Mitigating leakage-induced correlated errors for superconducting quantum error correction

Leakage into non-computational states threatens the stability of quantum error correction. We present the operation of a multilevel reset protocol [1] in the context of quantum error correction, and discuss how the removal of otherwise long-lived leakage-induced correlated errors improves error correction performance. The multilevel reset protocol prepares the qubit ground state with high fidelity after starting in any of the first three excited states, thereby providing an efficient sink for leakage states. By reducing the reset error of this protocol and optimizing the gate duration, we position this gate to be highly compatible with superconducting quantum error correction codes.

[1] McEwen, M., Kafri, D., Chen, Z. et al. Removing leakage-induced correlated errors in superconducting quantum error correction. Nat Commun 12, 1761 (2021).