Transverse Non-Hermitian Drift Induced by the Quantum Metric of Exceptional Rings

Exceptional rings are sets of non-Hermitian singularities stemming from Dirac points. We study them theoretically and experimentally in an atomic vapor cell. We demonstrate the formation of an exceptional ring in a photonic honeycomb lattice by showing a transition between conical diffraction and non-Hermitian broadening of a beam in real space. We further predict and demonstrate an original non-Hermitian effect: the transverse non-Hermitian drift. It is similar to the anomalous Hall effect, but it occurs in reciprocal space, and its description requires a biorthogonal quantum metric. The non-Hermitian drift can be used for applications in beam steering.