Vacuum Rabi splitting of a dark plasmonic cavity mode revealed by fast electrons

TL;DR

This paper demonstrates that electron energy loss spectroscopy can detect strong coupling between dark plasmonic modes and quantum emitters in a bowtie nanoantenna, revealing Rabi splitting and advancing the study of non-emissive photonic modes.

Contribution

It introduces a novel application of EEL spectroscopy to probe dark plasmonic modes interacting with quantum emitters, showing strong coupling at the nanoscale.

Findings

Dark plasmonic modes can strongly couple with quantum emitters.

Rabi splitting of up to 85 meV observed in the spectra.

Coupling occurs at the bowtie gap periphery, detectable at the center by EEL.

Abstract

Recent years have seen a growing interest in strong coupling between plasmons and excitons, as a way to generate new quantum optical testbeds and influence chemical dynamics and reactivity. Strong coupling to bright plasmonic modes has been achieved even with single quantum emitters. Dark plasmonic modes fare better in some applications due to longer lifetimes, but are difficult to probe as they are subradiant. Here, we apply electron energy loss (EEL) spectroscopy to demonstrate that a dark mode of an individual plasmonic bowtie can interact with a small number of quantum emitters, as evidenced by Rabi-split spectra. Coupling strengths of up to 85 meV place the bowtie-emitter devices at the onset of the strong coupling regime. Remarkably, the coupling occurs at the bowtie gap periphery, even while the electron beam probes their center. Our findings pave the way for using EEL spectroscopy to study exciton-plasmon interactions involving non-emissive photonic modes.