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Dr. Andreas Trenkwalder

University of Innsbruck

Thursday, November 24th, 2011 at 10:00:00 AM

Conference room Querzoli - LENS - via Nello Carrara 1 - Sesto Fiorentino (Florence)

Published on-line at 05:01:46 PM on Thursday, November 10th, 2011

Metastability and coherence of repulsive polarons in a strongly interacting Fermi mixture

The 6Li and 40K Fermi-Fermi mixture is challenging but rewarding: we demonstrated it can be brought into the strongly interacting regime.

Mixtures of ultracold fermions offer many control parameter and new phases are expected to emerge at low temperatures. We investigate the 6Li and 40K Fermi-Fermi mixture which is challenging but rewarding. The Feshbach resonances are closed-channel dominated, which means, they are narrow and the universal regime is small. Therefore, a good control of the experimental parameters and a field stability in the mG regime are required [D. Naik et.al., EPJD (2011)].

Having achieved this, we could recently demonstrate that the 6Li-40K system can be brought into the strongly interacting regime [A. Trenkwalder et.al., PRL 106, 115304 (2011)]. We observe hydrodynamic behavior during expansion at one of the broader Feshbach resonances. As the next step we use radio-frequency spectroscopy to obtain the excitation spectrum across this resonance. Our conditions are such that we are in the polaron regime of 40K atoms acting as impurities in a large Fermi sea of 6Li atoms. We observe the attractive polaron branch connecting the atomic state with the molecular state. Moreover, we observe the metastable repulsive branch. We measure its interaction energy and lifetime deep into the strongly interacting regime. The quasiparticle residue is obtained from the frequency of Rabi oscillations. We conclude that the non-zero effective range of the interparticle interaction leads to an increased lifetime of the metastable repulsive polaron [C. Kohstall et.al., in preparation].

For further informations, please contact Dr. Marco Fattori.