arXiv subjects

Kunio Ishida

Publications and source records attributed to Kunio Ishida.

10 recordsLinked to original sources

arXiv2026

Transient Information Partition in Coherent Exciton-Phonon-Photon Dynamics

We study transient information partition in a coherent exciton-phonon-photon system using subsystem-resolved quantum mutual information (QMI). By employing a model with excitonic, phononic, and photonic degrees of freedom, we analyze the dynamics in the $J$-$ν$ plane, where $J$ characterizes excitonic delocalization and $ν$ denotes the exciton-phonon coupling strength. By comparing time-averaged QMI maps with the absorbed photon number, we show that optical activity alone does not determine the character of the light-induced transient state. The exciton-centered information partition identifies a broad crossover between polariton-like and polaron-like transient responses, depending on whether excitonic information is mainly shared with the photon or phonon subsystem. In contrast, the phonon-centered partition reveals a sharper boundary-adjacent redistribution ridge near the boundary between the zero- and one-exciton ground-state sectors. This ridge is absent from both the ground-state sector map and the photon-absorption map, indicating that it is neither a static sector boundary nor an enhancement of optical absorption. A variational strength-function analysis connects the ridge to a region-II-like finite-energy polaronic excitation whose dominant spectral weight lies near the one-phonon energy, and thus the ridge represents a hidden transient correlation structure in which a limited amount of phonon-related information is preferentially shared with the photon subsystem before being predominantly allocated to exciton-phonon dressing. These results show that QMI-based information partition provides a correlation-based framework for characterizing coherent light-induced transient states in which optical and material degrees of freedom jointly participate quantum mechanically.

quant-ph↗

arXiv2025

Quantum-coherent nonlinear interferometry using electron-phonon systems for entanglement-assisted terahertz sensing

We present a theoretical framework for quantum-coherent nonlinear interferometry in which the nonlinear medium is modeled as active electron-phonon quantum systems rather than a passive $χ^{(2)}$ converter. By explicitly retaining the quantum coherence of the coupled electron-phonon-photon dynamics, our model describes a two-stage buildup of entanglement - first between signal and idler photons and subsequently between idler photons mediated by material coherence. This coherent light-matter interaction imprints the internal dynamics of the medium onto the interferometer output, yielding phase-sensitive interference that enables indirect readout of terahertz-band signal modes via near-infrared detection. The results reveal a route toward entanglement-assisted terahertz sensing and establish a general framework for treating nonlinear quantum media as active components in interferometric architectures.

quant-ph↗

arXiv2023

Dynamics of an Exciton-phonon Triangle under Photoirradiation

Herein, the dynamics of excitons coupled with optical phonons in a triangular system is numerically studied. By representing the excitons by quasi-spin states, the similarity between the chiral spin states and the exciton chiral states is discussed. In particular, the optical control of excitons is discussed, where photoirradiation causes the switching of the exciton states on the ultrafast time scale by Raman scattering. A phase diagram is obtained based on the ground-state properties of the system determined by the magnitudes of the exciton-phonon interactions and exciton transfer energy. By varying the frequency and/or intensity of light, a transition between exciton-phonon composite states is induced, which suggests the possibility of the coherent control of the chiral properties of excitonic systems via phonon excitation.

cond-mat.mes-hall↗

arXiv2021

Two-step dynamics of photoinduced phonon entanglement generation between remote electron-phonon systems

The generation of quantum entanglement between phonons in photoirradiated remote electron-phonon systems is numerically studied. Upon excitation by a visible/ultraviolet laser pulse, the entanglement of electrons is immediately generated and that of phonons follows via electron-phonon interactions, i.e., the entanglement generation of phonons is a two-step process. Therefore, it is important to design the temporal properties of incident optical pulses in order to control the entanglement of electrons and/or phonons. These features are revealed by the quantum mutual information and the composite modes derived from the Heisenberg equation of motion. The calculated results also show that the dynamics of the phonon entanglement can be observed by time-resolved spectroscopy on the scattered light.

cond-mat.mes-hall↗

arXiv2018

Interplay of electron-phonon nonadiabaticity and Raman scattering in the wavepacket dynamics of electron-phonon-photon systems

Ultrafast wavepacket dynamics of electron-phonon-photon systems is studied by numerical calculations. When nonadiabaticity of electron-phonon systems is taken into account, Raman scattering process plays an important role in the dynamics of the system. We found that the interplay of the electron-phonon nonadiabaticity and the Raman scattering determines the wavepacket motion particularly in the vicinity of the conical intersection of adiabatic potential energy surfaces, which shows that we should consider this effect in order to reveal the photoexcitation/deexcitation process of materials in femtosecond time scale.

cond-mat.mes-hall↗

arXiv2016

Doping-Induced Alterations in Electronic Structure of Copper Oxide Superconductors and a New Horizon for Higher Tc materials

By paying special attention to the fact that the doped holes induce deformation of CuO6 octahedrons (or CuO5 pyramids) in cuprate superconductors, we develop a non-rigid band theory treating doping-induced alterations of energy-band structures in copper oxide superconductors. Thanks to this theory, we obtain a complete picture of the doping-induced alteration in the electronic structure of La2CuO4, from the spin-disordered insulating phase to the metallic phase. We conclude that the Fermi surface structure of this cuprate in the underdoped region consists of Fermi pockets in the antinodal region and Fermi arcs in the nodal region, and thus that the origin of a so-called pseudogap is closely related to the existence of Fermi pockets. Moreover, we show that the carriers on the Fermi pockets contribute to the phonon mechanism in d-wave superconductivity. Finally, we discuss how one will be able to find higher Tc materials, based on the conclusions mentioned above.

cond-mat.supr-con↗

arXiv2008

Quantum pattern formation dynamics of photoinduced nucleation process

We study the dynamics of quantum pattern formation processes in molecular crystals which is a concomitant with photoinduced nucleation. Since the nucleation process in coherent regime is driven by the nonadiabatic transition in each molecule followed by the propagation of phonons, it is necessary to take into account the quantum nature of both electrons and phonons in order to pursue the dynamics of the system. Therefore, we employ a model of localized electrons coupled with a quantized phonon mode and solved the time-dependent Schrödinger equation numerically. We found that there is a minimal size of clusters of excited molecules which triggers the photoinduced nucleation process, i.e., nucleation does not take place unless sufficient photoexcitation energy is concentrated within a narrow area of the system. We show that this result means that the spatial distribution of photoexcited molecules plays an important role in the nonlinearity of the dynamics and also of the optical properties observed in experiments. We calculated the conversion ratio, the nucleation rate, and correlation functions to reveal the dynamical properties of the pattern formation process, and the initial dynamics of the photoinduced structural change is discussed from the viewpoint of pattern formation.

cond-mat.other↗

arXiv2007

Nonlinearity in the dynamics of photoinduced nucleation process

Nonlinear dynamics of photoinduced cooperative phenomena is studied by numerical calculations on a model of molecular crystals. We found that the photoinduced nucleation process is triggered only when certain amount of excitation energy is supplied in a narrow part of the system, i.e., there exists a smallest cluster of excited molecules which makes the nucleation possible. As a result, the portion of the cooperatively converted molecules is nonlinearly dependent on the photoexcitation strength, which has been observed in various materials.

physics.comp-ph↗

arXiv2007

Nonlinear optical response of wave packets on quantized potential energy surfaces

We calculated the dynamics of nuclear wave packets in coupled electron-vibration systems and their nonlinear optical responses. We found that the quantized nature of the vibrational modes is observed in pump-probe spectra particularly in weakly interacting electron-vibration systems such as cyanine dye molecules. Calculated results based on a harmonic potential model and molecular orbital calculations are compared with experimental results, and we also found that the materials parameters regarding with the geometrical structure of potential energy surfaces are directly determined by accurate measurement of time-resolved spectra.

physics.chem-ph↗

arXiv2007

Coherent dynamics of photoinduced nucleation processes

We study the dynamics of initial nucleation processes of photoinduced structural change of molecular crystals. In order to describe the nonadiabatic transition in each molecule, we employ a model of localized electrons coupled with a fully quantized phonon mode, and the time-dependent Schrödinger equation for the model is numerically solved. We found a minimal model to describe the nucleation induced by injection of an excited state of a single molecule in which multiple types of intermolecular interactions are required. In this model coherently driven molecular distortion plays an important role in the successive conversion of electronic states which leads to photoinduced cooperative phenomena.

cond-mat.mtrl-sci↗