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ULTRACOLD GASES

Second sound seen

Nature Physics volume 17, pages 770–771 (2021)Cite this article

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A Publisher Correction to this article was published on 14 June 2021

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The two-fluid model of superfluids predicts a second, quantum mechanical form of sound. Ultracold atom experiments have now measured second sound in the unusual two-dimensional superfluid described by the Berezinskii–Kosterlitz–Thouless transition.

Ultracold gases have had spectacular success as a platform for studying low-temperature quantum many-body phenomena such as Bose–Einstein condensation and superfluidity, previously only accessible in experiments on liquid helium. In two-dimensional systems, Bose–Einstein condensation is ruled out by thermal fluctuations, but superfluidity can still be achieved at sufficiently low temperature. This is because of the Berezinskii–Kosterlitz–Thouless (BKT) transition, which has the peculiar feature of being of infinite order, meaning that all thermodynamic functions are continuous. In this case, the phase transition can only be revealed by exploring transport features rather than observing singularities in thermodynamic measurements. Now, writing in Nature, Panagiotis Christodoulou and colleagues1 report that they have observed two different kinds of sound propagation in a two-dimensional quantum gas, verifying the predictions of BKT superfluidity and confirming a universal jump of the superfluid density at the transition2.

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Fig. 1: Universal jump in superfluid density.

Image courtesy of Panagiotis Christodoulou and Zoran Hadzibabic, University of Cambridge.

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References

  1. Christodoulou, P. et al. Nature https://doi.org/10.1038/s41586-021-03537-9 (2021).

  2. Nelson, D. R. & Kosterlitz, J. M. Phys. Rev. Lett. 39, 1201–1205 (1977).

    Article  ADS  Google Scholar 

  3. Desbuquois, R. et al. Nat. Phys. 8, 645–648 (2012).

    Article  Google Scholar 

  4. Andronikashvili, E. L. J. Phys. USSR 10, 201–206 (1946).

    Google Scholar 

  5. Peshkov, V. J. Phys. 8, 381–389 (1944).

    Google Scholar 

  6. Sidorenkov, L. A. et al. Nature 498, 78–81 (2013).

    Article  ADS  Google Scholar 

  7. Ville, J. L. et al. Phys. Rev. Lett. 121, 145301 (2018).

    Article  ADS  Google Scholar 

  8. Ota, M. et al. Phys. Rev. Lett. 121, 145302 (2018).

    Article  ADS  Google Scholar 

  9. Ozawa, T. & Stringari, S. Phys. Rev. Lett. 112, 025302 (2014).

    Article  ADS  Google Scholar 

  10. Prokof’ev, N. V. & Svistunov, B. V. Phys. Rev. A 66, 043608 (2002).

    Article  ADS  Google Scholar 

Download references

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  1. INO-CNR BEC Center, Dipartimento di Fisica, Università di Trento, Trento, Italy

    Sandro Stringari

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  1. Sandro Stringari
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Correspondence to Sandro Stringari.

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Stringari, S. Second sound seen. Nat. Phys. 17, 770–771 (2021). https://doi.org/10.1038/s41567-021-01276-2

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