Pauli operator

An $n$-qubit Pauli operator is a tensor product of single-qubit Pauli matrices, possibly multiplied by a phase. Hermitian Pauli operators have eigenvalues $+1$ and $-1$.

A Pauli correlator is the expectation value of a tensor product of Pauli matrices, such as $⟨X\otimes Z⟩$. It measures a specified correlation between qubit observables.