A tunable-coupling architecture for superconducting circuits and solid-state spin ensembles (Part 2: Towards quantum state storage)

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 2 of this talk, we address quantum state dephasing in the presence of spin inhomogeneous broadening through strong refocusing pulses. These high-power pulses can interfere with the Josephson junctions in our coupling architecture. We simulate a ¹⁷¹Yb³⁺: Y₂SiO₅ crystal magnetically coupled to an on-chip superconducting circuit. We analyse low-power adiabatic pulse engineering strategies to achieve high inversion efficiency while maintaining compatibility with Josephson junctions, thus providing a path for ultra-long quantum state storage.

In combination with the tunable coupling architecture shown in part 1, our work outlines a strategy for combining controllable state transfer with refocusing-based quantum memory operation in a hybrid superconducting–spin platform.