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Feynman Diagrams Versus Fermi-gas Feynman Emulator

Dr Félix Werner
CNRS, Laboratoire Kastler Brossel, Ecole Normale Superieure, France

3:30 pm Friday, 4 May 2012, EN101 Lecture Theatre (EN Building), Hawthorn.

Precise understanding of strongly interacting fermions, from electrons in modern materials to nuclear matter, presents a major goal in modern physics. For the first time, we sum the series of Feynman diagrams for such a many-body problem to essentially infinite order. This is made possible by a new theoretical approach, Bold Diagrammatic Monte Carlo (BDMC), which combines a Monte Carlo process capable of sampling billions of diagram topologies, bold lines representing fully dressed propagators, and divergent-series resummation techniques.
Specifically, we compute the equation of state of the unitary gas - a prototypical example of a strongly correlated fermionic system - in the normal unpolarised phase. We cross-validate the results with new precision experiments on ultra-cold 6Li atoms at the broad Feshbach resonance. Excellent agreement demonstrates that a series of Feynman diagrams can be controllably resummed in a non-perturbative regime using BDMC. This opens the door to the solution of challenging problems across many areas of physics.
K. Van Houcke, F. Werner, E. Kozik, N. Prokofev, B. Svistunov, M. Ku, A.Sommer, L. W. Cheuk, A. Schirotzek, M. W. Zwierlein, Nature Physics (2012), doi:10.1038/nphys2273 []

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