Quantum Error Correction
Quantum error correction (QEC) is the set of techniques used to detect and correct errors in qubit states caused by decoherence and gate imperfections. It is the central engineering challenge of quantum-computing.
The catch: error correction itself requires many qubits performing many operations, introducing further error opportunities. For years this created a vicious cycle — the more correction applied, the worse the outcome.
Google Willow (2024) broke this cycle, demonstrating that with the right techniques (surface code error correction), adding more qubits reduces rather than increases error rates — crossing the fault-tolerant threshold. Published in Nature: “Quantum error correction below the surface code threshold” (cottier-2026-quantum-computing-breakthroughs).
At this threshold, a qubit can theoretically be stabilised indefinitely. This is the prerequisite for practical fault-tolerant quantum computing.
Qubit overhead: Prior estimates required millions of physical qubits per logical qubit for fault tolerance. A 2026 Caltech/Oratomic paper (cottier-2026-quantum-computing-breakthroughs) reduces this to ~10,000 qubits for running Shor’s algorithm — two orders of magnitude improvement.
See also: qubit, quantum-advantage, quantum-computing.
Sources: cottier-2026-quantum-computing-breakthroughs, babbush-neven-2026-quantum-vulnerabilities-cryptocurrency