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 Schrödinger 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.
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 Schrödinger 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.
Once its phase-space density is high enough, an interacting dilute Bose gas can be described by a macroscopic wave function obeying nonlinear dynamics. Ultracold Bose gases thus form coherent quantum fluids whose behavior becomes particularly rich in one dimension, where interactions and integrability tightly guide the evolution. In this thesis, we study a two-component weakly interacting 1D Bose gas that maps onto the attractive nonlinear Schrödinger equation (NLSE) in a certain limit, and more generally onto the Landau-Lifshitz equation (LLE), governing spin-chains. This correspondence enables the controlled preparation and exploration of multi-soliton solutions of both models. We first realize NLSE multi-solitons and characterize their dynamics, including their distinctive breathing behavior. Using the full LLE mapping, we then extend this implementation to multi-solitons with arbitrary depletion, thereby accessing a broader family of solitons and revealing features intrinsic to the underlying spin-chain description. Finally, we investigate weak integrability breaking and show that it drives the decomposition of multi-solitons into their constituents, rendering their encoded scattering data experimentally accessible. This provides a controlled pathway to probe integrable structures, opening prospects for studying soliton gases, interacting nonlinear waves, and the emergence of complex dynamics from nearly integrable systems.
We investigate the dynamics of vector solitons in a two-component Bose–Einstein condensates governed by the system of Gross–Pitaevskii equations. Using a gauge-transformation approach, we construct a four-soliton solution and analyze their interactions, including superposition states, fission, and shape-preserving collisions. We explore the ability of time-dependent parameters, such as the intra- and intercomponent interaction coefficients and trapping potential, to control the soliton properties. In particular, we demonstrate controlled four-soliton fission, highlighting its potential applications to quantum data processing and coherent matter-wave transport. The results suggest experimental realization in BEC systems and provide insights into nonlinear wave interactions in multicomponent quantum fluids.
États multi-solitons dans un mélange de spin de Condensats de Bose-Einstein Pour une densité de l'espace de phase suffisamment élevée, un gaz de Bose dilué en interaction peut être décrit par une fonction d'onde macroscopique obéissant à une dynamique non linéaire. Les gaz de Bose ultrafroids forment ainsi des fluides quantiques cohérents dont le comportement devient particulièrement riche à une dimension, où les interactions et l'intégrabilité guident fortement l'évolution. Dans cette thèse, nous étudions un gaz de Bose 1D à deux composantes en interaction faible, qui se décrit par l'équation de Schrödinger non linéaire attractive (NLSE) dans un certain régime, et plus généralement par l'équation de Landau-Lifshitz (LLE), régissant la dynamique de chaînes de spin. Cette correspondance permet la préparation et l'exploration contrôlées de solutions multi-solitons des deux modèles. Nous réalisons d'abord des solitons multiples NLSE et caractérisons leur dynamique, notamment leur comportement respirant distinctif. En utilisant une description complète via LLE, nous étendons ensuite cette mise en œuvre à des solitons multiples avec une déplétion arbitraire, accédant ainsi à une famille plus large de solitons et révélant des caractéristiques intrinsèques à la description sous-jacente de la chaîne de spin. Enfin, nous étudions la brisure de l'intégrabilité et montrons qu'elle entraîne la décomposition des multi-solitons en leurs constituants, rendant ainsi leurs données de diffusion accessibles expérimentalement. Cela fournit une voie contrôlée pour sonder les structures intégrables, ouvrant des perspectives pour l'étude des gaz de solitons, des ondes non linéaires en interaction et de l'émergence de dynamiques complexes à partir de systèmes presque intégrables.
We present a series of experimental investigations on binary mixtures of Bose-Einstein condensates. Our focus lies on the regime where the interaction parameters place the system at the threshold of miscibility. We demonstrate that the dynamics of such mixtures can be effectively reduced to a single nonlinear equation. This framework is illustrated through the discussion of stable solitonic solutions in one and two dimensions. Furthermore, we show that employing a binary mixture enables exploration beyond the dynamics governed by the nonlinear Schrödinger equation, allowing us to address other fundamental equations in nonlinear physics, such as the Landau-Lifshitz equation describing the motion of spin chains in ferromagnetic materials.
In this work, we employ the SO(2) rotations of a two-component, one-, two-, and three-dimensional nonlinear Schr\"odinger system at and near the Manakov limit to construct vector solitons and vortex structures. In this way, stable stationary dark-bright solitons and their higher-dimensional siblings are transformed into robust oscillatory dark-dark solitons (and generalizations thereof) with and without a harmonic confinement. By analogy to the one-dimensional case, vector higher-dimensional structures take the form of vortex-vortex states in two dimensions and, e.g., vortex-ring--vortex-ring ones in three dimensions. We consider the effects of unequal (self- and cross-) interaction strengths, where the SO(2) symmetry is only approximately satisfied, showing the dark-dark soliton oscillation is generally robust. Similar features are found in higher dimensions too, although our examples suggest that phenomena such as phase separation may contribute to the associated dynamics. These results, in connection with the experimental realization of one-dimensional variants of such states in optics and Bose-Einstein condensates, suggest the potential observability of the higher-dimensional bound states proposed herein.
Ultracold gases provide an unprecedented level of control for the investigation of soliton dynamics and collisions. We present a scheme for deterministically preparing pairs of three-component solitons in a Bose-Einstein condensate. Our method is based on local spin rotations which simultaneously imprint suitable phase and density distributions. This enables us to observe striking collisional properties of the vector degree of freedom which naturally arises for the coherent nature of the emerging multicomponent solitons. We find that the solitonic properties in the quasi-one-dimensional system are quantitatively described by the integrable repulsive three-component Manakov model.