Extreme Polaritonic Interactions in a Room-Temperature Designable Sub-Nanocavity Quantum Electrodynamic Platform.

Area of Science:

• Quantum physics
• Materials science
• Nanotechnology

Background:

• Nano-cavity quantum electrodynamics (nano-cQED) aims for ultimate light confinement, approaching quantum limits.
• Achieving stable and controllable extreme confinement for nano-cQED remains a significant challenge.
• Picocavities and atomic protrusions are key to emulating extreme confinement.

Purpose of the Study:

• To introduce a novel van der Waals material-based nano-cQED platform.
• To couple monolayer molybdenum disulfide (MoS2) excitons to plasmonic sub-nanocavities.
• To achieve deep-subwavelength mode volumes and study light-matter interactions.

Main Methods:

• Assembled ultrasmall gold clusters (3-5 nm) in a nanoparticle-on-mirror nanocavity nanogap.
• Utilized the lightning-rod effect of gold clusters for resonance-insensitive field confinement.
• Coupled monolayer MoS2 excitons to the plasmonic sub-nanocavities.

Main Results:

• Observed pronounced multi-branch Rabi splittings exceeding 200 meV.
• Achieved a coupling strength of Ω/Γ ≃ 0.8.
• Demonstrated ultrastrong polaritonic photoluminescence with up to 10^4-fold enhancement.

Conclusions:

• The developed platform provides a controllable pathway to picocavity-like behavior.
• This nano-cQED testbed enables exploration of fundamental quantum phenomena.
• Opens new opportunities for single-molecule spectroscopy and advanced nano-cQED research.