Dynamical Instability of internally excited localised BEC in an anti-trapping waveguide
We have experimental evidence of dynamical instability of a BEC with lowlying excitations in an antitrapping waveguide. Using a novel almostnondestructive imaging technique, we are able to image a single condensate in a trap up to 10 times at a 7:1 SNR with a no change in atom number attributable to imaging induced population loss. This technique uniquely enables us to image the dynamics of stochastic processes in condensates. In a recent experiment, we have been able to image the instability induced breakup of a localized condensate in an antitrapping waveguide in the selfattractive interaction regime. Forming a condensate in a conventional crossed optical dipole trap, the cloud is released along the waveguide by instantaneously switching this trap off, after which the density profile is spontaneously modulated by a periodic perturbation which ultimately results in the formation of a soliton train. The mathematical analysis of this process is compounded by the presence of lowlying excitations in the condensate due to the fast release. These influence the timescales of salient processes of the system, in particular the Bosenovalike collapse.
Because the antitrapping is weak, the system is amenable to a crude analysis of the axial breakup using the standard linear stability analysis of the modulational instability of a perturbed plane wave in the NLSE. This provides reasonable agreement with experimental results with the number of components which form in the soliton train. However, experimental and theoretical estimates of other import parameters, in particular the time for onset of the instability disagree substantially.