  We perform the first demonstration of a quantum interface for frequency
down-conversion from visible to telecommunication bands by using a nonlinear
crystal. This interface has a potential to work over wide bandwidths, leading
to a high-speed interface of frequency conversion. We achieve the conversion of
a pico-second visible photon at 780 nm to a 1522-nm photon, and observe that
the conversion process retain entanglement between the down-converted photon
and another photon.
