  I study theoretically quadrupolar topological insulators under applied static
electric field rotated along the crystal axis. I demonstrate, that the energy
spectrum of this structure is a Wannier-Stark ladder that is quantized and
directly distinguishes between the topological phase, possessing localized
corner states, and the trivial phase, lacking the corner states. These results
may find applications in the characterization of rapidly emerging higher-order
topological phases of light and matter.
