Magnetic defects in an unbalanced mixture of two Bose-Einstein condensates

TL;DR

This paper investigates magnetic defects in unbalanced two-component Bose-Einstein condensates, analyzing their properties, conditions for formation, and potential experimental realization, especially near the demixing transition and with unequal interactions.

Contribution

It introduces a detailed theoretical analysis of magnetic defects in unbalanced BEC mixtures, including conditions for their existence and methods for experimental creation.

Findings

Magnetic defect width depends on coupling constant differences.

Critical filling threshold exists for minority atoms to remain in defect cores.

Applications to sodium BECs in uniform and trapped setups are discussed.

Abstract

When the spectrum of magnetic excitations of a quantum mixture is much softer than the density spectrum, the system becomes effectively incompressible and can host magnetic defects. These are characterized by the presence of a topological defect in one of the two species and by a local modification of the density in the second one, the total density being practically unaffected. For miscible mixtures interacting with equal intraspecies coupling constants the width of these magnetic defects is fixed by the difference between the intraspecies and interspecies coupling constants and becomes larger and larger as one approaches the demixing transition. When the density of the filling component decreases, the incompressibility condition breaks down and we predict the existence of a critical filling, below which all the atoms of the minority component remain bound in the core of the topological defect. Applications to the sodium case both in uniform and harmonically trapped configurations are considered and a protocol to produce experimentally these defects is discussed. The case of binary mixtures interacting with unequal intraspecies forces and experiencing buoyancy is also addressed.