Long-range interactions between optical solitons

Solitons are self-localized wave packets arising from a robust balance between dispersion and nonlinearity. They are a universal phenomenon, exhibiting properties typically associated with particles. Thus far, interactions between solitons have been observed only between neighbouring solitons at close proximity. Here, we study interactions between solitons in highly non-local nonlinear media, and demonstrate experimentally attraction between solitons propagating in different samples, where their optical fields never overlap and the interaction is mediated solely by a non-optical wire. This increases the soliton interaction range by orders of magnitude, and breaks the close-proximity and nearest-neighbour limitations on soliton interactions. We also experiment with three-dimensional interactions between solitons that are far apart, where the solitons capture each other into a spiralling motion with a circular orbit, and a tangential velocity that does not depend on the separation between solitons. Our study suggests that these phenomena could be used in the construction of novel model systems for studying the behaviour of complex nonlinear networks.