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Parité Science

Accueil > Événements > Actualités > Seminars

Séminaire interne LPMMC

Vijay Singh (Université de Hamburg)
Sound-propagation and superfluidity in ultracold quantum gases
Lieu : Salle de lecture 2, maison des Magistères,
le mardi 18 décembre 2018 à 11h00
Personne à contacter : Vincent Rossetto ()

Ultracold atom systems are well-controlled and tunable quantum systems, and thereby enable us to explore many-body quantum effects, such as BEC-BCS crossover, or superfluidity. In this talk, I will examine sound-propagation and superfluidity in ultracold quantum gases using analytical and simulation techniques. I will report on the second sound measurements in the BEC-BCS crossover and their theoretical analysis [1]. Here, I will demonstrate that the second sound velocity vanishes at the superfluid-thermal boundary, which is a defining feature of second sound. I will then study sound propagation in a uniform 2D Bose gas across the superfluid-thermal transition, motivated by the recent experiments in the Dalibard group. As a key result, I will show that the sound velocity undergoes a qualitatively different temperature dependence in the critical regime, which occurs due to an interplay between the superfluid and thermal mode [2]. In the second part of this talk, I will investigate superfluidity in ultracold quantum gases via laser stirring. I will present the stirring experiments in the BEC-BCS crossover and provide a quantitative analysis of the onset of dissipation associated with the breakdown of superfluidity [3]. I will then explore superfluidity across the Kosterlitz-Thouless (KT) transition with laser stirring and provide a quantitative understanding of the 2D stirring experiments performed in the Dalibard group [4]. I will also present the noise correlations of the time-of-flight images of 2D clouds and use them to determine the phase coherence of the recent experiments at Hamburg [5].


[1] D. Hoffmann, V. P. Singh, T. Paintner, W. Limmer, L. Mathey, and J. H. Denschlag, “Second sound in the BEC-BCS crossover”, forthcoming.
[2] V. P. Singh, and L. Mathey, “Sound propagation in a 2D Bose gas across the superfluid transition”, forthcoming.
[3] W. Weimer, K. Morgener, V. P. Singh, J. Siegl, K. Hueck, N. Luick, L. Mathey, and H. Moritz, Phys. Rev. Lett. 114, 095301 (2015); V. P. Singh et al., Phys. Rev. A 93, 023634 (2016).
[4] V. P. Singh, C. Weitenberg, J. Dalibard, and L. Mathey, Phys. Rev. A 95, 043631 (2017).
[5] V. P. Singh and L. Mathey, Phys. Rev. A 89, 053612 (2014).

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