  We study transport at finite bias, i.e. beyond the linear regime, through two
interacting resonant levels connected by a Fermi sea, by means of
time-dependent density matrix renormalization group. We first consider
methodological issues, like the protocol that leads to a current-currying state
and the characterization of the steady state. At finite sizes both the current
and the occupations of the interacting levels oscillate as a function of time.
We determine the amplitude and period of such oscillations as a function of
bias. We find that the occupations on the two dots oscillate with a relative
phase which depends on the distance between the impurities and on the Fermi
momentum of the Fermi sea, as expected for RKKY interactions. Also the
approximant to the steady-state current displays oscillations as a function of
the distance between the impurities. Such a behavior can be explained by
resonances in the free case. We then discuss the incidence of interaction on
such a behavior. We conclude by showing the effect of the bias on the current,
making connection with the one-impurity case.
