The Intrinsic Cost of Quantum Syndrome Extraction

Abstract: How much time is fundamentally required to extract the syndrome of a stabilizer code on hardware with a given connectivity graph? Previous work by Delfosse--Beverland--Tremblay (2021) and Baspin--Fawzi--Shayeghi (2023) established bounds connecting syndrome extraction to locality constraints on quantum hardware. Here, we address this question by first formulating an intrinsic measure of the interaction required for syndrome extraction directly from the stabilizer group, independent of the generating set used to describe the code. We then show that this measure yields hardware-dependent lower bounds on exact syndrome-extraction depth for arbitrary stabilizer codes. Guided by this measure, we also construct annular surface-code examples with constant-depth local syndrome extraction that provide a counterexample to Corollary 1 of DBT21. Furthermore, for a fixed quantum Tanner family, this measure strengthens the depth bound explicitly stated in BFS23 and, together with our matching construction, establishes an asymptotically tight space--depth tradeoff. In theory, our results connect the information required by syndrome extraction to the communication capacity of a device; while in practice, they provide a way to assess unavoidable circuit costs before committing to a hardware layout.