Explorations with Erbium

Rob Smith, Clarendon Laboratory, University of Oxford, Oxford, UK 

First, I will present our measurements of the modification of transition temperature for Bose Einstein Condensation (BEC) due to dipole-dipole interactions. The effect of dipolar interactions on harmonically trapped BECs has been the subject of intense and fruitful research over recent years, but despite being theoretically calculated over 15 years ago [Phys. Rev. Lett. 98, 080407 (2007)] the modification of the BEC transition temperature due to dipole-dipole interactions has, up to now, not been experimentally observed. We use an ultracold erbium gas confined in a highly prolate trap to directly observe the dependence of the critical temperature on the orientation of the dipoles relative to the trap and compare the results with theoretical expectations. 

Second, I will discuss the challenges and progress towards (i) the realization of a box-trapped dipolar gas, and (ii) the realization of a potassium-erbium mixture. I will then briefly outline the new research directions that these developments will enable.

Polaron spectroscopy of many-body systems

Ivan Amelio, Université Libre de Bruxelles, Belgium

We investigate polaron formation when immersing an impurity in a few instances of correlated many-body states. Peculiar spectral features allow to distinguish whether the bath features charge density waves, BCS pairing, topological phases, a BKT transition, etc. On the methodological side, we will illustrate pros and cons of different approaches, including T-matrix resummation, Chevy ansatz, exact diagonalization and tensor networks.

Our work is motivated by realizations in cold atomic systems as well as recent experiments in few-layer heterostructures