  We investigate the collective non-Markovian dynamics of two fully excited
two-level atoms coupled to a one-dimensional waveguide in the presence of
delay. We demonstrate that analogous to the well-known superfluorescence
phenomena, where an inverted atomic ensemble synchronizes to enhance its
emission, there is a `subfluorescence' effect that synchronizes the atoms into
an entangled dark state depending on the interatomic separation. Our results
are pertinent to long-distance quantum networks, presenting a mechanism for
spontaneous entanglement generation between distant quantum emitters.
