6月13日 | 応用物理学輪講 I | 輪講 | 東京大学工学部物理工学科・大学院工学系研究科物理工学専攻

工学部物理工学科

応用物理学輪講 I

6月13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6月13日(金) 16：50～18：50

Aグループ

座長: 山内　健聖
指導 教員名: 関　真一郎　准教授

座長: 山岡　良太
指導 教員名: 中島　多朗　准教授

発表者名	佐野　智紀
指導教員名	小芦　雅斗　教授
発表題目（英語）	Privacy Amplification of Quantum Key Distribution and its Optimization
要旨（英語）	Quantum Key Distribution (QKD) has attracted attention as a cryptographic scheme based on the principles of quantum mechanics that ensures long-term security independent of advances in computational power. Among various security proofs for QKD, a well-established framework based on the concept of complementarity has been developed. In this framework, privacy amplification corresponds to error correction in the complementary basis. In this presentation, we introduce this approach and explain how privacy amplification can be optimized.
発表言語	日本語

発表者名	柴田　祐大
指導教員名	高橋　陽太郎　准教授
発表題目（英語）	Magnetically-induced second harmonic generation in a compensated antiferromagnet
要旨（英語）	Magnetic materials include ferromagnets, where spins align parallel, and antiferromagnets, where spins align antiparallel. The former have been widely applied by utilizing broken time-reversal symmetry, while the latter have found limited applications due to preserved symmetry. Recently, it has been found that even in antiferromagnets where magnetization cancels out, time-reversal symmetry can be broken by specific crystal structures, leading to novel electromagnetic responses such as the anomalous Hall effect. In this study, we focus on higher-order responses that are allowed even when the anomalous Hall effect is forbidden due to zero magnetization. We observe magnetically-induced second harmonic generation (SHG) in an antiferromagnet with broken time-reversal symmetry. Furthermore, we visualize antiferromagnetic domains through spatial mapping of SHG intensity and investigate the possibility of domain control using external magnetic fields.
発表言語	日本語

発表者名	白鳥　惇也
指導教員名	石坂　香子　教授
発表題目（英語）	Observation of Nucleation and Growth in Photoinduced Phase Transition of VO₂
要旨（英語）	Vanadium dioxide (VO₂) is one of the prototypical correlated-electron materials, exhibiting a phase transition between a Mott-Peierls insulating phase and a metallic phase. This transition can be induced thermally at around 340 K, as well as optically. The photoinduced phase transition, which involves dramatic sub-picosecond changes in resistivity, transmittance, and crystal structure, has been extensively studied using various ultrafast spectroscopy techniques. Recently, it has been suggested that this ultrafast transition proceeds via a nucleation and growth process. However, direct observation of this process has been challenging due to the need for nanometer–picosecond-scale resolution for tracking the phase transition. In this presentation, we report the direct observation of the nucleation and growth process in VO₂ using ultrafast time-resolved scanning transmission electron microscopy (5D-STEM), which provides time- and spatially-resolved electron diffraction patterns on nanometer–picosecond scales. In this presentation, I will first introduce the photoexcited dynamics of VO₂ and the principles of the 5D-STEM technique. Then, I will present our findings on the nucleation and growth process observed in VO₂.
発表言語	日本語

Bグループ

座長: 山下　涼介
指導 教員名: 森本　高裕　准教授

座長: 山根　悠都
指導 教員名: 小芦　雅斗　教授

発表者名	鈴木　滉平
指導教員名	芦原　聡　教授
発表題目（英語）	Development of infrared background-free spectroscopy
要旨（英語）	Infrared spectroscopy is a technique to identify molecular species based on their absorption spectrum of IR light. Conventional IR transmission absorption spectroscopy is limited in sensitivity by the dynamic range of the detector. A new method called “Background-free Spectroscopy” enables detection of molecules beyond this limitation by removing background light through destructive interference, and has been demonstrated for the detection of gas molecules. In this study, we attempt to apply this new method to the detection of some target molecules that require higher sensitivity compared with gases. In this presentation, the current progress toward demonstration experiments will be presented.
発表言語	日本語

発表者名	鈴木　勇力
指導教員名	十倉　好紀　卓越教授
発表題目（英語）	Emergent electromagnetic induction in polar Weyl semimetal PrAlGe
要旨（英語）	Emergent electric field is fictitious electric field generated by spin dynamics. Especially, it is expected that emergent electric field by curret-induced spin dynamics leads to downsizing inductors by nm. To generate emergent electric field, it was considered that non-collinear magnetic structure was required, but recently, even in ferromagnets, we can observe emergent electric field when spacial inversion symmetry is broken. I will introduce emergent electric field observed in polar magnetic semimetal PrAlGe. I talk about the way to observe emergent electric field, the mechanism of generation of emergent electric field, and the relationship between Weyl nodes and emergent electric field.
発表言語	日本語

発表者名	砂田　桂花
指導教員名	中村　泰信　教授
発表題目（英語）	Spatiotemporal Encoding of Itinerant Microwave Photons and Mode-Selective Absorption
要旨（英語）	Quantum communication between distant superconducting qubits via itinerant microwave photons has been studied to realize distributed quantum computing. To enhance information capacity and fault tolerance in quantum networks, it is crucial to encode larger quantities of quantum information using auxiliary degrees of freedom of these photons. In this work, we experimentally explore the potential of utilizing spatiotemporal degrees of freedom. This approach is promising as it allows for the straightforward generation of a large family of orthogonal modes temporally overlapping along a single propagation path through waveform engineering. By employing the photon-shaping technique based on the temporal control of a microwave-driven parametric transition between a superconducting transmon qubit and a resonator coupled to it, we generate single itinerant photons in multiple orthogonal spatiotemporal modes, propagating along a waveguide coupled to the resonator. We evaluate the quality of the generated photon set in the orthogonal basis and the mode-selective absorption via the time-reversal process at the receiver. We discuss the effectiveness of utilizing spatiotemporal modes for future multiplexed quantum communication and their advantages over other encoding schemes.
発表言語	英語

発表者名	滝之入　敬汰
指導教員名	長谷川　幸雄　教授
発表題目（英語）	Exploring Surface States and Local Transport in Tl-, Pb-, and Tl–Pb Layers on Si(111)
要旨（英語）	Scanning tunneling microscopy and potentiometry (STM/P) provide simultaneous access to atomic-scale topography and electrochemical potential distribution with microvolt resolution, making them powerful tools for investigating surface transport phenomena. In our laboratory, we have performed STP measurements under low temperatures and magnetic fields to explore possible transport behaviors driven by spin-orbit interaction and symmetry breaking at surfaces. Thallium-covered Si(111)-(1×1) surfaces are known to host spin-split surface states due to strong spin–orbit coupling. Previous angle-resolved photoemission spectroscopy (ARPES) studies, such as those by Sakamoto et al., have shown that even a small amount of excess Tl—beyond one monolayer—can shift the originally unoccupied surface band down to the Fermi level, resulting in a metallic state[1]. Motivated by this, we aim to probe the local manifestation of such band shifts and metallicity using low-temperature STM/P. We are also interested in Pb/Si(111)- and mixed Tl–Pb phases.By using STM/P, we seek to investigate how spin-orbit-induced features manifest in both local density of states and surface transport at the nanoscale. [1]K. Sakamoto et al., Prog. Surf. Sci. 97, 100665 (2022).
発表言語	日本語

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