Browsing by Author "Zhang, Yongping"
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Item Gap Solitons in Spin-Orbit-Coupled Bose-Einstein Condensates in Optical Lattices(American Physical Society, 2015-04-23) Zhang, Yongping; Xu, Yong; Busch, ThomasWhile different ways to realize spin-orbit coupling in Bose-Einstein condensates exist, not all are currently experimentally implementable. Here we present a detailed study of gap solitons in a Bose-Einstein condensate with experimentally realizable spin-orbit coupling and discuss two cases relating to a spin-dependent parity symmetry. In the parity symmetric case, two families of fundamental gap solitons in the second linear energy gap are demonstrated with the opposite sign of the parity, with one family having single-humped densities and the other double-humped ones. In the case of broken parity symmetry, the fundamental modes manifest spin polarization. Both families possess an opposite sign of the spin polarization.Item Superfluidity in the Absence of Kinetics in Spin-Orbit-Coupled Optical Lattices(Amer Physical Soc) Hui, Hoi-Yin; Zhang, Yongping; Zhang, Chuanwei; Scarola, V. W.; 0000 0000 3722 2361 (Zhang, C); 4042455 (Zhang, C); Zhang, ChuanweiAt low temperatures bosons typically condense to minimize their single-particle kinetic energy while interactions stabilize superfluidity. Optical lattices with artificial spin-orbit coupling challenge this paradigm, because here kinetic energy can be quenched in an extreme regime where the single-particle band flattens. To probe the fate of superfluidity in the absence of kinetics we construct and numerically solve interaction-only tight-binding models in flatbands. We find that superfluid states arise entirely from interactions operating in quenched kinetic energy bands, thus revealing a distinct and unexpected condensation mechanism. Our results have important implications for the identification of quantum condensed phases of ultracold bosons beyond conventional paradigms.