Sharp crossover from composite fermionization to phase separation in mesoscopic mixtures of ultracold bosons

TL;DR

This paper investigates how tuning interactions in a two-component ultracold atomic mixture causes a sharp transition from a composite fermionization regime to a phase-separated state, highlighting a mesoscopic quantum phase transition.

Contribution

It demonstrates a controllable crossover between quantum regimes in mesoscopic ultracold mixtures, revealing a sharp transition driven by interaction tuning that disappears in large systems.

Findings

Transition from composite fermionization to phase separation observed

Weakly interacting component becomes phase coherent and central

Strongly interacting component moves to trap edges

Abstract

We show that a two-component mixture of a few repulsively interacting ultracold atoms in a one-dimensional trap possesses very different quantum regimes and that the crossover between them can be induced by tuning the interactions in one of the species. In the composite fermionization regime, where the interactions between both components are large, none of the species show large occupation of any natural orbital. Our results show that by increasing the interaction in one of the species, one can reach the phase-separated regime. In this regime, the weakly interacting component stays at the center of the trap and becomes almost fully phase coherent, while the strongly interacting component is displaced to the edges of the trap. The crossover is sharp, as observed in the in the energy and the in the largest occupation of a natural orbital of the weakly interacting species. Such a transition is a purely mesoscopic effect which disappears for large atom numbers.