Hybrid atom–cavity-induced surface plasmon polaritons

We propose a cavity-assisted scheme to control surface plasmon polaritons (SPPs) on a surface-plasmon-resonance platform comprising a metal film and a dielectric layer embedded in a high-finesse optical cavity. The dielectric hosts a two-level atomic ensemble that couples coherently to a weak probe field and to a quantized cavity mode prepared in vacuum. The probe enters from the vacuum side and impinges on the metal interface at a specific incidence angle. Upon incidence, SPPs are launched at the metal–dielectric interface containing the atoms, and their excitation can be steered by the cavity–atom dynamics. Even without externally driving the cavity, a transparency window emerges when the atom–cavity coupling is strong and the cavity decay rate is much smaller than the atomic damping (κ≪γ). This cavity-induced transparency (CIT), the cavity analogue of electromagnetically induced transparency, suppresses probe absorption, enhances SPP generation, and enables tunable control of spectral line shapes via the coupling strength, detunings, and incident angle. For realistic cavity-QED parameters, we find that the SPP propagation length is on the order of 90μm, with a typical lifetime of about 100 nanoseconds. The optimal resonance occurs at an incidence angle of about 80 degrees and a metal-film thickness of 29 nanometers. SPP excitation is identified through characteristic features in the probe reflectance and transmittance. The scheme thus provides a compact, passive pathway for long-range, long-lifetime SPP control with relevance to cavity QED and plasmonic sensing.