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A: Fachverband Atomphysik

A 12: Poster I

A 12.29: Poster

Dienstag, 7. März 2023, 16:30–19:00, Empore Lichthof

Polarons and bipolarons in a two-dimensional square lattice — •Gustavo Alexis Dominguez Castro — Institute for Theoretical Physics, Hannover university

Quantum simulation experiments with cold atoms have in recent years advanced our understanding of isolated quasiparticles, but so far they have provided limited information regarding their interactions and possible bound states. Here, we show how exploring mobile impurities immersed in a Bose-Einstein condensate in a two-dimensional lattice can address this problem. First, the spectral properties of individual impurities are examined, and in addition to the attractive and repulsive polarons known from continuum gases, we identify a new kind of quasiparticle stable for repulsive boson-impurity interactions. The spatial correlations between the impurity and the bosons are calculated showing that there is an increased density of bosons at the site of the impurity both for repulsive and attractive interactions. We then derive an effective Schrödinger equation describing two polarons interacting via the exchange of density oscillations in the BEC. Using this, we show that the attractive nature of the effective interaction between two polarons mediated by the BEC combined with the two-dimensionality of the lattice leads to the formation of bound states. Our results show that optical lattices are a promising platform to explore the spatial properties of polarons as well as to finally observe the elusive bipolarons.