Routing-based technique for defect mitigation in quantum error correction

TL;DR

Halma is a defect mitigation technique for quantum error correction that uses an expanded gate set to improve logical error rates and reduce hardware footprint in defective quantum chips.

Contribution

Introducing Halma, a novel defect mitigation method utilizing the iSWAP gate, compatible with existing surface code techniques, to enhance fault tolerance in defective quantum hardware.

Findings

Order of magnitude improvement in logical error rate

Approximately 3x reduction in hardware footprint

Effective mitigation of ancilla qubit defects

Abstract

As quantum chips scale up for large-scale computation, hardware defects become inevitable and must be carefully addressed. In this work, we introduce Halma, a defect mitigation technique empowered by an expanded native gate set that incorporates the iSWAP gate alongside the conventional CNOT gate. Halma emerges as a supplementary technique within the defect mitigation toolbox, offering effective mitigation of ancilla qubit defects encountered during surface code stabilizer measurements while maintaining compatibility with existing superstabilizer-based methodologies. Halma introduces zero reduction in the spacelike distance of the code without further sacrifice to the timelike distance. Numerical simulation suggests that in comparison to previous methods, Halma could provide an order of magnitude improvement in the average logical error rate under realistic experimental settings, leading to a $\sim3\times$ reduction in the footprint of a teraquop. These results clearly demonstrate the capability of Halma in easing the near-term realization of fault-tolerant quantum computing on hardware with fabrication defects, and exemplifies how leveraging intrinsic hardware capabilities can enhance quantum hardware performance.