MACROSCOPIC SUPERPOSITIONS OF BOSE-EINSTEIN CONDENSATES

We consider two dilute gas Bose-Einstein condensates with opposite vel ocities from which a monochromatic light field detuned far from the re sonance of the optical transition is coherently scattered. In the ther modynamic limit, when the relative fluctuations of the atom number dif ference between the two condensates vanish, the relative phase between the Bose-Einstein condensates may be established in a superposition s tate by detections of spontaneously scattered photons, even though the condensates have initially well-defined atom numbers. For a finite sy stem, stochastic simulations show that the measurements of the scatter ed photons lead to a randomly drifting relative phase and drive the co ndensates into entangled superpositions of number states. This is beca use according to Bose-Einstein statistics the scattering to an already occupied state is enhanced. [S1050-2947(97)08012-8].