  The process of coherent creation of particle - hole excitations by an
electric field in graphene is quantitatively described beyond linear response.
We calculate the evolution of current density, number of pairs and energy in
ballistic regime for electric field E using the tight binding model. While for
small ballistic flight times the current is linear in E and independent of
time, for larger ballistic times the current increases and finally at yet
larger times Bloch oscillations set in. It is shown that the number of pairs
follows the 2D generalization of the Schwinger's creation rate only on certain
time segments with a prefactor different from that obtained using the
asymptotic formula.
