Subkilohertz optical homogeneous linewidth and dephasing mechanisms in Er3+:Y2O3 ceramics

We report an optical homogeneous linewidth of 580 +/- 20 Hz of Er3+:Y2O3 ceramics at millikelvin temperatures, narrowest so far in rare-earth doped ceramics, as well as a slow spectral diffusion of similar to 2 kHz over a millisecond time scale. Detailed investigations of temperature and field dependence of optical coherence and spectral diffusions reveal the remaining weak dephasing mechanisms as coupling to elastic two-level systems and superhyperfine interactions of Er3+ with nuclear spins. The measured transient coherence properties can be understood in part from frozen Er3+ spins at dilution temperatures. In addition to informing possible refinement in material synthesis to further suppress dephasings, these spectroscopic results put Er3+:Y2O3 ceramics as a promising candidate for quantum systems.