  We extend the imaginary-time formulation of the equilibrium quantum many-body
theory to steady-state nonequilibrium with an application to strongly
correlated transport. By introducing Matsubara voltage, we keep the finite
chemical potential shifts in the Fermi-Dirac function, in agreement with the
Keldysh formulation. The formulation is applied to strongly correlated
transport in the Kondo regime using the quantum Monte Carlo method.
