  The optical properties of sub-wavelength arrays of atoms or other quantum
emitters have attracted significant interest recently. For example, the strong
constructive or destructive interference of emitted light enables arrays to
function as nearly perfect mirrors, support topological edge states, and allow
for exponentially better quantum memories. In these proposals, the assumed
atomic structure was simple, consisting of a unique electronic ground state.
Within linear optics, the system is then equivalent to a periodic array of
classical dielectric particles, whose periodicity supports the emergence of
guided modes. However, it has not been known whether such phenomena persist in
the presence of hyperfine structure, as exhibited by most quantum emitters.
Here, we show that waveguiding can arise from rich atomic entanglement as a
quantum many-body effect, and elucidate the necessary conditions. Our work
represents a significant step forward in understanding collective effects in
arrays of atoms with realistic electronic structure.
