応用物理学輪講 I
7月4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7月4日(金) 16：50～18：50

Aグループ

座長
新井　敦郎
指導
教員名
求　幸年　教授
発表者名 西澤　優
指導教員名 武田　俊太郎　准教授
発表題目（英語） Programmable temporal-mode shaping of single-photon states for advanced photonic quantm information processing
要旨（英語） In recent years, research on quantum computers has progressed rapidly. Among the various platforms, optical quantum computers have attracted significant attention due to their ability to operate at room temperature, their high clock frequencies, and their compatibility with optical communication technologies. In optical quantum computing, computations are performed by manipulating quantum states generated within optical wavepackets. In particular, non-Gaussian quantum states—characterized by their strong nonclassicality—are indispensable for achieving quantum advantage.
It is well known that optimizing the temporal-mode of optical wavepackets can enhance computational performance, like enabling noise reduction, efficient quantum memory, and faster information readout. However, in conventional approaches, the temporal-mode of non-Gaussian states is fixed by the generation setup. Moreover, due to their high sensitivity to loss, direct temporal-mode shaping for these states has remained a significant challenge.
In this talk, we introduce a novel method for programmable temporal-mode shaping that we have implemented for the first time: modulating the intensity of the light used for photon detection during the generation of non-Gaussian states.
And then, we focus on the most basic non-Gaussian state—the single-photon state—and present experimental results of temporal mode shaping for it, concluding with future perspectives enabled by our programmable method.
発表言語 英語
発表者名 本多　健亮
指導教員名 芦原　聡　教授
発表題目（英語） Design of a Broadband, High-Resolution FTIR System for CO2 Jet Pump-Probe Spectroscopy
要旨（英語） Molecular vibration control is increasingly recognized as a promising　method for steering chemical reactions. Mid-infrared pulses can selectively excite specific vibrational modes, thereby imparting energy to reactions of interest. This research aims to elucidate the relationship between molecular vibrational modes and chemical reaction efficiency, focusing on the conversion of CO₂ into HCOO. In the experiment, a CO₂ molecular jet is introduced into a vacuum chamber, vibrationally excited using a mid-infrared pulse, and then collides with H atoms adsorbed on a Cu surface, facilitating its conversion to HCOO. Observing the vibrational modes of the CO₂ molecular jet is crucial for understanding the connection between vibrational excitation and conversion  efficiency. This is achieved through pump-probe experiments. For these experiments, a spectrometer with a wavelength range of 4 µm to 5 µm and a resolution of 0.05 cm⁻¹ is essential. This presentation will discuss the design and development of a high-resolution FTIR system tailored for CO₂ jet pump-probe spectroscopy, along with future perspectives of this study.
発表言語 日本語
発表者名 本田　和大
指導教員名 中村　泰信　教授
発表題目（英語） AC-Voltage Annealing for Resistance Trimming of Al/AlOₓ/Al Josephson Junctions
要旨（英語） Post-fabrication tuning of the normal-state resistance in Al/AlOₓ/Al Josephson junctions is essential for precise frequency control in multi-qubit systems. Conventional approaches, such as thermal annealing or laser annealing, rely on heating that can impact the underlying silicon substrate. As an alternative, voltage annealing—applying an AC bias directly to the junction at room temperature—offers a localized and substrate-friendly method for resistance tuning.

In this work, we investigate voltage annealing by applying AC voltages to Al/AlOₓ/Al junctions under ambient conditions using a lock-in amplifier. We observe systematic changes in junction resistance and successfully reproduce the characteristic “phase map” reported in prior studies. We further explore the dependence of annealing behavior on fabrication parameters and drive frequency.

To gain insight into the annealing mechanism and its effect on junction properties, we analyze room-temperature I–V characteristics before and after annealing using theoretical fits to extract key parameters. These findings contribute to a better understanding of post-fabrication tuning and support the development of reliable, room-temperature-compatible trimming techniques for scalable superconducting quantum circuits.
発表言語 日本語

Bグループ

座長
池上　草玄
指導
教員名
求　幸年　教授
発表者名 政岡　凜太郎
指導教員名 渡辺　悠樹　准教授
発表題目（英語） c-theorem and g-theorem
要旨（英語） The renormalization group is a powerful tool for analyzing phase transitions and critical phenomena in various phases of matter. It enables us to track how a model evolves under scale transformations and coarse-graining.

In (1+1)-dimensional quantum systems, two important theorems in the context of the renormalization group are the c-theorem and the g-theorem. The c-theorem asserts the existence of a function, called the c-function, which decreases monotonically along the renormalization group flow. The g-theorem makes a similar claim for boundary conditions imposed at critical points, stating that a g-function also decreases monotonically under the flow.

Both theorems can be understood from a unified perspective: under coarse-graining, microscopic degrees of freedom are eliminated, leading to a reduction in entropy.

If time permits, I will also introduce the z-theorem, which is of particular interest to the author in the context of non-relativistic systems.
発表言語 日本語
発表者名 松田　仁
指導教員名 有田　亮太郎　教授
発表題目（英語） Multiferroic Collinear Antiferromagnets with Hidden Altermagnetic Spin Splitting
要旨（英語） Altermagnets exhibit nonrelativistic spin splitting due to the breaking of time-reversal symmetry and have been garnering significant attention as promising materials for spintronic applications. In contrast, conventional antiferromagnets without spin splitting seem to not have any symmetry breaking and have drawn less attention. However, we show that conventional antiferromagnets with a nonzero propagation vector (Q vector) bring about nontrivial symmetry breakings. The incompatibility between the Q vector and nonsymmorphic symmetry leads to macroscopic symmetry breaking without lifting spin degeneracy. Moreover, the hidden altermagnetic spin splitting in the electronic structure gives rise to various emergent responses. To examine our prediction, we perform first-principles calculations for MnS2 and investigate its multiferroic properties, such as nonlinear transport and optical activity. Our findings reveal unique properties in conventional antiferromagnets, providing another perspective for designing spintronic materials.
発表言語 日本語
発表者名 松田　優馬
指導教員名 川﨑　雅司　教授
発表題目（英語） Shift Current in CuI Thin Films under Tensile Strain
要旨（英語） In recent years, response phenomena arising from the topology of the phase of electronic wavefunctions in solids have become a major trend in modern condensed matter physics, and the shift current is known as one example of  topological current in materials. Shift current is nonlinear photocurrent observed in materials with broken spatial inversion symmetry, driven by changes in the Berry connection before and after optical transitions. It exhibits unique properties, such as changes in the magnitude and sign of the current depending on the wavelength of the incident light, and the generation of current from excitons, which are charge-neutral quasiparticles. In CuI, the sign of the excitonic shift current is extremely sensitive to lattice strain, and it has been theoretically predicted that the sign reverses between compressive and tensile strain. I will discuss the shift current in single-domain CuI thin films under tensile strain introduced by utilizing the difference in thermal expansion coefficients between the film and the substrate.
発表言語 日本語
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