  Nuclear outflows driven by accreting massive black holes are one of the main
feedback mechanisms invoked at high-z to reproduce the distinct separation
between star-forming, disk galaxies and quiescent spheroidal systems. Yet, our
knowledge of feedback at high-z remains limited by the lack of observations of
the multiple gas phases in galaxy outflows. In this work we use new deep,
high-spatial resolution ALMA CO(3-2) and archival VLT/SINFONI H$\alpha$
observations to study the molecular and ionized components of the AGN-driven
outflow in zC400528 ---a massive, main sequence galaxy at z=2.3 in the process
of quenching. We detect a powerful molecular outflow that shows a positive
velocity gradient and extends for at least ~10 kpc from the nuclear region,
about three times the projected size of the ionized wind. The molecular gas in
the outflow does not reach velocities high enough to escape the galaxy and is
therefore expected to be reaccreted. Keeping in mind the various assumptions
involved in the analysis, we find that the mass and energetics of the outflow
are dominated by the molecular phase. The AGN-driven outflow in zC400528 is
powerful enough to deplete the molecular gas reservoir on a timescale at least
twice shorter than that needed to exhaust it by star formation. This suggests
that the nuclear outflow is one of the main quenching engines at work in the
observed suppression of the central star-formation activity in zC400528.
