Oscillation, interaction and collision of solitons in Bose-Einstein condensates

During the last decade the physics of ultracold quantum gases has matured into a highly active and versatile field of research. Experiments dedicated to the physics of Bose-Einstein condensates have been performed and diverse phenomena, which are distinguished by fundamentally different regimes of interaction, can be investigated. Particularly solitons, characterized as non-spreading wavepackets, are stabilized against dispersion by a suitable non-linear interaction and can propagate in a condensate[1,2]. In the present work the dynamical evolution of long-lived dark solitons has been studied as a paradigm of non-linear physics for the first time. We have been able to observe oscillations of dark solitons in elongated Bose-Einstein condensates and good agreement with the theoretically predicted oscillation frequency of ω/√2 has been obtained [1]. Moreover the results of detailed studies of the collision of two dark solitons distinguished by different depths are presented. This particular feature enables the identification of the individual solitons beyond the actual collision process and as a central result we show shown that these peculiar entities interpenetrate without significantly influencing each other [3]. The theoretical description of solitons as weakly interacting quasi particles is in good agreement with these findings. Continuative studies on vectorial “dark-bright” solitons and their dynamical properties complement the investigations on dark solitons.