STAGE Quantum magnetism of ultracold fermions in optical lattices

We offer an experimental internship in the field of ultracold atoms. Our research topic is
quantum magnetism, i.e., the collective behavior of ensembles of interacting spin-carrying
particles. We experiment on ensembles of strontium atoms, arranged on a periodic structure
created by interfering laser beams: an optical lattice potential. Our aim is to study the
conditions for the emergence of antiferromagnetic ordering. We will be able to realize
situations analogous to those encountered by electrons (of spin ½) in crystalline materials, but
also situations that strongly contrast with those, as a consequence of the spin 9/2 of our atomic
species. For studies of magnetism, atomic physics offers an interesting new set of tools; in
particular, the narrow lines of Sr, of use to atomic clocks, will be exploited in original
protocols to prepare alternating-spin textures and thus study the low-energy behavior of our
system.
Our experiment produces since 2019 degenerate fermionic quantum gases of 87Sr. We are
presently building the optical lattice, such that our system will realize the antiferromagnetic
Heisenberg Hamiltonian. The internship project, and its extension into a PhD thesis, will be
the following:
- The intern will be responsible for installing a high-resolution imaging system (~1.2 μm)
orthogonal to the lattice planes. A homemade mechanical support with fine position and angle
adjustments, required for aberration-free imaging, will be designed and built.
- The intern will contribute to loading the sample in the optical lattice. The first objective will
be to load the ground Bloch band. The imaging system will enable measurements of the
quasi-momentum distribution. We aim at reaching two distinct physical regimes: the band
insulator, with a sample polarized in a single spin state; and the Mott insulator ensured by
interactions, with an unpolarized sample.
If the progresses allow it, we will start the implementation of our protocols for preparing lowenergy
spin textures, that relies on a laser system already built. The response of the sample to
these manipulations, e.g. their degree of reversibility, will provide insight into the low-energy
magnetic properties of the system.