  Optical spectral weight transfer associated with the onset of
superconductivity at high energy scales compared with the superconducting gap
has been observed in several systems such as high-$T_c$ cuprates. While there
are still debates on the origin of this phenomenon, a consensus is that it is
due to strong correlation effects beyond the BCS theory. Here we show that
there is another route to a nonzero spectral weight transfer based on the
quantum geometry of the conduction band in multiband systems. We discuss
applying this idea to the cuprates and twisted multilayer graphene.
