Collective excitation frequencies and vortices of a Bose-Einstein condensed state with gravity-like interatomic attraction

Abstract

We study the collective excitations of a neutral atomic Bose-Einstein condensate with gravity-like $1/r $ interatomic attraction induced by electromagnetic wave. Using the time-dependent variational approach, we derive an analytical spectrum for monopole and quadrupole mode frequencies of a gravity-like self-bound Bose condensed state at zero temperature. We also analyze the excitation frequencies of the Thomas-Fermi-gravity (TF-G) and gravity (G) regimes. Our result agrees excellently with that of Giovanazzi {\em et al}. [Europhysics Letters, {\bf 56}, 1 (2001)], which is obtained within the sum-rule approach. We also consider the vortex state. We estimate the superfluid coherence length and the critical angular frequencies to create a vortex around the $ z $-axis. We find that the TF-G regime can exhibit the superfluid properties more prominently than the G-regime. We find that the monopole mode frequency of the condensate decreases due to the presence of a vortex.