Measuring and modeling the impact of radiation on superconducting qubits protected through gap engineering

Impacts from high-energy particles have been demonstrated to cause correlated errors in superconducting qubits by increasing the quasiparticle density in the Josephson junction (JJ) leads. These correlated errors are particularly harmful as they cannot be remedied via conventional error correcting codes. It was recently demonstrated that these correlated errors can be reduced or eliminated by engineering the difference in superconducting gap across the JJ to be larger than the qubit frequency. In order to test the efficacy of this strategy we have exposed arrays of this type of "gap-engineered" qubits to a variety of radioactive sources, scanning both particle type and energy deposited in the substrate. We also characterize the effect of another layer of gap-engineering away from the JJ to help suppress QP-induced dephasing errors. In this talk, we will describe both the measurements performed and a quasiparticle model consistent with these measurements, discussing the implications for the future of preventing correlated errors.