The cross-over from Townes solitons to droplets in a 2D Bose mixture

When two Bose-Einstein condensates-labelled 1 and 2-overlap spatially, the equilibrium state of the system depends on the miscibility criterion for the two fluids. Here, we theoretically focus on the non-miscible regime in two spatial dimensions and explore the properties of the localized wave packet formed by the minority component 2 when immersed in an infinite bath formed by component 1. We address the zero-temperature regime and describe the two-fluid system by coupled classical field equations. We show that such a wave packet exists only for an atom number N (2) above a threshold value corresponding to the Townes soliton state. We identify the regimes where this localized state can be described by an effective single-field equation up to the droplet case, where component 2 behaves like an incompressible fluid. We study the near-equilibrium dynamics of the coupled fluids, which reveals specific parameter ranges for the existence of localized excitation modes.

Automated summary

In this theoretical study, we investigate the non-miscible regime of two Bose-Einstein condensates labeled 1 and 2 in two-dimensional space. We focus on the properties of a localized wave packet formed by the minority component 2 when immersed in an infinite bath formed by component 1. Using coupled classical field equations, we analyze the system at zero temperature and determine the existence of the wave packet above a threshold atom number N (2) corresponding to the Townes soliton state. We also identify the regimes where an effective single-field equation can describe the localized state up to the droplet case where component 2 behaves as an incompressible fluid. We study the near-equilibrium dynamics of the coupled fluids and find specific parameter ranges for the presence of localized excitation modes.