Table 3 Non-zero elements of the 2-ORDM \(\rho ^{(2)}_{i, j}\) for molecular orbitals \(i\), \(j\). All other elements are null by global fermionic symmetries. Each operator \(\mathcal {O}\) corresponds to one of the 16 terms labelled in Eq. (3), denoted by its subscript. The superscripts outside the angular brackets denote the position of the element in the 16\(\times\)16 matrix. Faded terms correspond to those elements which are set to 0 when taking into account local fermionic SSRs. Left column labels the local electron number (\(n_e\)) and spin (\(s_z\)) sectors.

From: Measuring correlation and entanglement between molecular orbitals on a trapped-ion quantum computer