Coupling of a hole double quantum dot in planar germanium to a microwave cavity

In recent years, notable progress has been made in the study of hole qubits in planar germanium, and circuit quantum electrodynamics (circuit QED) has emerged as a promising approach for achieving long-range coupling and scaling up of qubits. Here, we demonstrate the coupling between holes in a planar germanium double quantum dot (DQD) and photons in a microwave cavity. Specifically, a real-time calibrated virtual gate method is developed to characterize this hybrid system, which in turn allows us to determine the typical parameters sequentially through a single-parameter fitting instead of conventional multiparameter fitting with additional uncertainty, giving a hole-photon coupling rate of ${g}_{0}$/2\ensuremath{\pi} = 21.7 MHz. This work is a step toward further research on hole-photon interactions and long-range qubit coupling in planar germanium. The experimental method developed in this work contributes to a more accurate and efficient characterization of hybrid cavity-QED systems.