Oliver Thewalt

    Oliver Thewalt

    Theoretical Physics | Quantum Biology | Dark Matter Research | Energy Consulting | Creation of Hydrogen ATOM in the Higgs Field >> Vote for Nobel Prize


    Zoom of a 1D simulation matching the lower middle frame of Fig. 2 showing the total density n=n+n as a function of time in the region where the dynamic instability first appears. Dashed lines are the three group velocities vg=E(k) at the quasimomenta k where the inverse effective mass m1=E′′(k) first becomes negative (steepest line), the point of maximum m1 (middle), and the point where the m1 returns to positive (least steep line). Red points demonstrate where the local quasimomentum lies in the negative-mass region. Note that, as described in the text, the pileup initially contains many density fluctuations, but sharpens as solitons and phonons “radiate” energy away from the wall.

    Image Courtesy:

    Negative-Mass Hydrodynamics in a Spin-Orbit–Coupled Bose-Einstein Condensate 

    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.

    Negative-Mass Hydrodynamics in a Spin-Orbit\char21{}Coupled Bose-Einstein Condensate
    M. A. Khamehchi et al.
    Physical Review Letters
    American Physical Society
    Apr 10, 2017