arXiv subjects

Nobuhiko Yokoshi

Publications and source records attributed to Nobuhiko Yokoshi.

At least 19 recordsLinked to original sources

arXiv2026

Structured-light-mediated hybrid entanglement between photon polarization and electronic orbital angular momentum

We propose a minimal quantum-optical scheme for generating hybrid entanglement between photon polarization and electronic orbital angular momentum in a semiconductor quantum disk. A spin--orbit structured two-photon state excites two channels in the same disk: a radiatively recombining zero-orbital-angular-momentum channel and a finite-orbital-angular-momentum channel that stores the electronic orbital qubit. An effective coherent mapping prepares a selected two-excitation state, followed by emission of a photon whose polarization is entangled with the residual electronic orbital state. A master-equation analysis shows that the heralded state conditioned on single-photon occupation of the selected output mode approaches the target entangled state in the ideal coherent limit. We also discuss orbital relaxation and perturbative validity conditions for branch-dependent Coulomb shifts, orbital-angular-momentum mixing, and finite-orbital-angular-momentum radiative leakage. This proof-of-principle effective model suggests a route toward structured-light-mediated photon--electron hybrid entanglement in semiconductor nanostructures.

quant-ph↗

arXiv2026

Optical vortex probe of loop-current chirality in moir\'e materials

We propose a symmetry-resolved optical probe of intrinsic loop-current chirality in moir\'e materials, with twisted bilayer graphene as a representative realization. Interlayer interference generates chiral electronic circulation on triangular plaquettes, giving rise to an intrinsic geometric chirality that enters the second-order response through a $C_3$-selected angular harmonic of the Berry curvature and can be isolated by the orbital-angular-momentum difference $\Delta\ell$ of interfering optical vortex beams. When moir\'e $C_3$ symmetry is preserved, the intrinsic contribution appears in the $\Delta\ell=3$ channel of the helicity-dependent dc photocurrent, whereas $C_3$-breaking perturbations activate additional channels. These results establish angular-momentum-resolved nonlinear optics as a route to probing geometric chirality in moir\'e and other symmetry-engineered quantum materials.

cond-mat.mes-hall↗

arXiv2026

Nonlocal current-response theory of structured-light dichroism

We develop a nonlocal minimal-coupling theory of structured-light dichroism. Optical absorption is written as a bilinear functional of the incident vector potential and the nonlocal current-response kernel, retaining the spatial structure of optical vortex beams and other inhomogeneous fields. Circular dichroism, helical dichroism, and helical circular dichroism are treated as distinct reversal channels that project different reversal-odd components of the same microscopic response. The resulting signal is resolved into symmetry, tensor, and angular-mode sectors. Single azimuthal-mode fields probe diagonal OAM-channel components, whereas mixed modes access off-diagonal mode-space coherence through interference between different OAM channels. The relative polarization of the mixed field further selects scalar, axial-vector, or rank-2 tensor sectors of the response. This decomposition gives selection rules for high-symmetry systems and a diagnostic scheme for low-symmetry nanophotonic structures, finite systems, and extended materials, where several angular-channel responses may coexist. It also connects the nonlocal current-response formulation to local-gradient descriptions based on spatial dispersion, optical chirality, and tensorial anisotropy.

physics.optics↗

arXiv2026

Effective electron coupling to phonon mechanical angular momentum in helical systems

In chiral crystals, two types of phonon angular momenta have been introduced. One is crystal angular momentum (CAM) arising from the rotational or screw-rotational symmetry and the other is mechanical angular momentum (MAM) associated with the circular motion of atomic displacements about equilibrium positions. Recently, the electron-phonon coupling that respects the screw-rotational symmetry is derived, whereby the CAM between electrons and phonons is interconverted. Here, we show that, in addition to CAM, MAM can also be converted to the electronic degrees of freedom by deriving a second-order perturbative Hamiltonian proportional to phonon MAM. This finding highlights that the electronic motion is directly affected by phonon MAM, and consequently, that phonon degrees of freedom can play a crucial role in phenomena related to electronic orbital polarization.

cond-mat.mtrl-sci↗

arXiv2025

Kelvin-Wave-Inspired Optical Vortex Excitation in Kerr Nonlinear Media

We demonstrate a direct one-to-one correspondence between nonlinear optical fields in defocusing Kerr media and wave functions in weakly interacting Bose-Einstein condensates or quantum fluids. Based on this correspondence, we propose the existence of excitations in an optical vortex beam characterized by a helical deformation of its phase singularity core. These excitations are direct analogues of Kelvin waves known in quantum and classical fluid dynamics. We further show that the excitations exhibit two distinct branches, one of which includes a stationary solution. A feasible experimental scheme for generating these excitations is also discussed.

physics.optics↗

arXiv2024

Description of molecular chirality and its analysis with high harmonic generation

To clarify the microscopic origin of chirality-induced optical effect, we develop an analytical method that extracts the chiral part of the Hamiltonian of molecular electronic states. We demonstrate this method in a model chiral molecule consisting of two helically stacked $N$-sided regular polygons, and compare it with numerical calculation for chiral discrimination via high-harmonic generation (HHG) of the same molecule. The discrimination signal here is the Kuhn $g$ factor, the difference between the harmonic intensity from the bicircular laser field and that from its reflected laser field normalized by their average. The $g$ factor is a pseudoscalar quantity that reflects the chirality of the molecule. As a result, we find that the $g$ factor becomes large over a wide range of harmonic orders making HHG suitable for chiral discrimination. We further find that, to increase the difference of harmonic intensity from the above two fields, the unnormalized $g$ factor, the increase of capacity to generate the longitudinal dipole moment is more advantageous than maximizing the transverse-to-longitudinal conversion efficiency via the optimization of molecular chirality. We speculate this criteria may be extended to other optical and current-induced processes relevant to the chiral molecules and materials.

cond-mat.mtrl-sci↗

arXiv2021

Twisted light-induced spin-spin interaction in a chiral helimagnet

We theoretically investigate how the orbital angular momentum of light can affect a chiral magnetic order. Here, we consider a metallic chiral helimagnet, which is under stationary radiation of a resonant optical vortex beam. We propose a novel interaction between local spins considering microscopic interactions between an optical vortex and electrons. This vortex-induced interaction modulates the chiral magnetic order in an entirely different way than an external magnetic field does. Our spin modulation technique may pave a route to create a unique topological or chiral structure for future opto-spintronics devices.

cond-mat.mes-hall↗

arXiv2020

Theoretical Analysis of Optically Selective Imaging in Photoinduced Force Microscopy

We present a theoretical study of the measurements of photoinduced force microscopy (PiFM) for composite molecular systems. Using the discrete dipole approximation, we calculate the self-consistent response electric field of the entire sample including the PiFM tip, substrate, and composite molecules. We demonstrate a higher sensitivity for the PiFM measurement on resonant molecules than by the previously obtained tip-sample distance dependency $z^{-4}$ owing of the multifold enhancement of the field between the localized electric field induced at the tip-substrate nanogap and the molecular polarization. The enhanced localized electric field induced at the tip-substrate nanogap in PiFM allows high-resolution observation of the forbidden optical electronic transition in dimer molecules. We investigated the wavelength dependence of PiFM for dimer molecules and obtained images at incident light wavelengths corresponding to allowed and forbidden transitions. We reveal that these PiFM images drastically change with the frequency-dependent spatial structures of the localized electric field vectors and resolve different types of nanoparticles beyond the resolution for the optically allowed transitions. This study demonstrates that PiFM provides multifaceted information based on microscopic interactions between nanomaterials and light.

physics.optics↗

arXiv2017

Weak-Light Nonlinearity Using a Dark State in Coupled Quantum Dots

We propose a scheme to induce weak-light nonlinearity in a double quantum dot. The scheme positively utilizes locality and dissipation of an external auxiliary system. As a plausible setup, we consider a complex system in which a localized plasmon field from a metallic nanotip couples with only one of the coupled quantum dots. The perturbative calculation with respect to the light intensity shows that, even by a sufficiently weak light, a dipole-forbidden two-exciton NOON state is prepared as the steady state. This result can be explained by combining the two factors: decoherence-induced quantum state preparation and two-photon resonance. The present work implies that the positive usage of both the locality and the dissipation in the external auxiliary system is promising for inducing two-photon processes effectively, and provides one guideline to weak-light nonlinearities.

cond-mat.mes-hall↗

arXiv2017

Synchronization dynamics in a designed open system

We theoretically propose a unifying expression for synchronization dynamics between two-level constituents. Although synchronization phenomena require some substantial mediators, the distinct repercussions of their propagation delays remain obscure, especially in open systems. Our scheme directly incorporates the details of the constituents and mediators in an arbitrary environment. As one example, we demonstrate the synchronization dynamics of optical emitters on a dielectric microsphere. We reveal that the whispering gallery modes (WGMs) bridge the well-separated emitters and accelerate the synchronized fluorescence, known as superfluorescence. The emitters are found to overcome the significant and nonuniform retardation, and to build up their pronounced coherence by the WGMs, striking a balance between the roles of resonator and intermediary. Our work directly illustrates the dynamical aspects of many-body synchronizations and contributes to the exploration of research paradigms that consider designed open systems.

cond-mat.other↗

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↗

arXiv2010

Proposal of a full Bell state analyzer for spin qubits in a double quantum dot

We propose a scheme for full Bell state measurement of spin qubits in a double quantum dot. Our scheme consists of Pauli spin-blockade measurements and biaxial electron-spin resonance. In order to eliminate the average of the Zeeman fields, the double quantum dot is designed so that the Landé g-factors of first and second dots satisfy g1=g2 with the use of g-factor engineering. Thus, we can swap one of the three spin-triplet states for the spin-singlet state without disturbing the other states. Our study shows that the sequential spin-to-charge conversions enable us to implement the full Bell state measurement of electron-spin qubits.

cond-mat.mes-hall↗

arXiv2010

Instability of superfluid Fermi gases induced by a roton-like density mode in optical lattices

We study the stability of superfluid Fermi gases in deep optical lattices in the BCS--Bose-Einstein condensation (BEC) crossover at zero temperature. Within the tight-binding attractive Hubbard model, we calculate the spectrum of the low-energy Anderson-Bogoliubov (AB) mode as well as the single-particle excitations in the presence of superfluid flow in order to determine the critical velocities. To obtain the spectrum of the AB mode, we calculate the density response function in the generalized random-phase approximation applying the Green's function formalism developed by Côté and Griffin to the Hubbard model. We find that the spectrum of the AB mode is separated from the particle-hole continuum having the characteristic rotonlike minimum at short wavelength due to the strong charge-density-wave fluctuations. The energy of the rotonlike minimum decreases with increasing the lattice velocity and it reaches zero at the critical velocity which is smaller than the pair breaking velocity. This indicates that the superfluid state is energetically unstable due to the spontaneous emission of the short-wavelength rotonlike excitations of the AB mode instead due to pair-breaking. We determine the critical velocities as functions of the interaction strength across the BCS-BEC crossover regime.

cond-mat.quant-gas↗

arXiv2009

Electrical measurement of a two-electron spin state in a double quantum dot

We propose a scheme for electrical measurement of two-electron spin states in a semiconductor double quantum dot. We calculated the adiabatic charge transfer when surface gates are modulated in time. Because of spin-orbit coupling in the semiconductor, spatial displacement of the electrons causes a total spin rotation. It follows that the expectation value of the transferred charge reflects the relative phase as well as the total spin population of a prepared singlet-triplet superposition state. The precise detection of the charge transfer serves to identify the quantum superposition.

cond-mat.mes-hall↗

arXiv2009

Stability of superfluid Fermi gases in optical lattices

Critical velocities of superfluid Fermi gases in optical lattices are theoretically investigated across the BCS-BEC crossover. We calculate the excitation spectra in the presence of a superfluid flow in one- and two-dimensional optical lattices. It is found that the spectrum of low-lying Anderson-Bogoliubov (AB) mode exhibits a roton-like structure in the short-wavelength region due to the strong charge density wave fluctuations, and with increasing the superfluid velocity one of the roton-like minima reaches zero before the single-particle spectrum does. This means that superfluid Fermi gases in optical lattices are destabilized due to spontaneous emission of the roton-like AB mode instead of due to Cooper pair breaking.

cond-mat.other↗