Common Error Types

The three fundamental quantum error classes and hardware-specific additions.

Bit Flip Error ((X) Error)	Changes a qubit according to (X|0rangle = |1rangle) and (X|1rangle = |0rangle). Similar to a classical binary bit error, directly affecting the qubit’s state value.
Phase Flip Error ((Z) Error)	Changes the phase of a quantum state without changing the measured state value: (Z|0rangle = |0rangle), (Z|1rangle = -|1rangle). It affects the relative phase between quantum states.
Combined Error ((Y) Error)	Occurs when both bit-flip and phase-flip effects happen together, represented by (Y = iXZ). It affects both the state and phase of a qubit, making it more difficult to detect and correct.
Leakage Error	Population escapes outside the computational subspace, for example (|1rangle rightarrow |2rangle). Standard QEC assumes a two-level system; leakage requires specialised detection and reset.
Erasure Error	An error whose location is known (e.g., a qubit loss is flagged). Erasure errors are easier to correct than unknown Pauli errors.