  The problem of non-linear transport near a quantum phase transition is solved
within the Landau theory for the dissipative insulator-superconductor phase
transition in two dimensions. Using the non-equilibrium Schwinger round-trip
Green function formalism, we obtain the scaling function for the non-linear
conductivity in the quantum disordered regime. We find that the conductivity
scales as $E^2$ at low field but crosses over at large fields to a universal
constant on the order of $e^2/h$. The crossover between these two regimes
obtains when the length scale for the quantum fluctuations becomes comparable
to that of the electric field within logarithmic accuracy.
