Fig. 4: Er³⁺ spin qubit coherence in the C_3i site.

a Spin lifetime measured by a π inversion pulse followed by delayed optical readout. b Spin Ramsey coherence. The fringe contrast is extracted from the normalized readout signal difference when alternating between a 0 and π phase of the second π/2 pulse. A fit to \({{{{\rm{e}}}}}^{-{(t/{T}_{2,s}^{*})}^{n}}\) yields a \({T}_{2,s}^{*}\) = 102  ± 5 μs with n = 2.1  ± 0.1. The error bars represent one standard deviation. c Hahn echo T_2,s, XY8 and CPMG dynamically decoupled spin coherence for the Er³⁺ ion in the C_3i site. For the CPMG measurement, the π pulse separation is fixed at 8 μs. The plot shows the CPMG readout with increasing number of refocusing pulses. The applied magnetic field is 130 mT.