Vortex nucleation through fragmentation in a stirred resonant Bose-Einstein condensate

Superfluids are distinguished from ordinary fluids by the quantized manner the rotation is manifested in them. Precisely, quantized vortices are known to appear in the bulk of a superfluid subject to external rotation. In this work we study a trapped ultracold Bose gas of $N=101$ atoms in two spatial dimensions that is stirred by a rotating beam. We use the multiconfigurational Hartree method for bosons, that extends the mainstream mean-field theory, to calculate the dynamics of the gas in real time. As the gas is rotated the wavefunction of the system changes symmetry and topology. We see a series of resonant rotations as the stirring frequency is increased. Fragmentation accompanies the resonances and change of symmetry of the wavefunction of the gas. We conclude that fragmentation of the gas appears hand-in-hand with resonant absorption of energy and angular momentum from the external agent of rotation.