Mapping multiple photonic qubits into and out of one solid-state atomic ensemble.

The future challenge of quantum communication is scalable quantum networks, which require coherent and reversible mapping of photonic qubits onto atomic systems (quantum memories). A crucial requirement for realistic networks is the ability to efficiently store multiple qubits in one quantum memory. In this study, we show a 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 predetermined storage time of ≳ 1 μs. We can then encode many qubits in short (<10 ns) temporal modes (time-bin qubits). We show the good coherence of mapping by simultaneously storing and analysing multiple time-bin qubits.