CSS code

A CSS code (Calderbank-Shor-Steane) is a quantum error correction code built from two classical linear codes. The construction requires that one code's dual be contained in the other, ensuring that the stabilizers commute. The Surface Code is the most famous CSS code, and most practical quantum error correction proposals use CSS constructions.

Recent breakthroughs in quantum LDPC codes rely on CSS constructions built from classical LDPC codes with expanding properties. The CSS framework remains the primary bridge between classical and quantum coding theory, though non-CCSS constructions such as quantum Reed-Muller codes may yet prove superior for specific hardware constraints.