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Fig. 6.3, Collapse dynamics of a dBEC in a 1D lattice:

Evolution of the system

for increasing holding time

hold

and diﬀerent ﬁnal lattice depth

, following

the experimental sequence described in section 6.2.1. Each image is an average

of ﬁve absorption pictures with the thermal cloud removed and the color scale

is adjusted individually for better visibility (ﬁeld of view: 190 × 337 m

stable regime with

a > a

. The ramping time is still considerably shorter than in the

case of the interaction-induced collapse, where the ramp duration is typically restricted to

around 1

[36]. Hence, this technique provides a new and powerful tool to investigate

the dynamics of dipolar BECs close to the stability threshold.

6.2.2 Collapse of a Coherent Array of dBECs

Following the procedure described above, we measure the time evolution of the system

for a varying holding time

hold

and for diﬀerent ﬁnal lattice depths

U ≤ U

init

= 12

Our results are shown in Fig. 6.3. Each image of the density distribution is obtained by

averaging ﬁve absorption pictures, taken under exactly the same experimental conditions.

Before the averaging process, we ﬁt the broad isotropic thermal cloud, present on each

picture, by a Gaussian and subtract it from the absorption images. Therefore, the images

in Fig. 6.3 show only the interference patterns of the remaining coherent atoms.

We ﬁrst consider the two smallest lattice depths

= 0 and

= 3

, well below the

stability threshold located at around 7

. We observe a decay of the number of coherent

atoms when increasing the in-trap holding time, which is indicated by the increasing

background noise in the images. From this observation we infer that the dBEC is collapsing

in-trap, i.e. while still conﬁned by the external trapping potential. In addition, we observe

that the collapsed clouds show mainly structures in the

-direction, transversal to the

external B-ﬁeld and the lattice direction.

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Bose 2.2 User Manual Page 106