arXiv subjects

Juan Jose Saenz

Publications and source records attributed to Juan Jose Saenz.

10 recordsLinked to original sources

arXiv2021

A Chirality-Based Quantum Leap

Chiral degrees of freedom occur in matter and in electromagnetic fields and constitute an area of research that is experiencing renewed interest driven by recent observations of the chiral-induced spin selectivity (CISS) effect in chiral molecules and engineered nanomaterials. The CISS effect underpins the fact that charge transport through nanoscopic chiral structures favors a particular electronic spin orientation, resulting in large room-temperature spin polarizations. Observations of the CISS effect suggest opportunities for spin control and for the design and fabrication of room-temperature quantum devices from the bottom up, with atomic-scale precision. Any technology that relies on optimal charge transport, including quantum devices for logic, sensing, and storage, may benefit from chiral quantum properties. These properties can be theoretically and experimentally investigated from a quantum information perspective, which is presently lacking. There are uncharted implications for the quantum sciences once chiral couplings can be engineered to control the storage, transduction, and manipulation of quantum information. This forward-looking perspective provides a survey of the experimental and theoretical fundamentals of chiral-influenced quantum effects, and presents a vision for their future roles in enabling room-temperature quantum technologies.

cond-mat.mes-hall↗

arXiv2020

Surface-Enhanced Circular Dichroism spectroscopy on periodic dual nanostructures

Increasing the sensitivity of chiral spectroscopic techniques such as circular dichroism (CD) spectroscopy is a current aspiration in the research field of nanophotonics. Enhancing CD spectroscopy depends upon of two complementary requirements: the enhancement of the electromagnetic fields perceived by the molecules under study and the conservation of the helicity of those fields, guaranteed by duality symmetry. In this work, we introduce a systematic method to design nanostructured dual periodic photonic systems capable of enhancing molecular CD spectroscopy resonantly. As an illustration, we engineer a dual 1D silicon nanoparticle array and show that its collective optical modes can be efficiently employed to resonantly enhance by two orders of magnitude the local density of optical chirality and, thus, the CD signal obtained from a given molecular sample on its vicinity.

physics.optics↗

arXiv2019

Sectoral Multipole Focused Beams

We discuss the properties of pure multipole beams with well-defined handedness or helicity, with the beam field a simultaneous eigenvector of the squared total angular momentum and its projection along the propagation axis. Under the condition of hemispherical illumination, we show that the only possible propagating multipole beams are `sectoral' multipoles. The sectoral dipole beam is shown to be equivalent to the non-singular time-reversed field of an electric and a magnetic point dipole Huygens' source located at the beam focus. Higher order multipolar beams are vortex beams vanishing on the propagation axis. The simple analytical expressions of the electric field of sectoral multipole beams, exact solutions of Maxwell's equations, and the peculiar behaviour of the Poynting vector and spin and orbital angular momenta in the focal volume could help to understand and model light-matter interactions under strongly focused beams.

physics.optics↗

arXiv2018

Asymmetry and spin-orbit coupling of light scattered from subwavelength particles

Light scattering and spin-orbit angular momentum coupling phenomena from subwavelength objects, with electric and magnetic dipolar responses, are receiving an increasing interest. Under illumination by circularly polarized light, spin-orbit coupling effects have been shown to lead to significant shifts between the measured and actual position of particles. Here we show that the remarkable angular dependence of these "optical mirages" and those of the intensity, degree of circular polarization (DoCP), and spin and orbital angular momentum of scattered photons, are all linked and fully determined by the dimensionless "asymmetry parameter" g, being independent of the specific optical properties of the scatterer. Interestingly, for g different from 0, the maxima of the optical mirage and angular momentum exchange take place at different scattering angles. In addition we show that the g parameter is exactly half of the DoCP at a right-angle scattering. This finding opens the possibility to infer the whole angular properties of the scattered fields by a single far-field polarization measurement.

physics.optics↗

arXiv2018

Light induced "Mock Gravity" at the nanoscale

The origin of long-range attractive interactions has fascinated scientist along centuries. The remarkable Fatio-LeSage's corpuscular theory, introduced as early as in 1690 and generalized to electromagnetic waves by Lorentz, proposed that, due to their mutual shadowing, two absorbing particles in an isotropic radiation field experience an attractive force which follows a gravity-like inverse square distance law. Similar "Mock Gravity" interactions were later introduced by Spitzer and Gamow in the context of Galaxy formation but their actual relevance in Cosmology has never been unambiguously established. Here we predict the existence of Mock-Gravity, inverse square distance, attractive forces between two identical molecules or nanoparticles in a quasi monochromatic isotropic random light field, whenever the light frequency is tuned to an absorption line such that the real part of the particle's electric polarizability is zero, i.e. at the so-called Froehlich resonance. These interactions are scale independent, holding for both near and far-field separation distances.

physics.optics↗

arXiv2015

Controlling dispersion forces between small particles with artificially created random light fields

Appropriate combinations of laser beams can be used to trap and manipulate small particles with "optical tweezers" as well as to induce significant "optical binding" forces between particles. These interaction forces are usually strongly anisotropic depending on the interference landscape of the external fields. This is in contrast with the familiar isotropic, translationally invariant, van der Waals and, in general, Casimir-Lifshitz interactions between neutral bodies arising from random electromagnetic waves generated by equilibrium quantum and thermal fluctuations. Here we show, both theoretically and experimentally, that dispersion forces between small colloidal particles can also be induced and controlled using artificially created fluctuating light fields. Using optical tweezers as gauge, we present experimental evidence for the predicted isotropic attractive interactions between dielectric microspheres induced by laser-generated, random light fields. These light induced interactions open a path towards the control of translationally invariant interactions with tuneable strength and range in colloidal systems.

physics.optics↗

arXiv2012

Demonstration of zero optical backscattering from single nanoparticles

We present the first experimental demonstration of zero backscattering from nanoparticles at op- tical frequencies as originally discussed by Kerker et. al. [M. Kerker, D. Wang, and C. Giles, J. Opt. Soc. A 73, 765 (1983)]. GaAs pillars were fabricated on a fused silica substrate and the spectrum of the backscattered radiation was measured in the wavelength range 600-1000 nm. Suppression of backscattering occurred at ~725 nm, agreeing with calculations based on the discrete dipole approximation. Particles with zero backscattering provide new functionality for metamaterials and optical antennas.

physics.optics↗

arXiv2006

Controlling absorption resonances from sub-wavelength cylinder arrays

The absorption and extinction spectra of sub-wavelength cylinder arrays are shown to present two different kind of resonances. Close to the Rayleigh anomalies, the diffractive coupling with the lattice periodicity leads to sharp peaks in the extinction spectra with characteristic Fano line shapes for both s and p-polarizations. When the material exhibits an absorption line or in the presence of localized surface plasmon/polaritons, the system is shown to present resonant absorption with wider and symmetric line shapes. For s-polarization our analysis predicts a theoretical limit of 50 % of absorption. Interestingly, for p-polarized light and an appropriate choice of parameters, subwavelength cylinder arrays can present perfect (100 %) absorption.

physics.optics↗

arXiv2005

Spatial wave intensity correlations in quasi-one-dimensional wires

Spatial intensity correlations between waves transmitted through random media are analyzed within the framework of the random matrix theory of transport. Assuming that the statistical distribution of transfer matrices is isotropic, we found that the spatial correlation function can be expressed as the sum of three terms, with distinctive spatial dependences. This result coincides with the one obtained in the diffusive regime from perturbative calculations, but holds all the way from quasi-ballistic transport to localization. While correlations are positive in the diffusive regime, we predict a transition to negative correlations as the length of the system decreases.

cond-mat.mes-hall↗

arXiv2001

Electron correlation in the Si(100) surface

Motivated by the controversy between quantum chemists and solid-state physicists, and by recent experimental results, spin-polarized density-functional (DFT) calculations are used to probe electron correlation in the Si(100) reconstructed surface. The ground state displays antiferromagnetic spin polarization for low dimer inclinations indicating, not magnetic order, but the importance of Mott-like correlations among dangling bonds. The lowest energy corresponds to a higher dimer inclination with no spin. DFT energies, however, should be taken with caution here. Our results together with quantum-chemical findings suggest dimers with highly correlated electrons that tend to buckle due to interactions with other dimers.

cond-mat.mtrl-sci↗