Exploring erbium-doped ceria as a new platform for telecom-wavelength quantum memory

Scalable solid-state quantum memory systems that operate at telecom wavelengths are essential for building wide-area fiber optic-based quantum networks. A particularly promising platform for such a quantum memory is erbium-doped ceria (Er:CeO₂), which combines the shielded telecom-wavelength (~1.5 µm) 4f-4f transition of erbium with the long (47 ms) predicted spin coherence time of CeO₂ [1]. Here, we demonstrate growth of epitaxial Er:CeO₂ thin films using molecular beam epitaxy (MBE) with controlled crystal quality and Er concentration (0.01% and lower). We present a study of the optical properties of a resonantly-excited Er ensemble, which shows long excited state lifetimes (up to 6 ms) and well-resolved crystal field splitting with narrow inhomogeneous peaks (<100 GHz). Further optical investigation also yields spectral diffusion-limited homogeneous linewidths that are sufficiently narrow to suggest that Er:CeO₂ may be a candidate for exploring quantum memory nanophotonic devices. Overall, we present a viable platform for scalable and usable quantum memories based on erbium-doped cerium oxide.