Two-level quantum system as a macroscopic scatterer for ultraconfined two-dimensional photonic modes

Abstract

We study the scattering of a single photon in the surface plasmon polariton mode propagating on a two-dimensional surface, by a two-level quantum system in the regime where the photon wavelength becomes comparable or smaller than the size of the electron wave function. In this interesting regime, the scattering spectral signature becomes highly dependent on the shape of the ground and excited state electron wave functions and shows a significant departure from the Lorentzian response obtained from the usual perturbative method of multipole expansion. We interpret the observed multipeaked line shape by considering the two-level atom as a combination of a quantum system with macroscopic current distribution which adds structural resonances to the radiation spectrum.