6月23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23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: 2023年6月23日（金）16：50～18：50

Aグループ

座長: 米虫　遼太郎
指導 教員名: 川﨑　雅司　教授

発表者名	木倉　清吾
指導教員名	小芦　雅斗　教授
発表題目（英語）	A single-photon source based on cavity quantum electrodynamics considering the re-excitation problem
要旨（英語）	Single photons play a crucial role in quantum information processing and have a multitude of applications, from quantum computation to quantum communication. While there are several physical implementations of single-photon sources, the cavity QED system is a physical system that can generate photons on demand. In single-photon generation by this system, the use of a Λ-type three-level atom allows control of the photon waveform. In this method, there is a process that inhibits ideal photon generation due to the relaxation of excited atoms to the initial state, which degrades the performance of quantum information processing utilizing photons. To address this issue, we propose a novel photon generation scheme using a four-level atom. We demonstrate that the relaxation process described above can be made arbitrarily small by manipulating experimentally tunable parameters.
発表言語	日本語

発表者名	河野　秀城
指導教員名	小芦　雅斗　教授・藤井　啓祐　委嘱教授
発表題目（英語）	Fault Tolerant Non-Clifford State Preparation for Arbitrary Rotations
要旨（英語）	Since quantum computers are vulnerable to noise, it is necessary to use logical qubits encoded with quantum error-correcting codes to perform highly accurate quantum algorithms. However, it is known that existing calculation methods using T-gates incur significant resource overhead for logical operations on logical qubits. This is because a large number of logical T-gates with an enormous cost are required to perform arbitrary logical rotation operations. This paper[1] proposes an approach to rotating qubits directly without using T-gates to perform arbitrary rotation operations. Specifically, it is achieved fault-tolerantly by state preparation using post-selection and gate teleportation. In this presentation, I will explain this method and its effectiveness in the early-FTQC era. [1] H. Choi, et.al., arXiv preprint arXiv: 2303.17380 (2023).
発表言語	日本語

発表者名	小林　尚暉
指導教員名	中島　多朗　准教授
発表題目（英語）	Introduction of a new detector for magnetic structure analysis using neutron scattering
要旨（英語）	To understand the physical properties of materials, the determination of crystal and magnetic structures is one of the most effective ways. One of the methods to investigate these structures is to use neutron scattering. Neutrons are scattered due to the magnetic dipole interaction with magnetic moments in the material, therefore by measuring the scattering intensity, it is possible to distinguish ferromagnetism, antimagnetism, and even helical magnetism. Recently, rare-earth intermetallic compounds have attracted attention for their novel magnetic ordering such as skyrmions, and neutron methods are particularly effective in analyzing these compounds. In this presentation, we will introduce the theory of the neutron analysis method and our research on the introduction of a new experimental apparatus.
発表言語	日本語

Bグループ

座長: 韓　東学
指導 教員名: 石坂　香子　教授

発表者名	小林　海翔
指導教員名	求　幸年　教授
発表題目（英語）	Thermally-robust spatiotemporal parallel reservoir computing in frustrated magnets
要旨（英語）	Physical reservoir computing is a cutting-edge framework for neuromorphic machine learning that exploits the nonlinear phenomena in a physical system to achieve low-power, high-speed, and versatile hardware implementation for real-time machine learning [1]. Magnetic materials are one of the most promising platforms for physical reservoir computing, utilizing the nonlinearity and high dimensionality of complicated spin dynamics [2]. Meanwhile, two major obstacles remain for device applications of the spintronic physical reservoirs. One is robustness against thermal fluctuations, which is crucial for retaining short-term memory, the essence of neuromorphic computing. The other is that parallel processing techniques, a key aspect for high integration, remain largely unexplored. 　In this study, we demonstrate, for a simple model of frustrated magnets, both robustness to thermal fluctuations and feasibility of frequency division multiplexing [3]. We find that when the input is provided through an AC magnetic field, the information is retained in the spin dynamics at around the same frequency as the input AC field, even though the overall memories are quickly disrupted by thermal noise. This observation motivates the use of a frequency filter to remove thermal noise from irrelevant frequencies, leading to the preservation of the short-term memory even at finite temperatures. Moreover, we achieve parallel processing with frequency division multiplexing by utilizing a superposed magnetic field that carries multiple information at different frequencies. Our scheme can be coupled with parallelization in spatial domain at the level of a single spin, yielding a vast number of spatiotemporal computational units. Furthermore, we show that the nonlinearity arising from the exchange interaction allows information processing between different frequency threads, including linearly-inseparable logic gate tasks such as XOR and XNOR, without the need for dedicated communication channels. Our framework can be implemented on a variety of magnetic materials, paving a way for the device realization of physical reservoir computing [4]. [1] H. Jaeger and H. Haas, Science 304, 78-80 (2004). [2] J. Torrejon et al., Nature 547, 428-431 (2017). [3] K. Kobayashi and Y. Motome, arXiv:2302.14496 (2023). [4] 求幸年、小林海翔、特願2023-25883 「情報処理システム、情報処理方法およびプログラム」
発表言語	日本語

発表者名	佐藤　真武
指導教員名	平山　元昭　特任准教授
発表題目（英語）	Ideal Spinless Dirac Semimetal RE8CoX3 (RE = rare earth elements, X = Al, Ga, or In)
要旨（英語）	Topological phases of quantum matter have been the subject of intense research in recent years. In the theoretical search for topological materials, the symmetry of the system plays a crucial role. The development of the representation theory of space groups has allowed an exhaustive search for topological insulators and topological semimetals in the crystal database, and thousands of topological materials have been discovered [1]. However, the detailed classification and the characterization of topological semimetals are still lacking. It is difficult to design an ideal semimetal from symmetry information alone. In addition, the design of band inversions, which are closely related to the nontrivial topology, is difficult in spinless systems. Due to these problems, some topological phases have not yet been discovered in real materials. In this work, we have discovered the first material to realize spinless Dirac semimetal phases and characterized its nontrivial topology. In the presentation, design guidelines for spinless Dirac semimetal phases and various topological phase transitions will also be presented. [1] T. Zhang, et al. Nature 566, 475 (2019).
発表言語	英語

発表者名	清水　一希
指導教員名	石坂　香子　教授
発表題目（英語）	Current induced macroscopic stripe patterns in K-TCNQ
要旨（英語）	Macroscopic order formation in nonlinear non-equilibrium open systems, often referred to as -(dissipative structure,)- is known in various fields. An example of spatially dissipative structures in electronic systems is the current-induced stripe patterns in the one-dimensional organic chargetransfer complex Potassium Tetracyanoquinodimethane (K-TCNQ). K-TCNQ undergoes a Spin-Peierls transition at 395 K, resulting in dimerization of the molecules along the stacking axis. Below the Spin-Peierls transition temperature, the degree of dimerization decreases with the application of a high electric field, and a state of intermediate resistivity between metals and insulators is observed.[1][2] At room temperature, a stripe patterns with a width of several microns is observed at the same time. [1][2] This length scale is much longer than the wavelength of typical spin density waves.[2] The purpose of this study is to investigate the formation mechanism of the stripe patterns and conduction properties of K-TCNQ in detail, and this presentation will report that under certain boundary conditions, different from previous studies, we observed the emergence of dynamic, band-like patterns parallel to the direction of the electric current. [1] Y. Okimoto et al., Phys. Rev. B 70, 115104 (2004). [2] R. Kumai, Y. Okimoto and Y. Tokura, Science 284, 1645 (1999).
発表言語	日本語

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