Quantum error correction (QEC) is a set of techniques used to protect quantum information from errors due to decoherence and other sources of noise. Quantum error correction is one approach to fault-tolerant quantum computing that can reduce the effects of noise on stored quantum information, faulty quantum gates, faulty quantum state preparation, and faulty measurements. Effective quantum error correction allows quantum computers to execute algorithms of higher complexity or greater circuit depth.
Many proposals exist for the implementation of quantum error correction. A popular approach is to compute with sets of entangled physical qubits, called “logical qubits”, that enable the detection and correction of errors without breaking quantum physics’ “no-cloning theorem” while circumventing the “measurement problem”.
Copying quantum information is not possible due to the no-cloning theorem. To get around this you can spread the (logical) information of one logical qubit onto a highly entangled state of several (physical) qubits. Peter Shor first discovered this method of formulating a quantum error correcting code by storing the information of one qubit onto an entangled state of nine qubits.