Proposal for Monitoring and Heralding Position States of Atoms in a   One-Dimensional Waveguide
  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. 
Alexandre Roulet, Colin Teo, Huy Nguyen Le, and Valerio Scarani
quant-ph