Quantum Error Correction
Techniques for detecting and correcting errors in quantum computations without directly measuring (and thereby collapsing) the quantum state.
Quantum error correction (QEC) is a family of techniques for protecting quantum information from errors. Quantum systems are fragile: interactions with the environment cause errors through decoherence and other mechanisms. Classical computers use simple error correction (send data three times, take the majority); quantum computers cannot copy quantum states due to the no-cloning theorem, requiring more sophisticated approaches.
QEC works by encoding logical qubits (the information you want to protect) across many physical qubits (the actual hardware). By measuring relationships between physical qubits without directly measuring the logical qubit, errors can be detected and corrected.
The number of physical qubits required per logical qubit is a key metric: current estimates for fault-tolerant quantum computing range from roughly 1,000 to 10,000 physical qubits per logical qubit, depending on the hardware's error rate.
Quantinuum has published landmark results in quantum error correction, demonstrating logical qubit performance on their trapped ion H-Series systems. Their high gate fidelity makes error correction more tractable than on lower-fidelity platforms.