Quantum rotor in a two-dimensional mesoscopic Bose gas

TL;DR

This paper explores the behavior of a quantum rotor within a two-dimensional Bose-Einstein condensate, focusing on the angulon quasiparticle concept and its limitations in large or high-angular-momentum systems.

Contribution

It introduces a real-space mean-field approach to study the angulon in 2D Bose gases and identifies the conditions under which angulon characteristics emerge or break down.

Findings

Angulon features appear when the bosonic cloud is sufficiently large.

Departure from angulon behavior occurs at large system sizes or angular momenta.

Collective excitations dominate the system's properties in the large-size or high-angular-momentum regime.

Abstract

We investigate a molecular quantum rotor in a two-dimensional Bose-Einstein condensate. The focus is on studying the angulon quasiparticle concept in the crossover from few- to many-body physics. To this end, we formulate the problem in real space and solve it with a mean-field approach in the frame co-rotating with the impurity. We show that the system starts to feature angulon characteristics when the size of the bosonic cloud is large enough to screen the rotor. More importantly, we demonstrate the departure from the angulon picture for large system sizes or large angular momenta where the properties of the system are determined by collective excitations of the Bose gas.