  We present a unified view of electric transport in undoped clean graphene for
finite electric field. The weak field results agree with the Kubo approach. For
strong electric field, the current increases non-linearly with the electric
field as E^{3/2}. As the Dirac point is moved around in reciprocal space by the
field, excited states are generated, in a way analogous to the generation of
defects in a quench through a quantum critical point. These results are also
analyzed in terms of Schwinger's pair production and Landau-Zener tunneling. An
experiment for cold atoms in optical lattices is proposed to test these ideas.
