Magnetic waves in an ultracold gas behave like elastic cords. Two or three such cords can twist into a single knot that breathes: it contracts and expands, but never unravels. For the first time, scientists assembled such knots in the lab and confirmed that their breathing matches calculations exactly.
The gas consisted of two atomic species that do not mix, like oil and water. The magnetic properties of this gas are described by an equation similar to the one for waves on a rope. This equation has special solutions — solitons, solitary waves that do not spread out. From them, one can build composite states resembling a bundle of several ropes.
A weak point-like perturbation on such a knot destroys its integrity. The knot breaks into individual cords — fundamental solitons. This decay is like a reverse mathematical operation: recovering simple components from a complex wave. The experiment showed that composite magnetic solitons are real, and they can be created and disassembled piece by piece.
as written by the authors arXiv:2603.09357
We report the deterministic experimental realization and controlled fission of magnetic multi-soliton states in a uniform quasi-one-dimensional immiscible two-component Bose gas. We explore the Manakov regime, where the spin dynamics is well described by the easy-axis Landau-Lifshitz equation (LLE). The gauge equivalence between the easy-axis LLE and the attractive nonlinear Schr\"odinger equation (NLSE) enables the direct construction of magnetic multi-solitons from the well-known NLSE solutions. We observe the two- and three- soliton states, which exhibit robust breathing in quantitative agreement with integrable theory. By introducing a weak, localized perturbation, we controllably break integrability and induce the splitting of a two-soliton into its fundamental constituents. This process reveals the composite structure of multi-soliton states and realizes an experimental analog of the inverse scattering transform.
Solitons were first noticed in 1834 by engineer John Scott Russell: he saw a wave in a canal that traveled several kilometers without changing shape.