Coherence Properties of Rare-Earth Spins in Micrometer-ThinFilms

Rare-earth ions in bulk crystals are excellent solid-state quantum systems in quantum information science owing to their exceptional optical and spin coherence properties. However, the weak fluorescence of single rare-earth ions presents a significant challenge for scalability, necessitating the integration into microcavities. Thin films serve as a promising material platform for the integration, yet fabrication without compromising the properties of the materials and rare-earth ions remains challenging. In this work, we fabricate micrometer-thin yttrium aluminum garnet (YAG) films from bulk crystals using ion implantation techniques. The resulting films preserve the single-crystalline structure of the original bulk crystal. Notably, the embedded rare-earth ions are photostable and exhibit bulk-like spin coherence properties. Our results demonstrate the compatibility of bulk-like spin properties with the thin-film fabrication technique, facilitating the efficient integration of rare-earth ions into on-chip photonic devices and advancing the applications of rare-earth ions in quantum technologies.