  We characterize the electron doping evolution of
(Sr$_{1-x}$La$_x$)$_3$Ir$_2$O$_7$ by means of angle-resolved photoemission.
Concomitant with the metal insulator transition around $x\approx0.05$ we find
the emergence of coherent quasiparticle states forming a closed small Fermi
surface of volume $3x/2$, where $x$ is the independently measured La
concentration. The quasiparticle weight $Z$ remains large along the entire
Fermi surface, consistent with the moderate renormalization of the low-energy
dispersion. This indicates a conventional, weakly correlated Fermi liquid state
with a momentum independent residue $Z\approx0.5$ in lightly doped
Sr$_3$Ir$_2$O$_7&.
