Develops rare-earth-ion-doped crystal platforms for quantum internet hardware. Directions: (1) Er3+-doped crystal quantum memories with >1 ms coherence time in nanophotonic waveguides; (2) microwave-to-optical quantum transduction using Er spins coupled to superconducting resonators; (3) photon-number-resolving detectors for quantum communication; (4) integrated rare-earth nanophotonic circuits on thin-film LiNbO3. Key goal: scalable room-temperature-compatible quantum repeater nodes.