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Hajime Ishihara

Publications and source records attributed to Hajime Ishihara.

28 records · Page 2Linked to original sources
arXiv2016

Two-photon up-conversion affected by inter-molecule correlations near metallic nanostructure

We investigate an efficient two-photon up-conversion process in more than one molecule coupled to an optical antenna. In the previous work [Y. Osaka et al., PRL 112, 133601 (2014)], we considered the two-photon up-conversion process in a single molecule within one-dimensional input-output theory, and revealed that controlling the antenna-molecule coupling enables the efficient up-conversion with radiative loss in the antenna suppressed. In this work, aiming to propose a way to enhance the total probability of antenna-photon scattering, we extend the model to the case of multiple molecules. In general, the presence of more than one molecule decreases the up-conversion probability because they equally share the energy of the two photons. However, it is shown that we can overcome the difficulty by controlling the inter-molecule coupling. Our result implies that, without increasing the incident photon number (light power), we can enlarge the net probability of the two-photon up-conversion.

physics.optics↗
arXiv2015

Up-converted photoluminescence induced by radiative coupling between excitons

We propose an unconventional scheme of photoluminescence in a semiconductor thin film, where the nonlocal correlation between an excitonic wave and a light wave prominently enhances the exciton-light coupling beyond the long-wavelength approximation (the so-called excitonic superradiance regime). On the basis of the developed method extending input-output theory, we elucidate atypical photoluminescence effects due to the strong wave-wave correlation. In particular, the up-converted photoluminescence based on the coherent superposition of excitons is found to be highly efficient, i.e., it can be realized by weak pumping without auxiliary systems such as cavities or photonic antennas.

cond-mat.mes-hall↗
arXiv2015

Enhanced up-conversion of entangled photons and quantum interference under localized field in nanostructures

We theoretically investigate up-conversion process of entangled two photons on a dimer molecule, which is coupled by a cavity or nanoscale metallic structure. Within one-dimensional input-output theory, the propagators of the photons are derived analytically and the up-conversion probability is calculated numerically. It is shown that the coupling with the nanostructure clearly enhances the process. We also find that the enhancement becomes further pronounced for some balanced system parameters such as the quantum correlation between photons, radiation decay rates and coupling between the nanostructure and molecule. The non-monotonic dependencies are reasonably explained in view of quantum interference between the coupled modes of the whole system. This result can provide a guideline for nonlinear optical reactions by weak light of a few photons.

cond-mat.mes-hall↗
arXiv2015

Radiation-Induced Correlation between Molecules Nearby Metallic Antenna Array

We theoretically investigate optical absorption of molecules embedded nearby metallic antennas by using discrete dipole approximation method. It is found that the spectral peak of the absorption is shifted due to the radiation-induced correlation between the molecules. The most distinguishing feature of our work is to show that the shift is largely enhanced even when the individual molecules couple with localized surface plasmons near the different antennas. Specifically, we first consider the case that two sets of dimeric gold blocks with a spacing of a few nanometer are arranged, and reveal that the intensity and spectral peak of the optical absorption strongly depends on the position of the molecules. In addition, when the dimeric blocks and the molecules are periodically arranged, the peak shift is found to increase up to ~1.2 meV (300 GHz). Because the radiation-induced correlation is essential for collective photon emission, our result implies the possibility of plasmon-assisted superfluorescence in designed antenna-molecule complex systems.

cond-mat.mes-hall↗
arXiv2011

Theoretical framework of entangled-photon generation from biexcitons in nano-to-bulk crossover regime with planar geometry

We have constructed a theoretical framework of the biexciton-resonant hyperparametric scattering for the pursuit of high-power and high-quality generation of entangled photon pairs. Our framework is applicable to nano-to-bulk crossover regime where the center-of-mass motion of excitons and biexcitons is confined. Material surroundings and the polarization correlation of generated photons can be considered. We have analyzed the entangled-photon generation from CuCl film, by which ultraviolet entangled-photon pairs are generated, and from dielectric microcavity embedding a CuCl layer. We have revealed that in the nano-to-bulk crossover regime we generally get a high performance from the viewpoint of statistical accuracy, and the generation efficiency can be enhanced by the optical cavity with maintaining the high performance. The nano-to-bulk crossover regime has a variety of degrees of freedom to tune the entangled-photon generation, and the scattering spectra explicitly reflect quantized exciton-photon coupled modes in the finite structure.

quant-ph↗
arXiv2010

Entangled-photon generation in nano-to-bulk crossover regime

We have theoretically investigated a generation of entangled photons from biexcitons in a semiconductor film with thickness in nano-to-bulk crossover regime. In contrast to the cases of quantum dots and bulk materials, we can highly control the generated state of entangled photons by the design of peculiar energy structure of exciton-photon coupled modes in the thickness range between nanometers and micrometers. Owing to the enhancement of radiative decay rate of excitons at this thickness range, the statistical accuracy of generated photon pairs can be increased beyond the trade-off problem with the signal intensity. Implementing an optical cavity structure, the generation efficiency can be enhanced with keeping the high statistical accuracy.

cond-mat.other↗
arXiv2008

QED of excitons with nonlocal susceptibility in arbitrary-structured dielectrics

We have constructed a complete quantum theory for an optical process of excitons with nonlocal susceptibility originating from their center-of-mass motion. This theory provides a practical calculation method for arbitrary-structured nano-to-macro scale dielectrics where excitons are weakly confined. We obtain good correspondences with underlying theories, semiclassical microscopic nonlocal theory, and QED theories for dispersive and absorptive materials with local susceptibility.

physics.optics↗
arXiv2004

Drastic effects of damping mechanisms on the third-order optical nonlinearity

We have investigated the optical response of superradiant atoms, which undergoes three different damping mechanisms: radiative dissipation ($γ_r$), dephasing ($γ_d$), and nonradiative dissipation ($γ_n$). Whereas the roles of $γ_d$ and $γ_n$ are equivalent in the linear susceptibility, the third-order nonlinear susceptibility drastically depends on the ratio of $γ_d$ and $γ_n$: When $γ_d \ll γ_n$, the third-order susceptibility is essentially that of a single atom. Contrarily, in the opposite case of $γ_d \gg γ_n$, the third-order susceptibility suffers the size-enhancement effect and becomes proportional to the system size.

quant-ph↗
arXiv2004

Two-photon nonlinearity in general cavity QED systems

We have investigated the two-photon nonlinearity at general cavity QED systems, which covers both weak and strong coupling regimes and includes radiative loss from the atom. The one- and two-photon propagators are obtained in analytic forms. By surveying both coupling regimes, we have revealed the conditions on the photonic wavepacket for yielding large nonlinearity depending on the cavity Q-value. We have also discussed the effect of radiative loss on the nonlinearity.

quant-ph↗