Quantum Algorithms, Quantum Computing, Physics, Mathematics, Education.
the state indicated by each index. Remember that |0⟩ has an eigenvalue of +1 and |1⟩ an eigenvalue of -1. And when measuring multi-qubit states, the eigenvalue of the whole system is the eigenvalues of the subsystems multiplied. That’s why we take |11⟩ to have eigenvalue +1 when calculating ⟨ZZ⟩.