  Quantum error correction (QEC) provides a practical path to fault-tolerant
quantum computing through scaling to large qubit numbers, assuming that
physical errors are sufficiently uncorrelated in time and space. In
superconducting qubit arrays, high-energy impact events produce correlated
errors, violating this key assumption. Following such an event, phonons with
energy above the superconducting gap propagate throughout the device substrate,
which in turn generate a temporary surge in quasiparticle (QP) density
throughout the array. When these QPs tunnel across the qubits' Josephson
junctions, they induce correlated errors. Engineering different superconducting
gaps across the qubit's Josephson junctions provides a method to resist this
form of QP tunneling. By fabricating all-aluminum transmon qubits with both
strong and weak gap engineering on the same substrate, we observe starkly
different responses during high-energy impact events. Strongly gap engineered
qubits do not show any degradation in T1 during impact events, while weakly gap
engineered qubits show events of correlated degradation in T1. We also show
that strongly gap engineered qubits are robust to QP poisoning from increasing
optical illumination intensity, whereas weakly gap engineered qubits display
rapid degradation in coherence. Based on these results, gap engineering removes
the threat of high-energy impacts to QEC in superconducting qubit arrays.
