  We study the correlated transport of photons through a chain of three-level
emitters that are coupled chirally to a photonic mode of a waveguide. It is
found that this system can transfer a classical input into a strongly
correlated state of light in a unitary manner, i.e. without the necessity of
nonlinear photon losses. In particular, we shows that the collective
interaction with the emitter ensemble leads to the emergence of highly
antibunched light with long-range correlations upon crossing a critical length
of the chain. By operating close to conditions of electromagnetically induced
transparency of the three-level medium, the high degree of antibunching and
photon transmission can be maintained in the presence of moderate losses. These
features, combined with the robustness against number fluctuations, suggest a
promising mechanism for single-photon generation and may open the door to
exploring correlated quantum many-body states of light.
