Production and Characterisation of Dipolar Bose–Einstein Condensates

Péter Juhász - Pembroke College - University of Oxford
2023 - PhD thesis

Remarkable progress in the field of ultracold atoms has enabled the study of a great variety of topics in many-body quantum mechanics.Theprecisecontrolofkeyparameters, such as interactions, temperature, density, internal and external degrees of freedom, di mensionality and the trapping geometry makes them apowerful and flexible experimental platform. The ability to create degenerate samples of atoms which feature long-range and anisotropic dipole–dipole interactions besides the more conventional short-range and iso tropic contact interactions drew considerable attention, enabling the creation of quantum droplets and a supersolid phase. This thesis reports on experimental and theoretical progress in investigating dipolar many-body quantum systems. We present an overview of our experimental apparatus and the techniques used for obtaining a Bose–Einstein condensate (BEC) of erbium. We then discuss our experimental sequence for producing a quantum degenerate gas, creating a quasi-pure BEC with 2.2×105 atoms. To optimise the production of erbium BECs, we explore density- and temperature-dependent losses in 166Er and identify six previously unreported resonant loss features. Finally, to enable studies of density-dependent phenomena, we present a theoretical investigation of di polar condensates in box-like traps, where we explore stability and how one can use it to replicate properties of an infinite, homogeneous system to study dipolar physics. We found that traps with hard walls trigger roton-like density oscillations even if the bulk of the system is far from the roton regime, so smoother potentials are better suited to recreate homogeneous conditions. This sets the ground for future experiments, where the atoms will be loaded into a box trap to enable studies of systems which are tightly trapped in one direction but homogeneous in the other two.