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 [1]. 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 [2]. Our equation of state can be directly used to describe low density neutron matter such as the outer shell of neutron stars. [1] S. Nascimbène, N. Navon, K. Jiang, F. Chevy, and C. Salomon, arXiv:0911.0747, accepted for publication in Nature (2010) [2] 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.
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