  Error-corrected quantum computers can only work if errors are small and
uncorrelated. Here I show how cosmic rays or stray background radiation affects
superconducting qubits by modeling the phonon to electron/quasiparticle
down-conversion physics. For present designs, the model predicts about 57\% of
the radiation energy breaks Cooper pairs into quasiparticles, which then
vigorously suppress the qubit energy relaxation time ($T_1 \sim$ 160 ns) over a
large area (cm) and for a long time (ms). Such large and correlated decay kills
error correction. Using this quantitative model, I show how this energy can be
channeled away from the qubit so that this error mechanism can be reduced by
many orders of magnitude. I also comment on how this affects other solid-state
qubits.
