Two-orbital quantum discord in fermion systems

A simple expression to compute the quantum discord between two orbitals in fermion systems is derived using parity superselection rule. As correlation depends on basis chosen, we discuss a special orbital basis, natural one. We show that correlations pairs disappear when pairing tensor zero, i.e., particle number symmetry preserved. The Hartree-Fock within Slater determinant state, Hartree-Fock-Bogoliubov quasiparticle vacuum, or ground state of Hamiltonian with and their corresponding are some relevant examples bases states. Since have property, seek non-natural bases. analyze our findings context Lipkin-Meshkov-Glick Agassi models.