Removing leakage-induced correlated errors in superconducting quantum error correction

TL;DR

This paper introduces a reset protocol for superconducting qubits that reduces leakage-induced correlated errors, leading to lower logical error rates and improved scalability in quantum error correction.

Contribution

A novel reset protocol effectively mitigates leakage errors in superconducting qubits, enhancing error correction performance and scalability.

Findings

Lower logical error rates with the reset protocol

Improved error suppression scaling with qubit number

Reduced leakage-related correlated errors

Abstract

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 the qubits can become excited, creating leakage states that are long-lived and mobile. Particularly for superconducting transmon qubits, this leakage opens a path to errors that are correlated in space and time. Here, we report a reset protocol that returns a qubit to the ground state from all relevant higher level states. We test its performance with the bit-flip stabilizer code, a simplified version of the surface code for quantum error correction. We investigate the accumulation and dynamics of leakage during error correction. Using this protocol, we find lower rates of logical errors and an improved scaling and stability of error suppression with increasing qubit number. This demonstration provides a key step on the path towards scalable quantum computing.