Towards quantum memory with rare-earth-ions in crystals

Quantum memory is essential to the future of quantum information. At cryogenic temperatures, solids containing rare-earth-ions (REI) offer naturally trapped atomic systems for quantum memory implementations. The properties of REI in crystals enable broadband, efficient, and long-lived quantum memory in solid state materials. Progress to-date toward ensemble-based quantum memory with REI solids has been hampered by inhomogeneous broadening. Recent progress on stoichiometric materials narrows down the inhomogeneous broadening by 2 orders of magnitude, opening up new avenues for quantum memory. We report progress toward quantum memory with $\mathrm{Eu^{3+}}$ in crystals.