Speaker: Sascha Zöllner, NBI Torsdag 19. maj 2011 15.15 in 1525-323 Title: Impurities in a Two-Dimensional Fermi Gas Abstract: The state of an impurity atom immersed in a quantum gas is a fundamental model of many-body physics. In this talk, I discuss how such a simple model can tell us something about highly imbalanced Fermi gases ? i.e., a Fermi gas of one component with a low concentration of a ?minority? species added. The picture that emerges is that: For weak attraction between impurity and majority atoms, the state is well described by an impurity atom dressed by particle-hole excitations of the Fermi gas (often called a ?polaron?). For stronger attraction, a sharp transition occurs to a simple ?dimer? state of the impurity with one majority atom ? at least in three dimensions. I argue that in lower dimensions, the situation is more subtle, and particle-hole fluctuations play a crucial role. This also has implications for small ensembles of impurities, where quantum statistics come into play. ---------------------------- Nikolaj Thomas Zinner, Ph.D. Department of Physics and Astronomy University of Aarhus Ny Munkegade 120 DK-8000 Aarhus C (+45)8942 3653 phone (+45)8612 0740 fax Office: 1520-534 E-mail: zinner@phys.au.dk URL: http://www.phys.au.dk/~zinner