• BEC
• Bose Einstein condensate
• optical lattice
• tunneling

Bose Einstein condensation is a phase transition emerging in systems of
integer-spin particles whose temperature is lowered under a critical value. One of the signatures of this phenomenon is the emergence of a
phase coherence through the whole system, so that its behaviors can be de-
scribed by single particle wavefunctions. After two-decades-long efforts in
the development of laser cooling techniques, Bose-Einstein conden-
sation was achieved in dilute gases of neutral atoms. Apart from its
fundamental interest, this experimental result opened the way to the study
of the quantum world with macroscopic samples.
In parallel with the research on cooling, the developments on laser physics
led to the creation of artificial atomic crystals by use of light-induced periodic
potentials, so-called optical lattices. These potentials were applied to
Bose-Einstein condensates shortly after their discovery.
In the last decade, a large part of the BEC community showed a strong
interest in ultra-cold atoms loaded into optical lattices. The periodic
potentials proved to be an exceptional tool for manipulating BECs, because
of their feasibility in the laboratory with the present technology, and be-
cause only few parameters govern the behavior of the sample. In fact, this
is described by the interplay between two fundamental physical processes:
atom-atom interactions and quantum tunneling.
The unifying theme of this thesis is the quantum tunneling in an ultra-cold
gas loaded into an optical lattice. In the experiments that we performed we
were able to observe effects due to quantum tunneling as well as to develop
experimental techniques to control it.