Properties of a Rare-Earth-Ion-Doped Waveguide at Sub-Kelvin Temperatures for Quantum Signal Processing

Abstract

We characterize the 795nm ^{3}H_{6} to ^{3}H_{4} transition of Tm^{3+} in a Ti^{4+}:LiNbO_{3} waveguide at temperatures as low as 800mK. Coherence and hyperfine population lifetimes-up to 117 μs and 2.5h, respectively-exceed those at 3K at least tenfold, and are equivalent to those observed in a bulk Tm^{3+}:LiNbO_{3} crystal under similar conditions. We also find a transition dipole moment that is equivalent to that of the bulk. Finally, we prepare a 0.5GHz-bandwidth atomic frequency comb of finesse >2 on a vanishing background. These results demonstrate the suitability of rare-earth-ion-doped waveguides created using industry-standard Ti indiffusion in LiNbO_{3} for on-chip quantum applications.