Since qubits suffer from [[decoherence]], they must be corrected from time to time to preserve the quantum information they encode. Otherwise, the delicate quantum states essential for computation and communication will be inevitably lost. The field of research dedicated to addressing this challenge is known as *quantum error correction (QEC)*. While error correction is not unique to quantum systems—classical computers also employ robust error correction mechanisms—the quantum realm introduces fundamentally different challenges. The [[No-Cloning Theorem|no-cloning theorem]], a cornerstone of quantum mechanics, prohibits creating identical copies of an arbitrary quantum state. This constraint renders classical approaches to error correction, such as majority voting or duplicating data, infeasible for quantum systems. Classical systems, for example, handle bit flips by redundantly storing information and using majority voting to detect and correct errors. In contrast, qubits, with their inherent inability to be copied and their susceptibility to unique types of errors (e.g., bit-flip and phase-flip errors), require entirely novel strategies. ![[quantum_error_correction.excalidraw.light.svg]] Quantum error correction involves encoding quantum information in highly entangled states distributed across multiple [[Physical Qubit|physical qubits]]. These physical qubits collectively form a single [[Logical Qubit|logical qubit]], which is more robust against errors. Through clever encoding, error-detection protocols, and recovery operations, QEC schemes can detect and correct errors without directly measuring and collapsing the quantum state—a process that would otherwise destroy the encoded information. Pioneering QEC codes, such as the **Shor Code**, **Steane Code**, and more advanced techniques like the **surface code**, demonstrate how redundancy and entanglement can mitigate the effects of noise and decoherence. These codes are the foundation of fault-tolerant quantum computing, a critical milestone toward scalable and reliable quantum processors. >[!read]- Further Reading >- [[Logical Qubit]] >- [[Quantum Algorithm]] >[!ref]- References