Radio-Frequency Spectroscopy of Ultracold Atomic Fermi Gases

This thesis presents experiments investigating the phase diagram of ultracold atomic Fermi gases using radio-frequency spectroscopy. The tunability of many experimental parameters including the temperature, the interparticle interaction strength and the relative population of different fermions allows to access very different physical regimes. Radio-frequency spectroscopy has been developed into an ideal tool to probe correlations between particles in these different phases. In particular, radio-frequency spectroscopy of highly population imbalanced atomic Fermi systems gives access to the impurity problem: A single fermion, or boson, immersed in a sea of fermions constitutes a polaron, which can be described by Landau’s Fermi liquid theory. A critical interaction strength can be identified separating the regime of a fermionic polaron and a bosonic polaron. Radio-frequency spectroscopy of the polarized superfluid phase allows an accurate measure of the superfluid gap ∆ and allows to identify the importance of Hartree Mean-field energies. Furthermore, it is shown how these different physical regimes are connected. Thesis Supervisor: Wolfgang Ketterle Title: John D. MacArthur Professor of Physics Thesis Supervisor: Martin W. Zwierlein Title: Assistant Professor of Physics