Real-Time Tunable Strong Coupling: From Individual Nanocavities to Metasurfaces

Strong light–matter coupling, characterized by a coherent exchange of energy between an emitter and cavity, plays an important role in, for example, quantum information science and thresholdless lasing. To achieve strong coupling, precise spatial and spectral overlap between the emitter and cavity is required, presenting a significant challenge to move from individually strongly coupled cavities to a large number of cavity-coupled systems, as required for future practical applications. Here we demonstrate a versatile platform for realizing strong coupling that scales uniformly from individual nanocavities up to millimeter-scale metasurfaces, while the coupling strength can be tuned dynamically. Fluorescent dye molecules are sandwiched between silver nanocubes and a metallic film creating a plasmonic cavity with a mode volume of only ∼0.002 (λ/n)3. A prominent anticrossing behavior is observed which corresponds to a large Rabi splitting energy of 152 meV. The plasmon resonance can be tuned up to 45 nm (∼210 meV) enabling real-time control of the Rabi splitting as well as tuning from the weak to the strong coupling regime. This scalable, easily fabricated structure opens the door for use in integrated on-chip nanophotonic devices.