応用物理学輪講 I
11月1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
2024年11月1日（金）16：50～18：50

Aグループ

座長
岸本　竜太
指導
教員名
小芦　雅斗　教授
座長
コラック　尚芸仁平
指導
教員名
井手上　敏也　准教授
発表者名 梶原　葵
指導教員名 求　幸年　教授
発表題目（英語） Exploring methods for spin current generation in metal with topological spin texture
要旨（英語） In recent years, topological spin textures have attracted enormous research interest. Among them, magnetic skyrmions, a prominent example of two-dimensional topological spin textures, have been the most extensively studied due to their high stability and current-driven properties, making them promising candidates for applications such as information carriers and logic devices. In addition to skyrmion, other topological spin textures like bimeron, hopfion and hedgehog, are also gaining attention.
We have focused on the giant emergent electromagnetic fields generated by topological spin textures and started research aimed at applying them to spin current generation. In this presentation, I will provide a review of topological spin textures, including those other than skyrmions, and then explain the results of simulations on spin current generation in a Kondo lattice model within the linear response regime.
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） Continuous extraction of laser-cooled Sr atoms using magnetic fields
要旨（英語） The frequency of lasers stabilized by optical lattice clocks has achieved a relative systematic uncertainty level of 10^-19. However, since the transitions used for cooling and spectroscopy share the same lower energy level, these processes need to be performed sequentially over time, resulting in periods without feedback. During these times, the effects of aliasing lead to a longer duration to reach this precision. To achieve this level of precision more quickly, it is necessary to spatially separate these processes, allowing them to be conducted continuously.

In this study, we explored the use of magnetic fields generated by printed circuit boards to continuously transport cooled atoms to the spectroscopy region. By designing the wiring of the printed circuit board, we can create magnetic fields at will, enabling us to move the atoms in the desired direction. This approach resolves the issue encountered with conventional linear transport of optical lattice beams, where spontaneous emission light produced during the cooling process heats the atoms at the spectroscopy region. Additionally, the size of the printed circuit board is on the millimeter scale, contributing to the simplification and miniaturization of the apparatus. This presentation will discuss the simulation results of guiding cooled atoms using magnetic fields.
発表言語 日本語
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） Alternating-bias assisted annealing on the Josephson potential in superconducting qubits
要旨（英語） Over the past 25 years, superconducting qubits have been extensively studied. A transmon, the simplest and most widely used superconducting qubits, consists of a capacitor and a nonlinear inductor via a Josephson junction. Traditionally, the Josephson potential has been approximated as cosine potential, but recent findings suggest that this may be inadequate due to the presence of pinholes affecting conductance. By applying alternating-bias assisted annealing across the junction, the scheme allows to change junction’s property without affecting the thickness of the junction barrier noticeably. Thus, from the analysis of the spectra of a transmon, we will present prospects for engineering Josephson potentials using annealing scheme.
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） Angle-resolved photoemission spectroscopy (ARPES) study of twisted bilayer WTe2
要旨（英語） Twisted van der Waals assembly is attracting great attention because of its artificial structure depending on the twist angle and heterostructure. Twisted bilayer WTe2 is one good example showing 1D-Moire structure and electronic transport resembling a Tomonaga-Luttinger liquid (TLLs) state is reported.
In this presentation, I will explain what ARPES can do to investigate TLLs, followed by device fabrication suitable for ARPES study.
発表言語 日本語

Bグループ

座長
佐々木　猛
指導
教員名
長谷川　達生　教授・矢代　航　委嘱教授
座長
佐藤　葵
指導
教員名
芦原　聡　教授
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） Magnetization dynamics in semi-magnetic topological insulators
要旨（英語） Topological insulator(TI)s, insulators with finite Chern number in their ground states, have atracted attention and been intensely studied throughout a decade. Topological surface states, which appear due to
non-trivial band topology, have strong spin-orbit coupling and provides an ideal platform to explore physics of electrons described by Dirac Hamiltonian.

From a perspective of spintronics, spin-orbit torque(SOT) arising from spin-polarized surface states plays a vital role to control magnetism. In fact, current-induced magnetization switching by SOT has been reported in semi-magnetic TIs. However, the previous works have been limited to ones induced by pulse current to minimize Joule heating.

In our work, we focus on alternating current(AC)-induced magnetization dynamics in (Bi,Sb)<sub>2<\sub>Te<sub>3<\sub>/(Cr,Bi,Sb)<sub>2<\sub>Te<sub>3<\sub> which is known to show large anomalous Hall resistivity and highly efficient charge-to-spin conversion. Through time-domain measurements of nonlinear Hall responses, we unveil the behavior of magnetization under AC. The results of our work provides a new mechanism of nonlinear transport and paves the way to explore emergent phenomena in TIs.
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） Emergence and Control of Polar Crystal Structures in Layered Organic Semiconductors by the Effect of Molecular Mixing
要旨（英語） Many organic semiconductor molecules with π-electron backbones that are asymmetrically substituted with alkyl chains exhibit remarkably high layered crystallinity, allowing the construction of single-crystal thin films through solution coating. Recently, the emergence of polar crystal structures has been reported in these layered organic semiconductors, where the molecules, lacking a center of symmetry, are all stacked in the same direction. Such polar organic semiconductors are expected to give rise to new device functionalities that utilize polarity, such as piezoelectric effects, electro-optic effects, and bulk photovoltaic effects. However, the types of molecular species that adopt polar crystal structures remain limited, and clear design guidelines for imparting strong polarity to materials have yet to be established. In this study, we discovered that the emergence and control of polar crystal structures can be achieved by mixing similarly shaped highly polar molecules.

In this presentation, I will introduce the results of XRD(X-ray diffraction), SHG (Second Harmonic Generation) measurements, and electro-optic effect measurements.
発表言語 日本語
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） Practical Quantum Algorithm for Heisenberg-limited Multiple Observables Estimation
要旨（英語） Evaluating the expectation values of physical quantities is a crucial task in various quantum computing applications. One of the most promising approaches is to employ the quantum gradient estimation (QGE) algorithm, which achieves both Heisenberg-limited scaling with estimation accuracy and quadratic speedup with the number of observables. Concretely, for a target accuracy p and the number of observables M, the QGE algorithm requires only O(√M log M / p) queries to an oracle that prepares the quantum state of interest. This query complexity is nearly optimal, suggesting potential computational benefits over existing estimation algorithms. However, the advantage of the QGE algorithm becomes significant only for impractically large M because its query complexity involves a relatively large prefactor, undermining its practical applicability even in future quantum computers.

In this talk, we significantly improve the practicality of the QGE algorithm by reducing the prefactor via leveraging physical properties of target systems such as symmetry. By refining the constants involved, we lower the threshold of M at which QGE becomes advantageous over other methods by up to four orders of magnitude. We also provide concrete instances of problems where our improved algorithm demonstrates resource savings compared to other estimation methods. Our proposal broadens the practical applicability of the QGE algorithm in fault-tolerant quantum computing.
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） Temperature dependence of ortho-to-paraexciton conversion rate in Cu_2O
要旨（英語） The yellow 1s excitons in a cuprous oxide (Cu_2O) crystal are split into two distinct states depending on the spin configuration: a triply degenerate orthoexciton state and a singly degenerate paraexciton state. Because 1s paraexciton is pure spin triplet state, paraexcitons interact weakly with the radiative field and thus exhibit long lifetimes. Typically, paraexcitons are generated from optically accessible orthoexcitons via an ortho-to-para conversion process. Owing to their long lifetimes, paraexcitons have attracted attention as a candidate for exciton Bose-Einstein condensation (BEC). To investigate the characteristics of a condensate and the kinetics of orthoexcitons and paraexcitons, it is crucial to analyze the ortho-to-para conversion process, which determines the time scales of paraexciton generation.

In this presentation, we review the temperature dependence of the ortho-to-para conversion rate measured at temperatures ranging from 2 K to 20 K. We also present a conversion model that explains experimental results, based on transverse acoustic (TA) phonon scattering [1]. Furthermore, we present the latest results from our group on measurements of the ortho-to-para conversion rate at sub-Kelvin temperatures and validate the proposed conversion model against the experimental data taken at sub-Kelvin temperatures.

[1] J. I. Jang, K. E. O’Hara, and J. P. Wolfe, Phys. Rev. B, 70, 195205 (2004).
発表言語 日本語
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