Loss-Enabled Chirality Inversion in Terahertz Metasurfaces

Exceptional points (EPs), known as non-Hermitian degeneracies featuring missing eigenspace dimensions, have led to a variety of intriguing wave phenomena in various physical platforms. Chiral EPs collapsing in two orthogonal eigenstates can lead to unique effects and applications, such as loss-induced transparency, EP-enhanced sensing, and chirality-reversal electronics, etc. However, in previous experiments, chiral EPs were typically induced in fixed structures with inherent active gains or nearby nanotips, which are unfavorable for on-chip integrations with low-power elements. Here, we demonstrate the active control of EPs chirality in situ with exceptional-line metasurface. Selective chirality inversion can be well achieved by only light-induced loss without altering the metasurface size. We also perform an ultrafast chirality switch in the picosecond level within transient disturbance. In a broader view, our results provide a platform for the investigation of metasurface-based non-Hermitian physics and active EP modulation, which can stimulate exciting works along this line in near future. locked icon locked icon locked icon locked icon locked icon locked icon locked icon locked icon Physics Subject Headings (PhySH)MetasurfacesExceptional pointsOptical-pump terahertz-probe spectroscopy