The future challenge of quantum communication are scalable quantum networks,
which require coherent and reversible mapping of photonic qubits onto
stationary atomic systems (quantum memories). A crucial requirement for
realistic networks is the ability to efficiently store multiple qubits in one
quantum memory. Here we demonstrate coherent and reversible mapping of 64
optical modes at the single photon level in the time domain onto one
solid-state ensemble of rare-earth ions. Our light-matter interface is based on
a high-bandwidth (100 MHz) atomic frequency comb, with a pre-determined storage
time of 1 microseconds. We can then encode many qubits in short <10 ns temporal
modes (time-bin qubits). We show the good coherence of the mapping by
simultaneously storing and analyzing multiple time-bin qubits.Comment: 7 pages, 6 figures + Supplementary materia