  We study the single-photon transport in a single-mode waveguide, in which
two-level atoms in spatial superpositions are embedded. We find that the
transmission of the photon can be used as a non-destructive probe for coherence
of the superposition. The protocol proposed is shown to be independent of the
distance between the wells in which the atoms are trapped. Furthermore, we show
that by looking at the transmission in a suitable regime, a maximally entangled
state can be post-selected from an unknown superposition.
