Center motions of nonoverlapping condensates coupled by long-range dipolar interaction in bilayer and multilayer stacks

TL;DR

This paper analyzes how anisotropic long-range dipole-dipole interactions influence the collective center motions of nonoverlapping Bose-Einstein condensates in layered structures, revealing mode-specific dependencies and phonon-like behaviors.

Contribution

It provides analytical and numerical insights into the role of dipolar interactions on condensate dynamics in bilayer and multilayer stacks, highlighting mode-dependent effects.

Findings

Out-of-phase mode frequency depends on dipolar strength in bilayers.

Transverse modes in multilayers exhibit optical phonon-like behavior.

Phonon velocity scales with the square root of dipolar interaction strength.

Abstract

We investigate the effect of anisotropic and long-range dipole-dipole interaction (DDI) on the center motions of nonoverlapping Bose-Einstein condensates (BEC) in bilayer and multilayer stacks. In the bilayer, it is shown analytically that while DDI plays no role in the in-phase modes of center motions of condensates, out-of-phase mode frequency ($\omega_o$) depends crucially on the strength of DDI ($a_d$). At the small-$a_d$ limit, $\omega_o^2(a_d)-\omega_o^2(0)\propto a_d$. In the multilayer stack, transverse modes associated with center motions of coupled condensates are found to be optical phonon like. At the long-wavelength limit, phonon velocity is proportional to $\sqrt a_d$.