This kata covers the simplest of the quantum error-correction (QEC) codes - the three-qubit bit-flip code. This code encodes each logical qubit in three physical qubits and protects against single bit-flip error (equivalent to applying an X gate). In practice quantum systems can have other types of errors, which will be considered in the subsequent katas on quantum error correction.

This code is a quantum equivalent of the classical repetition code, adjusted to take into account the impossibility of simply cloning the quantum state.

• This code is described in the error correction article in the Q# documentation.
• Another description can be found in the Wikipedia article.
• An introduction to QEC can be found in "Quantum Error Correction for Beginners", see section IV for more information on the 3-qubit code.