High-Temporal-Resolution Measurements of the Impacts of Ionizing Radiation on Superconducting Qubits
We measure the effect of ionizing radiation on superconducting qubits with a timing resolution of 1 $\mu s$ using microwave kinetic inductance detectors (MKIDs) fabricated on the same substrate. We observe no correlation between two-level system (TLS) scrambling events and ionizing radiation events detected with the MKIDs, suggesting TLS scrambling events may not arise from ionizing radiation and instead the previously reported apparent correlation may be due to events without sufficient energy to trigger our MKIDs. We characterize the fast-time system recovery of transmons following a radiation event, where we observe the recovery of the enhanced qubit relaxation and excitation to be well-described by an exponential recovery to the baseline quasiparticle density, with a characteristic time of $13\pm1\ \mu$s, and a peak quasiparticle density at the junction per deposited energy of $240/\mu m^3/MeV$. The fast recovery is consistent with literature reported values for Nb-based devices with direct injection of 2$\Delta_{\text{Al}}$ phonons, demonstrating the recovery is strongly dependent on the proximity of niobium to the junction.