Berlin 2014 – scientific programme
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Q: Fachverband Quantenoptik und Photonik
Q 60: Ultracold atoms, ions and BEC VI (with A)
Q 60.2: Talk
Friday, March 21, 2014, 10:45–11:00, BEBEL E34
Universal spin dynamics in two-dimensional Fermi gases — •Marco Koschorreck1,2, Daniel Pertot1,2, Enrico Vogt1, and Michael Köhl1,2 — 1University of Cambridge — 2Universität Bonn
Spin transport has unique properties, setting it aside from charge transport: first, the transport of spin polarization is not protected by momentum conservation and is greatly affected by scattering. Therefore, the question arises: what is the limiting case of the spin transport coefficients when interactions reach the maximum value allowed by quantum mechanics? Second, unlike charge currents (which lead to charge separation and the buildup of an electrical field, counteracting the current), spin accumulation does not induce a counteracting force.
Fermionic quantum gases allow the study of spin transport from first principles because interactions can be precisely tailored and the dynamics is on directly observable timescales. In particular, at unitarity, spin transport is dictated by diffusion and the spin diffusivity is expected to reach a universal, quantum-limited value on the order of the reduced Planck constant divided by the particle mass. Here, we study a two-dimensional Fermi gas after a quench into a metastable, transversely polarized state [1]. Using the spin-echo technique, for strong interactions, we measure the lowest transverse spin diffusion constant of 0.0063(8) ℏ/m so far. For weak interactions, we observe a collective transverse spin-wave mode that exhibits mode softening when approaching the strongly interacting regime.
[1] Koschorreck, M., Pertot, D., Vogt, E. & Köhl, M. Nature Physics 9, 405-409 (2013).