Photon-Photon Entanglement with an Atom-Cavity System

We report on the implementation of a deterministic protocol where a single rubidium atom trapped within a high-finesse optical cavity mediates entanglement between two subsequent photons [1]. First, the atom is entangled with an emitted single photon. After a chosen time, the atomic state is mapped onto a second photon, thus generating an entangled photon pair. The cavity ensures controlled photon generation and high photon collection efficiencies. Compared to previous experiments [2], our single atom trapping scheme allows for the generation of 10$^{5}$ times more entangled photons per atom. We analyze the entanglement and coherence time of the atomic qubit using a Bell inequality measurement and quantum state tomography. A promising application of trapped atom-cavity systems is deterministic photonic coupling of distant atomic qubits [3]. We report on recent progress towards two-photon interference from two independent systems. \newline \newline [1] B. Weber et al., PRL \textbf{102}, 030501 (2009) \newline [2] T. Wilk et al., Science \textbf{317}, 488 (2007) \newline [3] J.I. Cirac et al., PRL \textbf{78}, 3221 (1997)