Quantum light-matter interfaces using rare-earth ions in solids

I will provide an overview of the quantum optical systems that can be investigated using rare-earth ions in solids, and their applications. Rare-earth ions have microwave and optical transitions that can be coupled to optical and microwave resonators. Experiments can be performed either with single ions or ensembles of ions, enabling the exploration of various regimes of cavity quantum electrodynamics. Interesting phenomena can be explored, including superradiance, one-axis twisting, coherence protection via cavity mediated all to all interaction, collective induced transparency, time crystals. Applications include quantum networking, microwave to optical transduction, and quantum memories.