Parity-Time Symmetry in a Coherent Atomic Medium

Parity-time (PT) symmetry has attracted considerable attention since optics was realized with the ability to provide a fertile platform for the exploration of PT symmetry. Although many of the previous researches on PT symmetry have been conducted in solid-state system and the network of fiber loops, coherent atomic medium offers another platform for the exploration of PT symmetry due to its easy reconfigurability and flexible tunability in parameters. This dissertation mainly focuses on the investigations of the phenomena related to PT-symmetric optical lattice in a coherent atomic medium. First, a controllable photonic crystal with periodic Raman gain was constructed in a coherent atomic medium. The dependence of the periodic Raman gain on the temperature of the atomic medium and total power of the pump beams has been investigated. Second, a new scheme to observe the PT-symmetric optical lattice in a coherent atomic medium was realized in experiment. The phase difference between the gain and loss waveguides was measured and the phase transition point was observed. Last, integer and fractional Talbot effects from PT-symmetric optical lattice, quasi-PT-symmetric optical lattices, and conventional electromagnetically induced transparency (EIT) optical lattice have been investigated. We find the intensity of the diffracted signal wave from the PT-symmetric optical lattice and quasi-PT -symmetric optical lattices can be substantially increased due to the gain channels in the optical lattice, while for the conventional EIT optical lattice, the intensity of the diffracted wave is decreased because of the absorption in the optical lattice. Moreover, the visibilities of the fractional Talbot image from the PT-symmetric optical lattice and quasi-PT-symmetric optical lattices are larger than that from the conventional EIT optical lattice for most of the propagation distances