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 periphery of the bowtie gaps, 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.
Highlights
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
The energy loss (EEL) spectrum measured from a Plasmonic cavities (PCs) depends on the position of the electron beam, as different positions excite a different combination of plasmonic modes[18]
When the electron beam passes through the center of the PC gap, a mode at 2.1 eV is excited, whose charge distribution identifies it as the lowest-energy dark mode
Summary
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. 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. When this interaction is large enough to reach the so-called strong coupling limit, coherent excitations comprising both cavity modes and emitter modes are generated by excitation with resonant EM radiation These coherent excitations are manifested by phenomena such as vacuum Rabi splitting, namely the appearance of two branches in optical spectra. Dark modes might be of significant interest for quantum optical studies, since they are expected to have longer lifetimes than bright modes and should be able to store EM energy for longer times[14,15] It is difficult, though, to excite and probe dark modes of individual plasmonic structures, due to their inability to couple radiatively to the far-field. It probes the out-of-plane component of the electric field around a plasmonic device[16], and the EEL signal is closely related to the optical extinction spectrum of a plasmonic structure[16,21,22]
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