  We reformulate and extend our recently introduced quantum kinetic theory for
interacting fermion and scalar fields. Our formalism is based on the coherent
quasiparticle approximation (cQPA) where nonlocal coherence information is
encoded in new spectral solutions at off-shell momenta. We derive explicit
forms for the cQPA propagators in the homogeneous background and show that the
collision integrals involving the new coherence propagators need to be resummed
to all orders in gradient expansion. We perform this resummation and derive
generalized momentum space Feynman rules including coherent propagators and
modified vertex rules for a Yukawa interaction. As a result we are able to set
up self-consistent quantum Boltzmann equations for both fermion and scalar
fields. We present several examples of diagrammatic calculations and numerical
applications including a simple toy model for coherent baryogenesis.
