  Pair vibrations are studied for a Hamiltonian with neutron-neutron,
proton-proton and neutron-proton pairing. The spectrum is found to be rich in
strongly correlated, low-lying excited states. Changing theratio of diagonal to
off-diagonal pairing matrix elements is found to have a large impact on the
excited-state spectrum. The variational configuration interaction (VCI) method,
used to calculate the excitation spectrum, is found to be in very good
agreement with exact solutions for systems with large degeneracies having equal
T=0 and T=1 pairing strengths.
