Polaritonic states in a dielectric nanoguide: localization and strong coupling

Propagation of light through dielectrics lies at the heart of optics. However, this ubiquitous process is commonly described using phenomenological dielectric function \(\varepsilon\) and magnetic permeability \(\mu\), i.e. without addressing the quantum graininess of the dielectric matter. Here, we present a theoretical study where we consider a one-dimensional ensemble of atoms in a subwavelength waveguide (nanoguide) as fundamental building blocks of a model dielectric. By exploring the roles of the atom-waveguide coupling efficiency, density, disorder, and dephasing, we establish connections among various features of polaritonic light-matter states such as localization, super and subradiance, and strong coupling. In particular, we show that coherent multiple scattering of light among atoms that are coupled via a single propagating mode can gives rise to Rabi splitting. These results provide important insight into the underlying physics of strong coupling reported by recent room-temperature experiments with microcavities and surface plasmons.