  Quite recently a novel variety of unconventional fourfold linear band
degeneracy points has been discovered in certain condensed-matter systems.
Contrary to the standard 3-D Dirac monopoles, these quadruple points referred
to as the charge-2 Dirac points are characterized by nonzero net topological
charges, which can be exploited to delve into hitherto unknown realms of
topological physics. Here, we report on the experimental realization of the
charge-2 Dirac point by deliberately engineering hybrid topological states
called super-modes in a 1-D optical superlattice system with two additional
synthetic dimensions. Utilizing direct reflection and transmission
measurements, we exhibit the existence of super-modes attributed to the
synthetic charge-2 Dirac point, which has been achieved in the visible region
for the first time. We also show the experimental approach to manipulating two
spawned Weyl points that are identically charged in synthetic space. Moreover,
topological end modes uniquely resulting from the charge-2 Dirac point can be
delicately controlled within truncated superlattice samples, opening a pathway
for us to rationally engineer local fields with intense enhancement.
