We report the realization of a strong coupling between a Gd3+ spin ensemble hosted in a scheelite (CaWO4) single crystal and the resonant mode of a coplanar stripline superconducting cavity leading to a large separation of spin-photon states of 146 MHz. The interaction is well described by the Dicke model and the crystal-field Hamiltonian of the multilevel spin system. We observe a change of the crystal-field parameters due to the presence of photons in the cavity that generates a significant perturbation of the crystal ground state. Using finite-element calculations, we numerically estimate the cavity sensing volume as well as the average spin-photon coupling strength of g0≈ 620 Hz. Lastly, the dynamics of the spin-cavity states are explored via pulsed measurements by recording the cavity ring-down signal as a function of pulse length and amplitude. The results indicate a potential method to initialize this multilevel system in its ground state via an active cooling process.
@article{arxiv.2210.05053,
title = {Strong coupling of a Gd$^{3+}$ multilevel spin system to an on-chip superconducting resonator},
author = {Giovanni Franco-Rivera and Josiah Cochran and Seiji Miyashita and Sylvain Bertaina and Irinel Chiorescu},
journal= {arXiv preprint arXiv:2210.05053},
year = {2023}
}