Strong coupling of a quantum emitter in a plasmonic dimer

We present a theoretical description of the electromagnetic coupling between a two-level system and the localized modes supported by the most paradigmatic plasmonic cavity: a pair of metallic spheres separated by a nanometric gap. Our method exploits the invariance of Maxwell's Equations under geometric transformations to obtain analytical expressions for the spectral density evaluated in the surroundings of this nanostructure. We use this tool to perform a thorough analysis of the Wigner-Weisskopf problem for this system. Specifically, we investigate in detail the material and geometric conditions giving rise to single exciton-plasmon strong coupling phenomena.