Parity-time symmetry in chain of scatterers

We demonstrate the Parity-Time (PT) symmetry properties of Bloch eigenmodes in chains of pairs of dipolar scatterers. Modes guided by such structures can develop a condition, identified as an exceptional point of degeneracy (EPD) in the dispersion diagram, where at least two modes coalesce. We examine how this EPD is associated with PT-symmetry conditions when the scatterers have identical properties with balanced gain and loss. These finding allows for realizing high Q resonators for sensor applications, as well as low-threshold lasing.