Roton confinement in trapped dipolar Bose-Einstein condensates

Abstract

Roton excitations constitute a key feature of dipolar gases, connecting these gases with superfluid helium. We show that the density dependence of the roton minimum results in a spatial roton confinement, particularly relevant in pancake dipolar condensates with large aspect ratios. We show that roton confinement plays a crucial role in the dynamics after roton instability, and that arresting the instability may create a trapped roton gas revealed by confined density modulations. We discuss the local susceptibility against density perturbations, which we illustrate for the case of vortices. Roton confinement is expected to play a key role in experiments.

Roton excitations in a trapped dipolar Bose-Einstein condensate

“…However, some aspects of the lowest energy rotons in the trapped system have emerged in studies of condensate structure and stability [21][22][23][24][25][26]. Recent work [27] presented an approximate description of the trapped rotons by requantizing a local density treatment of the excitation spectrum, enabling an analytic prediction for the roton spectrum and wave functions.…”

Nonintegral Form of the Gross–pitaevskii Equation for Polarized Molecules

“…Rotons and maxons are most fascinating features of the polar BEC spectrum revealed by a dilute two-dimensional Bose-condensed dipolar gas [6], [9], [10]. Instability of the three-dimensional dipolar BEC leads to shift of the attention on the quasi twoand one-dimensional BEC [11].…”

Measurement of collective excitations in a spin-orbit-coupled Bose-Einstein condensate

“…However, if long-range interactions, such as dipolar interactions, are present, the collective excitation spectrum of a BEC can exhibit a more complex structure: in addition to the typical low energy phonon spectrum, a roton-like structure can appear. It is characterised by a shoulder in the spectrum, which for certain parameters can turn into a parabolic minimum at a finite momentum [2][3][4][5].Interestingly, a similar parabolic minimum at a finite momentum can also exist in spin-orbit coupled (SOC) systems. In cold atomic gases, spin-orbit coupling can be implemented by Raman dressing of two or more atomic hyperfine states, which play the role of different (pseudo-)spins.…”

“…However, if long-range interactions, such as dipolar interactions, are present, the collective excitation spectrum of a BEC can exhibit a more complex structure: in addition to the typical low energy phonon spectrum, a roton-like structure can appear. It is characterised by a shoulder in the spectrum, which for certain parameters can turn into a parabolic minimum at a finite momentum [2][3][4][5].…”