  Photonic lattices have emerged as a promising approach to localize light in
space, for example, through topologically protected edge states and
Aharonov-Bohm caging. They are of particular importance in the study of flat
band systems via the associated nondiffracting compact localized states.
However, such states typically appear static, thus not allowing adaptive or
evolutionary features of light localization. Here we report on the first
experimental realization of an oscillating compact localized state (OCLS). We
observe an oscillatory intensity beating during propagation in a
two-dimensional photonic decorated Lieb lattice. The photonic system is
realized by direct femtosecond laser writing and hosts multiple flat bands at
different eigenenergies in its band structure. Our results open new avenues for
evolution dynamics in the up to now static phenomenon of light localization in
periodic waveguide structures.
