Resonances and Dynamical Fragmentation in a Stirred Bose-Einstein Condensate

Superfluids are distinguished from ordinary fluids by the quantized manner in which 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 atoms interacting with finite-range potential in two spatial dimensions that is stirred by a rotating beam. We use the multiconfigurational Hartree method for bosons, which goes beyond 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 resonances, i.e., peaks in the total energy, as the stirring frequency is increased. Fragmentation and a change of the symmetry of the density of the gas accompany the appearance of these resonances. 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.