  Chirality, or handedness, is a geometrical property denoting a lack of mirror
symmetry. Chirality is ubiquitous in nature and is associated with the
non-reciprocal interactions observed in complex systems ranging from
biomolecules to topological materials. Here, we demonstrate that chiral
arrangements of dipole-coupled atoms or molecules can facilitate the
unidirectional transport of helical photonic excitations without breaking
time-reversal symmetry. We show that such helicity dependent transport stems
from an emergent spin-orbit coupling induced by the chiral geometry, which
results in nontrivial topological properties. We also examine the effects of
collective dissipation and find that many-body coherences lead to helicity
dependent photon emission: an effect we call helical superradiance. Our results
demonstrate an intimate connection between chirality, topology, and photon
helicity that may contribute to molecular photodynamics in nature and could be
probed with near-term quantum simulators.
