  We study the dynamical depinning following a sudden turn off of an optical
lattice for a gas of impenetrable bosons in a tight atomic waveguide. We use a
Bose-Fermi mapping to infer the exact quantum dynamical evolution. At long
times, in the thermodynamic limit, we observe the approach to a non-equilibrium
steady state, characterized by the absence of quasi-long-range order and a
reduced visibility in the momentum distribution. Similar features are found in
a finite-size system at times corresponding to half the revival time, where we
find that the system approaches a quasi-steady state with a power-law
behaviour.
