Photon-Photon Entanglement with a Single Trapped Atom
  An experiment is performed where a single rubidium atom trapped within a high-finesse optical cavity emits two independently triggered entangled photons. The entanglement is mediated by the atom and is characterized both by a Bell inequality violation of S=2.5, as well as full quantum-state tomography, resulting in a fidelity exceeding F=90%. The combination of cavity-QED and trapped atom techniques makes our protocol inherently deterministic - an essential step for the generation of scalable entanglement between the nodes of a distributed quantum network. 
B. Weber, H. P. Specht, T. Mueller, J. Bochmann, M. Muecke, D. L.   Moehring, and G. Rempe