  The out-of-equilibrium transport properties of a double quantum dot system in
the Kondo regime are studied theoretically by means of a two-impurity Anderson
hamiltonian with interimpurity hopping. The hamiltonian is solved by means of a
non-equilibrium generalization of the slave-boson mean-field theory. It is
demonstrated that measurements of the differential conductance dI/dV, for the
appropriate values of voltages and tunneling couplings, can give a direct
observation of the coherent superposition between the many-body Kondo states of
each dot.
  For large voltages and arbitrarily large interdot tunneling, there is a
critical voltage above which the physical behaviour of the system is again that
of two decoupled quantum dots, i.e two Kondo singularities pinned at each
chemical potential.
