Fig. 3: Dual Er³⁺ spin-photon interfaces and optical coherence.

a Narrow photoluminescence excitation spectrum is observed from single Er³⁺ ions in the C₂ (B = 113 mT) and C_3i (B = 130 mT) sites of Y₂O₃. (Right inset) g⁽²⁾ auto-correlation measurement for an Er³⁺ ion in the C₂ site shows g⁽²⁾(0)= 0.025. (Left inset) Histogram of photon counts during a 100-pulse readout for an ion in the C₂ site. b Long-term spectral stability of an Er³⁺ emitter in the C₂ site. c Short-term optical spectral diffusion of Er³⁺ in the C₂ site as optical T₁ lifetime is tuned. Inset shows the tuning of Purcell enhancement. Grey line indicates the fit to a spectral diffusion model with a dominant logarithmic component. d Optical Ramsey (π/2 − π/2) measurement for an Er³⁺ ion in the C_3i site. e. Optical T₂ measured by (π/2 − π − π/2) photon echo for the same ion in (d). Results for additional optical measurements on the single Er³⁺ ion in the C₂ site are presented in the Supplementary Fig. 1 and Supplementary Fig. 2.