Optical coherence and energy-level properties of a Tm³⁺-doped LiNbO₃ waveguide at subkelvin temperatures

Abstract

We characterize the optical coherence and energy-level properties of the 795-nm ³H₆ to ³H₄ 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.

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