Cold atoms by kinematic cooling

We report the preparation and observation of translationally cold atoms using kinematic cooling. In these experiments, krypton atoms are cooled to subkelvin temperatures by elastic collisions in crossed atomic beams. Two independent velocity measurements indicate an upper-bound mean velocity of 13 m/s (E-trans/k = 850 mK) and are consistent with a much lower mean velocity of 4m/s (E-trans/k = 80 mK) (k is Boltzmann's constant). The density of the cold atoms is measured to be 109 atoms/cm(3). Scattering calculations and diffusion models support these velocity and density measurements. The results demonstrate that cold, dense samples of ground-state atoms and molecules can be prepared by elastic collisions between identical collision partners.