TL;DR: The surface code is the leading quantum error correction scheme. Physical qubits are arranged on a 2D lattice; each logical qubit requires d² physical qubits for code distance d. Google's Willow proce
The surface code is the leading quantum error correction scheme. Physical qubits are arranged on a 2D lattice; each logical qubit requires d² physical qubits for code distance d. Google's Willow processor demonstrated below-threshold surface code operation in 2024, where adding more qubits reduced errors exponentially. This was the first experimental proof that quantum error correction works as theory predicts.
Overhead
~1,000 physical qubits per logical qubit (code distance d=31)
Threshold
~1% error rate per gate
Key Result
Google Willow demonstrated below-threshold error correction (Dec 2024); exponential error suppression achieved