Self-trapped quantum balls in binary Bose-Einstein condensates

TL;DR

This paper investigates the formation, stability, and collisions of self-trapped quantum balls in binary Bose-Einstein condensates, highlighting the roles of higher-order interactions beyond mean-field theory.

Contribution

It demonstrates that beyond-mean-field interactions can stabilize binary BEC quantum balls and explores their collision dynamics, providing a comprehensive analysis of these phenomena.

Findings

Higher-order interactions stabilize quantum balls.

Collisions are elastic at high velocities.

Inelastic collisions occur at lower velocities.

Abstract

We study the formation of a stable self-trapped spherical quantum ball in a binary Bose-Einstein condensate (BEC) with two-body inter-species attraction and intra-species repulsion employing the beyond-mean-field Lee-Huang-Yang and the three-body interactions. We find that either of these interactions or a combination of these can stabilize the binary BEC quantum ball with very similar stationary results, and for a complete description of the problem both the terms should be considered. These interactions lead to higher-order nonlinearities, e.g. quartic and quintic, respectively, in a nonlinear dynamical equation compared to the cubic nonlinearity of the two-body contact interaction in the mean-field Gross-Pitaevskii equation. The higher-order nonlinearity makes the energy infinitely large at the center of the binary ball and thus avoids its collapse. In addition to the formation of stationary binary balls, we also study a collision between two such balls. At large velocities, the collision is found to be elastic, which turns out to be inelastic as the velocity is lowered. We consider the numerical solution of a beyond-mean-field model for the binary ball as well as a single-mode variational approximation to it in this study.