arXiv subjects

Mario Zapata-Herrera

Publications and source records attributed to Mario Zapata-Herrera.

10 recordsLinked to original sources

arXiv2026

Extreme Optical Field Confinement and Enhancement in a Plasmonic Picopatch within a Nanoparticle-on-Mirror Resonator

Plasmonic resonances in metallic nanogaps can confine light into nanometric regions, but reaching modes of volume $\approx 1$ nm$^3$ remains challenging. We present a detailed theoretical analysis of the optical modes of an experimentally-motivated nanoresonator configuration that contains a picopatch formed by the lifting of a few gold atoms in the gap of a Nanoparticle-on-Mirror (NPoM) structure. Classical simulations indicate that the plasmonic modes associated with the picopatch geometry can confine light to extremely small regions and are highly sensitive to the picopatch size and shape, enabling broad tunability. Furthermore, these modes can couple strongly with other nanocavity modes of the structure, as identified from a clear anti-crossing behavior of the polaritonic resonances. Remarkably, up to $\approx 2000$-fold electric field enhancement inside the picopatch and tiny effective mode volumes approaching $\approx 1$ nm$^3$ are obtained. Further, changing the morphology of the picopatch does not modify the qualitative findings, and increasing the absorption losses in the classical simulations, to mimic quantum (non-local) effects in the metal permittivity, decreases the electric field enhancement only moderately. Compared to the standard picocavities formed by single-atom protrusions, picopatches are an intriguing alternative to reach extreme optical field confinement and enhancement in plasmonic cavities.

physics.optics↗

arXiv2025

Nano-resolved sensing of 3D electromagnetic fields via single emitters' extreme variation of enhanced spontaneous emission

Controlling quantum light-matter interactions at scales smaller than the diffraction limit at the single quantum emitter level is a critical challenge to the goal of advancing quantum technologies. We introduce a novel material platform that enables precise engineering of spontaneous emission changes in molecular single emitters through 3D nanofields. This platform is based on a 3D hollow plasmonic nanomaterial arranged in a square lattice, uniformly scalable to the centimeter scale while maintaining unit cell geometry. This coupled system leads to billions of Purcell-enhanced single emitters integrated into a nanodevice. Using far-field single-molecule super-resolution microscopy, we investigate emission modifications at the single-emitter level, enabling molecular position sensing with resolution surpassing the diffraction limit. By combining the nanolocalization with time correlation single photon counting, we probe molecule per molecule enhanced quantum light-matter interactions. This 3D plasmonic geometry significantly enhances light-matter interactions, revealing a broad range of lifetimes -- from nanoseconds to picoseconds -- significantly increasing the local density of states in a manner that depends on both molecular position and dipole orientation, offering extreme position sensitivity within the 3D electromagnetic landscape. By leveraging these plasmonic nanostructures and our method for measuring single-molecule Purcell-enhanced nano-resolved maps, we enable fine-tuned control of light-matter interactions. This approach enables the on-demand control of fast single-photon sources at room temperature, providing a powerful tool for molecular sensing and quantum applications at the single-emitter level.

physics.optics↗

arXiv2024

Chiro-Optical Structures with Magnetizable Plasmonic Elements for Modulating the Chiral Transmission of Light

Manipulating external stimuli is crucial for enhancing and controlling the optical response in chiral structures. This study introduces chiral structures composed of single, dimer, or trimer arrays of plasmonic and magneto-plasmonic trapezoidal and triangular nanoantennas. Through modeling, we demonstrate how these systems can (i) function as chiral metasurfaces, (ii) modulate chiral light absorption via an external magnetic field, (iii) magnetically enhance the chiro-optical response, and (iv) improve the chiro-optical and magneto-chiral response through structural engineering. By optimizing the nanoantenna geometry, we achieve enhancements larger than 100 in the chiro-optical signal of a magnetized Ni monomer compared to a non-magnetized system. Additionally, we model bimetallic systems, showing a ~2-fold increase in chiro-optical response for hybrid Au and Ni magneto-plasmonic systems compared to purely plasmonic Au systems, while simultaneously enabling magnetic tuning of the optical response. Our results highlight the potential of structurally engineered magneto-plasmonic nanoantennas for advanced applications in chiro-optical sensing and tunable photonic devices.

physics.optics↗

arXiv2024

Giant Purcell broadening and Lamb shift for DNA-assembled near-infrared quantum emitters

Controlling the light emitted by individual molecules is instrumental to a number of novel nanotechnologies ranging from super-resolution bio-imaging and molecular sensing to quantum nanophotonics. Molecular emission can be tailored by modifying the local photonic environment, for example by precisely placing a single molecule inside a plasmonic nanocavity with the help of DNA origami. Here, using this scalable approach, we show that commercial fluorophores experience giant Purcell factors and Lamb shifts, reaching values on par with those recently reported in scanning tip experiments. Engineering of plasmonic modes enables cavity-mediated fluorescence far detuned from the zero-phonon-line (ZPL) - at detunings that are up to two orders of magnitude larger than the fluorescence linewidth of the bare emitter and reach into the near-infrared. Our results evidence a regime where the emission linewidth is dominated by the excited state lifetime, as required for indistinguishable photon emission, baring relevance to the development of nanoscale, ultrafast quantum light sources and to the quest toward single-molecule cavity-QED. In the future, this approach may also allow to design efficient quantum emitters at infrared wavelengths, where standard organic sources have a reduced performance.

physics.optics↗

arXiv2023

On-demand reversible switching of the emission mode of individual semiconductor quantum emitters using plasmonic metasurfaces

The field of quantum technology has been rapidly expanding in the past decades, yielding numerous applications as quantum information, quantum communication and quantum cybersecurity. The central building block for these applications is a quantum emitter (QE), a controllable source of single photons or photon pairs. Semiconductor QEs such as perovskite nanocrystals (PNCs) and semiconductor quantum dots (QDs) have been demonstrated to be a promising material for pure single-photon emission, and their hybrids with plasmonic nanocavities may serve as sources of photon pairs. Here we have designed a system in which individual quantum emitters and their ensembles can be traced before, during, and after the interaction with the external plasmonic metasurface in controllable way. Upon coupling the external plasmonic metasurface to the array of QEs, the individual QEs switch from single-photon to photon-pair emission mode. Remarkably, this method does not affect the chemical structure and composition of the QEs, allowing them to return to their initial state after decoupling from the plasmonic metasurface. By employing this approach, we have successfully demonstrated the reversible switching of the ensemble of individual semiconductor QEs between single-photon and photon pair emission modes. This significantly broadens the potential applications of semiconductor QEs in quantum technologies.

physics.optics↗

arXiv2023

Molecular-Induced Chirality Transfer to Plasmonic Lattice Modes

Molecular chirality plays fundamental roles in biology. The chiral response of a molecule occurs at a specific spectral position, determined by its molecular structure. This fingerprint can be transferred to other spectral regions via the interaction with localized surface plasmon resonances of gold nanoparticles. Here, we demonstrate that molecular chirality transfer occurs also for plasmonic lattice modes, providing a very effective and tunable means to control chirality. We use colloidal self-assembly to fabricate non-close packed, periodic arrays of gold nanoparticles, which are embedded in a polymer film containing chiral molecules. In the presence of the chiral molecules, the SLRs become optically active, i.e. showing handedness-dependent excitation. Numerical simulations with varying lattice parameters show circular dichroism peaks shifting along with the spectral positions of the lattice modes, corroborating the chirality transfer to these collective modes. A semi-analytical model based on the coupling of molecular and plasmonic resonances rationalizes this chirality transfer.

physics.optics↗

arXiv2021

Hybrid Photonic-Plasmonic Cavities based on the Nanoparticle-on-a-Mirror Configuration

Hybrid photonic-plasmonic cavities have emerged as a new platform to increase light-matter interaction capable to enhance the Purcell factor in a singular way not attainable with either photonic or plasmonic cavities separately. In the hybrid cavities proposed so far, mainly consisting of metallic bow-tie antennas, the plasmonic gap sizes defined by lithography in a repeatable way are limited to minimum values \approx 10 nm. Nanoparticle-on-a-mirror (NPoM) cavities are far superior to achieve the smallest possible mode volumes, as gaps smaller than 1 nm can be created. Here, we design a hybrid cavity that combines a NPoM plasmonic cavity and a dielectric-nanobeam photonic crystal cavity operating at transverse-magnetic (TM) polarization. The metallic nanoparticle can be placed very close (< 1 nm) to the upper surface of the dielectric cavity, which acts as a low-reflectivity mirror. We demonstrate through numerical calculations that this kind of hybrid plasmonic-photonic cavity architecture exhibits quality factors, Q, above 10^{3} and normalized mode volumes, V , down to 10^{\num{-3}}, thus resulting in high Purcell factors (FP \approx 10^5), whilst being experimentally feasible with current technology. Our results suggest that hybrid cavities with sub-nm gaps should open new avenues for boosting light-matter interaction in nanophotonic systems.

physics.optics↗

arXiv2021

Ultrafast demagnetization in a ferrimagnet under electromagnetic field funneling

The quest to improve density, speed and energy efficiency of magnetic memory storage has led to exploration of new ways of optically manipulating magnetism at the ultrafast time scale, in particular in ferrimagnetic alloys. While all-optical magnetization switching is well-established on the femtosecond timescale, lateral nanoscale confinement and thus potential significant reduction of the size of the magnetic element remains an outstanding challenge. Here we employ resonant electromagnetic energy-funneling plasmon nanoantennas to influence the demagnetization dynamics of a ferrimagnetic TbCo alloy thin film. We demonstrate how Ag nanoring-shaped antennas under resonant optical femtosecond pumping reduce the overall magneto-optical response due to demagnetization in the underlying films up to three times compared to non-resonant illumination. We attribute such substantial reduction to the nanoscale confinement of the demagnetization process. This is qualitatively supported by the electromagnetic simulations that strongly evidence the optical energy-funneling to the nanoscale from the nanoantennas into the ferrimagnetic film. This is the first and defining step for reaching deterministic ultrafast all-optical magnetization switching at the nanoscale in such systems, opening a route to develop nanoscale ultrafast magneto-optics.

physics.optics↗

arXiv2016

Near field enhancement due to the optical response of small nanoparticles

In this work we study the strong confinement effects on the electromagnetic response of metallic nanoparticles. We calculate the field enhancement factor for nanospheres of various radii by using optical constants obtained from both classical and quantum approaches and compare their size-dependent features. To evaluate the scattered near-field, we solve the electromagnetic wave equation within a finite element framework. When quantization of electronic states is considered for the input optical functions, a significant blue-shift in the resonance of the enhanced field is observed, in contrast to the case in which functions obtained classically are used. Furthermore, a noticeable underestimation of the field amplification is found in the calculation based on a classical dielectric function. Our results are in good agreement with available experimental reports and provide relevant information on the cross-over between classical and quantum regime, useful in potentiating nanoplasmonics applications.

cond-mat.mes-hall↗

arXiv2014

Size change effect on the optical behavior of ultra small metal particles

In this paper we analyse the importance of a detailed description of the electronic transitions in ultra-small nanoparticles through the optical response to very small changes of size in systems, whose dimensions are in the subnanometric scale. We present a carefully calculation of the optical response of these systems by using the exact eigen-energies and wave functions for nanospheres with diameter smaller than 10nm, to obtain the dielectric function under different conditions of confinement. The aim is to use the so obtained dielectric function to present the absorption spectra of one electron confined in a sphere in two cases: 1) infinite confinement and 2) finite confinement, in which, the value of the wells depth is carefully calculated after adjusting the number of atoms that composed each sphere, so that the energies and dipole matrix elements give a more accurate information of the optical response. Moreover, we extend the calculation of this dielectric function for obtaining the optical constants needed to find the plasmon frequency, throught a numerical method of finite elements that solves the Maxwells equations, in order to obtain the enhancement of the near electric field. We show an interesting behavior for particles sizes less than 10 nm, finding that the variation induced in the eigen-energies, through slight size changes in the particle, provides significant variations in the optical response of these nanoparticles. This effect, can be observed in the optical absorption spectra and in the localized surface plasmon energies as confirmed in recent observation of plasmonic phenomena at the subnanometer to atomic scale.

cond-mat.mes-hall↗