  We experimentally demonstrate a high-fidelity visible-to-telecommunication
wavelength conversion of a photon by using a solid-state-based difference
frequency generation. In the experiment, one half of a pico-second visible
entangled photon pair at 780 nm is converted to a 1522-nm photon, resulting in
the entangled photon pair between 780 nm and 1522 nm. Using superconducting
single-photon detectors with low dark count rates and small timing jitters, we
selectively observed well-defined temporal modes containing the two photons. We
achieved a fidelity of $0.93 \pm 0.04$ after the wavelength conversion,
indicating that our solid-state-based scheme can be used for faithful frequency
down-conversion of visible photons emitted from quantum memories composed of
various media.
