Explanation of critical angular velocities of the vortex formation in a stirred Bose-Einstein condensate

The problem of explaining the critical angular velocity Omega (c) when the formation of a vortex in the stirred Bose-Einstein condensate becomes energ etically possible is considered in the framework of the variational approac h. The origin of smallness of the calculated Omega (c) in comparison with t he measured values, which takes place for a pure quantum state with the uni t angular momentum per condensed particle, is uncovered. The agreement with the measured Omega (c) is achieved upon admitting a small admixture of the zero angular-momentum state in the wave function of the one-vortex quantum state prepared after stirring. A portion of this admixture amounts to 10-1 3% of the total condensed atoms. A possible test of this hypothesis is prop osed. (C) 2000 MAIK "Nauka/Interperiodica".