Observation of Parity-Time Symmetry in Optically Induced Atomic Lattices

Abstract

We experimentally demonstrate $PT$-symmetric optical lattices with periodical gain and loss profiles in a coherently prepared four-level $N$-type atomic system. By appropriately tuning the pertinent atomic parameters, the onset of $PT$-symmetry breaking is observed through measuring an abrupt phase-shift jump between adjacent gain and loss waveguides. The experimental realization of such a readily reconfigurable and effectively controllable $PT$-symmetric waveguide array structure sets a new stage for further exploiting and better understanding the peculiar physical properties of these non-Hermitian systems in atomic settings.