Quantum error correction

Methods that detect and fix errors in a quantum computer while it runs, without disturbing the information being computed.

• Qubits cannot be copied (the 'no-cloning' rule) and measuring them destroys their state, so ordinary backup-copy tricks don't work.
• Instead, helper qubits repeatedly check whether neighbouring data qubits agree, revealing where an error occurred without revealing the data itself.
• A classical computer must decode those check results and choose corrections in about a microsecond per cycle on superconducting chips.
• Below a hardware 'threshold' error rate, bigger codes mean fewer errors; Google showed this in 2024, roughly halving logical errors per size step.