Angular dependent micro-ESR characterization of a locally doped Gd3+:Al2O3 system

Interfacing rare-earth doped crystals with superconducting circuit architectures provides an attractive platform for quantum memory and transducer devices. Here we present the detailed characterization of such a hybrid system: a locally implanted rare-earth Gd$^{3+}$ in Al$_2$O$_3$ spin system coupled to a superconducting micro-resonator. We investigate the properties of the implanted spin system through angular dependent micro-resonator electron spin resonance (micro-ESR) spectroscopy. We find, despite the high energy near-surface implantation, the resulting micro-ESR spectra to be in excellent agreement with the modelled Hamiltonian, supporting the integration of dopant ions into their relevant lattice sites whilst maintaining crystalline symmetries. Furthermore, we observe clear contributions from individual microwave field components of our micro-resonator, emphasising the need for controllable local implantation.