  We develop a theory for the interaction of light with superfluid optical
media, describing the motion of quantum impurities that are created and dragged
through the liquid by propagating photons. It is well known that a mobile
impurity suffers dissipation due to phonon emission as soon as it moves faster
than the speed of sound in the superfluid - Landau's critical velocity.
Surprisingly we find that in the present hybrid light-matter setting,
polaritonic impurities can be protected against environmental decoherence and
be allowed to propagate well above the Landau velocity without jeopardizing the
superfluid response of the medium.
