  Multiplexed quantum memories capable of storing and processing entangled
photons are essential for the development of quantum networks. In this context,
we demonstrate the simultaneous storage and retrieval of two entangled photons
inside a solid-state quantum memory and measure a temporal multimode capacity
of ten modes. This is achieved by producing two polarization entangled pairs
from parametric down conversion and mapping one photon of each pair onto a
rare-earth-ion doped (REID) crystal using the atomic frequency comb (AFC)
protocol. We develop a concept of indirect entanglement witnesses, which can be
used as Schmidt number witness, and we use it to experimentally certify the
presence of more than one entangled pair retrieved from the quantum memory. Our
work puts forward REID-AFC as a platform compatible with temporal multiplexing
of several entangled photon pairs along with a new entanglement certification
method useful for the characterisation of multiplexed quantum memories.
