[Seminar] "Ion polarons in Bose gases: from perturbative regime to many-body bound states" Prof. Gregory Astrakharchik, Polytechnic University of Catalonia (UPC), Barcelona, Spain 

Speaker

G. E. Astrakharchik, Professor, Polytechnic University of Catalonia (UPC), Barcelona, Spain 

Abstract

Charged impurities embedded in quantum gases provide a paradigmatic platform for studying strong coupling between few-body physics and many-body correlations. In this talk, I will discuss recent quantum Monte Carlo studies of ionic polarons in a bosonic bath, focusing on one and two impurity problems. We show how the long-range atom–ion interaction leads to qualitatively different regimes depending on the interaction strength and the number of two-body bound states supported by the potential. We find that for a single impurity, the system forms a polaron whose properties can deviate strongly from weak-coupling predictions in the non-perturbative regime. When two ionic impurities are introduced, the interplay between medium-induced interactions and few-body binding gives rise to three distinct bipolaronic regimes: a perturbative regime reminiscent of neutral impurities, a strongly correlated non-perturbative regime where the quasiparticle picture breaks down, and a many-body bound state regime that emerges only when the underlying atom–ion potential supports a two-body bound state. We further show that the bosonic environment mediates strong effective interactions between impurities. These results highlight the importance of fully many-body numerical approaches for understanding ionic polarons and demonstrate the rich phase diagram arising from the competition between few-body binding and medium-induced correlations.

Looking forward to seeing many of you at the seminar!

Quantum Systems Unit