  We show that when an individual particle is dragged through an assembly of
other particles in the presence of quenched disorder, a viscous decoupling
transition occurs between the dragged particle and the surrounding particles
which is controlled by the quenched disorder. A counterintuitive consequence of
this transition is that the velocity of the dragged particle can be increased
by increasing the strength or density of the quenched disorder. The decoupling
transition can also occur when the external drive on the dragged particle is
increased, and is observable as a clear signature in the velocity-force
response.
