Cold Trapped Atoms: A Mesoscopic System

The Bose-Einstein condensates recently created in trapped atomic gases are mesoscopic systems, in two senses: (a) Their size fall between macroscopic and microscopic systems; (b) They have a quantum phase that can be manipulated in experiments. We review the theoretical and experimental facts about trapped atomic gases, and give examples that emphasize their mesoscopic characters. One is the dynamics of collapse of a condensate with attractive interactions. The other is the creation of a 1D kink soliton that can be used as a mode-locked atom laser.