  We report drive-response experiments on individual superconducting vortices
on a plane, a realization for a 1+1-dimensional directed polymer in random
media. For this we use magnetic force microscopy (MFM) to image and manipulate
individual vortices trapped on a twin boundary in YBCO near optimal doping. We
find that when we drag a vortex with the magnetic tip it moves in a series of
jumps. As theory suggests the jump-size distribution does not depend on the
applied force and is consistent with power-law behavior. The measured power is
much larger than widely accepted theoretical calculations.
