Heterogeneous integration of high kinetic inductance resonator with thin-film lithium niobate nanomechanical resonators*

Entering the strong coupling regime is an important step towards the quantum control of a system. In this work, we demonstrate coupling GHz nanomechanical resonators to frequency-tunable superconducting microwave resonators via cross-chip wire bond and flip-chip bump bond methods. By implementing galvanic contacts, which minimize parasitic capacitance and inductance, and tuning the microwave resonators with an external magnetic field, we observe a series of anti-crossings with the mechanical modes and report strong coupling strengths larger than 10 MHz at dilution fridge temperatures. The demonstrated multiple-chip architecture provides flexibility, simplified fabrication, and could potentially enable coupling between a vast variety of quantum systems such as spins with different host materials. Our work represents an important step towards a plug-and-play architecture for hybrid quantum systems.