Counterflow dynamics of two correlated impurities immersed in a bosonic gas

20 July 2022

Photo: AG Schmelcher

The immersion of impurity atoms into an ultracold environment is a widely studied research field and sheds light on many fundamental aspects in quantum mechanics. For instance, the development of correlations between the bath and the impurities can lead to the dressing of the latter by the excitations of the bath such that they can be interpreted as quasi-particles (polarons). Moreover, this impurity-bath correlation can induce correlations among the impurities themselves, even when they are initially non-interacting. In the case of bosonic impurities, this effect is expressed in an induced attractive force between them and, eventually, lead to their coalescence.

In this work, we study the counterflow dynamics of two bosonic impurities immersed in an ultracold gas. We initially load the impurities into a double-well potential and superimpose a bosonic medium, trapped either in a box or harmonic oscillator potential. The dynamics are initiated by suddenly ramping down the central barrier of the impurities' double well potential, triggering their counterflow (top left panel). In the weakly-coupled regime, the impurities' one-body density exhibits a periodic breathing oscillation (see the top right panel). However, a more complex mechanism taking place at the two-body level is unraveled by projecting two eigenstates of the initial double well potential on the impurities' many-body wave function (see bottom panels). First, the impurities favor an occupation at the same double-well site which slowly changes over the course of time as they increasingly avoid each other.

Publication:

F. Theel, S. I. Mistakidis, K. Keiler and P. Schmelcher

"Counterflow dynamics of two correlated impurities immersed in a bosonic gas"

Physical Review A 105, 053314 (2022)