Optical billiards for atoms

One of the central paradigms for classical and quantum chaos in conservativ e systems is the two-dimensional billiard in which particles are confined t o a closed region in the plane, undergoing elastic collisions with the wall s and free motion in between. We report the first realization of billiards: using ultracold atoms bouncing off beams of light. These beams create the desired spatial pattern, forming an "optical billiard." We find excellent a greement between theory and our experimental demonstration of chaotic and s table motion in optical billiards, establishing a new testing ground fur cl assical and quantum chaos.