  Charge order appears to be an ubiquitous phenomenon in doped Mott insulators,
which is currently under intense experimental and theoretical investigations
particularly in the high $T_c$ cuprates. This phenomenon is conventionally
understood in terms of Hartree-Fock type mean field theory. Here we demonstrate
a mechanism for charge modulation which is rooted in the many-particle quantum
physics arising in the strong coupling limit. Specifically, we consider the
problem of a single hole in a bipartite $t-J$ ladder. As a remnant of the
fermion signs, the hopping hole picks up subtle phases pending the fluctuating
spins, the so-called phase string effect. We demonstrate the presence of charge
modulations in the density matrix renormalization group solutions which
disappear when the phase strings are switched off. This form of charge
modulation can be understood analytically in a path-integral language, showing
that the phase strings give rise to constructive interferences leading to
self-localization. When the latter occurs, left- and right-moving propagating
modes emerge inside the localization volume and their interference is
responsible for the real space charge modulation.
