Optical coherence of ¹⁶⁶Er:⁷LiYF<inf>4</inf> crystal below 1 K

Abstract

© 2018 The Author(s). Published by IOP Publishing Ltd on behalf of Deutsche Physikalische Gesellschaft. We explore optical coherence and spin dynamics of an isotopically purified 166Er:7LiYF4 crystal below 1 K and at weak magnetic fields < 0.3T. Crystals were grown in our lab and demonstrate narrow inhomogeneous optical broadening down to 16 MHz. Solid-state atomic ensembles with such narrow linewidths are very attractive for implementing of off-resonant Raman quantum memory and for the interfacing of superconducting quantum circuits and telecom C-band optical photons. Both applications require a low magnetic field of ∼10 mT. However, at conventional experimental temperatures T > 1.5 K, optical coherence of Er:LYF crystal attains time scale only at strong magnetic fields above 1.5 T. In the present work, we demonstrate that the deep freezing of Er:LYF crystal below 1 K results in the increase of optical coherence time to at weak fields.