Quantum state of two coupled Bose-Einstein condensates

Summary form only given.Due to interatomic collisions, the ground state of a Bose-Einstein condensate of dilute atoms is not, as is commonly assumed, a coherent state. First recognizing this point, Lewenstein and You concluded that the condensate is actually an amplitude quadrature eigenstate. We have extended this work by studying the quantum state for two condensates with a linear coupling provided by either spatial tunneling or laser coupling between magnetic substates. As the system is closed, the ground state is unambiguously a pure state, and as we deal only with relative phases, there is no need to invoke broken symmetry.