Observation of roton mode population in a dipolar quantum gas

authored by: L. Chomaz, R. M.W. Van Bijnen, D. Petter, G. Faraoni, J. H. Becher, M. J. Mark, Falk Wächtler, Luis Santos, F. Ferlaino, Simon Baier
Abstract: The concept of a roton, a special kind of elementary excitation forming a minimum of energy at finite momentum, has been essential for the understanding of the properties of superfluid ⁴ He (ref. ¹ ). In quantum liquids, rotons arise from the strong interparticle interactions, whose microscopic description remains debated ² . In the realm of highly controllable quantum gases, a roton mode has been predicted to emerge due to magnetic dipole-dipole interactions despite their weakly interacting character ³ . This prospect has raised considerable interest ^4-12 ; yet roton modes in dipolar quantum gases have remained elusive to observations. Here we report experimental and theoretical studies of the momentum distribution in Bose-Einstein condensates of highly magnetic erbium atoms, revealing the existence of the long-sought roton mode. Following an interaction quench, the roton mode manifests itself with the appearance of symmetric peaks at well-defined finite momentum. The roton momentum follows the predicted geometrical scaling with the inverse of the confinement length along the magnetization axis. From the growth of the roton population, we probe the roton softening of the excitation spectrum in time and extract the corresponding imaginary roton gap. Our results provide a further step in the quest towards supersolidity in dipolar quantum gases ¹³ .
Organisation(s): Institute of Theoretical Physics
CRC 1227 Designed Quantum States of Matter (DQ-mat)
External Organisation(s): University of Innsbruck
Austrian Academy of Sciences
University of Florence (UniFi)
Type: Article
Journal: Nature Physics
Volume: 14
Pages: 442-446
No. of pages: 5
ISSN: 1745-2473
Publication date: 05.2018
Publication status: Published
Peer reviewed: Yes
ASJC Scopus subject areas: Physics and Astronomy(all)
Electronic version(s): https://doi.org/10.1038/s41567-018-0054-7 (Access: Closed)

BibTeX

@article{923ce66718ee4ee0b1477501ba967903,
title = "Observation of roton mode population in a dipolar quantum gas",
abstract = " The concept of a roton, a special kind of elementary excitation forming a minimum of energy at finite momentum, has been essential for the understanding of the properties of superfluid 4 He (ref. 1 ). In quantum liquids, rotons arise from the strong interparticle interactions, whose microscopic description remains debated 2 . In the realm of highly controllable quantum gases, a roton mode has been predicted to emerge due to magnetic dipole-dipole interactions despite their weakly interacting character 3 . This prospect has raised considerable interest 4-12 ; yet roton modes in dipolar quantum gases have remained elusive to observations. Here we report experimental and theoretical studies of the momentum distribution in Bose-Einstein condensates of highly magnetic erbium atoms, revealing the existence of the long-sought roton mode. Following an interaction quench, the roton mode manifests itself with the appearance of symmetric peaks at well-defined finite momentum. The roton momentum follows the predicted geometrical scaling with the inverse of the confinement length along the magnetization axis. From the growth of the roton population, we probe the roton softening of the excitation spectrum in time and extract the corresponding imaginary roton gap. Our results provide a further step in the quest towards supersolidity in dipolar quantum gases 13 . ",
author = "L. Chomaz and {Van Bijnen}, {R. M.W.} and D. Petter and G. Faraoni and Becher, {J. H.} and Mark, {M. J.} and Falk W{\"a}chtler and Luis Santos and F. Ferlaino and Simon Baier",
note = "Funding information: We are particularly grateful to B. Blakie for many inspiring exchanges. We thank D. O{\textquoteright}Dell, M. Baranov, E. Demler, A. Sykes, T. Pfau, I. Ferrier-Barbut and H. P. B{\"u}chler for fruitful discussions, and G. Natale for his support in the final stage of the experiment. This work is dedicated to the memory of D. Jin and her inspiring example. The Innsbruck group is supported through an ERC Consolidator Grant (RARE, no. 681432) and a FET Proactive project (RySQ, no. 640378) of the EU H2020. L.C. is supported within a Marie Curie Project (DipPhase, no. 706809) of the EU H2020. F.W. and L.S. thank the DFG (SFB 1227 DQ-mat). All authors thank the DFG/FWF (FOR 2247). Part of the computational results presented have been achieved using the HPC infrastructure LEO of the University of Innsbruck. We are particularly grateful to B. Blakie for many inspiring exchanges. We thank D. O'Dell, M. Baranov, E. Demler, A. Sykes, T. Pfau, I. Ferrier-Barbut and H. P. Buchler for fruitful discussions, and G. Natale for his support in the final stage of the experiment. This work is dedicated to the memory of D. Jin and her inspiring example. The Innsbruck group is supported through an ERC Consolidator Grant (RARE, no. 681432) and a FET Proactive project (RySQ, no. 640378) of the EU H2020. L.C. is supported within a Marie Curie Project (DipPhase, no. 706809) of the EU H2020. F.W. and L.S. thank the DFG (SFB 1227 DQ-mat). All authors thank the DFG/FWF (FOR 2247). Part of the computational results presented have been achieved using the HPC infrastructure LEO of the University of Innsbruck ",
year = "2018",
month = may,
doi = "10.1038/s41567-018-0054-7",
language = "English",
volume = "14",
pages = "442--446",
journal = "Nature Physics",
issn = "1745-2473",
publisher = "Nature Publishing Group",
number = "5",
}