Degenerate Bose-Fermi Mixtures

Here in the Chin lab, we have recently succeeded creating the first ever dual-degenerate mixture of Li and Cs. This has been a goal of the experiment since it first began! 

 

While these two atoms can hardly be less alike (Li is a light fermion and Cs is a heavy boson), we find they make a fantastic pair to study many-body physics.   Near 893 G, the absolute ground state of these atoms yields tunable interspecies interactions allowing excellent control over the system.  We make use of this to use the Cs atoms to cool Li atoms to a fraction of the Fermi temperature.

 

From this starting point we can explore the ways in which the BEC and degenerate Fermi gas interact together.  In our first experiment, we found two surprising results.  First, when the interspecies interactions are small and attractive, the BEC forms a trap for the fermions.  These atoms can then be separated from the rest of the cloud and represent a new type of quantum object.  Second, by going to stronger attractive interactions, we find that the mixture is stable even though mean-field theory predicts it should collapse. These findings are detailed in our recent paper here: https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.119.233401.  Stay tuned for more results from this exciting experiment!

 

 

This work was performed by Brian DeSalvo, Krutik Patel, and Jacob Johansen.