Skip to main content

Thank you for visiting You are using a browser version with limited support for CSS. To obtain the best experience, we recommend you use a more up to date browser (or turn off compatibility mode in Internet Explorer). In the meantime, to ensure continued support, we are displaying the site without styles and JavaScript.

Observation of roton mode population in a dipolar quantum gas


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 4He (ref. 1). In quantum liquids, rotons arise from the strong interparticle interactions, whose microscopic description remains debated2. 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 character3. This prospect has raised considerable interest4,5,6,7,8,9,10,11,12; 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 gases13.

This is a preview of subscription content, access via your institution

Relevant articles

Open Access articles citing this article.

Access options

Rent or buy this article

Get just this article for as long as you need it


Prices may be subject to local taxes which are calculated during checkout

Fig. 1: Roton mode in a dBEC.
Fig. 2: Observed roton peaks and characteristic scalings.
Fig. 3: Dynamics of the roton mode.
Fig. 4: Population growth and roton gap.


  1. Landau, L. D. The theory of superfluidity of helium II. J. Phys. (Mosc.) 5, 71–90 (1941).

    MATH  Google Scholar 

  2. Griffin, A. Excitations in a Bose-Condensed Liquid (Cambridge Univ. Press, Cambridge, 1993).

  3. Santos, L., Shlyapnikov, G. V. & Lewenstein, M. Roton–maxon spectrum and stability of trapped dipolar Bose–Einstein condensates. Phys. Rev. Lett. 90, 250403 (2003).

    Article  ADS  Google Scholar 

  4. Ronen, S., Bortolotti, D. C. E. & Bohn, J. L. Radial and angular rotons in trapped dipolar gases. Phys. Rev. Lett. 98, 030406 (2007).

    Article  ADS  Google Scholar 

  5. Bohn, J. L., Wilson, R. M. & Ronen, S. How does a dipolar Bose–Einstein condensate collapse? Laser Phys. 19, 547–549 (2009).

    Article  ADS  Google Scholar 

  6. Parker, N. G., Ticknor, C., Martin, A. M. & O’Dell, D. H. J. Structure formation during the collapse of a dipolar atomic Bose–Einstein condensate. Phys. Rev. A 79, 013617 (2009).

    Article  ADS  Google Scholar 

  7. Martin, A. D. & Blakie, P. B. Stability and structure of an anisotropically trapped dipolar Bose–Einstein condensate: Angular and linear rotons. Phys. Rev. A 86, 053623 (2012).

    Article  ADS  Google Scholar 

  8. Blakie, P. B., Baillie, D. & Bisset, R. N. Roton spectroscopy in a harmonically trapped dipolar Bose–Einstein condensate. Phys. Rev. A 86, 021604 (2012).

    Article  ADS  Google Scholar 

  9. Jona-Lasinio, M., Łakomy, K. & Santos, L. Roton confinement in trapped dipolar Bose–Einstein condensates. Phys. Rev. A 88, 013619 (2013).

    Article  ADS  Google Scholar 

  10. Wilson, R. M., Ronen, S. & Bohn, J. L. Critical superfluid velocity in a trapped dipolar gas. Phys. Rev. Lett. 104, 094501 (2010).

    Article  ADS  Google Scholar 

  11. Natu, S. S., Campanello, L. & Das Sarma, S. Dynamics of correlations in a quasi-two-dimensional dipolar Bose gas following a quantum quench. Phys. Rev. A 90, 043617 (2014).

    Article  ADS  Google Scholar 

  12. Pitaevskii, L. & Stringari, S. BoseEinstein Condensation and Superfluidity Vol. 164 (Oxford Univ. Press, Oxford, 2016).

  13. Boninsegni, M. & Prokof’ev, N. V. Colloquium: Supersolids: What and where are they? Rev. Mod. Phys. 84, 759–776 (2012).

  14. Henshaw, D. G. & Woods, A. D. B. Modes of atomic motions in liquid helium by inelastic scattering of neutrons. Phys. Rev. 121, 1266–1274 (1961).

    Article  ADS  Google Scholar 

  15. O’Dell, D. H. J., Giovanazzi, S. & Kurizki, G. Rotons in gaseous Bose–Einstein condensates irradiated by a laser. Phys. Rev. Lett. 90, 110402 (2003).

    Article  Google Scholar 

  16. Mottl, R. et al. Roton-type mode softening in a quantum gas with cavity-mediated long-range interactions. Science 336, 1570–1573 (2012).

    Article  ADS  Google Scholar 

  17. Khamehchi, M. A., Zhang, Y., Hamner, C., Busch, T. & Engels, P. Measurement of collective excitations in a spin–orbit-coupled Bose–Einstein condensate. Phys. Rev. A 90, 063624 (2014).

    Article  ADS  Google Scholar 

  18. Ji, S.-C. et al. Softening of roton and phonon modes in a Bose–Einstein condensate with spin–orbit coupling. Phys. Rev. Lett. 114, 105301 (2015).

    Article  ADS  Google Scholar 

  19. Ha, L.-C., Clark, L. W., Parker, C. V., Anderson, B. M. & Chin, C. Roton–maxon excitation spectrum of Bose condensates in a shaken optical lattice. Phys. Rev. Lett. 114, 055301 (2015).

    Article  ADS  Google Scholar 

  20. Griesmaier, A., Werner, J., Hensler, S., Stuhler, J. & Pfau, T. Bose–Einstein condensation of chromium. Phys. Rev. Lett. 94, 160401 (2005).

    Article  ADS  Google Scholar 

  21. Lu, M., Burdick, N. Q., Youn, S. H. & Lev, B. L. Strongly dipolar Bose–Einstein condensate of dysprosium. Phys. Rev. Lett. 107, 190401 (2011).

    Article  ADS  Google Scholar 

  22. Aikawa, K. et al. Bose–Einstein condensation of erbium. Phys. Rev. Lett. 108, 210401 (2012).

    Article  ADS  Google Scholar 

  23. Kadau, H. et al. Observing the Rosensweig instability of a quantum ferrofluid. Nature 530, 194–197 (2016).

    Article  ADS  Google Scholar 

  24. Ferrier-Barbut, I., Kadau, H., Schmitt, M., Wenzel, M. & Pfau, T. Observation of quantum droplets in a strongly dipolar Bose gas. Phys. Rev. Lett. 116, 215301 (2016).

    Article  ADS  Google Scholar 

  25. Chomaz, L. et al. Quantum-fluctuation-driven crossover from a dilute Bose–Einstein condensate to a macrodroplet in a dipolar quantum fluid. Phys. Rev. X 6, 041039 (2016).

    Google Scholar 

  26. Schmitt, M., Wenzel, M., Böttcher, F., Ferrier-Barbut, I. & Pfau, T. Self-bound droplets of a dilute magnetic quantum liquid. Nature 539, 259–262 (2016).

    Article  ADS  Google Scholar 

  27. Nguyen, J. H., Luo, D. & Hulet, R. G. Formation of matter-wave soliton trains by modulational instability. Science 356, 422–426 (2017).

    Article  ADS  Google Scholar 

  28. Wenzel, M., Böttcher, F., Langen, T., Ferrier-Barbut, I. & Pfau, T. Striped states in a many-body system of tilted dipoles. Phys. Rev. A. 96, 053630 (2017).

    Article  ADS  Google Scholar 

  29. Li, J.-R. et al. A stripe phase with supersolid properties in spin–orbit-coupled Bose–Einstein condensates. Nature 543, 91–94 (2017).

    Article  ADS  Google Scholar 

  30. Léonard, J., Morales, A., Zupancic, P., Esslinger, T. & Donner, T. Supersolid formation in a quantum gas breaking a continuous translational symmetry. Nature 543, 87–90 (2017).

    Article  ADS  Google Scholar 

  31. Chin, C., Grimm, R., Julienne, P. S. & Tiesinga, E. Feshbach resonances in ultracold gases. Rev. Mod. Phys. 82, 1225–1286 (2010).

    Article  ADS  Google Scholar 

  32. Lahaye, T. et al. d-wave collapse and explosion of a dipolar Bose–Einstein condensate. Phys. Rev. Lett. 101, 080401 (2008).

    Article  ADS  Google Scholar 

  33. Giovanazzi, S. et al. Expansion dynamics of a dipolar Bose–Einstein condensate. Phys. Rev. A 74, 013621 (2006).

    Article  ADS  Google Scholar 

  34. Baranov, M. Theoretical progress in many-body physics with ultracold dipolar gases. Phys. Rep. 464, 71–111 (2008).

    Article  ADS  Google Scholar 

  35. Blakie, P., Bradley, A., Davis, M., Ballagh, R. & Gardiner, C. Dynamics and statistical mechanics of ultra-cold Bose gases using c-field techniques. Adv. Phys. 57, 363–455 (2008).

    Article  ADS  Google Scholar 

Download references


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. Büchler 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.

Author information

Authors and Affiliations



F.F., L.C., D.P., G.F., M.J.M., J.H.B. and S.B. conceived and supervised the experiment and collected the experimental data. L.C. analysed the data. R.M.W.v.B. developed the Bogoliubov–de Gennes calculations. F.W., R.M.W.v.B. and L.S. performed the real-time simulations. L.S. derived the analytical model and the SSM. L.C., F.F., R.M.W.v.B. and L.S. wrote the paper with contributions from all of the authors.

Corresponding author

Correspondence to F. Ferlaino.

Ethics declarations

Competing interests

The authors declare no competing interests.

Additional information

Publisher’s note: Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

Supplementary information

Supplementary Information

Supplementary Figure 1–3, Supplementary Table 1–2, Supplementary References

Rights and permissions

Reprints and Permissions

About this article

Check for updates. Verify currency and authenticity via CrossMark

Cite this article

Chomaz, L., van Bijnen, R.M.W., Petter, D. et al. Observation of roton mode population in a dipolar quantum gas. Nature Phys 14, 442–446 (2018).

Download citation

  • Received:

  • Accepted:

  • Published:

  • Issue Date:

  • DOI:

This article is cited by


Quick links

Nature Briefing

Sign up for the Nature Briefing newsletter — what matters in science, free to your inbox daily.

Get the most important science stories of the day, free in your inbox. Sign up for Nature Briefing