Solitons and breathers in Bose-Einstein condensates
Solitons are localized wave packets that maintain their shape while propagating at a constant velocity. They form in nonlinear wave systems, where an attractive nonlinearity balances the wave dispersion. When multiple solitons collide, each soliton emerges from the collision with no change in their shape and velocity, but only gains a small shift in their trajectory. Such remarkable properties are a result of the integrability of the underlying equations, which prompted widespread research interest in solitons and their interactions. They have been observed experimentally in water wave, fiber optics, plasma, and Bose-Einstein condensates (BEC). In this talk, I will discuss three recent experiments on solitons in Bose-Einstein condensates. First, we prepare a pair of solitons in a quasi-1D harmonic confinement and observe their collisions as they oscillate in the trap. We show that the collision is a complex process depending on the relative phase of the solitons. The in-phase solitons may collapse due to the proximity to the 1D-3D crossover, while the out-of-phase solitons persist. Second, we can form a train of solitons from an elongated BEC by rapidly changing the sign of the nonlinear interaction. We study the effect of modulational instability on the formation of the soliton trains. Third, we can form a quasi-bound state of multiple solitons, known as breathers. We characterize the breather dynamics and measure the effect of the aspect ratio of the harmonic potential, the strength of the quench and the strength of the nonlinearity. The formation of breathers paves ways for studying beyond-mean-field physics in BECs.