  Recent experiments have demonstrated how quantum-mechanical impurities can be
created within strongly correlated quantum gases and used to probe the
coherence properties of these systems [S. Palzer, C. Zipkes, C. Sias, and M.
K\"ohl, Phys. Rev. Lett. 103, 150601 (2009).]. Here we present a
phenomenological model to simulate such an output coupler for a Tonks-Girardeau
gas that shows qualitative agreement with the experimental results for atom
transport and output coupling. Our model allows us to explore nonequilibrium
transport phenomena in ultracold quantum gases and leads us to predict a regime
of atom blockade, where the impurity component becomes localized in the parent
cloud despite the presence of gravity. We show that this provides a stable
mixed-species quantum gas in the strongly correlated limit.
