Tuning of heteronuclear interactions in a quantum-degenerate Fermi-Bose mixture

TL;DR

This paper demonstrates control over interactions in a quantum-degenerate Fermi-Bose mixture of 40K and 87Rb atoms using Feshbach resonances, revealing phase transitions, collapse, and phase separation in the system.

Contribution

It reports the first experimental tuning of heteronuclear interactions in a Fermi-Bose mixture, mapping the phase diagram and identifying a p-wave resonance.

Findings

Observation of enhanced mean-field energy near attractive interactions.

Induced collapse of the mixture beyond a certain interaction threshold.

Vertical phase separation on the repulsive side of the resonance.

Abstract

We demonstrate tuning of interactions between fermionic 40K and bosonic 87Rb atoms by Feshbach resonances and access the complete phase diagram of the harmonically trapped mixture from phase separation to collapse. On the attractive side of the resonance, we observe a strongly enhanced mean-field energy of the condensate due to the mutual mean-field confinement, predicted by a Thomas-Fermi model. As we increase heteronuclear interactions beyond a threshold, we observe an induced collapse of the mixture. On the repulsive side of the resonance, we observe vertical phase separation of the mixture in the presence of the gravitational force, thus entering a completely unexplored part of the phase diagram of the mixture. In addition, we identify the 515 G resonance as p-wave by its characteristic doublet structure.