Instabilities and the roton spectrum of a quasi-1D Bose-Einstein condensed gas with dipole-dipole interactions

TL;DR

This paper explores how reversing dipolar interactions in a quasi-1D Bose-Einstein condensate can stabilize a roton spectrum, enabling control over excitations and potential density wave formation.

Contribution

It demonstrates the possibility of stabilizing a roton spectrum in a dipolar BEC by reversing interaction sign, allowing tunable roton features and insights into system stability.

Findings

Reversing dipolar interactions stabilizes the condensate.

A roton minimum appears in the excitation spectrum.

Tuning interaction strength affects roton depth and system stability.

Abstract

We point out the possibility of having a roton-type excitation spectrum in a quasi-1D Bose-Einstein condensate with dipole-dipole interactions. Normally such a system is quite unstable due to the attractive portion of the dipolar interaction. However, by reversing the sign of the dipolar interaction using either a rotating magnetic field or a laser with circular polarization, a stable cigar-shaped configuration can be achieved whose spectrum contains a `roton' minimum analogous to that found in helium II. Dipolar gases also offer the exciting prospect to tune the depth of this `roton' minimum by directly controlling the interparticle interaction strength. When the minimum touches the zero-energy axis the system is once again unstable, possibly to the formation of a density wave.