Hole spins enable fast and all-electric control , due to strong intrinsic spin-orbit interaction (SOI). Since the SOI also couples spins to the electric field of a photon in a microwave resonator, strong hole-spin-photon coupling is expected. Recent experiment with holes in silicon indeed confirms this prediction , with the coupling largely exceeding the best figures reported with electrons [3, 4].
Here we report on hole double quantum dots (DQD) hosted in Ge/SiGe heterostructure coupled to a granular aluminum (grAl) resonator. grAl offers high kinetic inductance, magnetic field resilience and compatibility with multilayer lift-off based fabrication . Assessing these properties, we demonstrate a resonator with a characteristic impedance of Z ~ 13 k$\Omega$ (due to the large kinetic inductance of L ~ 2 nH/sq) resilient to out of plane magnetic fields exceeding B ~ 300 mT with $\kappa$/2$\pi$ < 5 MHz, well suited for spin-photon coupling experiments. We will also present our recent results of integrating these resonators with germanium DQDs in a cQED architecture, which aims for long-range coupling of hole spin qubits.
 Scappucci, G., et al. "The germanium quantum information route." Nature Reviews Materials 6.10 (2021): 926-943.
 Yu, C. X., et al. "Strong coupling between a photon and a hole spin in silicon." arXiv preprint arXiv:2206.14082 (2022).
 Mi, X., et al. "Strong coupling of a single electron in silicon to a microwave photon." Science 355.6321 (2017): 156-158.
 Harvey-Collard, P., et al. "Coherent spin-spin coupling mediated by virtual microwave photons." Physical Review X 12.2 (2022): 021026.
 Grünhaupt, L., et al. "Granular aluminium as a superconducting material for high-impedance quantum circuits." Nature materials 18.8 (2019): 816-819.