Localization of bosonic atoms by fermionic impurities in a 3d optical lattice

TL;DR

This paper demonstrates that fermionic impurities induce a localized phase in ultracold bosonic gases within a 3D optical lattice, revealing disorder effects beyond mean-field predictions.

Contribution

It provides experimental evidence of impurity-induced localization in a 3D lattice and highlights the significant role of disorder effects in the transition.

Findings

Fermionic impurities cause a shift in the superfluid to Mott insulator transition.

The observed shift exceeds mean-field predictions, indicating disorder effects.

Localization of bosonic atoms is induced by a small concentration of fermionic impurities.

Abstract

We observe a localized phase of ultracold bosonic quantum gases in a 3-dimensional optical lattice induced by a small contribution of fermionic atoms acting as impurities in a Fermi-Bose quantum gas mixture. In particular we study the dependence of this transition on the fermionic 40K impurity concentration by a comparison to the corresponding superfluid to Mott insulator transition in a pure bosonic 87Rb gas and find a significant shift in the transition parameter. The observed shift is larger than expected based on a mean-field argument, which is a strong indication that disorder-related effects play a significant role.