New Telecom Qubit System Based on Er³⁺ in Thin Film CeO₂ on Silicon

Trivalent erbium ions (Er³⁺) are promising spin defects for developing quantum memories in quantum communication networks due to their unique spin-photon interface at telecommunication band. To this end, controlling the local host environment to enable long-lived Er³⁺ electron spins in a technology compatible platform is key. Here, we report on a new qubit system Er³⁺: CeO₂ (cerium dioxide) epitaxially grown on silicon. The near-zero nuclear spin environment provided by CeO₂ is critical for supporting long-lived spins with predicted long spin coherence¹. Its silicon compatibility also points to the feasibility of this platform for device integration². We verify the host structure via thorough microstructural study² and explore routes towards improvement of the optical and spin linewidths via growth optimization and post-growth treatment of the Er:CeO₂ films. Additionally, we study the optical and spin coherence properties of Er³⁺ in this system and demonstrate narrow homogeneous linewidth of 440 kHz with an optical coherence time of 0.72 μs at 3.6 K³. The slow spin-lattice relaxation enables direct observation of spin dynamics at 3.6 K. The Er³⁺ electron spins have a spin relaxation of 2.5 ms and a spin coherence of 0.66 μs (in the isolated ion limit)³. Further exploration of spin dynamics at sub-Kelven temperature is undergoing. All these findings indicate the potential of Er³⁺:CeO₂ qubit systems as a scalable platform for quantum networks and communication applications.<br/>(1) S. Kanai, et al. PNAS. 119, e2121808119 (2022).<br/>(2) G. Grant, et al. APL Mater. 12, 021121 (2024).<br/>(3) J. Zhang, et al. arXiv:2309.16785 (2023).<br/>* This work was primarily supported by the U.S. Department of Energy, Office of Science, Basic Energy Sciences, Materials Sciences and Engineering Division with additional support from Q-NEXT, a U.S. Department of Energy Office of Science National Quantum Information Science Research Centers and Air Force Office of Scientific Research.