https://www.sciencedaily.com/releases/2019/12/191219214153.htm

"Our team experimentally detected an exceptional surface, a continuous three-dimensional curving surface of exceptional points," said Xufeng Zhang, who led this international research project and works as an assistant scientist at the Center for Nanoscale Materials (CNM) at Argonne, a DOE Office of Science User Facility. Past research by others had detected exception points, and subsequent researchers had plotted lines of measured exceptional points, but this is the first time researchers have plotted surfaces.

"Think of two systems, each of which has its own loss of energy to the environment," explained Zhang. "Also imagine that these systems are coupled so that they can exchange energy between them."