Tuning the structural and dynamical properties of a dipolar Bose-Einstein condensate: Ripples and instability islands

TL;DR

This paper demonstrates how a Gaussian barrier can be used to control the structural and dynamical stability of a dipolar Bose-Einstein condensate, revealing instability islands and ripple-like ground states through mean-field analysis.

Contribution

It introduces a novel method of tuning dipolar BEC stability using a Gaussian barrier, predicting instability islands and structured ground states near a roton-like instability.

Findings

Existence of instability islands in phase diagram

Ripple-like oscillations in stable ground states

Softening of Bogoliubov excitation modes

Abstract

It is now well established that the stability of aligned dipolar Bose gases can be tuned by varying the aspect ratio of the external harmonic confinement. This paper extends this idea and demonstrates that a Gaussian barrier along the strong confinement direction can be employed to tune both the structural properties and the dynamical stability of an oblate dipolar Bose gas aligned along the strong confinement direction. In particular, our theoretical mean-field analysis predicts the existence of instability islands immersed in otherwise stable regions of the phase diagram. Dynamical studies indicate that these instability islands, which can be probed experimentally with present-day technology, are associated with the going soft of a Bogoliubov--de Gennes excitation frequency with radial breathing mode character. Furthermore, we find dynamically stable ground state densities with ripple-like oscillations along the radial direction. These structured ground states exist in the vicinity of a dynamical radial roton-like instability.