  We investigate the AC Josephson current through a quantum dot with strong
Coulomb interaction attached to two superconducting and one normal lead. To
this end, we perform a perturbation expansion in the tunneling couplings within
a diagrammatic real-time technique. The AC Josephson current is connected to
the reduced density matrix elements that describe superconducting correlations
induced on the quantum dot via proximity effect. We analyze the dependence of
the AC signal on the level position of the quantum dot, the charging energy,
and the applied bias voltages.
