Surface code
The leading quantum error correction code — qubits in a grid where only neighbours need to talk to each other.
The surface code lays physical qubits out in a two-dimensional lattice. Half carry information, half measure syndromes on their nearest neighbours. That all interaction is local is the decisive property: it matches exactly what superconducting chips can do, where qubits connect only to their neighbours on the surface.
Its great virtue is an unusually generous threshold — around one per cent error per operation, against far stricter demands in earlier codes. That is why it became the mainstream route despite its high overhead. Google demonstrated in 2023 and 2024 that the error rate genuinely falls as the lattice grows, which was the decisive experimental evidence that the approach scales.