“It’s long been thought that two’s company and three’s a crowd. But electrical and systems engineers at Washington University in St. Louis and their collaborators have shown that the addition of a third nanoscatterer, complementing two “tuning” nanoscatterers, to a photonics resonator makes for a fascinating physics party. Specifically, the two tuning nanoscatterers set the resonator at an “exceptional point,” a special state of a system at which unusual phenomena may occur. The third nanoscatterer perturbs the system, and like a nasty playground bully, the smaller it is, the more response it gets. The Washington University team, led by Lan Yang, the Edwin H. & Florence G. Skinner Professor of Electrical & Systems Engineering, has made major strides recently in the study and manipulation of light. The team’s most recent discovery of the sensing capability of microresonators could have impacts in the creation of biomedical devices, electronics and biohazard detection devices. “It’s challenging to detect nanoscale objects, such as nanoparticles,” Yang said. “If the object is very small, it introduces little perturbation to a sensing system. We utilize an unusual topological feature associated with exceptional points of a physical system to enhance the response of an optical sensor to very small perturbations, such as those introduced by nanoscale objects. The beauty of the exceptional point sensor is the smaller the perturbation, the larger the enhancement compared to a conventional sensor.”“