Ultralong-lived Coherent States in Eu${}^{3+}$:Y${}_2$O${}_3$ Optical Ceramics for Quantum Memories

Abstract

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 $\pm$ 10.5 $\mu$s for the ${}^7$F${}_0{\to }^5$D${}_0$ transition and more than 30 hours lifetime for the ${}^7$F${}_0$ hyperfine spin states in Eu${}^{3+}$:Y${}_2$O${}_3$ 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 $\mu$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.

10 pages, 4 figures