  Using the Trotter-Kato theorem we prove the convergence of the unitary
dynamics generated by an increasingly singular Hamiltonian in the case of a
single field coupling. The limit dynamics is a quantum stochastic evolution of
Hudson-Parthasarathy type, and we establish in the process a graph limit
convergence of the pre-limit Hamiltonian operators to the
Chebotarev-Gregoratti-von Waldenfels Hamiltonian generating the quantum Ito
evolution.
