Macroscopic quantum self-trapping in a Bose-Josephson junction with fermions

TL;DR

This paper investigates how a mixture of bosons and fermions in a double-well potential affects macroscopic quantum self-trapping, revealing that fermions significantly alter the phenomenon's onset and properties, including inducing population inversion.

Contribution

It introduces a semi-analytical mean-field model showing how fermions modify self-trapping in Bose-Einstein condensates, including population inversion effects.

Findings

Fermions significantly modify the self-trapping behavior.

Repulsive interactions cause population inversion of bosonic levels.

Results are applicable to $^{40}$K-$^{87}$Rb experimental systems.

Abstract

We study the macroscopic quantum self-trapping effect in a mixture of Bose-Einstein condensate and a large number of quantum degenerate fermions, trapped in a double-well potential with a variable separation between the wells. The large number of fermions localized in each well form quasi-static impurities that affect the dynamics of the bosonic cloud. Our semi-analytical analysis based on a mean-field model shows that main features of macroscopic quantum self trapping in a pure bosonic system are radically modified by the influence of fermions, with both the onset of self-trapping and properties of the self-trapped state depending on the fermion concentration as well as on the type of inter-species interaction. Remarkably, repulsive inter-species interaction leads to population inversion of the bosonic energy levels in the trapping potential and hence to the inversion of symmetry of the macroscopic wavefunction. Realistic physical estimates are given based on experimental parameters for a $^{40}$K-$^{87}$Rb system.