Roton excitations in a trapped dipolar Bose-Einstein condensate

TL;DR

This paper investigates the excitation spectrum of trapped dipolar Bose-Einstein condensates, revealing discrete roton modes and demonstrating control over angular rotons via perturbations, advancing understanding of dipolar quantum gases.

Contribution

It introduces a mapping of excitations to radial and angular momentum, revealing discrete roton modes and methods to engineer angular rotons in trapped dipolar BECs.

Findings

Roton modes appear as discrete features in parameter space.

Application of perturbations can selectively create angular rotons.

Roton properties vary with dipole interaction strength.

Abstract

We consider the quasi-particle excitations of a trapped dipolar Bose-Einstein condensate. By mapping these excitations onto radial and angular momentum we show that the roton modes are clearly revealed as discrete fingers in parameter space, whereas the other modes form a smooth surface. We examine the properties of the roton modes and characterize how they change with the dipole interaction strength. We demonstrate how the application of a perturbing potential can be used to engineer angular rotons, i.e. allowing us to controllably select modes of non-zero angular momentum to become the lowest energy rotons.