Long optical coherence times in a rare-earth-doped antiferromagnet

Abstract

The absorption spectra of rare-earth ions have very narrow linewidths. Even in solid-state crystals, exceedingly long coherence times have been observed for the spin and optical transitions of rare-earth-ion dopants. The influence of electronic and nuclear spins in the host crystal is a key factor limiting these coherence times. Here we suppress the effects of electron spins by using erbium dopants in a gadolinium vanadate host that is fully concentrated in electron spins but operated at sufficiently low temperatures that the spins form an antiferromagnetically ordered state. We achieve long optical coherence times and, furthermore, observe avoided crossings in the optical spectra, which are caused by strong coupling between the erbium ions and gadolinium magnons in the host crystal. This indicates the possibility of magnon-mediated microwave-to-optical quantum transduction using rare-earth ions, which would provide a connection between telecommunications technology and solid-state quantum devices operating in the microwave regime.