| Summary: | We study the long-range force arising from the absorption of non-saturating
laser beams in a two-dimensional cloud of cold atoms. The force created by the lasers is attractive
and similar to the usual Newtonian gravity along the beam. The cloud is composed
of bosonic strontium 88 cooled and trapped on the intercombination line. Transferring the
atoms in a two-dimensional optical dipole trap in a magical wavelength configuration, a
canonical non-equilibrium phase transition is expected. Below a critical temperature, selfgravitating
particles in two dimensions can collapse, nearly by the same mechanism stars
are forming. We observed experimentally transient compressions, a halfway satisfactory
result originating from the power limitation of our dipole trap. The second part of the
thesis focuses on the theoretical realization a minimal Brownian motor within a system of
trapped particles in 2D, similarly to our experimental situation. The phenomenon characterizing
the Brownian motor is the appearance of a macroscopic current of particles.
We have shown that this direct transport of particles is independent of the details of the
trapping potential and obtained if and only if two symmetries are jointly broken: By the
presence of two heat baths along orthogonal directions together and an anisotropic trap
misaligned from the temperature axes.
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