Coherent control and characterization of interacting Er³⁺ ions

Optically addressed atomic defects in the solid-state are widely used as single-photon sources and memories for quantum network applications. The solid-state environment allows for a high density of electron spins with the potential to form registers for coherent information processing. However, it is challenging to scale the number of mutually interacting spin defects while maintaining coherent individual control over them. Here, we explore this possibility of using a cluster of Er³⁺ ions implanted in CaWO₄ integrated with Si photonic cavity. We can achieve frequency selective individual coherent control on both spin and optical transitions, so that we can characterize the spin coherence, mutual interaction between the ions, as well as the interaction with the ¹⁸³W nuclear spins in the host. This could be helpful towards building multi-qubit quantum network nodes.