Bound states and entanglement generation in waveguide quantum   electrodynamics
  We investigate the behavior of two quantum emitters (two-level atoms) embedded in a linear waveguide, in a quasi-one-dimensional configuration. Since the atoms can emit, absorb and reflect radiation, the pair can spontaneously relax towards an entangled bound state, under conditions in which a single atom would instead decay. We analyze the properties of these bound states, which occur for resonant values of the interatomic distance, and discuss their relevance with respect to entanglement generation. The stability of such states close to the resonance is studied, as well as the properties of non resonant bound states, whose energy is below the threshold for photon propagation. 
Paolo Facchi, M. S. Kim, Saverio Pascazio, Francesco V. Pepe, Domenico   Pomarico, Tommaso Tufarelli
quant-ph