Demonstration of a stable atom-photon entanglement source for quantum repeaters

We demonstrate a novel way to efficiently create a robust entanglement between an atomic and a photonic qubit. A single laser beam is used to excite one atomic ensemble and two different modes of Raman fields are collected to generate the atom-photon entanglement. With the help of built-in quantum memory, the entanglement still exists after 20.5 mu s storage time which is further proved by the violation of Clauser-Horne-Shimony-Holt type Bell's inequality. The entanglement procedure can serve as a building block for a novel robust quantum repeater architecture [Zhao , Phys. Rev. Lett. 98, 240502 (2007)] and can be extended to generate high-dimensional atom-photon entanglements.