# CMT seminar: Virial expansion in cold quantum gases

Thursday, March 20, 2014 – 1:30pm – 3:00pm

Regents 351

Johannes Hofmann

Joint Quantum Institute of UMD and NIST

Ultracold gases offer us a unique way to study strongly interacting systems, the most prominent example being the unitary Fermi gas. Although these many-body systems are notoriously difficult to study, it is possible to perform two-particle and even three-particle calculations explicitly. In my talk, I will discuss how we can harness the knowledge of the few-particle physics to make quantitative predictions for the corresponding many-particle systems in the normal phase by using the virial expansion. I will start by introducing a diagrammatic framework to derive the virial expansion for nonrelativistic systems and proceed by giving two examples of the virial expansion: first, I will discuss the virial expansion as applied to the pair correlation function of the electron gas. Second, I will present results on the spectral function of a two-dimensional Fermi gas with short-range interactions. The results for the spectral function agree well with recent experiments. In particular, our results show that an experimentally observed ‘back-bending’ of the spectral functions’ lower branch cannot be interpreted as a sign of pseudogap physics but is rather explained by two-particle pairing at high temperature.

Host: Jim Freericks