We experimentally demonstrate PT-symmetric optical lattices with periodicalgain and loss profiles in a coherently-prepared four-level N-type atomicsystem. By appropriately tuning the pertinent atomic parameters, the onset ofPT-symmetry breaking is observed through measuring an abrupt phase-shift jumpbetween adjacent gain and loss waveguides. The experimental realization of suchreadily reconfigurable and effectively controllable PT-symmetric waveguidearray structure sets a new stage for further exploiting and betterunderstanding the peculiar physical properties of these non-Hermitian systemsin atomic settings.
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