In 2005 we produced the first Chromium-BEC and we showed that it exhibits non-negligible dipolar effects. Nevertheless, the dipole-dipole interactions were only a small perturbation compared to the usual contact interactions. After exploring a lossless cooling method for a thermal cloud, which exploits the fast dipolar relaxation, we focused on the strong-dipolar effects in the quantum degenerate regime. In 2007 we achieved the first quantum ferrofluid, i.e. a BEC with comparable contact and dipole-dipole interactions, and shortly afterwards a purely dipolar BEC. Due to the anisotropic character of the dipole-dipole interactions the stability the BEC depends on the trap geometry and shows an universal behavior in the large N regime. We have observed instabilities - the so-called dipolar collapse involving an anisotropic d-wave symmetry. We have then investigated the phase coherence of collapsed condensates. We induced the collapse in several condensates simultaneously and let them interfere. By observing high fringe contrast, we proved that the collapsed cloud contains a remnant condensate. Also dipolar interaction in optical lattices was observed.
Since 2014 we have replaced the Chromium quantum gas by a Dysprosium BEC. Dysprosium has the highest magnetic moment of all atoms in the periodic table and due to its larger mass a reduced contact interaction. It is therefore best suited to study the dipolar phenomena. With this new system we have observed the equivalent of the Rosensweig instability which happens for classical ferrofluids, with our dipolar BEC, a quantum ferrofluid. This instability is characterized by the formation of regular patterns of peaks and valleys in the denity of the BEC.
As opposed to what was previously thought, the resulting state is actually stable, characterized by the formation of droplets. These droplets are actually made of a novel quantum liquid, where the attraction due to the dipolar interaction, which tends to drive a collapse, is balanced by quantum fluctuations of the BEC field as dictated by Heisenberg uncertainty principle.
We are looking for motivated new team members!
Magnetic quantum gases and liquids of Dysprosium atoms
We are planning a new setup for a degenerate Dysprosium gases and are looking for
- a PhD student
If you are interested in working on exotic states of matter and like to setup new things, contact Tilman Pfau via email/phone or just come by and visit our labs.
Interested? Here you find the recent papers on our quantum liquid
M. Schmitt, M. Wenzel, B. Böttcher, I. Ferrier-Barbut, T. Pfau
Self-bound droplets of a dilute magnetic quantum liquid
Nature 539, 259 (2016), arXiv:1607.07355
I. Ferrier-Barbut, H. Kadau, M. Schmitt, M. Wenzel, T. Pfau
"Observation of quantum droplets in a strongly dipolar Bose gas"
Phys. Rev. Lett. 116, 215301 (2016)