Coherence Properties of Single Erbium Ions in CaWO₄

Erbium ions in crystalline hosts, which have an optical transition at 1.5 μm, are promising as single photon sources and quantum memories for quantum repeater networks operating directly in the telecom-band. These ions can be incorporated into a wide range of host materials, which influence their spin and optical coherence properties through the concentration of other magnetic spins and the Er site symmetry, which can affect the sensitivity to electric field noise. In this work, we present a study of the spin and optical coherence properties of Er3+ implanted into CaWO4. CaWO4 is magnetically quiet, and Er substitutes for Ca on a non-polar symmetry site, where a permanent electric dipole moment is forbidden. Using heterogeneously integrated silicon photonic crystal cavities, we isolate single erbium ions, and probe their spin properties using optically detected magnetic resonance with single-shot spin readout. With this approach, we have studied sources of decoherence, and developed materials processing techniques and device architectures to improve ions performance.

Support for this work was provided by AFOSR, C2QA DOE DE-FOA-0002253 and DARPA DRINQS.