Sang Won Seo, Jae-yoon Choi, Yong-il Shin
We observe concentric density ripples in mechanically perturbed and freely expanding quasi-two-dimensional Bose-Einstein condensates, and show that the ripples develop from quantized vortices in the condensates. Free expansion of a condensate containing a vortex is numerically simulated under the assumption of no atom-atom interactions, and the experimental data are found to be in good quantitative agreement with the numerical results for a singly charged vortex, in particular, including the defocus effect in imaging due to the gravitational freefall of the condensate. In the defocused image, the vortex core becomes magnified and appears to be filled after a certain expansion time. We show that the vortex charge number can be determined from the onset time of the core-filling in the defocused image.
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http://arxiv.org/abs/1305.4689
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