Stability Spectroscopy of Rotons in a Dipolar Bose Gas

TL;DR

This paper investigates the stability of a dipolar Bose-Einstein condensate with a roton-maxon spectrum under a weak lattice, revealing how certain lattice wavelengths induce instability, which can help measure the roton wavelength.

Contribution

It introduces a stability diagram method to directly measure the roton wavelength in quasi-one-dimensional dipolar Bose gases using lattice perturbations.

Findings

Instability occurs when lattice wavelength matches half the roton wavelength.

System destabilizes at low roton subharmonics.

Stability diagram can measure roton wavelength directly.

Abstract

We study the stability of a quasi-one-dimensional dipolar Bose-Einstein condensate (dBEC) that is perturbed by a weak lattice potential along its axis. Our numerical simulations demonstrate that systems exhibiting a roton-maxon structure destabilize readily when the lattice wavelength equals either half the roton wavelength or a low roton subharmonic. We apply perturbation theory to the Gross-Pitaevskii and Bogoliubov de Gennes equations to illustrate the mechanisms behind the instability threshold. The features of our stability diagram may be used as a direct measurement of the roton wavelength for quasi-one-dimensional geometries.