Common Error Types
==================

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

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   * - **Bit Flip Error (\(X\) Error)**
     - Changes a qubit according to \(X\|0\rangle = \|1\rangle\) and \(X\|1\rangle =
                    \|0\rangle\). 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:
                    \(Z\|0\rangle = \|0\rangle\), \(Z\|1\rangle = -\|1\rangle\). 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 \(\|1\rangle
                    \rightarrow \|2\rangle\). 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.