We investigate the relevant spectroscopic properties of the 795 nm 3H6↔3H4 transition in 1% Tm3+:Y3Ga5O12 at temperatures as low as 1.2 K for optical quantum memories based on persistent spectral tailoring of narrow absorption features. Our measurements reveal that this transition has uniform coherence properties over a 56 GHz bandwidth, and a simple hyperfine structure split by ±44 MHz/T with lifetimes of up to hours. Furthermore, we find a 3F4 population lifetime of 64 ms -- one of the longest lifetimes observed for an electronic level in a solid --, and an exceptionally long coherence lifetime of 490 μs -- the longest ever observed for optical transitions of Tm3+ ions in a crystal. Our results suggest that this material allows realizing broadband quantum memories that enable spectrally multiplexed quantum repeaters.
@article{arxiv.1408.1978,
title = {Tm$^{3+}$:Y$_3$Ga$_5$O$_{12}$ materials for spectrally multiplexed quantum memories},
author = {Charles W. Thiel and Neil Sinclair and Wolfgang Tittel and Rufus L. Cone},
journal= {arXiv preprint arXiv:1408.1978},
year = {2014}
}