Polarization-Driven Reversible Switching between Weak and Strong Coupling in Plasmonic Nanocavities

Achieving dynamic control of light–matter coupling regimes in plasmonic nanocavities at room temperature is pivotal for quantum technologies but remains challenging due to limitations in polarization-selective excitation efficiency. Here, we demonstrate a polarization-driven reversible switch between weak and strong coupling at the vertical incidence. Leveraging radial vector beam (RVB’s) cylindrical symmetry, we generate a confined longitudinal electric field that directly couples to nanoparticle-on-mirror plasmonic modes without sample tilting. This strategy enhances the local electric field by 327-fold (71% higher than linearly polarized beam, LPB) and compresses the mode field volume, amplifying the coupling strength to g = 107 meV, surpassing the strong coupling criterion. Using Rhodamine 800 as a quantum emitter, we demonstrate reversible all-optical switching between a Purcell-enhanced weak coupling regime (under LPB) and a strong coupling regime with 32.8 meV Rabi splitting (under RVB) within the molecule–nanocavity coupling system characterized by highly resolved Rabi splitting in the fluorescence spectra. Further optimization via Au nanoparticle size (R = 40 nm) and collective molecular coupling (N ≥ 5) establishes a ternary synergy for robust quantum control. This noninvasive, polarization-mediated platform enables on-demand manipulation of quantum states for reconfigurable nanophotonic devices.