2004/05/31 by Yuki Kawaguchi, Mikio Nakahara, Tetsuo Ohmi
Physics and Astronomy · #cond-mat.soft #cond-mat.mtrl-sci
paper · pdf · doi:10.1103/physreva.70.043605
published as Phys. Rev. A 70, 043605 (2004) · 7 pages, 3 figures submitted to PRA
arxiv created 2004/07/23 · arxiv updated 2009/12/01
Topological phase imprinting is a unique technique for vortex formation in a Bose-Einstein condensate (BEC) of alkali metal gas, in that it does not involve rotation: BEC is trapped in a quadrupole field with a uniform bias field which is reversed adiabatically leading to vortex formation at the center of the magnetic trap. The scenario has been experimentally verified by MIT group employing 23Na atoms. Recently similar experiments have been conducted at Kyoto University, in which BEC of 87Rb atoms has been used. In the latter experiments they found that the fine-tuning of the field reverse time T\rm rev is required to achieve stable vortex formation. Otherwise, they often observed vortex fragmentations or a condensate without a vortex. It is shown in this paper that this behavior is attributed to the heavy mass of the Rb atom. The confining potential, which depends on the eigenvalue mB of the hyperfine spin \bvF along the magnetic field, is now shifted by the gravitational field perpendicular to the vortex line. Then the positions of two weak-field-seeking states with mB=1 and 2 deviate from each other. This effect is more prominent for BEC with a heavy atomic mass, for which the deviation is greater and, moreover, the Thomas-Fermi radius is smaller. We found, by solving the Gross-Pitaevskii equation numerically, that two condensates interact in a very complicated way leading to fragmentation of vortices, unless T\rm rev is properly tuned.