# Observation of a Degenerate Fermi Gas Trapped by a Bose-Einstein Condensate

## TL;DR

This paper reports the creation of a stable quantum degenerate mixture of fermionic lithium and bosonic cesium, revealing new regimes of interaction and stability mechanisms in such mixtures.

## Contribution

It demonstrates the formation of a stable fermion-boson mixture near a Feshbach resonance and explores stability under strong attractive interactions without collapse.

## Key findings

- Degenerate Fermi gas confined in a Bose-Einstein condensate without external potential
- Stability observed even under conditions where collapse is expected
- Dynamic equilibrium and three-body loss prevent mean-field collapse

## Abstract

We report on the formation of a stable quantum degenerate mixture of fermionic $^6$Li and bosonic $^{133}$Cs in an optical trap by sympathetic cooling near an interspecies Feshbach resonance. New regimes of the quantum degenerate mixtures are identified. With moderate attractive interspecies interactions, we show that a degenerate Fermi gas of Li can be fully confined in the Cs condensate without external potentials. For stronger attraction where mean-field collapse is expected, no such instability is observed. In this case, we suggest the stability is a result of dynamic equilibrium, where the interspecies three-body loss prevents the collapse. Our picture is supported by a rate equation model, and the crossover between the thermalization rate and the observed inelastic loss rate in the regime where the mean-field collapse is expected to occur.