Researchers from the Quantronics group at SPEC (Joint research unit UMR CEA-CNRS), working with the Sherbrooke University, the Chinese University of Hong Kong, Chimie ParisTech – PSL, l’IM2NP et l’Institut Néel (CNRS), have shown that a spectral pattern created by microwaves in an erbium-doped crystal can persist for more than a week when cooled to…