4D and 5D Layer Codes through Color Routing
This work provides a theoretical construction of higher-dimensional quantum LDPC codes that saturate optimal bounds, which is significant for quantum error correction theory but remains incremental as it extends existing Layer code ideas.
The authors introduce a CSS code construction generalizing Layer codes to 4D and 5D, achieving parameters that saturate the BPT bounds exactly. Using good qLDPC codes as input, they obtain codes with parameters [[Θ(n^{D/(D-2)}), k, Θ(dn^{1/(D-2)})]] and energy barrier Ω(Δ).
We introduce and explicit Calderbank-Shor-Steane (CSS) code construction that generalizes the Layer codes to $D=4,5$ dimensions. Much like its predecessor, the present construction is based on embedding quantum low-density parity check (qLDPC) codes; from an $[[n,k,d]]$ code with energy barrier $Δ$, we obtain a $D=4,5$ dimensional Layer code with parameters $[[Θ(n^{D/(D-2)}), k, Θ(dn^{1/(D-2)})]]$ and energy barrier $Ω(Δ)$. Using good qLDPC codes as input, our construction saturates the $D=4,5$ dimensional BPT bounds exactly. The higher dimensional Layer Codes are modular, and thus well suited to architectures composed of modular network patches, despite our physical limitation to three dimensions. We overcome the hurdles encountered by previous generalization attempts through the use of \textit{color routing}, allowing us to resolve the structure of the check layers and line defects.