Optical decoherence in Er${}^{3+}$-doped CeO${}_2$ spin qubit platforms

Abstract

Erbium ions (Er${}^{3+}$) in cerium dioxide (CeO${}_2$) 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 Ce${}^{3+}$ polarons and their complexes with oxygen vacancies and Er${}^{3+}$ 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 Er${}^{3+}$. This resonance enables photoionization of the polarons and photoluminescence quenching of Er${}^{3+}$, leading to the broadening of optical linewidths, shortening of excited-state lifetimes, and introduction of charge noise. Our concentration-dependent photocurrent measurements in Er${}^{3+}$-doped CeO${}_2$ films under 0.8 eV illumination validate the predicted decoherence pathway. Our combined computational and experimental results identify a concrete defect-engineering target for improving the Er${}^{3+}$-doped CeO${}_2$ platform, and point to a decoherence mechanism likely relevant to other Er${}^{3+}$-doped multivalent-oxide quantum platforms.

7 pages, 4 figures