  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.

Quantum Gases