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Published on: December 4, 2017
Negative-Mass Hydrodynamics in a Spin-Orbit-Coupled Bose-Einstein Condensate
M A Khamehchi1, Khalid Hossain1, M E Mossman1
1Department of Physics and Astronomy, Washington State University, Pullman, Washington 99164, USA.
Abstract:
A negative effective mass can be realized in quantum systems by engineering the dispersion relation. A powerful method is provided by spin-orbit coupling, which is currently at the center of intense research efforts. Here we measure an expanding spin-orbit coupled Bose-Einstein condensate whose dispersion features a region of negative effective mass. We observe a range of dynamical phenomena, including the breaking of parity and of Galilean covariance, dynamical instabilities, and self-trapping. The experimental findings are reproduced by a single-band Gross-Pitaevskii simulation, demonstrating that the emerging features-shock waves, soliton trains, self-trapping, etc.-originate from a modified dispersion. Our work also sheds new light on related phenomena in optical lattices, where the underlying periodic structure often complicates their interpretation.
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