Article Describes Motions of Impurities in Bose-Einstein Condensate

Wolfgang Ketterle of MIT reports that his group published a paper in Physical Review Letters entitled "Suppression and Enhancement of Impurity Scattering in a Bose-Einstein Condensate" with authors A.P. Chikkatur, A. Görlitz, D.M. Stamper-Kurn, S. Inouye, S. Gupta, and W. Ketterle (Phys. Rev. Lett. 85, 483-486 (2000)). This paper studies the motion of impurity atoms through a Bose-Einstein condensate.  Impurity atoms propagating at variable velocities were produced using a stimulated Raman transition that accelerated the atoms by the photon recoil.  Collisions of the impurity atoms with the condensate were observed by analyzing the velocity distribution of the ballistically expanding condensate.  The collision cross-section was dramatically reduced when the impurity velocity was reduced below the condensate speed of sound, in agreement with the Landau criterion for superfluidity.