応用物理学輪講 I
6月30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30日（金）16：50～18：50

Aグループ

座長
姜　東彦
指導
教員名
小林　洋平　教授
発表者名 洲鎌　英行
指導教員名 芦原　聡　教授
発表題目（英語） Intra-pulse DFG of mid-infrared pulses using Cr:ZnS mode-locked laser laser
要旨（英語） The mid-infrared wavelength region has many resonance lines of molecular vibration. Mid-infrared ultrashort pulse lasers with a broad spectrum in this wavelength region are extremely useful for vibration spectroscopy and we have developed mode-locked lasers and single-pass amplifiers using the gain media of Cr:ZnS polycrystals as enough broadband light source. In this study, we report on intra-pulse difference frequency generation using Cr:ZnS femtosecond laser as a pump source, aiming at mid-infrared pulses generation in the "fingerprint region" at wavelengths above 6.7 µm(wavenumber below 1500 cm-1), which is important for molecular identification.
発表言語 日本語
発表者名 高橋　一真
指導教員名 古澤　明　教授
発表題目（英語） Fault-tolerant qubit generation for ultra-fast optical quantum computation
要旨（英語） Quantum computing is currently one of the most exciting areas not only in academics but also in industry. Quantum computers perform certain tasks such as quantum simulations and optimization much faster than classical computers. Generally speaking, we take the advantages only in the case where the tasks could be solved via specific quantum algorithms. On the other hand, optical quantum computers perform calculations at higher clock frequency than modern computers.

Quantum processors of optical quantum computers, which control quantum bits and perform logical operations, have been developed. A basic technique of 43 GHz clock frequency computation has recently developed[1]. One of the biggest challenges for the realization of optical computers is to achieve fault-tolerance computing. Gottesman-Kitaev-Preskill (GKP) states [2] are the greatest candidate for fault-tolerance qubits but it is extremely difficult to produce it. In recent work, a generation of GKP states on optical traveling waves has succeeded [3]. However, its generation rate is a few Hz, which is much far from tens GHz of optical quantum computers'
performance. We have to generate complex quantum states such as GKP states at high rates in the future. As a first step, I'm working on high generation rates of Fock states.

[1] A.Inoue *et al.,* Appl. Phys. Lett. *122*, 104001 (2023) [2] D.Gottesman, A. Kitaev, and J. Preskill Phys. Rev. A *64*, 012310 (2001)
発表言語 英語
発表者名 陳　遥知
指導教員名 小芦　雅斗　教授
発表題目（英語） Numerical analysis of the Gottesman-Kitaev-Preskill codes under non-Gaussian error
要旨（英語） Quantum information processing with continuous variables is the promising approach for tasks such as quantum computing or quantum key distributions especially in the optical systems. To accomplish such tasks, the quantum error correction is necessary to protect fragile quantum systems from noise. For continuous variable system, the Gottesman-Kitaev-Preskill (GKP) codes[1] which encode a qubit into an oscillator are amongst the leading candidates. This code is known for its high performance under the Gaussian error such as photon loss[2]. However, the influence of non-Gaussian error is generally unknown. In this talk we take the random squeezing channel as an example of such kind of error and show the result of numerical analysis of the GKP codes error correction properties under this noise.

Ref.
[1] Gottesman, Daniel, Alexei Kitaev, and John Preskill. "Encoding a qubit in an oscillator." Physical Review A 64.1 (2001): 012310.
[2] Albert, Victor V., et al. "Performance and structure of single-mode bosonic codes." Physical Review A 97.3 (2018): 032346.
発表言語 日本語

Bグループ

座長
張　凌志
指導
教員名
求　幸年　教授
発表者名 摂待　裕生
指導教員名 関　真一郎　准教授
発表題目（英語） Introduction of “altermagnetizm” and its candidate material a new collinear antiferromagnet.
要旨（英語） The typical classification of magnetic phases consists of ferromagnetism and antiferromagnetism. Antiferromagnets have attracted much attention after it is revealed that collinear antiferromagnets can break time-reversal symmetry.[1] Such antiferromagnets generate anomalous responses without net magnetization such as the anomalous Hall effect which is typical of ferromagnets. A recent analysis of nonrelativistic spin-symmetry groups offers a third magnetic phase, altermagnetism.[2] It was also revealed that altermagnet can be a new source of spin current originating from spin-splitter effect.[3]
In this presentation, I will overview the altermagnetism and talk about the experimental results of a candidate material. Single crystal samples of an altermagnet are prepared and their magnetic and transport properties are investigated in detail. In addition, its magnetic structure is determined by spin-polarized and unpolarized neutron diffraction experiments.

[1] L. Šmejkal, et al., Science Advances 6, 23, eaaz8809 (2020)
[2] L. Šmejkal, et al., Physical Review X 12, 031042 (2022)
[3] R González-Hernández, et al., Physical Review Letters 126, 127701 (2021)
発表言語 日本語
発表者名 千葉　速樹
指導教員名 香取　秀俊　教授
発表題目（英語） A compact Zeeman slower and magneto-optical trap based on permanent magnets in a hexagonal arrangement
要旨（英語） Laser cooling of the atoms is required to operate the optical lattice clock. One elemental technique in laser cooling is the Zeeman slower and magneto-optical trap. In our experiments, permanent magnets are used instead of the coils which were conventionally used to create the magnetic fields required for these techniques. This has led to a reduction in power consumption of the optical lattice clock. In this presentation, we will discuss the details of this system and the experimental results.
発表言語 日本語
発表者名 坪内　健人
指導教員名 沙川　貴大　教授
発表題目（英語） Cost-optimal quantum error mitigation based on universal cost bound
要旨（英語） In this work, we present two lower bounds on the sampling cost of quantum error mitigation (QEM) and a cost-optimal QEM method that achieves these lower bounds. Our first bound applies to generic layered quantum circuits under a wide class of Markovian noise: we showed that the sampling cost required to construct an unbiased estimator of an observable grows exponentially with the circuit depth. Particularly, under the global depolarizing noise, we find that the bound can be asymptotically saturated by simply rescaling the measurement results. Our second bound shows that for random circuits with local noise, where each gate is drawn from unitary 2-design, the cost also grows exponentially with the qubit count. Through numerical simulations, we extend this result to more general random circuits. Even if the circuit has only linear connectivity, such as the brick-wall structure, we observe that each noise channel converges to the global depolarizing channel, with its strength growing exponentially with the qubit count. This not only implies the exponential growth of cost both with the depth and qubit count, but also validates the rescaling technique for sufficiently deep quantum circuits. Our results contribute to the understanding of the physical limitations of quantum error mitigation and provide practical guidelines toward cost-optimal QEM.
発表言語 日本語
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