Optical and spin coherence of Er$^{3+}$ in epitaxial CeO$_2$ on silicon

TL;DR

This study demonstrates that Er$^{3+}$ ions in epitaxial CeO$_2$ films on silicon exhibit narrow optical linewidths and long electron spin coherence times at cryogenic temperatures, making them promising for quantum communication.

Contribution

It provides the first detailed measurements of optical and spin coherence properties of Er$^{3+}$ in epitaxial CeO$_2$ on silicon, highlighting their potential for quantum network applications.

Findings

Optical homogeneous linewidth of 440 kHz at 3.6 K

Electron spin coherence time of 0.66 μs at 3.6 K

Spin relaxation time of 2.5 ms

Abstract

Solid-state atomic defects with optical transitions in the telecommunication bands, potentially in a nuclear spin free environment, are important for applications in fiber-based quantum networks. Erbium ions doped in CeO$_2$ offer such a desired combination. Here we report on the optical homogeneous linewidth and electron spin coherence of Er$^{3+}$ ions doped in CeO$_2$ epitaxial film grown on a Si(111) substrate. The long-lived optical transition near 1530 nm in the environmentally-protected 4f shell of Er$^{3+}$ shows a narrow homogeneous linewidth of 440 kHz with an optical coherence time of 0.72 $\mu$s at 3.6 K. The reduced nuclear spin noise in the host allows for Er$^{3+}$ electron spin polarization at 3.6 K, yielding an electron spin coherence of 0.66 $\mu$s (in the isolated ion limit) and a spin relaxation of 2.5 ms. These findings indicate the potential of Er$^{3+}$:CeO$_2$ film as a valuable platform for quantum networks and communication applications.