How much entanglement can be generated between two atoms by detecting   photons?
  It is possible to achieve an arbitrary amount of entanglement between two atoms using only spontaneously emitted photons, linear optics, single photon sources and projective measurements. This is in contrast to all current experimental proposals for entangling two atoms, which are fundamentally restricted to one entanglement bit or ebit. 
L. Lamata, J.J. Garcia-Ripoll, J.I. Cirac