Observation of a Chiral State in a Microwave Cavity

A microwave experiment has been realized to measure the phase difference of the oscillating electric field at two points inside the cavity. The technique has been applied to a dissipative resonator which exhibits a singularity—called exceptional point—in its eigenvalue and eigenvector spectrum. At the singularity, two modes coalesce with a phase difference of [Formula presented]. We conclude that the state excited at the singularity has a definitive chirality. © 2003 The American Physical Society.