応用物理学輪講 I
12月5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12月5日(金) 16：50～18：50

Aグループ

座長
川畑　光瑠
指導
教員名
香取　秀俊　教授
座長
中島　将貴
指導
教員名
古澤　明　教授
発表者名 廣田　佑我
指導教員名 吉岡　孝高　准教授
発表題目（英語） Time-Resolved 1s-2p Absorption Imaging of Quantum Degenerate 1s Paraexcitons in Cuprous Oxide at Sub-Kelvin Temperatures
要旨（英語） In 2022, a Bose-Einstein condensate of 1s paraexcitons in bulk cuprous oxide (Cu2O) was directly observed [1] via mid-infrared absorption imaging [2]. However, the condensate fraction reached only 0.016, a value significantly smaller than the maximum of 1 achievable in an ideal Bose gas. This remarkably small condensate fraction cannot be explained by conventional theories and is considered to be a characteristic feature of condensates formed in a non-equilibrium open system.

In order to elucidate this new type of Bose-Einstein condensation, we performed time-resolved absorption imaging and observed the formation and decay dynamics of the condensate. The experiment was conducted under quasi-steady-state conditions achieved with 606.1 nm excitation. For this purpose, we built a setup capable of chopping a 9.85 μm continuous-wave laser into probe pulses with a duration of 40 ns. In this presentation, I will report on the time evolution of the density and spatial extent of the condensate.

[1] Y. Morita, K. Yoshioka, and M. Kuwata-Gonokami, Nat. Commun. 13, 5388 (2022).
[2] K. Yoshioka, and M. Kuwata-Gonokami, Phys. Rev. B 91, 195207 (2015).
発表言語 日本語
発表者名 星野　佳嗣
指導教員名 古澤　明　教授
発表題目（英語） Pulse PSA and Multi-wavelength homodyne measurement for ultra-fast quantum information processing
要旨（英語） Optical quantum computer is highly promising due to its ability to operate with high clock frequencies (~THz). However, there is a significant difficulty to use ultra-fast homodyne detectors, so we have to develop new method because it has low quantum efficiency. To overcome this limitations, we propose and demonstrate Pulse Phase-Sensitive Amplifier (PSA) Homodyne Measurement. By amplifying the specific quadrature of the signal using an optical parametric amplifier (OPA) prior to detection, we can effectively compensate for the optical loss of ultra-fast homodyne detectors. In this study, we constructed an experimental setup for 2.5 GHz repetition-rate coherent states. We successfully demonstrated the PSA measurement method for high-repetition-rate pulses. Currently, we are extending this approach to Multi-Wavelength Homodyne Measurement by spectrally slicing the broadband quantum state. This frequency-domain multiplexing aims to bridge the gap between generation and measurement bandwidths, paving the way for scalable, multi-core quantum processors.
発表言語 英語
発表者名 三木　孝馬
指導教員名 金澤　直也　准教授
発表題目（英語） Quantum Geometric Photocurrent in Ferroelectric Halide Perovskite Thin Films
要旨（英語） The Berry connection, a quantum-geometric phase of electronic wavefunctions, characterizes the center position of Bloch-electron wave packets. In this seminar, I will mainly introduce shift current as a phenomenon in which the Berry connection plays a central role. Shift current is a second-order nonlinear optical effect and one of the primary origins of the bulk photovoltaic effect, in which steady-state photocurrents are generated in homogeneous noncentrosymmetric materials. It arises from changes in the Berry connection of electronic wavefunctions upon optical transition. We report a gigantic photocurrent response in ferroelectric halide perovskites, exhibiting hallmark features of the shift current, exceeding those ever reported in various compounds. We believe these findings establish ferroelectric halide perovskite as a promising platform for exploring the fundamental physics of shift current.
発表言語 日本語

Bグループ

座長
東條　開斗
指導
教員名
沙川　貴大　教授
座長
永山　裕一
指導
教員名
木村　隆志　准教授
発表者名 宮﨑　大輝
指導教員名 武田　俊太郎　准教授
発表題目（英語） Implementation of a nonlinear optical quantum circuit towards the realization of a repeat-until-success cubic phase gate
要旨（英語） Continuous-variable optical quantum computers are considered as a promising platform because they operate at room temperature and have high clock frequencies. However, a major challenge is that they cannot yet perform universal quantum computation. Universal computation requires both arbitrary linear operations and at least one nonlinear operation. While linear operations are already established, nonlinear operations remain unimplemented.
Moreover, nonlinear operations are essential for demonstrating quantum advantage, so implementing them is a significant goal in this field. To address this, we aim to implement the cubic phase gate, which is a type of nonlinear operation, using the “repeat-until-success” scheme. This method allows us to execute the gate in an effectively deterministic manner by repeating the process until it succeeds.
In this presentation, we describe the principle of this method and the current status.
発表言語 英語
発表者名 三好　真生
指導教員名 長谷川　達生　教授
発表題目（英語） Layered Organic Semiconductor Structure Prediction
要旨（英語） It is known that layered crystallinity and high symmetry within the layers contribute to the high performance of organic semiconductor materials. Therefore, efficiently predicting high-performance crystal structures via computation would greatly accelerate material development.

We propose a Stepwise Crystal Structure Optimization method. This technique constructs the crystal structure by optimizing parameters sequentially, starting from the intra-layer arrangement and moving to the inter-layer arrangement. This approach reduces the number of parameters and provides physical insight into which structures are stable.

In this presentation, we demonstrate the utility of this method by applying it to both polyacene-based and perfluoroacene-based systems.
発表言語 日本語
発表者名 村松　春紀
指導教員名 石坂　香子　教授
発表題目（英語） Electronic Structure of the Misfit Layered Compound (PbSe)1.16(TiSe2)2
要旨（英語） Van der Waals layered materials have attracted significant interest as a platform for investigating two-dimensional electronic states, as monolayers can be obtained through techniques such as exfoliation. Various physical properties, including superconductivity and charge density waves (CDW), have been reported in these systems. In recent years, efforts have been made to realize novel physical properties by stacking these materials in diverse combinations and at varying twist angles; these systems are attracting attention as "van der Waals heterostructures".

Against this background, a class of materials known as "misfit layered compounds"—natural heterostructures—has recently gained prominence. These compounds consist of alternating stacks of transition metal dichalcogenide (TX2) layers and rock-salt-type (MX) layers. Their physical properties, arising from this unique heterostructure and the incommensurate crystal structure, are currently the subject of active research.

In this presentation, we report on the electronic structure of the misfit layered compound (PbSe)1.16(TiSe2)2, investigated using angle-resolved photoemission spectroscopy (ARPES). We will specifically discuss the electronic states originating from lattice incommensurability observed in our results.
発表言語 日本語
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