Ultrafast Coherent Coupling of Atomic Hyperfine and Photon Frequency   Qubits
  We demonstrate ultrafast coherent coupling between an atomic qubit stored in a single trapped cadmium ion and a photonic qubit represented by two resolved frequencies of a photon. Such ultrafast coupling is crucial for entangling networks of remotely-located trapped ions through photon interference, and is also a key component for realizing ultrafast quantum gates between Coulomb-coupled ions. 
M. J. Madsen, D. L. Moehring, P. Maunz, R. N. Kohn Jr., L.-M. Duan and   C. Monroe