  Coulomb interaction between charged particles is a well-known phenomenon in
many areas of researches. In general the Coulomb repulsion force broadens the
pulse width of an electron bunch and limits the temporal resolution of many
scientific facilities such as ultrafast electron diffraction and x-ray
free-electron lasers. Here we demonstrate a scheme that actually makes use of
Coulomb force to compress a relativistic electron beam. Furthermore, we show
that the Coulomb-driven bunch compression process does not introduce additional
timing jitter, which is in sharp contrast to the conventional radio-frequency
buncher technique. Our work not only leads to enhanced temporal resolution in
electron beam based ultrafast instruments that may provide new opportunities in
probing material systems far from equilibrium, but also opens a promising
direction for advanced beam manipulation through self-field interactions.
