In this review, we discuss the properties of a few impurity atoms immersed in a gas of
ultracold fermions—the so-called Fermi polaron problem. On one hand, this many-body …

Polaron quasiparticles are formed when a mobile impurity is coupled to the elementary
excitations of a many-particle background. In the field of ultracold atoms, the study of the …

The notion of quasi-particles is essential for understanding the behaviour of complex many-
body systems. A prototypical example of a quasi-particle is a polaron, formed by an impurity …

We employ radio-frequency spectroscopy to investigate a polarized spin mixture of ultracold
Li 6 atoms close to a broad Feshbach scattering resonance. Focusing on the regime of …

Recent experimental and theoretical progress has elucidated the tunable crossover, in
ultracold Fermi gases, from BCS-type superconductors to BEC-type superfluids. The BCS …

The fastest possible collective response of a quantum many-body system is related to its
excitations at the highest possible energy. In condensed matter systems, the time scale for …

Mobile impurities in a Bose-Einstein condensate form quasiparticles called polarons. Here,
we show that two such polarons can bind to form a bound bipolaron state. Its emergence is …

We study the thermal evolution of a highly spin-imbalanced, homogeneous Fermi gas with
unitarity limited interactions, from a Fermi liquid of polarons at low temperatures to a …

Understanding the behavior of an impurity strongly interacting with a Fermi sea is a long-
standing challenge in many-body physics. When the interactions are short ranged, two …

Recent experiments with ultra-cold atoms have demonstrated the possibility of realizing
fermionic superfluids with imbalanced spin populations experimentally. We discuss how …