Collision-induced frequency shifts in bright matter-wave solitons and soliton molecules

TL;DR

This paper models collision-induced frequency shifts in bright matter-wave solitons, compares predictions with recent experiments, and proposes new experiments to observe soliton molecules and bound states in cold atom systems.

Contribution

It introduces a particle model to accurately predict frequency shifts and suggests experimental conditions for observing soliton molecules and bound states.

Findings

Frequency shifts can be much smaller than previous predictions.

Reducing trap frequency may enable observation of soliton molecules.

Soliton bound states are highly phase-dependent and sensitive to 3D effects.

Abstract

A recent experiment has detected collision-induced frequency shifts in bright matter-wave solitons for the first time [Nat. Phys. 10, 918 (2014)]. Using a particle model, we derive the frequency shift for two solitons in a harmonic trap, and compare it to the results of the recent experiment and reported theoretical approximation. We find regimes where the frequency shift is much smaller than previously predicted, and propose experiments to test these findings. We also predict that reducing the experimental trap frequency will reveal for the first time soliton molecules or soliton bound states in a cold atoms system. The dynamics of such bound states are found to be both highly phase-dependent, and sensitive to the residual 3D nature of the experiment.