Language：Japanese   Publishing type：(MISC) Introduction and explanation (scientific journal)   Publisher：電子情報通信学会  

DOI： 10.1587/essfr.15.4_310

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AIP Publishing  

DOI： 10.1063/5.0081113

Language：English   Publishing type：Research paper (scientific journal)   Publisher：IOP Publishing  

DOI： 10.35848/1882-0786/ac039d

Other Link： https://iopscience.iop.org/article/10.35848/1882-0786/ac039d/pdf

Language：Japanese   Publishing type：Research paper (scientific journal)   Publisher：電子情報通信学会  

Language：Japanese   Publishing type：(MISC) Introduction and explanation (commerce magazine)   Publisher：日本工業出版  

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer Nature  

Generation of irregular time series based on physical processes is indispensable in computing and artificial intelligence. In this report, we propose and demonstrate the generation of Schubert polynomials, which are the foundation of versatile permutations in mathematics, via optical near-field processes introduced in a photochromic crystal of diarylethene combined with a simple photon detection protocol. Optical near-field excitation on the surface of a photochromic single crystal yields a chain of local photoisomerization, forming a complex pattern on the opposite side of the crystal. The incoming photon travels through the nanostructured photochromic crystal, and the exit position of the photon exhibits a versatile pattern. We emulated trains of photons based on the optical pattern experimentally observed through double-probe optical near-field microscopy, where the detection position was determined based on a simple protocol, leading to Schubert matrices corresponding to Schubert polynomials. The versatility and correlations of the generated Schubert matrices could be reconfigured in either a soft or hard manner by adjusting the photon detection sensitivity. This is the first study of Schubert polynomial generation via physical processes or nanophotonics, paving the way for future nano-scale intelligence devices and systems.

DOI： 10.1038/s41598-020-59603-1

PubMed

Other Link： https://www.nature.com/articles/s41598-020-59603-1

Language：English   Publishing type：Research paper (scientific journal)  

DOI： 10.1038/s41598-018-32862-9

Other Link： https://www.nature.com/articles/s41598-018-32862-9

Language：English   Publishing type：Research paper (scientific journal)   Publisher：Physical Society of Japan  

We report the discovery of the anomalous enhancement of quantum coherent dynamics (CD) due to a non-Markovian mechanism originating from not thermal-equilibrium phonon baths but nonequilibrium coherent phonons. CD is an elementary process for quantum phenomena in nanosystems, such as excitation transfer (ET) in semiconductor nanostructures and light-harvesting systems. CD occurs in homogeneous nanosystems because system inhomogeneity typically destroys coherence. In real systems, however, nanosystems behave as open systems surrounded by environments such as phonon systems. Typically, CD in inhomogeneous nanosystems is enhanced by the absorption and emission of thermal-equilibrium phonons, and the enhancement is described by the conventional master equation. On the other hand, CD is also enhanced by synchronization between population dynamics in nanosystems and coherent phonons
namely, coherent phonons, which are self-consistently induced by phase matching with Rabi oscillation, are fed back to enhance CD. This anomalous enhancement of CD essentially originates from the nonequilibrium and dynamical non-Markovian nature of coherent phonon environments, and the enhancement is firstly predicted by applying time-dependent projection operators to nonequilibrium and dynamical environments. Moreover, CD is discussed by considering ET from a donor to an acceptor. It is found that the enhancement of ET by synchronization with coherent phonons depends on the competition between the output time from a system to an acceptor and the formation time of coherent phonons. These findings in this study will stimulate the design and manipulation of CD via structured environments from the viewpoint of application to nano-photoelectronic devices.

DOI： 10.7566/JPSJ.87.054001

Scopus

Other Link： https://journals.jps.jp/doi/abs/10.7566/JPSJ.87.054001

Authorship：Lead author,　Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer  

To design optoelectronic functionalities in nanometer scale based on interactions of electronic system with optical near-fields, it is essential to evaluate the relationship between optical near-fields and their sources. Several theoretical studies have been performed, so far, to analyze such complex relationship to design the interaction fields of several specific scales. In this study, we have performed detailed and high-precision measurements of optical near-field structures woven by a large number of independent polarizations generated in the gold nanorods array under laser light irradiation at the resonant frequency. We have accumulated the multi-layered data of optical near-field imaging at different heights above the planar surface with the resolution of several nm by a STM-assisted scanning near-field optical microscope. Based on these data, we have performed an inverse calculation to estimate the position, direction, and strength of the local polarization buried under the flat surface of the sample. As a result of the inverse operation, we have confirmed that the complexities in the nanometer scale optical near-fields could be reconstructed by combinations of induced polarization in each gold nanorod. We have demonstrated the hierarchical properties of optical near-fields based on spatial frequency expansion and superposition of dipole fields to provide insightful information for applications such for secure multi-layered information storage..

DOI： 10.1007/s00339-017-1478-0

Scopus

Authorship：Corresponding author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：Springer  

DOI： 10.1007/s00339-017-143

Language：English   Publishing type：Research paper (scientific journal)   Publisher：WILEY-V C H VERLAG GMBH  

Excitation transfer in semiconductor nanostructure is an elemental process of next generation optoelectronic devices. Energy relaxation process in exciton transfer from the lowest state of a quantum well to the lowest state of the next well was studied. The energy relaxation process is essential for the completion of the transfer. Longitudinal optical (LO) phonon assisted energy relaxation was found to be most effective for exciton injection into the lowest state of very thin quantum wells on the basis of PLE measurements. A three-quantum-well structure including a 0.6-nm thick (Zn, Cd, Mn) Se well and a 1.2-nm thick (Zn, Cd) Se well separated by a 15-nm ZnSe barrier was prepared. Energy difference of exciton in the two wells was close to the LO phonon energy. The exciton transfer efficiency between the two wells was measured as a function of external magnetic field. (C) 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim

DOI： 10.1002/pssc.201300599

Web of Science

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

We studied the excitation transfer in double quantum wells of a diluted magnetic semiconductor using a scanning near-field optical microscope at 7 K in external magnetic fields up to 9 T. In each quantum well, local energy minima are generated by local fluctuation of layer thickness and doping concentration of magnetic components. Excitons relax into the local energy minima and transfer between the minima via near-field optical interactions even across quantum wells toward stable sites at which to localize. We measured the intensity maps of near-field photoluminescence with spatial resolution estimated to be 30 nm under varying external magnetic fields. The measurement position reproducibility was confirmed by scanning tunneling microscope images. Analysis of the maps derived the magnetic-field dependence of the typical size of exciton-localization sites for each quantum well. Based on these results, we investigated the excitation transfer between the two quantum wells lying in different layers of the double quantum well system, and showed that the exciton transfer takes place at the two specific applied magnetic-field intensities that result in the crossing of Zeeman-split energy levels of the two different wells. We concluded that both the localization and the inter-quantum-well transfer of excitons are able to be controlled by an external magnetic field. This provides the basis for functional devices operating without any wiring.

DOI： 10.1007/s00339-013-8005-8

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：SPRINGER  

Optical near-field (ONF) phenomena observed in nanoscale systems have been applied to nano-fabrication and nano-photoelectronic devices for the last decade. Excitation transfer (ET) is an elementary process caused by ONF interaction localized at the nanoscale in real space. Recently, we have observed spin-dependent ET controlled by an external field and discovered the sign of assistance of phonons. In this work, we elucidate that the assistance of coherent phonons in ET originates from two types of mechanism: energy resonance between exciton levels renormalized by phonon effects and enhancement by phase matching between coherent oscillation of populations and phonon oscillation. This study will stimulate the development of the application of ET via a ONF to nano-photoelectronic devices.

DOI： 10.1007/s00339-013-7929-3

Web of Science

Authorship：Lead author   Language：English   Publishing type：Research paper (scientific journal)   Publisher：ELSEVIER SCIENCE BV  

We have observed the vortex creep in high magnetic field up to 4 Tat low temperature of 0.45 K in a type II superconductor YNi2B2C by scanning tunneling microscopy. The measurement time for one STM image was about 15 s. The fast STM measurements enable the observation of vortex motions in real time and space. Vortex lattices in high magnetic field have been found to be divided into vortex bundles separated by the glide planes of edge dislocations. The elementary motion of the vortex creep is the relative slide between vortex bundles mediated with the glides of dislocations. (C) 2009 Elsevier B.V. All rights reserved.

DOI： 10.1016/j.physc.2009.10.118

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：AMERICAN PHYSICAL SOC  

It is demonstrated theoretically and experimentally that the low energy density of states N(E) is described by a singular V-shape form N(E)=N-0(H)+alpha vertical bar E vertical bar+O(E-2) for all clean superconductors in a vortex state, irrespective of the underlying gap structure. The linear term alpha|E| which has not been recognized so far is obtained by exactly evaluating the vortex contribution. Based on microscopic Eilenberger theory N(E) is evaluated for the isotropic gap, line, and point-node gaps to yield a V-shape N(E). Scanning tunneling spectroscopy-STM experiments on NbSe2 and YNi2B2C give direct evidence for this. We provide arguments on the significance of this finding and on the relevance to other experiments.

DOI： 10.1103/PhysRevLett.97.147001

Web of Science

Language：English   Publishing type：Research paper (scientific journal)   Publisher：PHYSICAL SOC JAPAN  

The local quasi-particle density of states, N-s(E, r), in the isolated vortex of YNi2B2C has been measured at 0.46 K by low-temperature scanning tunneling microscopy and spectroscopy. The vortex core is found to be fourfold-symmetric star-shaped in real space: Near E = 0 meV, N-s(E, r) extends toward (100) (the a-axis) and has a peak at the center of the vortex core. With increasing energy, N-s(E, r) comes to extend toward (110) and the peak of N-s(E, r) splits into four peaks toward (110). N-s(E, r) in the vortex core exhibits electron-hole asymmetry with the intensity, indicating the first observation of the vortex core in a quantum regime.

DOI： 10.1143/JPSJ.73.3247

Web of Science

Event date： 2022.7

Language：English   Presentation type：Oral presentation(general)  

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese   Presentation type：Oral presentation(general)  

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation(general)  

Event date： 2022.3

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese   Presentation type：Oral presentation(general)  

Event date： 2021.11

Language：English   Presentation type：Oral presentation(general)  

Event date： 2021.11

Language：English   Presentation type：Oral presentation(general)  

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Language：English   Presentation type：Oral presentation(general)  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation(general)  

Event date： 2021.9

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese   Presentation type：Oral presentation(general)  

Event date： 2021.3

Language：Japanese   Presentation type：Oral presentation(general)  

Language：Japanese   Presentation type：Oral presentation(general)  

Event date： 2021.3

Language：Japanese   Presentation type：Symposium workshop panel(nominated)  

ナノ領域のフォトクロミズムは、光異性化と結晶歪みの合成により自発的に分岐構造を生む。この構造を通過して検出される光子を用いて、意思決定上普遍的に重要な順序構造の数学的取り扱いであるシューベルト行列を生成した。さらに、この行列を用い複数のスロットマシンの当たり確率に応じた並べ替えに成功した。

Language：Japanese   Presentation type：Symposium workshop panel(nominated)  

ナノ領域のフォトクロミズムは、光異性化と結晶歪みの合成により自発的に分岐構造を生む。この構造を通過して検出される光子を用いて、意思決定上普遍的に重要な順序構造の数学的取り扱いであるシューベルト行列を生成した。さらに、この行列を用い複数のスロットマシンの当たり確率に応じた並べ替えに成功した。

Event date： 2020.8

Language：English   Presentation type：Oral presentation(general)  

Language：English   Presentation type：Oral presentation(general)  

Event date： 2020.3

Language：Japanese   Presentation type：Oral presentation(general)  

Venue：上智大学　四谷キャンパス  

Language：Japanese   Presentation type：Oral presentation(general)  

Venue：上智大学 四谷キャンパス  

Event date： 2019.3

Language：Japanese   Presentation type：Poster presentation  

Venue：東京工業大学大岡山キャンパス  

Event date： 2019.3

Language：Japanese   Presentation type：Oral presentation(general)  

Venue：東京工業大学大岡山キャンパス  

Event date： 2019.3

Language：Japanese   Presentation type：Poster presentation  

Venue：東京工業大学大岡山キャンパス  

Language：Japanese   Presentation type：Oral presentation(general)  

Venue：東京工業大学大岡山キャンパス  

Language：Japanese   Presentation type：Poster presentation  

Venue：東京工業大学大岡山キャンパス  

Language：Japanese   Presentation type：Poster presentation  

Venue：東京工業大学大岡山キャンパス  

Event date： 2018.9

Language：Japanese   Presentation type：Poster presentation  

Venue：名古屋国際会議場  

Event date： 2018.9

Language：Japanese   Presentation type：Poster presentation  

Venue：名古屋国際会議場  

Language：Japanese   Presentation type：Poster presentation  

Venue：名古屋国際会議場  

Language：Japanese   Presentation type：Poster presentation  

Venue：名古屋国際会議場  

Event date： 2018.8

Language：English   Presentation type：Poster presentation  

Venue：France  

Language：English   Presentation type：Poster presentation  

Venue：France