Fingerprinting Rotons in a Dipolar Condensate: Super-Poissonian Peak in the Atom-Number Fluctuations

TL;DR

This paper shows that atom-number fluctuation measurements in a dipolar condensate can detect roton excitations, revealing a super-Poissonian peak linked to roton wavelength, with temperature enhancing the effect.

Contribution

It introduces a method to identify roton excitations via atom-number fluctuations and develops a simple local density theory validated against numerical solutions.

Findings

Super-Poissonian peak in fluctuations indicates roton presence.

Fluctuation magnitude increases with temperature.

Fluctuations within a washer-shaped cell isolate individual roton modes.

Abstract

We demonstrate that measurements of atom-number fluctuations in a trapped dipolar condensate can reveal the presence of the elusive roton excitation. The key signature is a super-Poissonian peak in the fluctuations as the size of the measurement cell is varied, with the maximum occurring when the size is comparable to the roton wavelength. The magnitude of this roton feature is enhanced with temperature. The variation in fluctuations across the condensate demonstrates that the roton excitations are effectively confined to propagate in the densest central region, realizing a density trapped roton gas. While our main results are based on full numerical solutions of the meanfield equations, we also develop and validate a simple local density theory. Finally, we consider fluctuations measured within a washer-shaped cell which filters out the contribution of modes with nonzero angular momentum and provides a signal sensitive to individual roton modes.