Ground state and excitations of a Bose-Einstein condensate of atoms and their diatomic bound states

This is a theoretical study of a many-body system of spin-zero atoms and their diatomic bound states (molecules) which form a single Bose-Einstein condensate at zero temperature. The Gross-Pitaevskii approach is used to analyze the equilibrium states and dynamics of this system. It is shown that, depending on the binding energy of the system, the system can exist in two phases: an atom-molecule condensate and a molecular condensate. The basic thermodynamic characteristics and the criteria for their stability are found. Both phases have two branches of collective excitations, one of which is acoustic, while the other has an activation energy.