Barrier effects on the collective excitations of split Bose-Einstein condensates

We investigate the collective excitations of a single-species Bose gas at T = 0 in a harmonic trap where the confinement undergoes some splitting alon g one spatial direction. We mostly consider one-dimensional potentials cons isting of two harmonic wells separated by a distance 2z(0), since they esse ntially contain all the barrier effects that one may visualize in the three -dimensional situation. We find, within a hydrodynamic approximation, that regardless of the dimensionality of the system, pairs of levels in the exci tation spectrum, corresponding to neighboring even and odd excitations, mer ge together as one increases the barrier height up to the current value of the chemical potential. The excitation spectra computed in the hydrodynamic al or Thomas-Fermi limit are compared with the results obtained from exactl y solving the time-dependent Gross-Pitaevskii equation. We also analyze the characteristics of the spatial pattern of excitations of three-dimensional boson systems according to the amount of splitting of the condensate. [S10 50-2947(99)12105-X].