plane spin-polarized spin current at specific electron fillings, despite having zero net magnetization. The direction and polarization of the generated spin currents are explained by the symmetry of each magnetic texture. These results demonstrate that topological spin textures can serve as efficient sources of spin current even without net magnetization and expand the possibilities for spintronics based on magnetic metals.
発表言語 英語
発表者名 石岡　陸
指導教員名 関　真一郎　准教授
発表題目（英語） Spontaneous Hall effect and spontaneous Nernst effect in antiferromagnetic materials with broken time-reversal symmetry
要旨（英語） Traditionally, magnetic memory has utilized the magnetization of ferromagnetic materials to store information. However, recent research has shown that antiferromagnetic materials, in systems where time-reversal symmetry is broken, can also be used for magnetic memory and offer advantages over ferromagnetic materials in terms of miniaturization potential and response speed. Furthermore, in such antiferromagnetic materials, virtual magnetic fields appear, and it is predicted that they will exhibit responses such as the spontaneous Hall effect, which are equivalent to or even surpass those caused by the magnetization of ferromagnetic materials.
In this presentation, I will explain these antiferromagnetic materials with broken time-reversal symmetry, focusing on the spontaneous Hall effect and spontaneous Nernst effect, and discuss specific examples.
発表言語 日本語
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