Dipolar quantum gases of strongly magnetic atoms

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This project aims at investigating dipolar effects in the few- and many-body physics using quantum degenerate gases of magnetic atoms. More precisely, our experiment uses atomic erbium, member of the lanthanide family, which counts among the most magnetic species of the periodic table. The choice of erbium has the advantage of combining the richness of the dipole-dipole interaction together with the extended knowhow of the ultracold atomic gas community, as well as the particular features of the lanthanide atoms. Within the next years, we will build on the knowledge and control gained on such systems, and deepen them, in the aim to unveil new aspects of dipolar quantum phenomena. We aim to investigate two very different types of systems: On the one hand, we will study dipolar Bose-Einstein condensates (BECs) in anisotropic geometries. Here our focus will be on the spectrum of elementary excitations of these systems and our aim a better understanding of the physics related to a special excitation, forming a minimum in energy at a large momentum, the so-called roton mode. By studying the full spectrum, we want to unveil how the roton mode softens when the interaction are tuned, how this depends on the system geometry and how this leads to distinct beyond-mean field effects does. We will also study how does the BEC’s excitation spectrum connects to the apparition of the recently discovered droplet states when reaching a dipolar dominated regime. Our overall goal in this first part is to understand if the BEC can connect in some way to special ground states, in particular the debated supersolid state, showing simultaneously superfluid and crystalline properties.On the other hand, we will focus on a quantum system formed by a mixture of two fermionic spin states of erbium. We have recently shown our ability to produce such mixtures and to tune their interactions. Our aim will now be to realize and study superfluid pairings in this new system. By tuning the interaction, one could cross from a superfluid of delocalized pairs formed along a Bardeen-Cooper-Schrieffer type of mechanism to a BEC of bound fermions. While such a crossover has been studied for years in alkali gases, erbium brings an exceptional scattering scenario, including dipole-dipole interactions, anisotropic short range interactions and multi-channel resonant scattering. Our aim is to reveal how these few-body features modify the behavior of the fermions assemblies at a many-body level.