Ultracold Mixture of Metastable Helium and Rubidium for Universal Few-body Physics

Dr Steven Knoop

Vrije Universiteit, Faculty of Science, Amsterdam

3:30 pm Friday, 5 December 2014, EN101 Lecture Theatre (EN Building), Hawthorn.

Laser cooling and evaporative cooling of neutral atoms have revolutionized atomic physics, with major milestones the realization of Bose-Einstein condensation and degenerate Fermi gases. With these techniques atomic gases at temperatures below 1 microKelvin (much colder than the coldest places in the universe) are prepared and studied in many labs worldwide. They provide experimentalists extremely pure and controllable quantum gases. One remarkable property of those ultracold quantum gases is the tunability of the interparticle interaction using Feshbach resonances. In particular, for very strong interaction universal few-body phenomena appear, such as the emergence of Efimov trimer states. We are setting up a new experiment in which a mixture of metastable triplet helium ($^4$He*) and rubidium ($^{87}$Rb) is cooled to the ultracold regime, with the aim of observing heteronuclear Efimov trimers for which the large mass ratio between He and Rb plays a crucial role. Our cooling scheme starts with a two-species magneto-optical trap (MOT), loaded from a Zeeman slower (He*) and a 2D-MOT (Rb). Afterwards we load the atoms in a quadrupole magnetic trap (QMT), in which we do simultaneous RF- (He*) and MW-induced (Rb) forced evaporative cooling. We have studied interspecies thermalization, from which we have obtained a value of the interspecies scattering length, in agreement with recent ab initio quantum chemistry calculations [1]. Recently, we have realized a Bose-Einstein condensate of $^{87}$Rb in the $F=2$, $m_F=2$ hyperfine substate in a hybrid trap [2], consisting of a quadrupole magnetic field and a single beam ODT. We are currently exploring the application of this hybrid trap for He*.

[1] S. Knoop, P. S. Zuchowski, D. Kedziera, L. Mentel, M. Puchalski, H. P. Mishra, A. S. Flores, and W. Vassen, Phys. Rev. A 90, 022709 (2014)
[2] H. P. Mishra, A. S. Flores, W. Vassen, and S. Knoop, arXiv:1411.7628 (2014)

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