Experimental study of the high-order exceptional points in a four-state non-Hermitian microwave meta-atoms system

Non-Hermitian degeneracies, also known as exceptional points, have recently attracted increased attention due to their enhanced sensitivity and distinct topological features. We realize the non-Hermitian system experimentally using four coupled microwave meta-atoms with asymmetric losses. By tuning eigenfrequencies and dissipative losses of meta-atoms, we obtain both theoretically and experimentally that multiple EPs can collide and merge, leading to higher-order singularities much richer than those seen in two-state systems. These findings are expected to enrich our understanding of EP physics and provide a robust foundation for the exploration of high-order EP applications.