  Entangling quantum systems with different characteristics through the
exchange of photons is a prerequisite for building future quantum networks.
Proving the presence of entanglement between quantum memories for light working
at different wavelengths furthers this goal. Here, we report on a series of
experiments with a thulium-doped crystal, serving as a quantum memory for 794
nm photons, an erbium-doped fibre, serving as a quantum memory for
telecommunication-wavelength photons at 1535 nm, and a source of photon pairs
created via spontaneous parametric down-conversion. Characterizing the photons
after re-emission from the two memories, we find non-classical correlations
with a cross-correlation coefficient of $g^{(2)}_{12} = 53\pm8$; entanglement
preserving storage with input-output fidelity of
$\mathcal{F}_{IO}\approx93\pm2\%$; and non-locality featuring a violation of
the Clauser-Horne-Shimony-Holt Bell-inequality with $S= 2.6\pm0.2$. Our
proof-of-principle experiment shows that entanglement persists while
propagating through different solid-state quantum memories operating at
different wavelengths.
