Yijia Xu, Yixu Wang, Zi-Wen Liu (Jun 05 2026).
Abstract: Fault-tolerant quantum computation is inherently a spacetime problem, requiring not merely good static quantum error-correcting codes but also low-overhead protocols for protecting and manipulating encoded quantum information over time. Fault complexes provide a homological framework for treating such protocols as single spacetime objects. In this work, we initiate the study of low-overhead fault complexes by introducing spacetime lifting, a method that constructs fault complexes from symmetry-reduced product structures beyond standard foliation. We show that spacetime lifting yields fault complexes and in particular spacetime-lifted memory experiments with almost-linear fault distance in the total spacetime cost, which substantially outperforms existing constructions. We further interpret fault complexes as measurement-based cluster-state protocols and identify general conditions under which they realize fault-tolerant logical teleportation, showing that spacetime-lifted constructions combine favorable scaling with operational schemes. Our study opens a path toward more efficient quantum fault tolerance through general complex constructions.
