応用物理学輪講 I
6月6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6日(金) 16：50～18：50

Aグループ

座長
松田　優馬
指導
教員名
川﨑　雅司　教授
座長
松本　滉永
指導
教員名
木村　剛　教授
発表者名 菊池　春輝
指導教員名 中村　泰信　教授
発表題目（英語） Observation of Josephson harmonics before and after the alternating-bias assisted annealing
要旨（英語） Superconducting qubits have been studied all over the world to realize large-scale quantum computers. For example, a transmon, the simplest and most widely used superconducting qubit, consists of a capacitor and a Josephson junction. The Josephson junction acts as a nonlinear inductor and is realized using a superconductor–insulator–superconductor (SIS) junction. Conventionally, the Josephson potential of low-transparent SIS junctions used in transmons has been approximated simply as U_J=E_J cos⁡φ, where E_J is the Josephson energy and φ is the phase difference across the junction. This approximation assumes that the transparency (τ) of each conduction channel across the oxide barrier is sufficiently small. However, recent studies suggested that this approximation may be invalid for widely used Al/AlOx/Al junctions (FIG. 1). High-transparency conduction paths, originating from inhomogeneities in the amorphous AlOx insulating layer, violate the low-transparency assumption. Indeed, recent studies have revealed that Josephson harmonics U_J=-∑E_Jm cos⁡mφ (m=1,2,3,…) corresponding to higher-order terms in the Josephson potential, need to be considered to accurately explain qubit spectra [1]. Furthermore, recent studies have reported that Josephson harmonics can distort the potential near the qubit’s computational space, increase susceptibility to charge noise, and degrade the qubit anharmonicity.

Meanwhile, poor uniformity of Josephson-junction parameters in circuits is one of the major challenges for the integration of superconducting qubits. To address this issue, post-fabrication tuning methods such as the alternating-bias assisted annealing (ABAA) have been developed [2]. While these techniques have succeeded in the macroscopic resistance control, the microscopic changes in the oxide barrier remain poorly understood. Applying ABAA to AlOx junctions may enhance the uniformity of the insulator and suppress Josephson harmonics by microscopically reducing highly transparent conduction paths.

In this presentation, we will report on the measurement of Josephson harmonics of transmon qubits before and after the application of ABAA. Our approach elucidates the physical origins of Josephson harmonics and demonstrates a practical technique for improving qubit performance.
発表言語 日本語
発表者名 木村　文彦
指導教員名 石坂　香子　教授
発表題目（英語） charge density wave state in 4Hb-TaSe2
要旨（英語） Van der Waals materials have gathered much attention owing to their accessibility to atomic layer. They exhibit various physical properties such as charge density wave, superconductivity, correlated insulator, and magnetism. Breakthroughs in stacking atomically thin films have allowed us to investigate a variety of Van der Waals heterostructures. Thanks to the variety of materials and control of twist angle, Van der Waals heterostructures exhibit novel quantum phases, which pure 2D material does not show.

4Hb-TaSe2 is a natural Van der Waals heterostructure of 1T-TaSe2 and 2H-TaSe2. 1T-TaSe2 is a Mott insulator and exhibits Star-of-David √13 by √13 charge density wave (CDW). 2H-TaSe2 is a superconductor and exhibits 3 by 3 CDW. Interaction between 1T and 2H-TaSe2 may induce changes in CDW states, but its electronic structure remains elusive.

In this presentation, I will introduce angle-resolved photoemission spectroscopy of 4Hb-TaSe2. It shows CDW gap from 3 by 3 CDW and chiral constant-energy surface reflecting √13 by √13 CDW.
発表言語 日本語
発表者名 黒田　清太
指導教員名 長谷川　達生　教授
発表題目（英語） Measurement and Application of Nonlinear Optical Effects in Polar Organic Semiconductors
要旨（英語） Many organic semiconductor molecules with π-conjugated backbones asymmetrically substituted with alkyl chains or similar groups exhibit remarkably high layered crystallinity, enabling the formation of single-crystal thin films via solution-based coating methods. Recently, it has been reported that some of these layered organic semiconductors can form polar crystal structures, in which all molecules align in the same direction without a center of symmetry. Such polar organic semiconductors are expected to exhibit novel device functionalities based on their polarity, such as piezoelectric effects, electro-optic effects, and bulk photovoltaic effects. However, the physical properties of these polar organic semiconductor crystals, such as their nonlinear optical coefficients, remain unclear. Additionally, the orientation of the molecules—whether they face up or down on the substrate—has not been determined.
In this presentation, I will first introduce the evaluation of nonlinear optical coefficients in polar semiconductors. In the latter half, I will present the experiments and results related to determining the molecular orientation polarity.
発表言語 日本語
発表者名 佐藤　陽紀
指導教員名 長谷川　達生　教授
発表題目（英語） Development of organic devices using an organic transistor with sharp switching characteristics: FeFET and pressure sensor
要旨（英語） Organic materials, such as organic semiconductors, are considered promising candidates for realizing innovative devices, including flexible and wearable electronics, due to their characteristics such as being lightweight, thin, and mechanically flexible. This presentation introduces two devices fabricated using organic materials. 
The first is a FeFET, which is a type of non-volatile memory device that employs a semiconductor and a ferroelectric material. Compared to conventional memory devices, FeFET offers advantages such as high integration density, large signal output, and fast readout speed, so this device has attracted significant attention. 
The second is a pressure sensor, which combines a piezoelectric material with a transistor. Piezoelectric materials generate an electric charge in response to applied mechanical pressure, and this property is utilized in the operation of the pressure sensor. 
In this presentation, I will introduce the organic FeFET and pressure sensor, as well as the ferroelectric and piezoelectric materials utilized in each device.
発表言語 日本語

Bグループ

座長
松田　仁
指導
教員名
有田　亮太郎　教授
座長
八木　春樹
指導
教員名
Gong Zongping 准教授
発表者名 小泉　勇樹
指導教員名 沙川　貴大　教授
発表題目（英語） Faster Quantum Algorithm for Multiple Observables Estimation
要旨（英語） Achieving quantum advantage in efficiently estimating collective properties of quantum many-body systems remains a fundamental goal in quantum computing. While the quantum gradient estimation (QGE) algorithm has been shown to achieve doubly quantum enhancement in the precision and the number of observables, it remains unclear whether one benefits in practical applications. In this work, we present a generalized framework of adaptive QGE algorithm, and further propose two variants which enable us to estimate the collective properties of fermionic systems using the smallest cost among existing quantum algorithms. The first method utilizes the symmetry inherent in the target state, and the second method enables estimation in a single-shot manner using the parallel scheme. We show that our proposal offers a quadratic speedup compared with prior QGE algorithms in the task of fermionic partial tomography for systems with limited particle numbers. Furthermore, we provide the numerical demonstration that, for a problem of estimating fermionic 2-RDMs, our proposals improve the number of queries to the target state preparation oracle by a factor of 10 for the nitrogenase FeMo cofactor and by a factor of 10 for the Fermi-Hubbard model of 200 sites.
発表言語 日本語
発表者名 清永　優斗
指導教員名 十倉　好紀　卓越教授
発表題目（英語） Novel Physical Properties Arising from Quantum Geometric Aspects of Electronic Structures at Topological Interfaces
要旨（英語） The phase of the electron wavefunction in materials, through its geometric properties, serves as the origin of various physical phenomena. In recent years, “topological” materials have emerged as ideal platforms for realizing quantum properties driven by pronounced geometric effects, such as the generation of large Berry curvature resulting from nontrivial topology. In particular, spin-orbit coupling in topological materials gives rise to novel physical phenomena, including the emergence of geometrically-induced “emergent” electromagnetic fields associated with magnetism and its control. Furthermore, applying mechanical strain can significantly alter the electronic structure, revealing new aspects of topological materials such as the formation of flat bands and the emergence of superconductivity. In this study, we aim to explore novel quantum properties and functionalities arising from geometric effects by controlling magnetism and electronic structure at the interfaces of thin-film heterostructures composed of topological materials, such as the topological insulator (Bi,Sb)2Te3 and the topological crystalline insulator (Pb,Sn)(Se,Te).
発表言語 日本語
発表者名 齊藤　孝太朗
指導教員名 吉岡　孝高　准教授
発表題目（英語） Giant Rydberg excitons in the copper oxide Cu_2O
要旨（英語） In bulk semiconductors, excitons are quasiparticles composed of an electron and a hole bound by the Coulomb interaction. They possess hydrogen-like energy levels. Rydberg excitons, characterized by high principal quantum numbers, have attracted significant attention as solid-state analogies to Rydberg atoms, which are promising platforms for quantum computing and quantum simulation in atomic physics.

In this talk, I will present experimental results, which reported the first observation of Rydberg excitons with principal quantum numbers ranging from n = 2 to 25 [1]. In this study, a natural Cu_2O crystal was cooled to 1.2 K and its exciton absorption spectrum was probed by a narrow-linewidth monochromatic laser, while the transmitted intensity was recorded with high spectral resolution. As a result, excitons with principal quantum number up to n = 25 were observed; their wavefunctions extended beyond a 2 μm diameter. From their data, the authors estimated that exciton lifetimes are on the order of nanosecond timescale. Furthermore, they interpreted the experimental results as evidence of a dipole-blockade effect, in which Rydberg excitons with high principal quantum numbers prevent the excitation of neighboring excitons.

In this study, they suggested that positions where Rydberg excitons are generated can be controlled with high precision by applying spatially modulated strain fields to the crystal. In our current research, we are investigating a spin‐flip dynamics of excitons in a Cu_2O crystal under spatially inhomogeneous strain. By understanding exciton behavior under spatially inhomogeneous strain, we consider our research can provide a basis for developing techniques to precisely control the positions where Rydberg excitons are generated.

[1] T. Kazimierczuk, D. Fröhlich, S. Scheel, H. Stolz, and M. Bayer, Nature 514, 343–347 (2014).
発表言語 日本語
発表者名 佐藤　憩
指導教員名 長谷川　幸雄　教授
発表題目（英語） Exploration of Novel Capacitance Responses in Two-dimensional Multiferroic Materials
要旨（英語） Two-dimensional materials can be obtained by exfoliating van der Waals solids and possess high crystallinity. Due to their reduced dimensionality, they exhibit a variety of unique physical properties not seen in bulk materials, such as strong electron-electron interactions, quantum effects, and mesoscopic transport phenomena. Additionally, their ability to form arbitrary heterostructures and the wide range of material types—including metals and magnetic materials—provides excellent design flexibility and controllability, making them a powerful platform for exploring new physical phenomena.
However, the actual size of these materials is typically limited to several tens of micrometers in width and only a few nanometers in thickness. Because of this extreme smallness, many conventional measurement techniques used for bulk materials are not applicable. As a result, research has primarily focused on electronic transport and optical responses, limiting the range of accessible physical quantities. In this presentation, we focus on two-dimensional multiferroic materials and aim to explore new physical quantities through capacitance measurements—a method that has received little attention in the study of two dimensional materials. This approach opens a path to probing new aspects of low-dimensional systems.
発表言語 日本語
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