Rare earth ions (REI) in solid materials are among the leading systems for quantum technology applications. However, developing practical REI quantum devices with long-lived coherent states remains challenging due to great growth difficulties of high-quality REI materials and a lack of comprehensive understanding of REI's decoherence mechanisms. Here we realize a record optical coherence time of 421. 5 10. 5 s for the ⁷F₀⁵D₀ transition and more than 30 hours lifetime for the ⁷F₀ hyperfine spin states in Eu^3+: Y₂O₃ optical ceramics. We report the elimination of two-level-system induced optical decoherence in short-range ordered crystals. Meanwhile, a new decoherence mechanism caused by new kinds of perturbing magnetic centers is identified below 1. 5 K. We further demonstrate the coherent light storage over 5 s by using the atomic frequency comb protocol. These results open up prospects for the realization of practical quantum memories and large scale quantum communications with REI optical ceramics.
Liu et al. (Sat,) studied this question.