How Much Entanglement Can Be Generated between Two Atoms by Detecting Photons?
Lucas Lamata, Juan José García‐Ripoll, J. I. Cirac · Physical Review Letters · 2007
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."