Roton confinement in trapped dipolar Bose-Einstein condensates

TL;DR

This paper explores how roton excitations in dipolar Bose-Einstein condensates become spatially confined due to density dependence, affecting dynamics and potentially enabling trapped roton gases with observable density modulations.

Contribution

It introduces the concept of spatial roton confinement in dipolar BECs and analyzes its impact on instability dynamics and density modulations, a novel insight into dipolar quantum gases.

Findings

Roton confinement occurs in pancake-shaped dipolar condensates.

Roton confinement influences post-instability dynamics.

Confined density modulations can reveal trapped roton gases.

Abstract

Roton excitations constitute a key feature of dipolar gases, connecting these gases with superfluid helium. We show that the density dependence of the roton minimum results in a spatial roton confinement, particularly relevant in pancake dipolar condensates with large aspect ratios. We show that roton confinement plays a crucial role in the dynamics after roton instability, and that arresting the instability may create a trapped roton gas revealed by confined density modulations. We discuss the local susceptibility against density perturbations, which we illustrate for the case of vortices. Roton confinement is expected to play a key role in experiments.