  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.
