Indistinguishable Single Photon Emission from Single Erbium Ions

Individually addressed erbium ions in solid-state hosts are promising for application in long-distance quantum repeater networks because of their optical transition at 1.5 μm. However, their spin and optical coherence can be limited by noise from the solid-state environment. In this work we introduce a new host for single Er ions, CaWO4, that combines a non-polar site symmetry and low magnetic noise environment to significantly improve the optical and spin coherence properties. Using a high-Q, low mode-volume nanophotonic crystal cavity we isolate single Er ions and efficiently collect their emitted photons. We demonstrate indistinguishable photon emission, as well as significant improved spin coherence. This represents a significant step towards the development of quantum repeater networks based on individually addressed erbium ions.