Suppressing interface piezoelectric losses in superconducting qubits

We present electromechanical design strategies to mitigate phonon-radiation-induced loss in superconducting qubits. Recent observation of interface piezoelectricity at aluminum-silicon interfaces indicate piezoelectricity-induced phonon radiation can generally exist in superconducting qubits. In our study, we apply analytical modeling and finite-element simulations for aluminum-on-silicon superconducting qubits to identify fabrication-friendly approaches that suppress phonon-radiation. We found that the qubit lifetime varies by around two orders of magnitude when the metal thickness changes from tens to hundreds of nanometers, due to variation of acoustic interference effects. Furthermore, simulation shows that introducing undercuts at the edges of aluminum pads can also significantly suppress the phonon radiation and enhance T₁. These observations demonstrate that controlling metal thickness and edge profiles provides a viable approach for mitigating the interface piezoelectricity-induced qubit loss. Similar strategies may also help reduce two-level-system-related losses, where phonon radiation is believed to be the dominant dissipation mechanism.