Flag at origin: a modular fault-tolerant preparation for CSS codes
Diego Forlivesi, David Amaro

TL;DR
This paper presents a resource-efficient, modular fault-tolerant circuit construction for preparing logical states in CSS quantum error-correcting codes, improving error rates and circuit size.
Contribution
It introduces a modular method with flag gadgets for fault-tolerant CSS state preparation, optimizing resource use and error detection across arbitrary code distances.
Findings
Achieved a logical SPAM error rate of approximately 3.3e-4 on Quantinuum's H2-1 device.
Surpassed previous logical state preparation error rates and physical qubit error thresholds.
Developed an algorithm to find near-optimal flag gadgets reusable across codes.
Abstract
Fault-tolerant (FT) preparation of diverse logical stabilizer states in quantum error-correcting (QEC) codes is essential for FT computation. Existing constructions of these FT circuits are often constrained by classical computational resources or result in unnecessarily large quantum circuits. This work introduces a modular construction for FT preparation circuits in CSS codes of arbitrary distance, yielding significantly more resource-efficient circuits than previous approaches, especially for the largest codes studied. The key insight is that in bipartite CX circuits used to prepare CSS states, errors propagate in one direction across the qubit partition, while errors propagate in the opposite direction. By appending -detecting flag gadgets to the first partition and -detecting flag gadgets to the second, the circuit becomes FT. To manage the associated overhead, we…
Peer Reviews
No public reviews on file for this paper yet. If you reviewed it on a platform where reviews are public (OpenReview, ICLR, NeurIPS, ICML), you can paste yours below so the community can read it here.
Videos
No videos yet. Explain this paper in a talk, walkthrough, or lecture? Add one.
