Hannover 2010 – scientific programme
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Q: Fachverband Quantenoptik und Photonik
Q 58: Quantum Gases: Lattices II
Q 58.4: Talk
Friday, March 12, 2010, 11:15–11:30, E 001
Free expansion of ultracold fermions in an optical lattice — •Jens Philipp Ronzheimer1, Ulrich Schneider1, Lucia Hackermüller1, Sebastian Will1, Simon Braun1, Thorsten Best2, Tim Rom1, Michael Schreiber1, Kin Chung Fong1, and Immanuel Bloch1 — 1LMU München — 2ALU Freiburg
We investigate the free expansion of fermionic 40K atoms in an optical lattice. A balanced mixture of atoms in the |9/2,−9/2 ⟩ and |9/2,−7/2 ⟩ hyperfine states is initially prepared in a non-interacting band insulator state in the combination of a blue detuned optical lattice and a red detuned optical dipole trap. Using a Feshbach resonance, the interaction between the species is set to values varying from strongly attractive to strongly repulsive. The atoms are released by quickly ramping down the dipole trap to a strength that only compensates the anticonfinement due to the optical lattice while increasing the depth of the lattice in one direction, thereby creating sheets of homogeneous 2D lattices.
In the case of negligible interactions, the atomic cloud expands ballistically with a speed given by the tunneling rate. For interacting fermions, the expansion becomes diffusive with a density dependent diffusion constant. Independent of the sign of interactions, the outer regions of the cloud still expand ballistically while the expansion of the high density core slows down with increasing interaction strength. Eventually, the core stops expanding and instead starts to dissolve from the outside, shrinking over time.
These measurements demonstrate previously unobserved transport dynamics and give insight into timescales for density redistribution.