12月19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

12月19日

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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12月19日(金) 16：50～18：50

Aグループ

座長: 橋爪　智紀
指導 教員名: 山本　倫久　教授

発表者名	鷲川　紗弥
指導教員名	香取　秀俊　教授
発表題目（英語）	Demonstration of a Narrow-Linewidth Laser Using Stimulated Brillouin Scattering for Atomic Clocks
要旨（英語）	Developing single-frequency narrow-linewidth lasers is essential for precision measurements, such as frequency standards using atomic clocks. Clock lasers’ frequency is often stabilized to a high finesse cavities made of the Ultralow Expansion (ULE) glass using the Pound-Drever-Hall (PDH) servo lock. However, ULE cavities are inherently sensitive to vibration, making them difficult to use in space applications. One promising approach is the use of Stimulated Brillouin Scattering (SBS) fiber lasers. SBS is a nonlinear optical process where a pump light excites acoustic phonons within the fiber medium. This interaction generates a backward-propagating Stokes wave that is shifted by the Brillouin frequency. The long acoustic phonon lifetime and the extremely narrow gain bandwidth of SBS provide an intrinsic linewidth-narrowing mechanism that enables the generation of ultranarrow optical spectra. Consequently, SBS lasers can exhibit linewidths reduced by several orders of magnitude relative to their pump sources. In this work, we constructed an SBS laser based on several tens of meters of optical fiber and confirmed that its frequency stability was significantly improved compared to the pump laser. Further work will include addressing long-term drifts, such as those induced by temperature fluctuations.
発表言語	日本語

発表者名	王　麓翔
指導教員名	小林　洋平　教授
発表題目（英語）	Power Enhancement of a 3 µm Mid-Infrared Light Source for Spectroscopic Breath Diagnosis
要旨（英語）	Mid-infrared (MIR) molecular vibrational spectroscopy in the fingerprint region (3–20 µm) is promising for breath diagnostics—a non-invasive technique estimating health status via trace volatile organic compounds (VOCs). Unlike traditional methods like gas chromatography, which suffer from long measurement times, we previously proposed a rapid, high-sensitivity detection method using a broadband MIR source and an extremely high-order germanium immersion echelle grating (EGIG) [1]. This system achieved high-resolution spectral acquisition at video rates with a detection limit below 1 ppb. However, the source power was limited to ~100 µW. Here, we report on sensitivity improvements by significantly increasing the source power. Our system utilizes a ~3 µm mid-IR comb generated via difference-frequency generation seeded by a Yb-doped fiber oscillator. Optimization of the alignment yielded an output of 20 mW—more than two orders of magnitude higher than the previous setup. Additionally, a dual-beam configuration (signal and reference) sharing common optics and environment was implemented to suppress noise. [1] S. Tani, et al., Opt. Express, 30, 36813–36825(2022).
発表言語	日本語

発表者名	聞　駿軒
指導教員名	沙川　貴大　教授
発表題目（英語）	Symmetry and topology of quantum feedback control
要旨（英語）	This presentation introduces a novel framework to understand the topological aspects of quantum feedback control by applying the general theory of non-Hermitian topology to the quantum channels of dynamical control of quantum systems. With this framework, various “topological Maxwell demons” were proposed that achieve chiral or helical transport robust against disorder. However, the results of symmetry classification of quantum feedback control has been limited to the cases with one ideal projective measurement per cycle. This assumption reduces the system to the 10 AZ^$\dagger$ classes, a subset of the 38 general classes (Bernard-LeClair symmetry classes). I will also present our work to extend this classification to more general cases. We prove that for successive feedback control with non-adaptive bare measurements, the symmetry classification still falls within the 10 AZ$^\dagger$. Furthermore, we construct examples that go beyond the AZ$^\dagger$ regime.
発表言語	日本語

Bグループ

座長: 濵野　直紀
指導 教員名: 香取　秀俊　教授

発表者名	林　度勲
指導教員名	古澤　明　教授
発表題目（英語）	Error Correction of GKP-like States via ASIC-based Feedforward
要旨（英語）	Optical quantum computing faces several challenges in implementing quantum error correction(QEC). GKP qubits can supress small displacement errors in continuous-variable system. However, if we do not actively correct these displacements, the errors accumulated over many rounds of computation will flip the parity of GKP qubits and cause logical error in the quantum computation. This makes fast, hardware-level QEC is mandatory and it points to the need for concrete system that can realize it in practice, In this work, I will introduce a QEC scheme based on feedforward with an ASIC-based system combined with a syndrome measurement using QND gate implemented via in-line squeezer. The goal is to achieve a broadband QEC system using an ASIC, I will also describe test schemes based on single-quadrature GKP-like states (e.g., squeezed cat states) to evaluate the performance and feasibility of this architecture.
発表言語	英語

発表者名	云　惟逸
指導教員名	Max Hirschberger 准教授
発表題目（英語）	Neutron study of magnetic structure in Van der Waals materials HoTe3
要旨（英語）	The rare-earth tritellurides (RTe3) are quasi-two-dimensional van der Waals compounds with a layered orthorhombic structure, featuring Te square nets separated by RTe slabs. RTe3 compounds are typically regarded as prototypical charge-density-wave (CDW) ordered materials, where the CDW order is driven by Fermi surface nesting. Moreover, RTe3 compounds are ideal platforms for exploring exotic electronic orders, including pressure-driven unconventional superconductivity, and non-coplanar helimagnetism induced by spin-charge coupling [1]. Nevertheless, the general mechanism of the novel magnetic phase remains unclear, indicating the need for further investigations across the RTe3 family. Our presentation will briefly discuss the study of the magnetic structure in HoTe3 based on neutron scattering and symmetry analysis, aiming to broaden our understanding of magnetism in RTe3 compounds. [1] S. Akatsuka et al., Nat. Commun. 15, 4291 (2024).
発表言語	英語

発表者名	鐘　正揚
指導教員名	塚﨑　敦　教授
発表題目（英語）	Superconductivity in Bilayer Nickelates: Experimental Efforts Towards Ambient-Pressure Superconductivity
要旨（英語）	High-critical-temperature (Tc) superconductivity has attracted intense research interest for many decades. The discovery of superconductivity in the cuprate (La,Ba)2CuO4 with Tc ∼30 K initiated high-Tc superconductivity as one of the central topics in modern condensed-matter physics [1]. In 2023, superconducting signatures at 78 K were discovered in bulk La3Ni2O7 under high pressure, which attracted great attention [2]. Since then, ambient-pressure superconductivity in bilayer nickelates has been achieved in compressively strained thin films [3,4]. The superconducting mechanism in bilayer nickelates has been extensively studied in contrast to that in cuprates. In the first half of this presentation, I will introduce unconventional superconductors, focusing mainly on bilayer nickelates with comparisons to cuprates. In the second half, I will present our experimental approach to improve the superconducting properties at ambient-pressure based on the pulsed-laser deposition (PLD) technique. [1] J. G. Bednorz & K. A. Müller, Z. Physik B - Condensed Matter 64, 189–193 (1986). [2] H. Sun et al, Nature 621, 493–498 (2023). [3] E. Ko et al., Nature 638, 935–940 (2025). [4] G. Zhou et al., Nature 640, 641–646 (2025).
発表言語	日本語

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