  Motivated by recent experiments, we consider a single-electron transistor in
the Kondo regime which is coupled to three leads in the presence of large bias
voltages. Such a steady-state non-equilibrium system is to a large extent
governed by a decoherence rate induced by the current through the dot. As the
two-terminal conductance turns out to be rather insensitive to the decoherence
rate, we study the conductance in a three-terminal device using perturbative
renormalization group and calculate the characteristic splitting of the Kondo
resonance. The interplay between potential biases and anisotropy in coupling to
the three leads determines the decoherence rate and the conditions for strong
coupling.
