Coherent Erbium Spin Defects in Colloidal Nanocrystal Hosts

TL;DR

This paper demonstrates long spin coherence times in erbium-doped nanocrystals, highlighting their potential for quantum technologies and exploring factors affecting coherence in surface-proximate defects.

Contribution

It reports the first nearly microsecond spin coherence in Er3+ ions within colloidal nanocrystals, achieved by reducing dopant density and leveraging host symmetry.

Findings

Spin coherence up to nearly a microsecond in Er3+ doped nanocrystals.

Identification of surface Ce3+ as a source of paramagnetic noise.

Potential for further enhancement through nanocrystal engineering.

Abstract

We demonstrate nearly a microsecond of spin coherence in Er3+ ions doped in cerium dioxide nanocrystal hosts, despite a large gyromagnetic ratio and nanometric proximity of the spin defect to the nanocrystal surface. The long spin coherence is enabled by reducing the dopant density below the instantaneous diffusion limit in a nuclear spin-free host material, reaching the limit of a single erbium spin defect per nanocrystal. We observe a large Orbach energy in a highly symmetric cubic site, further protecting the coherence in a qubit that would otherwise rapidly decohere. Spatially correlated electron spectroscopy measurements reveal the presence of Ce3+ at the nanocrystal surface that likely acts as extraneous paramagnetic spin noise. Even with these factors, defect-embedded nanocrystal hosts show tremendous promise for quantum sensing and quantum communication applications, with multiple avenues, including core-shell fabrication, redox tuning of oxygen vacancies, and organic surfactant modification, available to further enhance their spin coherence and functionality in the future.