Hybrid quantum circuit with implanted erbium ions

We report on hybrid circuit quantum electrodynamics experiments with focused ion beam implanted Er³⁺ ions in Y₂SiO₅ coupled to an array of superconducting lumped element microwave resonators. The Y₂SiO₅ crystal is divided into several areas with distinct erbium doping concentrations, each coupled to a separate resonator. The coupling strength is varied from 5 MHz to 18.7 MHz, while the linewidth ranges between 50 MHz and 130 MHz. We confirm the paramagnetic properties of the implanted spin ensemble by evaluating the temperature dependence of the coupling. The efficiency of the implantation process is analyzed and the results are compared to a bulk doped Er:Y₂SiO₅ sample. We demonstrate the integration of these engineered erbium spin ensembles with superconducting circuits.