Leticia Tarruell, Daniel Greif, Thomas Uehlinger, Robert Joerdens, Niels Strohmaier, Henning Moritz and Tilman Esslinger.

Institute for Quantum Electronics, ETH Zurich, 8093 Zurich, Switzerland

We experimentally implement the Fermi-Hubbard model by trapping a repulsively interacting two-component Fermi gas in an optical lattice. The system is characterized though accurate measurements of the occupation of lattice sites. By comparing the experimentally measured double occupancy with DMFT simulations and high temperature series expansions we determine the temperature of the paramagnetic phase in both the metallic and the Mott insulator regimes.

A modulation of the lattice potential is used to pump energy into the system. The experiments are performed in the weak perturbation regime, where the response can be quantitatively interpreted in terms of Fermi’s golden rule. In the strongly interacting limit, it gives direct access to both density and spin nearest neighbor correlations of the unperturbed system. We use this probe to determine the amount of empty sites of the paramagnetic phase and perform a complementary temperature measurement. As this technique gives direct access to local spin correlations, it is an ideal candidate for studying the approach to the antiferromagnetic phase.