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Erbium telecom qubits in C3i centrosymmetric site in epitaxial yttrium oxide thin films are coupled to optical and microwave resonators, demonstrating millisecond spin coherence and kHz optical linewidths approaching the radiative limit.

We perform correlated optical-spin coherence spectroscopy on epitaxial rare-earth qubits in an oxide thin film. Single Er3+ ions are optically addressed and used to probe coupling to two-level-systems as a simultaneous optical-spin decoherence mechanism.

167Er3+ doped solids are a promising platform for quantum technology due to erbium’s telecom C-band optical transition and its long hyperfine coherence times. We experimentally study the spin Hamiltonian and dynamics of 167Er3+ spins in Y2O3 using electron paramagnetic resonance (EPR) spectroscopy. The anisotropic electron Zeeman, hyperfine and nuclear quadrupole matrices are fitted using data obtained by X-band (9.5 GHz) EPR spectroscopy. We perform pulsed EPR spectroscopy to measure spin relaxation time T1 and coherence time T2 for the 3 principal axes of an anisotropic g tensor. Long electronic spin coherence time up to 24.4 μs is measured for lowest g transition at 4 K, exceeding previously reported values at much lower temperatures. Measurements of decoherence mechanism indicates T2 limited by spectral diffusion and instantaneous diffusion. Long spin coherence times, along with a strong anisotropic hyperfine interaction makes 167Er3+:Y2O3 a rich system and an excellent candidate for spin-based quantum technologies.