  We report a single-stage bi-directional interface capable of linking Sr+
trapped ion qubits in a long-distance quantum network. Our interface converts
photons between the Sr+ emission wavelength at 422 nm and the telecoms C-band
to enable low-loss transmission over optical fiber. We have achieved both up-
and down-conversion at the single photon level with efficiencies of 9.4% and
1.1% respectively. Furthermore we demonstrate noise levels that are low enough
to allow for genuine quantum operation in the future.
