Observations on Sound Propagation in Rapidly Rotating Bose-Einstein Condensates

Repulsive laser potential pulses applied to vortex lattices of rapidly rotating Bose-Einstein condensates create propagating density waves which we have observed experimentally and modeled computationally to high accuracy. We have observed a rich variety of dynamical phenomena ranging from interference effects and shock-wave formation to anisotropic sound propagation.

Figure 1

Response of a vortex lattice to wide repulsive laser pulses. Upper row displays experimental pictures and the corresponding frames below them are from 3D numerical simulations. The pulse durations are 5 ms (a,d), 10 ms (b,e), and 30 ms (c,f). The experimental (computational) pictures are taken after 45 ms of antitrapped expansion (respectively, (12, 16, and 22) ms in-trap evolution) after the end of the pulse.

Figure 2

Kinetic $E_{\mathrm{k}}$, trap $E_{\mathrm{t}\mathrm{r}}$, and mean-field $E_{\mathrm{m}\mathrm{f}}$ energies and their sum as functions of time. The data is obtained from the same simulation as Fig. 1d.

Figure 3

Experimental (a) and theoretical (b,c) response of a vortex lattice to a localized 5 ms long repulsive laser pulse. Beam parameters are $P=0.64\mathrm{m}\mathrm{W}$ and $d=19\mu \mathrm{m}$. The experimental image is taken after 45 ms antitrapped expansion, whereas the 3D computational image is taken after 14 ms of in-trap evolution.

Figure 4

Simulations (3D) on sound propagation in a ground state (lhs) and in a vortex lattice (rhs). The ordinates are normalized according to the temporal peak density.

Figure 5

Anisotropic sound propagation as observed in an experiment (a) or in the 3D simulation (b). The duration of the pulse with $P=300\mu \mathrm{W}$, $d=18\mu \mathrm{m}$ is 2.5 ms. Experimental (computational) image taken after 60 ms of antitrapped expansion (16 ms in-trap evolution).