Dark soliton collisions in a toroidal Bose-Einstein condensate

TL;DR

This paper investigates the dynamics and collisions of gray solitons in a toroidal Bose-Einstein condensate, revealing velocity-dependent behaviors and energy exchange during collisions through Gross-Pitaevskii simulations.

Contribution

It provides a detailed analysis of soliton interactions in a toroidal trap, highlighting the role of vortices and energy loss mechanisms not extensively studied before.

Findings

Slow solitons collide elastically without energy loss.

Fast solitons involve vortices and lose energy during collisions.

Main features align with infinite 1D system predictions.

Abstract

We study the dynamics of two gray solitons in a Bose-Einstein condensate confined by a toroidal trap with a tight confinement in the radial direction. Gross-Pitaevskii simulations show that solitons can be long living objects passing through many collisional processes. We have observed quite different behaviors depending on the soliton velocity. Very slow solitons, obtained by perturbing the stationary solitonic profile, move with a constant angular velocity until they collide elastically and move in the opposite direction without showing any sign of lowering their energy. In this case the density notches are always well separated and the fronts are sharp and straight. Faster solitons present vortices around the notches, which play a central role during the collisions. We have found that in these processes the solitons lose energy, as the outgoing velocity turns out to be larger than the incoming one. To study the dynamics, we model the gray soliton state with a free parameter that is related to the soliton velocity. We further analyze the energy, soliton velocity and turning points in terms of such a free parameter, finding that the main features are in accordance with the infinite one-dimensional system.