A variational approach to Bogoliubov excitations and dynamics of dipolar Bose-Einstein condensates

TL;DR

This paper develops a variational method to analyze the stability, excitations, and dynamics of dipolar Bose-Einstein condensates with axial symmetry, accurately capturing phenomena like roton instability and angular collapse.

Contribution

It introduces an extended variational ansatz tailored for axial symmetry that reproduces Bogoliubov spectra and describes complex instabilities in dipolar condensates.

Findings

The variational ansatz accurately reproduces Bogoliubov eigenfrequencies.

It captures the roton instability in pancake-shaped condensates.

The method describes angular collapse dynamics effectively.

Abstract

We investigate the stability properties and the dynamics of Bose-Einstein condensates with axial symmetry, especially with dipolar long-range interaction, using both simulations on grids and variational calculations. We present an extended variational ansatz which is applicable for axial symmetry and show that this ansatz can reproduce the lowest eigenfrequencies of the Bogoliubov spectrum, and also the corresponding eigenfunctions. Our variational ansatz is capable of describing the roton instability of pancake-shaped dipolar condensates for arbitrary angular momenta. After investigating the linear regime we apply the ansatz to determine the dynamics and show how the angular collapse is correctly described within the variational framework.