  We show that pronounced modulations in spin and charge densities can be
induced by the insertion of a single hole in an otherwise half-filled 2-leg
Hubbard ladder. Accompanied with these modulations is a loosely bound structure
of the doped charge with a spin-1/2, in contrast to the tightly bound case
where such modulations are absent. These behaviors are caused by the
interference of the Berry phases associated a string of flipped spins (or
"phase strings") left behind as a hole travels through a spin bath with a
short-range anti-ferromagnetic order. The key role of the phase strings is also
reflected in how the system respond to increasing spin polarization, increasing
the on-site repulsion, addition of a second hole, and increasing asymmetry
between intra- and inter-chain hopping. Remarkably, all these properties
persist down to ladders as short as $\sim 10$ sites. They can therefore be
studied in cold atom experiments using the recently developed fermion
microscope.
