Long-range forces between cold atoms

Long-range interactions can substantially modify collision or interaction p rocesses among cold atoms. We are able to monitor their effects on two diff erent systems: Cs atoms which undergo photoassociation and highly excited C s Rydberg atoms. Although the length and the time scales of the interaction s are quite different, their effects can be described with the same resonan t dipole picture. [S0031-9007(99)08564-6].