  On-demand single-photon sources emitting pure and indistinguishable photons
at the telecommunication wavelength are a critical asset towards the deployment
of fiber-based quantum networks. Indeed, single photons may serve as flying
qubits, allowing communication of quantum information over long distances.
Self-assembled InAs quantum dots embedded in GaAs constitute an excellent
nearly deterministic source of high quality single photons, but the vast
majority of sources operate in the 900-950 nm wavelength range, precluding
their adoption in a quantum network. Here, we present a quantum frequency
conversion scheme for converting single photons from quantum dots to the
telecommunication C band, around 1550 nm, achieving 40.8% end-to-end
efficiency, while maintaining both high purity and a high degree of
indistinguishability during conversion with measured values of
$g^{(2)}(0)=2.4\%$ and $V^{\text{corr}}=94.8\%$, respectively.
