Removing leakage-induced correlated errors in superconducting quantum error correction - Theory

Quantum computing can become scalable through error correction, but logical error rates only decrease with system size when physical errors are sufficiently uncorrelated. During computation, unused high energy levels of superconducting qubits can become excited, creating leakage states that are long-lived and mobile. Here, we report a multilevel reset protocol that returns a transmon superconducting qubit to the ground state from all relevant higher level states. The protocol is based on an adiabatic transfer of photons from each transmon to its readout resonator. We develop a three-phase semiclassical model describing the protocol and find good agreement with experiment. We then discuss application of the reset gate to the bit flip repetition code.