Probing the spectral response of ultracold Fermi gases after quench to strong repulsive interactions.

Amico A., Scazza F., Tavares P., Valtolina G., Inguscio M., Zaccanti M., Roati G.
  Lunedì 11/09   14:30 - 18:30   Aula A224   II - Fisica della materia
We will present our recent investigations on ultracold Fermi gases with strong repulsive interactions employing reverse radio-frequency spectroscopy. In a first experiment, we focus on spin-imbalanced mixtures in the regime of strong repulsive interactions. We observe well-defined coherent quasiparticles (polaron) even for unitarity-limited interactions. In particular we find that above a critical value of repulsion, the polaron energy exceeds the Fermi energy of the bath while its effective mass diverges and even turns negative. In a second ongoing experiment we investigate the opposite limit of balanced Fermi mixtures. We use rapid radio-frequency transfers to quench repulsive interactions on a timescale comparable with the Fermi time. We probe the spectral response of the many-body system investigating both the growth of magnetic spin-correlation in the repulsive gas and the decay processes into a paired state or into an attractive polaron.