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