Three studies were performed as part of this project and each represent a step forward towards the study of multi-orbital strongly interacting systems in lattices (e.g. Kondo lattice model).
Firstly, we were able to load ytterbium atoms into an optical lattice at very low temperature and set up a tool to probe them locally. By varying the lattice strength, we studied the cross-over between the metallic and the Mott insulating phases by directly measuring the equation of state. This specifically allowed to probe the role of the extended SU(N)-symmetry present in ytterbium atoms. Although the SU(N) Fermi-Hubbard model is theoretically still mostly not understood, our equation of state measurements match those special limiting cases for which which theories exist, such as in certain weak and strong interaction regimes. We hope our results will serve as benchmark for theories addressing the challenging intermediate interaction case. Moreover, we show that our results pave the way to study interatomic magnetic correlations.
In our other line of research, we studied in detail the microscopic interactions between atoms in different orbital states, which is a necessary step towards the simulation of many-body orbital quantum magnetism. Based on our early results, a novel type of Feshbach resonance in ytterbium-173 was predicted by a group of theorists, which we subsequently could indeed identify for the first time. This resonance allows to tune the interaction strength between orbitals. By changing the magnetic field strength, we measured a variation in the interatomic collision rate by almost two orders of magnitude in the bulk.
Continuing the multi-orbital physics research, we constructed an orbital-dependent lattice and loaded ytterbium atoms into it. The atoms are distributed in two atomic orbitals (of type g and e) with distinct internal spin (down and up, respectively) and are trapped in one-dimensional tubes. We superimposed an orbital-dependent optical lattice along the longitudinal axis of the tubes, creating a strong lattice for atoms in the e orbital, but with a weak effect on atoms in the g orbital. Due to the spin-exchange nature of interactions, this system is predicted to display features of Kondo (lattice) physics, with the e orbital playing the role of impurity and the g orbital as the conducting electron. We are analyzing the many-body physics of this model system and have submitted a manuscript with our results.
The results obtained in the framework of this project demonstrated the remarkable potential and uniqueness of the ytterbium-173 isotope to simulate interesting many-body problems. Our first two studies resulted in publications in world-class peer-reviewed scientific journals and a third manuscript is submitted for publication.
