  Fiber-based quantum networks require photons at telecommunications
wavelengths to interconnect qubits separated by long distances. Trapped ions
are leading candidates for quantum networking with high-fidelity two-qubit
gates, long coherence times, and the ability to readily emit photons entangled
with the ion's internal qubit states. However, trapped ions typically emit
photons at wavelengths incompatible with telecommunications fiber. Here, we
demonstrate frequency conversion of visible photons, emitted from the S-P
dipole transition of a trapped Ba+ ion, into the telecommunications C-band.
These results are an important step towards enabling a long-distance trapped
ion quantum internet.
