Curator's Take
AI Commentary
This article pinpoints Ce³⁺ polarons and their vacancy‑complexes as the dominant source of optical decoherence in Er³⁺‑doped CeO₂, linking a specific defect resonance at 0.8 eV to linewidth broadening and charge noise that have long limited spin‑photon interfaces. By combining hybrid DFT predictions with concentration‑dependent photocurrent data, the authors provide a concrete defect‑engineering target that could lift the optical coherence of Er³⁺ emitters toward the sub‑MHz regime needed for quantum networking. The work also suggests that similar polaron‑mediated decoherence may be at play in other multivalent‑oxide hosts, giving researchers a clear pathway to improve a whole class of rare‑earth qubit platforms.
— Mark Eatherly
Summary
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.