SUPERFLUIDITY IN SYMPATHETIC COOLING WITH ATOMIC BOSE-EINSTEIN CONDENSATES

The dynamical structure of an atomic Bose-Einstein condensate limits t he efficiency of the condensate in cooling slow impurity atoms. To ill ustrate the point, we show that an impurity atom moving in a homogeneo us zero-temperature condensate is not scattered incoherently if its ve locity is lower than the condensate sound velocity c, limiting cooling to velocities v greater than or equal to c. This striking effect is a n expression of superfluidity and provides a direct means to detect th e fundamental property of superfluidity in atomic condensates. Further more, we show that the fermionic lithium isotope, Li-6, is a reasonabl e candidate for sympathetic cooling by a Na-23 condensate.