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

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内部学生向け(物工教務室)

応用物理学輪講 I

2020年7月10日(金)16:50〜 
Aグループ 
 座長:市川 弘貴、岩野 亜希人
Bグループ  
座長:稲垣 宗太朗
氏名: 中村 智裕
指導教員名: 古澤 明 教授
発表題目(英語): Quantum error correcting codes and 3-dimensional cluster state
要旨(英語): The error correction ability is indispensable to use quantum computation in practice. Quantum computation utilizes the quantum property that is very weak to noise. At present, the error correcting quantum computation has not been reported. We are conducting research on measurement based quantum computations[1] using light, and are reaching a very high level in the generation of cluster states[2,3], which are the large-scale entanglement states required for quantum computations. In order to perform error correction in our physical system, a method combining GKP[4] qubit and Surface code[5] is studied.
 The stabilizer code is a general theory of quantum error correction, and encodes information in a stabilizer space that is spanned by an operator called a stabilizer. When a small error occurs, the encoded state goes out of the stabilizer space, so it is detected by the stabilizer. The stabilizer does not destroy the quantum state because it distinguishes whether the quantum state is included in the stabilizer or not and does not reveal the specific state.
 GKP qubit is one of the stabilizer codes and encodes continuous variables into discrete variables. To protect against a large error occurred on the GKP, information is encoded with surface code. Also, in order to combine the surface code with one-way quantum computation, a three-dimensional cluster state[6] in which one dimension of the time region is added to the two-dimensional cluster state is required.
 In this presentation, we give an overview of the theory of error correction in quantum computation.

References
[1] R. Raussendorf et al., Phys. Rev. Lett. 81, 5188 (2001)
[2] J. Yoshikawa et al., APL Photonics 1, 060801 (2016)
[3] W. Asavanant et al., Science 366, 373 (2019)
[4] D. Gottesman et al., Phys. Rev. A 64, 012310 (2001)
[5] A. G. Fowler et al., Phys. Rev. A 86, 032324 (2012)
[6] Fukui et al., arXiv:2004.05750 [quant-ph]
発表言語: 英語
氏名: 畠山 康一郎
指導教員名: 香取 秀俊 教授
発表題目(英語): Nondestructive measurement for optical lattice clocks
要旨(英語): The frequency stability, one of the performance indices of clocks, of optical lattice clocks is now limited mainly by two noises, the Dick effect noise and the quantum projection noise.
The Dick effect noise is an aliasing noise caused by the interruption of the measurement, and the quantum projection noise is a statistical variation due to the binomial distribution of excitation probability obtained by N-atom projection measurement.
 To reduce or overcome these two noises, we implement a nondestructive measurement which uses dispersive properties of atoms.
 In this presentation, I will introduce the principle of the nondestructive measurement and previous researches, then report our progress.
発表言語: 日本語
氏名: 新原 寛太
指導教員名: 志村 努 教授
発表題目(英語): Dielectric metasurface for complete and independent control of the optical amplitude, phase, and polarization.
要旨(英語): Metasurface is a surface composed of nanostructures smaller than the wavelength of light. By properly designing the size and arrangement of scatterers, meta-surfaces can manipulate the amplitude, phase, and polarization of light with high precision.
 It has been shown that two of amplitude, phase, and polarization can be controlled independently: phase and polarization [1], amplitude and phase [2]. However, it has never been shown that all of amplitude, phase, and polarization can be controlled independently. By simulation, we showed independent control of three elements can be realized by the metasurface using the idea of Double Phase Hologram [3]: we call it double phase metasurface.
 In this talk, the essence of metasurface and Double Phase Hologram will be explained first. Then reasons that the double phase metasurface can control amplitude, phase, and polarization will be explained with results of simulation.

 [1] Amir Arbabi et al., Nature Nanotechnology, 10, 937 (2015)
 [2] Adam C. Overvig et al., Light: Science Applications, 8, 92 (2019)
 [3] C. K. Hsueh et al., Applied Optics, 17, 3874 (1978)
発表言語: 日本語
氏名: 林 太一
指導教員名: 長谷川 達生 教授
発表題目(英語): Anomalous Hydrodynamic Size Distributions of Alkylamine/Alkylacid-Encapsulated Silver Nanocolloids: Implications for Printing Ultrafine Conductive Patterns
要旨(英語): Alkylamine/alkylacid-encapsulated silver nanocolloids (amac-AgNCs) present a unique coexistence of their dispersion stability as nanocolloids and fusion reactivity after drying. This feature is useful for the printing-based production of ultrafine conductive patterns, though the origin is not yet understood. Here, we demonstrated the effects of the addition of a protic solvent on the colloidal states of amac-AgNCs as revealed by confocal dynamic light scattering. We observed an abrupt change in the hydrodynamic size distribution of amac-AgNCs depending on the methanol concentration.
 When the concentration of methanol exceeded 7 vol %, the nanoparticle size distribution exhibited a sudden and considerable broadening. Similar effects were observed with other protic solvents but not with aprotic polar solvents. We suggest that the feature could be ascribed to the solvation shell effect, which is responsible for the instability of nanoparticle aggregation. These findings provide a way to control the peculiar colloidal states and dispersion stability of the metal nanocolloids, allowing a major step forward in the printing ultrafine conductive patterns with the metal nanocolloids.
発表言語: 日本語 
氏名: 西谷 侑将
指導教員名: 福谷 克之 教授
発表題目(英語): Colossal resistance enhancement by H doping in a perovskite nickelate
要旨(英語): Some of perovskite nickelates RNiO3 (R = rare earth) are known to exhibit a thermally driven metal-insulator transition where a metallic state at high temperature changes to an insulating state at low temperature. On the other hand, recent studies suggest that a new insulating state emerges by hydrogen doping. Resistivity modulation of more than eight orders of magnitude is reported to occur in the SmNiO3 system at room temperature. However, the relationship between the amount of dopant and the resistivity modulation remains unclear due to the absence of quantitative measurements of the hydrogen density in the crystal, which hampers understanding of the mechanism of the hydrogen-induced metal-insulator transition.
 In this presentation, I will explain the proposed mechanisms of resistance enhancement in perovskite nickelates introducing previous researches, and then talk about the current status of my research and future experimental plans to clarify how H doping influences the electronic state and transport property.
発表言語: 日本語
氏名: 藤村 怜香
指導教員名: 十倉 好紀 卓越教授
発表題目(英語): Electrical manipulation of multi-layered topological phases in topological insulator heterostructures
要旨(英語): Three-dimensional magnetic topological insulators host exotic topological phases, such as the quantum anomalous Hall (QAH) insulator and the axion insulator. In particular, the QAH state, experimentally reached by magnetic doping or proximity effect with a ferromagnetic (TM) layer provides chiral dissipationless topological current whose direction is determined by the direction of magnetization. The electrical manipulation of the magnetization is essential not only as a potential energy-efficient spintronics technology but also in that it enables to control the topological invariant of the Chern number C and switching of topological
phases.
 In the heterostructure of topological insulators (TI) and ferromagnets (FM), owing to the spin-momentum locking at the TI surface, spin-polarized electrons are accumulated through the current flow at the interface, which leads to the generation of spin-orbit torques on the FM layer.
 In our research, topological van der Waals ferromagnetic semimetal Fe3GeTe2 is fabricated by molecular beam epitaxy and the spin-orbit torques from TI (Bi,Sb)2Te3 are studied. In the heterostructure, we observed large spin-orbit torques which lead to current-driven magnetization switching.
 Moreover, the fabricated 2~3 layers of Fe3GeTe2 thin film shows strong magnetic anisotropy and intrinsic anomalous Hall effect. These unique properties of Fe3GeTe2 thin films and the strong spin-orbit couplings with TI indicate the possibilities of layer-selective magnetization switching, as I will discuss in the talk, taking a step forward to the electrical manipulation of the topological states.
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