• Accepted Paper

Sequences of Bivariate Bicycle Codes from Covering Graphs

Benjamin C. B. Symons, Abhishek Rajput, and Dan E. Browne

PRX Quantum - Accepted 3 August, 2026

DOI: https://doi.org/10.1103/vxpb-vjwl

Abstract

We show that given an instance of a bivariate bicycle (BB) code, it is possible to generate an infinite sequence of new BB codes using increasingly large covering graphs of the original code’s Tanner graph. When a BB code has a Tanner graph that is a h-fold covering of the base BB code’s Tanner graph, we refer to it as a h-. We show that for a BB code to be a h-cover code, its lattice parameters and defining polynomials must satisfy simple algebraic conditions relative to those of the base code. By extending the graph covering map to a chain map, we show there are induced projection and lifting maps on (co)homology that enable the projection and lifting of logical operators and, in certain cases, automorphisms between the base and the cover code. The search space of cover codes is considerably reduced compared to the full space of possible polynomials and we find that many interesting examples of BB codes, such as the [[144,12,12]] gross code, can be viewed as cover codes. We also apply our method to search for BB codes with weight 8 checks and find many new codes, including a [[64,14,8]] and [[144,14,14]] code. For an h-cover code of an [[n,k,d]] BB code with parameters [[nh=hn,kh,dh]], we prove that khk for any h, and dhhd when h is odd. Furthermore if h is odd and kh=k, we prove the distance lower bound ddh. We conjecture it is always true that an h-cover BB code of a base [[n,k,d]] BB code obeys the distance bounds ddhhd. While the focus of this work is on bivariate bicycle codes, we expect these methods to generalise readily to many group algebra codes and to certain code constructions involving hypergraph, lifted, and balanced products.

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