  We analyze the transport properties of two artificial magnetic impurities
coupled togethervia a tunable RKKY interaction mediated by conduction electrons
of a finite size one dimensional wire. We show that the sign of the RKKY
interaction can be controlled by gating the wire. We investigate the interplay
between finite size effects and RKKY interaction and found that the two
artificial impurities start to interact each-other as soon as the Kondo
screening cloud length becomes larger that the length of the wire. This should
allow to give a lower experimental estimate of the Kondo screening cloud
length.
