Probing the roton excitation spectrum of a stable dipolar Bose gas

We measure the excitation spectrum of a stable dipolar Bose--Einstein condensate over a wide momentum-range via Bragg spectroscopy. We precisely control the relative strength, \(\epsilon_{\rm dd}\), of the dipolar to the contact interactions and observe that the spectrum increasingly deviates from t...

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Bibliographic Details
Published in:arXiv.org 2019-08
Main Authors: Petter, D, Natale, G, R M W van Bijnen, Patscheider, A, Mark, M J, Chomaz, L, Ferlaino, F
Format: Article
Language:English
Subjects:
Bogoliubov theory
Density
Excitation spectra
Momentum
Spectrum analysis
Stability
Online Access:Get full text
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Summary:We measure the excitation spectrum of a stable dipolar Bose--Einstein condensate over a wide momentum-range via Bragg spectroscopy. We precisely control the relative strength, \(\epsilon_{\rm dd}\), of the dipolar to the contact interactions and observe that the spectrum increasingly deviates from the linear phononic behavior for increasing \(\epsilon_{\rm dd}\). Reaching the dipolar dominated regime \(\epsilon_{\rm dd}>1\), we observe the emergence of a roton minimum in the spectrum and its softening towards instability. We characterize how the excitation energy and the strength of the density-density correlations at the roton momentum vary with \(\epsilon_{\rm dd}\). Our findings are in excellent agreement with numerical calculations based on mean-field Bogoliubov theory. When including beyond-mean-field corrections, in the form of a Lee-Huang-Yang potential, we observe a quantitative deviation from the experiment, questioning the validity of such a description in the roton regime.
ISSN:2331-8422
DOI:10.48550/arxiv.1811.12115