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Demixing phenomena in 2D Bose gases
Demixing is an everyday life phenomenon that takes place when different species with strong enough repulsive interactions are brought together: because the mixed state is unstable, a hydrodynamical instability develops, which tends to spatially segregate the two immiscible species. From the separation of oil and vinegar in a vinaigrette, to the tears of wine observable in a glass filled with alcohol, hydrodynamical instabilities are encountered in many mundane situations.
However, the description of cold atoms gases by hydrodynamic-like equations shows that these phenomena are also relevant for such systems. In this thesis, we explore the dynamics of such phenomena in 2D Bose gases confined in box potentials, both in a square and ring configuration, and see how the geometry of our box trap influences the emerging patterns. In particular, the absence of harmonic confinement allows us to study in depth the role of the box’s edges in the appearing dynamics.
We first describe the experimental setup, and present an iterative method to tailor arbitrary potentials with a Digital Micromirror Device (DMD). We then introduce the theoretical tools necessary to grasp the physics of immiscible Bose mixtures, before treating in details two distinct cases: the case of a gas confined in a 1D geometry with periodic boundary conditions (a ring), where we expect the patterns formation to be mainly triggered by density noise; and the case of a gas confined in a square, where the role of the box’s edges is important to start the demixing dynamics.