Evidence for unexpectedly low quasiparticle generation rates across Josephson junctions of driven superconducting qubits

Abstract: Microwave drives applied to superconducting qubits (SCQs) are central to high-fidelity control and fast readout. However, recent studies find that even drives far below the superconducting gap frequency may cause drive-induced quasiparticle generation (QPG) across Josephson junctions (JJs), posing a serious concern for fault-tolerant superconducting quantum computing. Here, we find experimental evidence that the actual QPG rates in strongly driven SCQs are remarkably lower than expected. We apply intense drive fields through readout resonators, reaching effective qubit drive amplitudes up to 300 GHz. The nonlinear response of the resonators enables quantification of the energy loss from SCQs into their environments, including the contribution from QPG. Even when conservatively attributing all measured dissipation to QPG, the observed energy dissipation rates are far lower than expected from the ideal QPG model. Meanwhile, calculations incorporating high-frequency cutoffs (HFCs) near 17-20 GHz in the QPG conductance can explain the experiments. These HFCs yield QPG rates a few orders of magnitude smaller than those without HFCs, providing evidence that the QPG rates are lower than predicted by the ideal model. Our findings prevent overestimation of drive-induced QPG and provide crucial guidance for operating superconducting quantum processors. Identifying the microscopic origin of the discrepancy opens new material and device opportunities to further mitigate QPG.