Generation of density waves in dipolar quantum gases by time-periodic modulation of atomic interactions

TL;DR

This paper investigates how periodic modulation of atomic interactions in dipolar Bose-Einstein condensates can induce density waves through parametric resonance, highlighting the excitation of roton modes and the influence of three-body interactions.

Contribution

It introduces a theoretical model to analyze density wave emergence in dipolar BECs under time-periodic interactions, including effects of three-body interactions and stationary solutions.

Findings

Roton modes are most effectively excited by sub-harmonics.

Density waves can persist after formation.

Three-body interactions significantly modify the excitation spectrum.

Abstract

We study the emergence of density waves in dipolar Bose-Einstein condensates (BEC) when the strength of dipole-dipole atomic interactions is periodically varied in time. The proposed theoretical model, based on the evolution of small perturbations of the background density, allows to compute the growth rate of instability (gain factor) for arbitrary set of input parameters, thus to identify the regions of instability against density waves. We find that among other modes of the system the roton mode is most effectively excited due to the contribution of sub-harmonics of the excitation frequency. The frequency of temporal oscillations of emerging density waves coincides with the half of the driving frequency, this being the hallmark of the parametric resonance, is characteristic to Faraday waves. The possibility to create density waves in dipolar BECs, which can persist after the emergence, has been demonstrated. The existence of a stationary spatially periodic solution of the nonlocal Gross-Pitaevskii equation has been discussed. The effect of three-body atomic interactions, which is relevant to condensates with increased density, upon the properties of emerging waves has been analyzed too. Significant modification of the condensate's excitation spectrum owing to three-body effects is shown.