In this talk, we will present recent experimental work performed at ENS on the thermodynamics of strongly interacting 6Li Fermi gases. We have developed a general method to probe with high precision the thermodynamics of locally homogeneous ultracold gases . This allows stringent tests of recent many-body theories. First, we focus on the finite-temperature Equation of State (EoS) of the unpolarized unitary gas. Precise thermometry is provided by adding to the trapped 6Li unitary gas a small amount of bosonic 7Li that is weakly perturbing the system. We show that the low-temperature properties of the strongly interacting normal phase are well described by Fermi liquid theory and we localize the superfluid phase transition. Second, we address the zero-temperature EoS of the spin-polarized system. Surprisingly, despite strong interactions, the normal polarized phase behaves as a mixture of two ideal gases: a Fermi gas of bare majority atoms and a non-interacting gas of dressed quasi-particles, the Fermi polarons. Finally, we will report on work in progress on the extension of our study to the BEC-BCS crossover . Our equation of state can be directly used to describe low density neutron matter such as the outer shell of neutron stars.
 S. Nascimbène, N. Navon, K. Jiang, F. Chevy, and C. Salomon, arXiv:0911.0747, accepted for publication in Nature (2010)
 N. Navon, S. Nascimbène, F. Chevy, C. Salomon, in preparation (2010)
Christophe Salomon obtained his PhD in 1984 at Paris 13 University (France) and moved for his post-doc to JILA (USA), where he worked with J. Hall on ultra-stable lasers and laser cooling of atoms. He currently works in Laboratoire Kastler Brossel. Now, as a Research Director at CNRS, he is Head of the cold Fermi gas group at Ecole Normale Supérieure and Principal Investigator for the ACES/PHARAO space clock Mission. His research interests are in quantum gases and fundamental physics tests with ultra- stable clocks. He has currently 180 publications. He received the "Three physicists" prize (FR), the Mergier-Bourdeix Grand Prize of the French Academy of Sciences, the European Time and Frequency Prize, and the Philip-Morris Prize.