Toward Cavity Quantum Electrodynamics with Hybrid Photon Gap-Plasmon States

Abstract

Combining localized surface plasmons (LSPs) and diffractive surface waves (DSWs) in metallic nanoparticle gratings leads to the emergence of collective hybrid plasmonic-photonic modes known as surface lattice resonances (SLRs). These show reduced losses and therefore a higher Q factor with respect to pure LSPs, at the price of larger volumes. Thus, they can constitute a flexible and efficient platform for light-matter interaction. However, it remains an open question if there is, in terms of the Q/V ratio, a sizable gain with respect to the uncoupled LSPs or DSWs. This is a fundamental point to shed light upon if such modes want to be exploited, for instance, for cavity quantum electrodynamic effects. Here, using aluminum nanoparticle square gratings with unit cells consisting of narrow-gap disk dimers-a geometry featuring a very small modal volume-we demonstrate that an enhancement of the Q/V ratio with respect to the pure LSP and DSW is obtained for SLRs with a well-defined degree of plasmon hybridization. Simultaneously, we report a 5× increase of the Q/V ratio for the gap-coupled LSP with respect to that of the single nanoparticle. These outcomes are experimentally probed against the Rabi splitting, resulting from the coupling between the SLR and a J-aggregated molecular dye, showing an increase of 80% with respect to the DSW-like SLR sustained by the disk LSP of the dimer. The results of this work open the way toward more efficient applications for the exploitation of excitonic nonlinearities in hybrid plasmonic platforms.

Topological Plasmonic Chain with Retardation and Radiative Effects

“…We also do not include a substrate, which could modify the dispersion relation of the plasmons, 60,61 but is avoidable by making use of a transparent substrate and index matching with the surrounding material. 10 Figure 1b shows the normalized extinction cross section of a single nanoparticle, where the solid lines are quasistatic and the dashed make use of the radiative correction. For particles of 5 nm radius, the QS approximation agrees with the radiative correction, but for particles with radius 20 nm radiative losses strongly affect the extinction cross section by reducing and broadening the resonance over wavelength.…”

Interaction and Coherence of a Plasmon–Exciton Polariton Condensate

“…15 SLRs arise from the coherent radiative coupling of LSPs of individual nanoparticles with diffractive modes propagating in the plane of the array, the so-called Rayleigh anomalies, [16][17][18] and are characterized by a strong suppression of losses (higher quality factor) with respect to individual nanoparticle LSPs, at the expense of a less confined electromagnetic field (larger mode volume). 16,19,20 As hybrid modes arising from a coherent coupling of LSPs, SLRs can maintain the strong EM field enhancement typical of plasmonic nanoparticles, 21,22 while simultaneously extending over the whole lattice area. PEPs in 2D lattices have shown peculiar features due to the unique dispersion of SLRs, [23][24][25][26] which make them similar to exciton polaritons in semiconductor microcavities.…”

Hybrid Plasmonic Modes in Multilayer Trench Grating Structures

“…Here ε d is the dielectric constant of air. Calculating the Q factor of hybrid mode should be meaningful, but the calculation method of LSPRs' hybrid mode reported by Todisco et al is not applicable for this SPP‐based structure . It is a complicated process and we will continue to investigate it in our further study.…”

“…In this case, the enhancement of plasmonic mode coupling through engineering of multiple structures may realize a reduction of the Ohmic losses, and some composite structures are constantly designed to achieve the mode coupling. Exciting surface lattice resonances (SLRs) is a line of thought for reducing losses, but it is usually supported by nanorods or nanoparticles, and coupled with localized surface plasmon resonances (LSPRs) . Thus, further investigations of novel microstructures based on propagating plasmon resonances are necessary.…”