Understanding noise and decoherence of rare earth qubits in epitaxial oxide thin films

Erbium (Er³⁺) ions in solids are promising spin-photon interfaces for quantum networks and hybrid quantum architectures due to their long spin coherence times and telecom C band optical transitions. Epitaxial Er³⁺ doped Y₂O₃ thin films can be grown on silicon such that it enables large scale device integration for quantum technologies. We perform noise spectroscopy of erbium (Er³⁺) dopants in 100 nm epitaxial Y₂O₃ thin film with high sensitivity pulsed electron spin resonance (ESR) using superconducting microwave resonator and photoluminescence (PL) from an optical Fabry-Perot fiber cavity at milliKelvin temperatures. Both the optical linewidth measurements on single Er³⁺ ions and the spin coherence studies suggest spectral diffusions induced by the two-level-systems (TLS). We also show that dephasing due to TLS could be alleviated by an applied magnetic field. The current optical, microwave noise spectroscopy deepens our understanding of the decoherence mechanisms of rare-earth dopants in oxide thin films, and could lead to improvements in the coherence times and the coherent control of rare earth qubits in thin films.