Optical coherence and energy-level properties of a Tm3+ -doped LiNb O3 waveguide at subkelvin temperatures

We characterize the optical coherence and energy-level properties of the 795-nm H63 to H43 transition of Tm3+ in a Ti4+:LiNbO3 waveguide at temperatures as low as 0.65 K. Coherence properties are measured with varied temperature, magnetic field, optical excitation power and wavelength, and measurement timescale. We also investigate nuclear spin-induced hyperfine structure and population dynamics with varying magnetic field and laser excitation power. Except for accountable differences due to different Ti4+- and Tm3+-doping concentrations, we find that the properties of Tm3+:Ti4+:LiNbO3 produced by indiffusion doping are consistent with those of a bulk-doped Tm3+:LiNbO3 crystal measured under similar conditions. Our results, which complement previous work in a narrower parameter space, support using rare-earth ions for integrated optical and quantum signal processing.