A tunable-coupling architecture for superconducting circuits and solid-state spin ensembles (Part 1: Parametrically pumped strong coupling)

Solid-state spin ensembles are promising candidates for quantum information storage due to their long coherence times. However, it remains an open challenge to achieve controlled and efficient quantum state transfer from components like superconducting qubits into these ensembles. We propose an architecture based on tunable parametric coupling between superconducting quantum circuits and a spin ensemble. In part one of this talk, we present a hybrid architecture for controllable coupling between a three-wave Josephson junction mixing element and a spin ensemble, mediated by a lumped-element 3D microwave cavity. We demonstrate parametrically controlled strong coupling to a zero-magnetic-field transition of ¹⁷¹Yb³⁺ ions implanted in a Y₂SiO₅ host crystal. These results show dynamic control over the interaction strength, representing a step toward a high-fidelity quantum interface and long-lived quantum state storage in a hybrid superconducting–spin memory.