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Résumé |
Understanding the properties of a large number of particles in
interaction is one of the frontiers of modern physics: from the
stability of sandpiles to the formation of large structures in the
universe or the behaviour of complex neural networks, it is at the
core of almost all current fields of research. In the quantum world
this question explores the properties of quantum materials or those of
nuclear matter and the combination of quantum mechanics and many-body
physics leads to the most complex challenges probably ever faced by
the physics community.
Thanks to the versatility of the manipulation techniques of ultracold
atoms with light and magnetic fields it is now possible to explore a
broad variety of quantum many-body systems with an unprecedented
control of the experimental parameters. In my talk, I will discuss the
case of the simplest yet non trivial situation where a single particle
(the so-called impurity) is immersed into a quantum many-body
ensemble. The interactions with the background creates a cloud of
excitations that dresses the impurity and gives rise to a
quasi-particle. The properties of this so-called polaron are strongly
affected by the nature of the background and I will show that
ultracold atoms can be used to explore several instances of this
problem: the Fermi polaron, where the background is an ideal gas of
spin polarized fermions, the Bose polaron where the impurity is
immersed in a Bose-Einstein condensate of weakly interacting bosons,
and finally the superfluid polaron where the medium is an attractive
gas of spin 1/2 fermions and that interpolates between the two
previous situations. |
