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arXiv · 2605.05881

Surface-Code Thresholds and Qubit Footprints in Shuttling-Based Spin-Qubit Railways

Arun John Moncy·Reza Dastbasteh·Josu Etxezarreta Martinez·Ryo Nagai·Pedro M. Crespo·Normann Mertig·Charles Smith·Ruben M. Otxoa
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Abstract

We present a fault-tolerant mapping of rotated surface codes onto a $2\times N$ silicon spin-qubit railway architecture, utilizing electron shuttling to resolve the wiring fan-out bottleneck. Employing circuit-level noise modeling, we evaluate threshold performances across various noise biases. We demonstrate that shuttling check qubits instead of data qubits fundamentally improves system thresholds. Crucially, under a noise model biased towards dephasing for spin-qubit shuttling, the non-CSS XZZX surface code outperforms standard CSS variants. By tailoring the topological code to this specific inherent bias, we show that the Megaquop footprint is achievable with a distance 7 code requiring a $p = 10^{-3}$ physical error rate, highlighting a pathway for substantial hardware reductions in early fault-tolerant quantum processors.

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Arun John Moncy, Reza Dastbasteh, Josu Etxezarreta Martinez, Ryo Nagai, Pedro M. Crespo, Normann Mertig, Charles Smith, Ruben M. Otxoa. 2026-05-07. Surface-Code Thresholds and Qubit Footprints in Shuttling-Based Spin-Qubit Railways. https://arxiv.org/abs/2605.05881

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