Formation of matter-wave soliton trains by modulational instability

Abstract

Nonlinear systems can exhibit a rich set of dynamics that are inherently sensitive to their initial conditions. One such example is modulational instability, which is believed to be one of the most prevalent instabilities in nature. By exploiting a shallow zero-crossing of a Feshbach resonance, we characterize modulational instability and its role in the formation of matter-wave soliton trains from a Bose-Einstein condensate. We examine the universal scaling laws exhibited by the system and, through real-time imaging, address a longstanding question of whether the solitons in trains are created with effectively repulsive nearest-neighbor interactions or rather evolve into such a structure. Modulational instability (MI) is a process in which broadband perturbations spontaneouslyseed the nonlinear growth of a nearly monochromatic wave disturbance (1). Owing to its generality, MI plays a role in a variety of different physical systems such as water waves, where it is known as a Benjamin-Feir instability (2); plasma waves; nonlinear optics (3-5); and ultracold atomic gases (6). The nonlinear interaction resulting in MI also supports solitons, which are localized waves whose dispersion is exactly balanced by the nonlinearity (7,8). Thus, the rapid 1 arXiv:1703.04662v2 [cond-mat.quant-gas]