Determining the site symmetry and crystal field splitting of individual erbium ions

The spin states of rare earth atoms such as erbium have long coherence times which makes them interesting for the use as quantum memories. These spin states can be accessed through optical transitions, with erbium having transitions at the convenient wavelength of 1540 nm. We use these optical transitions to study erbium’s spin states inside a silicon transistor in order to determine the local site symmetry as well as the crystal field splitting.