  In this paper we present a general formulation for electronic transport that
combines strong correlation effects with broadening and quantum coherence, and
illustrate it with a simple example ("spin blockade") that clearly demonstrates
all three effects. The standard master equation method for Coulomb blockade
captures the first effect, while a number of different approaches such as the
non-equilibrium Green function (NEGF) method are available for handling the
last two. But there is a need for a method that captures all three and in this
paper we propose an approach that appears to fulfill this need. The equations
look similar to the NEGF formalism but one basic distinction is that all
quantities (like the Hamiltonian) appearing in our formalism are defined in
Fock space and as such are matrices of dimension (2^N by 2^N), N being the
number of basis functions describing the one-electron Hilbert space. Similar
quantities appearing in the NEGF formalism are of dimension (N by N). Other
important differences arise from the fact that in Fock space there is no need
to include the exclusion principle explicitly and that elastic processes in
one-electron space look like inelastic processes in Fock space. A simple
numerical example is presented to show that our approach includes strong
electron-electron interaction, broadening due to coupling to contacts and
quantum coherence effects due to spin polarization in directions other than the
z-direction. The basic equations for this "Fock space Green's function" (FSGF)
are quite general and should be applicable to more interesting and exotic
transport problems involving the entanglement of many-electron states. How
effective it will be remains to be assessed for different problems, but our
preliminary results for the Kondo peak look encouraging.
