  Large-scale quantum networks will employ telecommunication-wavelength photons
to exchange quantum information between remote measurement, storage, and
processing nodes via fibre-optic channels. Quantum memories compatible with
telecommunication-wavelength photons are a key element towards building such a
quantum network. Here, we demonstrate the storage and retrieval of heralded
1532 nm-wavelength photons using a solid-state waveguide quantum memory. The
heralded photons are derived from a photon-pair source that is based on
parametric down-conversion, and our quantum memory is based on a 6
GHz-bandwidth atomic frequency comb prepared using an inhomogeneously broadened
absorption line of a cryogenically-cooled erbium-doped lithium niobate
waveguide. Using persistent spectral hole burning under varying magnetic
fields, we determine that the memory is enabled by population transfer into
niobium and lithium nuclear spin levels. Despite limited storage time and
efficiency, our demonstration represents an important step towards quantum
networks that operate in the telecommunication band and the development of
on-chip quantum technology using industry-standard crystals.
