Stability and Collapse Dynamics of Dipolar Bose-Einstein Condensates in One-Dimensional Optical Lattices

The subject of this thesis is the investigation of the stability and the collapse dynamics of a dipolar 52Cr Bose-Einstein condensate (BEC) in a one-dimensional (1D) optical lattice potential. In this work, it is experimentally shown that the stability of the dipolar BEC is strongly modified when increasing the modulation depth of the sinusoidal potential landscape: a cross-over from dipolar destabilization to dipolar stabilization is observed. For deep lattices, the dipolar BEC is split into a linear array of highly oblate, spatially separated “sub-condensates”, located on the different sites of the optical lattice. While stabilized by repulsive dipolar on-site interactions, numerical mean-field calculations reveal a significant destabilization of the system by dipolar inter-site interactions in this deep lattice regime. In a second set of measurements, the collapse of a coherent array of dipolar BECs, formed by the 1D lattice, is studied. The system is driven from the stable to the unstable region by lowering the lattice depth, while keeping the strength of the inter-atomic interactions fixed. Operating in the unstable regime, the time evolution of the collapsing system is found to be slowed down for larger lattice depths. Unexpectedly, when the system is released from a stable in-trap configuration, still a collapsed atomic cloud is observed after time-of-flight (TOF). Such novel collapse scenario, with the collapse being triggered by the TOF itself, is confirmed by real-time simulations and is identified to be a combined effect of the coherence between the sub-condensates and the anisotropy of the dipole-dipole interaction.