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Quantum simulation of two-dimensional fermionic systems

Final Report Summary - QUFERM2D (Quantum simulation of two-dimensional fermionic systems)

The main achievements accomplished during this project can be summarised in the following points:

_Realisation from scratch of a new-generation machine to produce ultracold Fermi gases of 6-lithium atoms. We have pushed forward the previous schemes creating a possible new standard. Our scheme consists in the combination of optical trapping and sub-Doppler grey molasses cooling. This set-up is compact and with reasonable costs allows the production of large and highly degenerate clouds of lithium atoms. This scheme is now replicated in several laboratories worldwide.
_Observation of Josephson effect in fermionic superfluids across the BEC-BCS crossover. Josephson effect is universally considered the hallmark of macroscopic quantum coherence. This is the first important outcome published in a high-impact journal as Science Magazine. It represented a great challenge, considering the technical difficulties that we had to tackle (no similar observation was previously reported). This scheme will be now extended to the two dimensional case that we have currently at our disposal in the laboratory.
_Observation of the onset of dissipation in an fermionic Josephson junction. We have for the first time characterized the connection between phase-slippage processes (in the form of vortices) and dissipation in an fermionic Josephson junction. This work complement the previous one (describe in point 1) and it shows how the physics of atomic superfluids of fermions nicely connect with the one of ordinary systems, such as 3He-4He liquids or superconducting metals. This work is going to be published in Physical Review Letters. Also in this case this studies will be extended soon in the case of two-dimensional case.
_Study of repulsive Fermi gases. This represent a particular hot topic of research, since repulsive fermions are the main ingredient for accessing high-Tc superconductivity in a lattice. In the case of highly-imbalanced spin mixtures (i.e. the so-called impurity limit), we have for the first time observed repulsive Fermi polarons. This work has been published in Physical Review Letters as Editor Suggestion. The study of the impurity limit will be extended in the near future in the case of our two-dimensional Fermi gas.
_We have also studied for the first time spin dynamics in the case of repulsive Fermi gases for a gas initially prepared in a ferromagnetic configuration. We have observed that for critical repulsive interaction, repulsion indeed overcomes attraction: this situation corresponds to the case when ferromagnetism is favoured with respect to pairing. This work has been published in Nature Physics.