Long-Lived Solid-State Optical Memory for High-Rate Quantum Repeaters.

We argue that long optical storage times are required to establish entanglement at high rates over large distances using memory-based quantum repeaters. Triggered by this conclusion, we investigate the 795.325  nm^{3} H_{6}↔^{3}H_{4} transition of Tm:Y_{3}Ga_{5}O_{12} (Tm:YGG).