Vacuum-gap transmon qubits realized using flip-chip technology

Significant progress has been made in building large-scale superconducting quantum processors based on flip-chip technology. In this work, we use technology to realize a modified transmon qubit, denoted as the “flipmon,” whose large shunt capacitor is replaced by vacuum-gap parallel plate capacitor. We place one of qubit pads and single Josephson junction bottom chip other pad top chip, which galvanically connected with through an indium bump. The electric field energy participation ratio can arrive at nearly 53% air when about 5 μm, thus potentially leading lower dielectric loss. coherence times flipmons are obtained range 30–60 μs, comparable that conventional transmons similar fabrication processes. simulation indicates metal-air interface's increases significantly may dominate flipmon's decoherence. This suggests more careful surface treatment needs be considered. No evidence shows bumps inside cause significant With well-designed geometry good treatment, further improved.