Spatial interference of coherent atomic waves by manipulation of the internal quantum state

A trapped Rb-87 Bose-Einstein condensate is initially put into a superposit ion of two internal states. Under the effect of gravity and by means of a s econd transition, we prepare two vertically displaced condensates in the sa me internal state. These constitute two coherent sources of matter waves wi th adjustable spatial separation. Fringe patterns, observed after free expa nsion, are associated with the interplay between internal and external degr ees of freedom and substantially agree with those for a double-slit experim ent. (C) 2001 Optical Society of America.