Nonlinear Dynamics in BECs ~  Quantum Shocks, Solitons, and Faraday Waves

Bose-Einstein Condensates (BECs) are a powerful tool for the study of nonlinear effects. In this talk, I will present several experiments from my group at WSU in which nonlinear hydrodynamics are investigated.

In a nonlinear context, apparently simple operations can lead to intriguingly rich behavior. As a particular example, we study the merging and splitting of BECs in the nonadiabatic regime. We observe soliton trains as a result of quantum shock (dispersive shock) during the merging of two BECs. When a BEC is split into two parts by a repulsive barrier, a transition from sound formation to shock generation and solitons is observed with increasing barrier strength.

In another set of experiments we investiagte the effects of a penetrable barrier that is swept through a BEC. Stable and unstable fluid flow regimes are observed. The unstable regime is characterized by the generation of many solitons.

Solitons in a BEC can also be generated without the application of an external perturbing potential, namely by crossing the transition from non-condensed to condensed atoms sufficiently rapidly. This effect, which we observe experimentally, may be related to the Kibble-Zurek mechanism.

Finally, I will present our experimental demonstration of Faraday waves in a BEC. These Faraday waves are longitudinal sound waves excited by a parametric resonance. They are an important example for pattern formation in driven systems.