Metastability and Coherence of Repulsive Polarons in a Strongly Interacting Fermi Mixture

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• Dr. Pietro Massignan, ICFO - The Institute of Photonic Sciences, Barcelona, Spain
• Thursday 15 December 2011, 14:15-15:15
• TCM Seminar Room, Cavendish Laboratory.

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We investigate theoretically and experimentally the properties of a strongly-interacting mixture of 40K and 6Li fermionic atoms, in the limit where few potassium atoms may be considered as impurities in a large Fermi sea of degenerate lithium atoms. Experimentally, we use rf spectroscopy to map out the complete excitation spectrum of the “impurity problem”, which contains two well-defined quasi-particles, the attractive polaron at negative energies and the metastable repulsive polaron at positive energies, in addition to a broad molecule-hole continuum. We measure quasiparticle energies, lifetimes, and residues, finding excellent agreement with a theory which explicitly includes the finite range of the Feshbach resonance. Interestingly, we find that the presence of a large range (of order the interparticle spacing) substantially increases the lifetime of repulsive polarons, opening new perspectives for the investigation of gases with strong repulsive interactions.

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