Creating macroscopic quantum superpositions with Bose-Einstein condensates

We use a simple two-mode model to investigate the quantum state dynamics of a two-species Bose-Einsten condensate, such as that produced in recent experiments, undergoing weak Josephson coupling. We find that in certain parameter regimes the quantum state of the system evolves into a macroscopic superposition of two states which differ in the atom number difference between the two species. The "size" of the macroscopic superposition created by such a method can be varied by adjusting the Josephson coupling coefficient, and is found to be near maximal for a certain critical value of this coefficient. [S1050-2947(99)01906-X].