Strong coupling as an interplay of quantum emitter hybridization with plasmonic dark and bright modes

Abstract

Strong coupling between a single quantum emitter and an electromagnetic mode is one of the key effects in quantum optics. In the cavity QED approach to plasmonics, strongly coupled systems are usually understood as single-transition emitters resonantly coupled to a single radiative plasmonic mode. However, plasmonic cavities also support nonradiative (or "dark") modes, which offer much higher coupling strengths. On the other hand, realistic quantum emitters often support multiple electronic transitions of various symmetries, which could overlap with higher order plasmonic transitions-in the blue or ultraviolet part of the spectrum. Here, we show that despite very large detuning between a bright mode and an excitonic transition, their strong coupling can be ensured by leveraging higher energy dark modes of the optical cavity. Specifically, when a dark mode interacts strongly with an excitonic transition, the lower polariton of the hybridized spectrum can be pushed to energies of the bright mode. The resulting interaction of the lower dark-mode-exciton polariton and bright mode yields significant vacuum Rabi splitting, which hinges on the existence of the dark mode. We develop a simple model illustrating the modification of the system response in the "dark" strong coupling regime and demonstrate single photon nonlinearity. These results may find important implications in the emerging field of room-temperature quantum plasmonics.

Collective strong coupling in a plasmonic nanocavity

“…This results from the collective coupling of all N e emitters to the dipolar LSP 1 mode. The LSP 1 mode radiatively leaks into the far-field so that such strong coupling regime can be recorded in the far-field zone [14,30]. For N e ∼ 50 the two strong coupling regimes occur at the same QE emission frequency ω 0 ≈ 2.85 eV and the two Rabi splittings become difficult to separate for higher number of QEs.…”

Strong Dipole-Quadrupole-Exciton Coupling Realized in a Gold Nanorod Dimer Placed on a Two-Dimensional Material

“…In order to explore the rich physics of polaritons, however, it is highly desirable to further enhance the coupling strength between plasmons and excitons. On the one hand, it was predicted that the nonradiative dark mode can enhance the coupling strength between a nanocavity and quantum emitters [ 42 ]. On the other hand, the strong coupling of three excitations has become the focus of many studies.…”

Greatly Enhanced Plasmon–Exciton Coupling in Si/WS2/Au Nanocavities

“…On the other hand, it was predicted that a nonradiative (or "dark") mode can be used to boost the coupling of a nanocavity with quantum emitters. 44 It has been demonstrated that strong photon−exciton coupling with a Rabi splitting of ∼190 meV can be realized by exploiting the "anapole" formed in a single nanodisk made of TMDCs. 45,46 This finding reminds us that the dark mode involved in the Fano resonance, which was revealed in Si/Au hybrid nanocavities, 36 can be exploited to realize strong coupling with the WS 2 monolayer.…”