Saving superconducting quantum processors from decay and correlated errors generated by gamma and cosmic rays

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 similar to 600 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.

Automated summary

This study investigates the impact of cosmic rays or stray background radiation on superconducting qubits by modeling the down-conversion process from phonons to electron/quasiparticles. The model predicts that a significant portion of radiation energy breaks Cooper pairs, leading to a suppression of qubit energy relaxation time. The author proposes a method to reduce this error mechanism by channeling energy away from the qubit.