  The population transfer dynamics of model donor-bridge-acceptor systems is
studied by comparing a recently developed polaron-transformed quantum master
equation (PQME) with the well-known Redfield and Forster theories of quantum
transport. We show that the PQME approach reduces to these two theories in
their respective limits of validity and naturally interpolates between them as
a function of the system-bath coupling strength. By exploring the parameter
space of our model problem, we identify novel regimes of transport dynamics in
bridged systems like those encountered in biological and organic energy
transfer problems. Furthermore, we demonstrate that three-level systems like
the ones studied herein represent ideal minimal models for the identification
of quantum coherent transport as embodied in super-exchange phenomena that
cannot be captured by Forster-like hopping approaches.
