Superfluidity and the Roton

University of Chicago scientists can create an exotic, particle-like excitation called a roton in superfluids with the tabletop apparatus pictured here. Posing left to right are graduate students Li-Chung Ha and Logan Clark, and Prof. Cheng Chin.

See: Cesium atoms shaken, not stirred, to create elusive excitation in superfluid 

We present experimental evidence showing that an interacting Bose condensate in a shaken optical lattice develops a roton-maxon excitation spectrum, a feature normally associated with superfluid helium. The roton-maxon feature originates from the double-well dispersion in the shaken lattice, and can be controlled by both the atomic interaction and the lattice modulation amplitude. We determine the excitation spectrum using Bragg spectroscopy and measure the critical velocity by dragging a weak speckle potential through the condensate—both techniques are based on a digital micromirror device. Our dispersion measurements are in good agreement with a modified Bogoliubov model. DOI: http://dx.doi.org/10.1103/PhysRevLett.114.055301
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