Collective excitations and instabilities in multi-layer stacks of dipolar condensates

TL;DR

This paper theoretically investigates collective excitations and instabilities in multi-layer dipolar condensates, revealing enhanced roton instabilities and analyzing their effects on system dynamics and decoherence.

Contribution

It provides a theoretical analysis of collective modes and instabilities in multi-layer dipolar condensates, connecting roton softening with dynamical instabilities and experimental observations.

Findings

Enhanced roton instability in multi-layer stacks

Interplay between dynamical instability and roton softening

Qualitative agreement with recent $^{39}$K experiments

Abstract

We analyze theoretically the collective mode dispersion in multi-layer stacks of two dimensional dipolar condensates and find a strong enhancement of the roton instability. We discuss the interplay between the dynamical instability and roton softening for moving condensates. We use our results to analyze the decoherence rate of Bloch oscillations for systems in which the s-wave scattering length is tuned close to zero using Feshbach resonance. Our results are in qualitative agreement with recent experiments of Fattori {\it et al.} on $^{39}$K atoms.