We characterize the 795 nm 3H6 to 3H4 transition of Tm3+ in a Ti4+:LiNbO3 waveguide at temperatures as low as 800 mK. Coherence and hyperfine population lifetimes -- up to 117 μs and 2.5 hours, respectively -- exceed those at 3 K at least ten-fold, and are equivalent to those observed in a bulk Tm3+:LiNbO3 crystal under similar conditions. We also find a transition dipole moment that is equivalent to that of the bulk. Finally, we prepare a 0.5 GHz-bandwidth atomic frequency comb of finesse >2 on a vanishing background. These results demonstrate the suitability of rare-earth-doped waveguides created using industry-standard Ti-indiffusion in LiNbO3 for on-chip quantum applications.
@article{arxiv.1605.02396,
title = {Properties of a rare-earth-ion-doped waveguide at sub-Kelvin temperatures for quantum signal processing},
author = {Neil Sinclair and Daniel Oblak and Charles W. Thiel and Rufus L. Cone and Wolfgang Tittel},
journal= {arXiv preprint arXiv:1605.02396},
year = {2017}
}