  The aim of this paper is to derive the global Hamiltonian form for a quantum
system and bath, or more generally a quantum network with multiple quantum
input field connections, based on the local descriptions. We give a new simple
argument which shows that the global Hamiltonian for a single Markov component
arises as the singular perturbation of the free translation operator. We show
that the Fermi analogue takes an equivalent form provided the parity of the
coefficients is correctly specified. This allows us to immediately extend the
theory of quantum feedback networks to Fermi systems.
