  We investigate the coupling between quantum Hall (QH) edge channels (ECs)
located at opposite sides of a 50-um-wide Hall bar by exciting a charged
wavepacket in one EC and detecting time-dependent current in the other EC. In a
QH state, the current shows a peak followed by a dip, demonstrating the
existence of capacitive coupling across the incompressible two-dimensional
electron system (2DES). The observed magnetic field dependence of the amplitude
and time delay of the current suggests that the capacitance is affected by the
presence of localized states. We also show that the dominant manner of the
coupling changes gradually as the system changes between the QH and non-QH
states.
