Self-induced density modulations in the free expansion of Bose-Einstein condensates

Abstract

We simulate numerically the free expansion of a repulsive Bose-Einstein condensate with an initially Gaussian density profile. We find a self-similar expansion only for weak interatomic repulsion. In contrast, for strong repulsion we observe the spontaneous formation of a shock wave at the surface followed by a significant depletion inside the cloud. In the expansion, contrary to the case of a classical viscous gas, the quantum fluid can generate radial rarefaction density waves with several minima and maxima. These intriguing nonlinear effects, never observed in free-expansion experiments with ultracold alkali-metal atoms, can be detected with the available setups

Quantum Bubbles in Microgravity

“…From left to right and from top to bottom, the condensate slices along the xz plane are taken at the times: 0 ms, 4.5 ms, 9 ms, and 18 ms. The hollow condensate expands both outwards and inwards, showing a qualitatively different interference pattern with respect to that of harmonic traps [37,46]. [37], here we observe the appearance of a central density peak around the final time of 18 ms.…”

Extended Thomas-Fermi density functional for the unitary Fermi gas

“…The gradient term, i.e. the quantum correction, is necessary in a superfluid to avoid unphysical phenomena like the formation of wave front singularities in the dynamics of dispersive shock waves [41].…”

Quantum transients

“…The effect is stable in a parameter range and could be observed with current technology. Interestingly enough, similar abrupt changes in time of the coupling constant g 1D [161] and density perturbations [162] can also induce self-modulations in the density profile and shock waves. The appearance of shock waves is a phenomenon also present in classical non-linear equations and is out of the scope of this review.…”