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Abstract

The subject of this thesis is the investigation of the stability and the collapse dynamics of

a dipolar

Cr 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.

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