  Using theory and simulations, we carried out a first systematic
characterization of DNA unzipping via nanopore translocation. Starting from
partially unzipped states, we found three dynamical regimes depending on the
applied force, f: (i) heterogeneous DNA retraction and rezipping (f < 17pN),
(ii) normal (17pN < f < 60pN) and (iii) anomalous (f > 60pN) drift-diffusive
behavior. We show that the normal drift-diffusion regime can be effectively
modelled as a one-dimensional stochastic process in a tilted periodic
potential. We use the theory of stochastic processes to recover the potential
from nonequilibrium unzipping trajectories and show that it corresponds to the
free-energy landscape for single base-pairs unzipping. Applying this general
approach to other single-molecule systems with periodic potentials ought to
yield detailed free-energy landscapes from out-of-equilibrium trajectories.
