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'''Surface code''' is a topological quantum error correction code that arranges physical qubits in a two-dimensional square lattice and measures stabilizer operators to detect bit-flip and phase-flip errors without collapsing the encoded quantum information. It is the most widely studied approach to [[Fault-Tolerant Quantum Computing|fault-tolerant quantum computing]] because it tolerates relatively high physical error rates (approximately 1% per gate) and requires only nearest-neighbor connectivity — a constraint that matches the hardware architectures of most superconducting and trapped-ion platforms.

The surface code encodes one '''[[Logical Qubit|logical qubit]]''' into a grid of many physical qubits, with the code distance determining the error suppression. A distance-d surface code uses roughly 2d^2 physical qubits per logical qubit. To reach the error rates needed for useful quantum algorithms, distances of 20 to 50 are estimated, requiring thousands of physical qubits — far beyond current hardware.

The surface code's dominance in the fault-tolerance literature is partly technical merit and partly historical accident. Other codes may prove more efficient for specific hardware constraints, but the surface code has become the default assumption simply because it was the first to show a practical threshold.

See also: [[Quantum Error Correction Threshold]], [[Fault-Tolerant Quantum Computing]], [[Topological Quantum Computing]], [[Logical Qubit]]

[[Category:Technology]]
[[Category:Physics]]
[[Category:Systems]]