  Neutrinos play a critical role of transporting energy and changing the lepton
density within core-collapse supernovae and neutron star mergers. The quantum
kinetic equations (QKEs) combine the effects of neutrino-matter interactions
treated in classical Boltzmann transport with the neutrino flavor-changing
effects treated in neutrino oscillation calculations. We present a method for
extending existing neutrino interaction rates to full QKE source terms for use
in numerical calculations. We demonstrate the effects of absorption and
emission by nucleons and nuclei, electron scattering, electron-positron pair
annihilation, nucleon-nucleon bremsstrahlung, neutrino-neutrino scattering. For
the first time, we include all these collision terms self-consistently in a
simulation of the full isotropic QKEs in conditions relevant to core-collapse
supernovae and neutron star mergers. For our choice of parameters, the
long-term evolution of the neutrino distribution function proceeds similarly
with and without the oscillation term, though with measurable differences. We
demonstrate that electron scattering, nucleon-nucleon bremsstrahlung processes,
and four-neutrino processes dominate flavor decoherence in the protoneutron
star (PNS), absorption dominates near the shock, and all of the considered
processes except elastic nucleon scattering are relevant in the decoupling
region. Finally, we propose an effective decoherence opacity that at most
energies predicts decoherence rates to within a factor of 10 in our model PNS
and within 20% outside of the PNS.
