Optical decoherence in Er3+-doped CeO2 spin qubit platforms

Erbium ions (Er3+) in cerium dioxide (CeO2) represent a promising spin–photon interface for quantum communication, but the mechanisms limiting their optical coherence remain poorly understood. Using periodic hybrid density functional theory calculations with finite-size corrections, we identify Ce3+ polarons and their complexes with oxygen vacancies and Er3+ dopants as likely sources of optical decoherence. These defects exhibit finite photoionization cross-sections at 0.8 eV, coinciding with both the laser excitation energy used experimentally and the emission energy of Er3+. The finite cross-section enables photoionization of the polarons and photoluminescence quenching of Er3+, contributing to the broadening of optical linewidths, shortening of excited-state lifetimes, and introduction of charge noise. Our concentration-dependent photocurrent measurements in Er3+-doped CeO2 films under 0.8 eV illumination validate the predicted decoherence pathway. Our combined computational and experimental results identify that removing Ce3+ polarons will improve the Er3+-doped CeO2 platform, and point to a decoherence mechanism likely relevant to other Er3+-doped multivalent-oxide quantum platforms.