Quantum telecommunication based on atomic cascade transitions

We report generation of an entangled pair of 1530 nm and 780 nm photons via atomic cascade emission in a cold ensemble of rubidium atoms. The former photon is ideal for long-distance quantum communication, and the latter is naturally suited for mapping to a long-lived atomic memory. Together with our demonstration of photonic-to-atomic qubit conversion, the essential elements for a telecommunication quantum repeater have been realized.