Hannover 2020 – scientific programme

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A: Fachverband Atomphysik

A 10: Collisions, scattering and correlation phenomena

A 10.7: Talk

Tuesday, March 10, 2020, 15:45–16:00, a320

From polarons to bipolarons in Bose-Einstein condensates. — •Luis Ardila — Institut für Theoretische Physik-Hannover Universität

Mobile impurities in a Bose-Einstein condensate can form quasi-particles termed Bose polarons. Here I show how these quasi-particles are originated when a single impurity is dressed by the excitations of the quantum bosonic bath. The most striking advantage of these polarons is the huge degree of controllability of the coupling strength between the impurity and the bosonic bath. Thus, one can realize polarons from weak all the way up to the strong interacting regime. For strong interactions two polaron can bind together forming bound bipolarons states. They emerge due to the induced nonlocal interaction mediated by density oscillations of the bath. It turns out that exploring low-dimensions, polarons can form many-body bound states even at intermediate coupling. Here, we use exact QMC to study an impurity immersed in a 2D superfluid and to compute the polaron energy, the effective mass and the quasiparticle residue for arbitrary coupling strength. We find important deviations of the quasiparticle properties from perturbation theory even at very weak coupling strengths. In the strongly interacting regime, the ground-state polaron loses the quasiparticle nature characteristic of weak interactions and forms a many-body bound state featuring a large effective mass, a vanishing wavefunction residue and a size that extends over many healing lengths of the bath .