The first dilute gas Bose-Einstein condensate (BEC) was made at JILA in 1995. The gas BEC is a superfluid and is related to another superfluid, which is liquid He. For years scientists have studied superfluid liquid He, trying to understand its properties, but the fact that this state of matter occurred in a strongly interacting liquid made this inherently difficult challenging from a theoretical perspective. One of the things that made the 1995 discovery so exciting was that we now have a much simpler system in which to understand Bose-Einstein condensation and superfluidity. Our BEC occurs in an ultracold, low density gas.
Our goal is to bridge the gap between these two superfluid systems. In our experiments we make Bose-Einstein condensates using a gas of Rb-85 atoms. We choose Rb-85 because there exists a magnetic-field tunable Fano-Feshbach resonance that one can use to tune the interactions between atoms from very weak to very strong. Because the strongly interacting condensate is short-lived, we study the dynamics of the system following a rapid change in the interaction strength. We probe our system using tools such as two-photon Bragg spectroscopy and rf spectroscopy, as well as with measurements of the momentum distribution.
This experiment is a joint project with the Cornell group.