Dipolar quantum droplets and striped states

I present experimental results on magnetic quantum fluids, consisting of a dilute Bose-Einstein condensate of dysprosium atoms.
First, we have observed in this system an unanticipated phase-transition between a gas and a liquid, characterized by the formation of self-bound droplets [1-3]. It forms in a parameter region where the existing theory, based on the mean-field approximation, predicted a mechanical collapse of the gas. We showed that the repulsive beyond meanfield corrections prevent the collapse and are responsible for the stabilization of the liquid [2]. These corrections arise from quantum fluctuations (zero-point motion) of the collective modes (Bogolyubov sound modes) in the quantum fluid.
In recent work we show that in constrained geometries, the ground-state is self-organized. Studying these geometries experimentally, we indeed observe stable self-organized ‘striped’ states, likely in metastable excited states [4]. Although we do not observe phase coherence in matter wave interference experiments, we point out a way to establish a common phase of multi-droplet states.

[1] H. Kadau, M. Schmitt, M. Wenzel, C. Wink, T. Maier, I. Ferrier-Barbut, and T. Pfau, Nature 530, 194 (2016)
[2] I. Ferrier-Barbut, H. Kadau, M. Schmitt, M. Wenzel, and T. Pfau, Phys. Rev. Lett. 116, 215301 (2016)
[3] M. Schmitt, M. Wenzel, F. Böttcher, I. Ferrier-Barbut and T. Pfau, Nature 539, 259 (2016)
[4] M. Wenzel, F. Böttcher, T. Langen, I. Ferrier-Barbut and T. Pfau, arXiv: 1706.09388