Spin coherence of Er³⁺in CeO₂ thin film on Silicon at sub-kelvin temperatures

Erbium ions (Er³⁺) are promising spin defects for telecom spin-photon interface as quantum memories for quantum communication networks. To this end, we have explored Er³⁺: CeO₂ (cerium dioxide) thin film epitaxially grown on silicon [1,2] as a new CMOS-compatible platform with near-zero nuclear spin environment critical for supporting long-lived spins [3]. This platform has shown promising narrow optical homogeneous linewidth (~440KHz) with a spin relaxation time of ~2.5ms and a spin coherence of ~0.66μs at 3.6K [2]. Here, we report on our studies on Er³⁺ spin coherence at 15-300mK utilizing on-chip low-impedance 2D superconducting microwave resonator. The design enables an ensemble spin coupling strength ~2MHz with ~4x10⁵ spins for on-chip ESR (electron spin resonance) studies. We find that Er³⁺ has a spin coherence up to ~180𝜇s at 15mK. We combine experimental data using both 2-pulse and 3-pulse Hahn-echo along with dynamical decoupling sequences and CCE (cluster-correlation expansion) based simulation to explore dominating dephasing processes. These studies point to possible approaches to improve Er³⁺ spin coherence and the potential of Er³⁺:CeO₂ qubit systems for quantum networks and communication applications.

[1] G. Grant, et al. APL Mater. 12, 021121 (2024).

[2] J. Zhang, et al. npj Quantum Information, in press (2024); arXiv:2309.16785 (2023).

[3] S. Kanai, et al. PNAS. 119, e2121808119 (2022).