Regensburg 2010 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 32: MLT: Quantum Liquids, Bose-Einstein Condensates, Ultra-cold Atoms, ... 2
TT 32.3: Vortrag
Donnerstag, 25. März 2010, 14:30–14:45, H18
Prethermalization and nonequilibrium BCS dynamics in ultracold Fermi gases — •Michael Möckel1 and Stefan Kehrein2 — 1Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Str. 1, 85748 Garching — 2Department für Physik and Arnold-Sommerfeld-Center, LMU München, Theresienstr. 37, 80333 München
Dynamical experiments with ultracold fermions in optical lattices are a growing field of research for which the time dependent (Fermi-) Hubbard model provides a paradigmatic description. Moreover, predictions on the nonequilibrium behavior of the BCS Hamiltonian have been made; the later describes effectively fermionic pair processes which are contained in the much richer structure of the Hubbard Hamiltonian. This newly motivates the question whether nonequilibrium BCS dynamics can be excited by a nonadiabatic switching of the Hubbard interaction without overheating the system.
Starting from an uncorrelated Fermi gas at zero temperature and in d>1 dimensions, we apply a nonadiabatic, linear and weak ramp of the Hubbard interaction. This allows us to investigate the nonequilibrium properties of a Fermi liquid beyond the adiabatic switching requirement of Landau's theory. We study the real-time evolution of the excited state after the ramping and observe that the relaxation time scales for the kinetic energy and the momentum distribution separate. Therefore a transient regime of prethermalization arises. During that regime the momentum distribution continues to show a discontinuity around the Fermi energy, indicating zero temperature. The delay of thermalization simplifies experimental observations.