Fermions, particles with half-integer spin like the electron, proton and neutron, obey the Pauli principle: They cannot share one and the same quantum state. This “anti social” behavior is directly observed in experiments with ultracold gases of fermionic atoms: Pauli blocking in momentum space for a free Fermi gas, and in real space in gases confined to an optical lattice. When fermions interact, new, rather “social” behavior emerges, i.e. hydrodynamic flow, superfluidity and magnetism. The interplay of Pauli’s principle and strong interactions poses great difficulties to our understanding of complex Fermi systems, from nuclei to high-temperature superconducting materials and neutron stars. I will describe experiments on atomic Fermi gases where interactions become as strong as allowed by quantum mechanics – the unitary Fermi gas, fermions immersed in a Bose gas and the Fermi-Hubbard lattice gas. Sound and heat transport distinguish collisionally hydrodnamic from superfluid flow, while spin transport reveals the underlying mechanism responsible for quantum magnetism.
Biography: Martin Zwierlein studied physics at the University of Bonn and at the Ecole Normale Supérieure in Paris. His doctoral thesis in the group of Wolfgang Ketterle at MIT focused on the observation of superfluidity in ultracold fermionic gases, a novel form of strongly interacting matter. After a postdoctoral stay at the University of Mainz in the group of Immanuel Bloch, he joined the MIT physics department in 2007. His group is using ultracold atomic gases to study models of many-body physics relevant for condensed matter, nuclear and astrophysics. He and his team recently observed Fermi polarons and the quantum limit of diffusion in strongly interacting Fermi gases. His awards include the Klung-Wilhelmy-Weberbank-Prize, Freie Universität Berlin (2007), Young Investigator Awards from the Air Force Office of Scientific Research, the Office of Naval Research and DARPA (2010), a David and Lucile Packard Fellowship (2010) and a Presidential Early Career Award for Scientists and Engineers (2010).