Transformation Optics Approach to Plasmon-Exciton Strong Coupling in Nanocavities

Abstract

We investigate the conditions yielding plasmon-exciton strong coupling at the single emitter level in the gap between two metal nanoparticles. A quasi-analytical transformation optics approach is developed that makes possible a thorough exploration of this hybrid system incorporating the full richness of its plasmonic spectrum. This allows us to reveal that by placing the emitter away from the cavity center, its coupling to multipolar dark modes of both even and odd parity increases remarkably. This way, reversible dynamics in the population of the quantum emitter takes place in feasible implementations of this archetypal nanocavity.PACS numbers: 73.20. Mf, 42.50.Nn, 71.36.+c Plasmon-exciton-polaritons (PEPs) are hybrid lightmatter states that emerge from the electromagnetic (EM) interaction between surface plasmons (SPs) and nearby quantum emitters (QEs) [1,2]. Crucially, PEPs only exist when these two subsystems are strongly coupled, i.e., they exchange EM energy coherently in a time scale much shorter than their characteristic lifetimes. Recently, much attention has focused on PEPs, since they combine the exceptional light concentration ability of SPs with the extreme optical nonlinearity of QEs. These two attributes makes them promising platforms for the next generation of quantum nanophotonic components [3].A quantum electrodynamics description of plasmonic strong coupling of a single QE has been developed for a flat metal surface [4], and isolated [5,6] and distant nanoparticles [7][8][9], where SP hybridization is not fully exploited. From the experimental side, in recent years, PEPs have been reported in emitter ensembles [10][11][12][13], in which excitonic nonlinearities are negligible [14][15][16]. Only very recently, thanks to advances in the fabrication and characterization of large Purcell enhancement nanocavities [17][18][19], far-field signatures of plasmonexciton strong coupling for single molecules have been reported experimentally [20].In this Letter, we theoretically investigate the plasmonic coupling of a single emitter in a paradigmatic cavity: the nanometric gap between two metallic particles [13,19,20]. We consider spherical-shaped nanoparticles, and develop a transformation optics (TO) [21,22] approach that fully accounts for the rich EM spectrum that originates from SP hybridization across the gap. Our method, which is the first application of TO concepts to treat quantum optical phenomena, yields quasianalytical insight into the Wigner-Weisskopf problem [23] for these systems, and enables us to reveal the prescriptions that nanocavities must fulfil to support single QE PEPs. (1) level system (with transition frequency ω E and z-oriented arXiv:1605.09443v2 [cond-mat.mes-hall]

Aluminum Nanotripods for Light‐Matter Coupling Robust to Nanoemitter Orientation

“…As the dipole source approaches the nanotripod core, rises gradually, indicating that the emitter‐LSP coupling strengthens. The enhancement in the light‐matter interaction originates from the excitation of higher order LSPs; the closer the nanoemitter is to the nanostructure surface, the more efficiently it couples to higher order LSPs . This holds true for any nanotripod geometry as the results for θ′ = 25° demonstrates in Figure S10.…”

“…Similar strategies have proven to be very successful in the case of crescent‐shaped and dimer antennas . More recently, TO‐based approaches have also been extended to the description of weak and strong coupling phenomena …”

Non-Markovian dynamics in plasmon-induced spontaneous emission interference

“…The above phenomena have been demonstrated mostly experimentally in the perturbative (weak-coupling) regime wherein quantum dynamics is irreversible [13][14][15][16][17][18][19] . Nevertheless, recently strong coupling at room temperature between an organic molecule and a plasmonic nanocavity has been demonstrated experimentally 20 , followed by a detailed theoretical analysis 21 . In this work we study theoretically the population dynamics of a V-type QE coupled electromagnetically to a MNP.…”

Suppressed Quenching and Strong-Coupling of Purcell-Enhanced Single-Molecule Emission in Plasmonic Nanocavities

“…Isolated spherical nanoparticle follow the well-known Mie theory, but the problem of two coupled plasmonic nanoparticles is analytically more complex. It has been solved in the quasi-static limit using several techniques, such as transformation optics [27][28][29] and multipole expansion [22][23][24]30]. However, here the formalism of [20,21] is more appropriate since it accounts for the coupling of the bare modes of the two plasmonic structures.…”

“…2(c,d)], which corresponds to the superposition of multiple highorder plasmonic modes, recently referred to as a 'pseudomode' [27,33]. However, the negligibleγ rad at λ pm shows the largeγ tot comes from emission coupled to the pseudo-mode decaying via non-radiative channels (γ tot =γ rad +γ nr ).…”