Superconducting hybrid systems are becoming an increasingly important platform to conduct investigations in the field of quantum information processing. Here, the authors report a highly cooperative coupling between the nuclear spin of an Yb(III) molecular complex with a superconducting microwave resonator achieving a large hyperfine-mediated coupling between a resonator mode and the nuclear spin that could be used for the realization and readout of qudits.

Nuclear spins are candidates to encode qubits or qudits due to their isolation from magnetic noise and potentially long coherence times. However, their weak coupling to external stimuli makes them hard to integrate into circuit quantum electrodynamics architectures, the leading technology for solid-state quantum processors. Here, we study the coupling of Yb-173(III) nuclear spin states in an [Yb(trensal)] molecule to superconducting cavities. Experiments have been performed on magnetically dilute single crystals placed on the inductors of lumped-element LC superconducting resonators with characteristic frequencies spanning the range of nuclear and electronic spin transitions. We achieve a high cooperative coupling to all electronic and most nuclear [Yb-173(trensal)] spin transitions, a necessary ingredient for the implementation of qudit protocols with molecular spins using a hybrid architecture.