Suppression of Penning ionization in a spin-polarized mixture of rubidium and He

This paper presents the first study of the collision dynamics of an ultra-cold spin-polarized mixture of rubidium and metastable helium (He*) atoms. Our experiment monitors ion production from the mixture for both magnetically polarized and unpolarized cases. In the unpolarized case, we observe an increase in our background ion rate. However, in the completely polarized sample the ion production is below the sensitivity of our experiment. Nonetheless, we determine an upper limit of 5 x 10(-12) cm(3) s(-1) for the polarized rate constant (beta(Rb-He*)), which is two orders of magnitude below the unpolarized rate constant. Such a suppression of the He*-Rb-87 polarized rate was not apparent a priori and opens the intriguing possibility of creating a dual Bose-Einstein condensate comprising an alkali ground-state atom and an excited-state noble-gas atom.