Topological broadband invisibility

Abstract When an electromagnetic wave is incident onto an object, the scattering from the object leads to its exposure. An invisibility cloak can bend the electromagnetic wave around the object with phase velocities exceeding the light speed in free space, which seems only possible over a narrow bandwidth, as manifested in the existing approaches, such as transformation optics and scattering cancellation. Here, it is experimentally demonstrated that this bandwidth limitation can be overcome by strategically positioning objects at topological nodes, characterized by minimal electromagnetic field amplitudes and indeterminate phases. This is accomplished using all‐dielectric photonic crystal slabs, which are engineered to exhibit a pair of topological nodes at fixed planes across an extensive bandwidth. This bandwidth expansion is facilitated not by resonance, but by the enforcement of mirror and time‐reversal symmetry. These findings thus introduce a novel topological paradigm for the broadband invisibility devices.