Improved error correction with leakage reduction units built into qubit measurement in a superconducting quantum processor

TL;DR

This paper introduces a high-fidelity leakage reduction unit (LRU) for superconducting qubits that operates concurrently with measurement, significantly reducing leakage errors and improving quantum error correction without additional time overhead.

Contribution

The authors develop and experimentally demonstrate a novel LRU protocol that reduces leakage during qubit measurement without increasing measurement time, enhancing quantum error correction.

Findings

Achieved 98.4% leakage removal fraction.

Maintained 99.2% computational-state assignment fidelity.

Successfully suppressed logical error rates in QEC experiments.

Abstract

Leakage to non-computational states is a source of correlated errors in both time and space that limits the effectiveness of quantum error correction (QEC) with superconducting circuits. We present and experimentally demonstrate a high-fidelity, leakage reduction unit (LRU) operating concurrently with transmon measurement without incurring time overhead. Adapted from double-drive reset of population (DDROP), the protocol utilizes simultaneous drives on the transmon and its readout resonator, leveraging the dispersive shift to create a directional process that returns the transmon to the computational subspace. The LRU achieves a 98.4% leakage removal fraction without compromising the computational-state assignment fidelity (99.2%). We combine LRU-enhanced measurement and neural-network decoding to successfully suppress logical error rates in both memory and stability QEC experiments without any post-selection.