The role of the initial state in the collapse of a Bose condensed gas

The stability of a Bose condensed gas with a negative scattering length is studied with regard to the role played by the initial state. A trapped ideal gas ground state is shown to be unstable when the Gross Pitaevskii equation still predicts the existence of a stable state. A possible relation to a recent experimental study of the critical conditions for stability or collapse of a Bose Einstein condensate (Roberts et al 2001 Phys. Rev. Lett. 86 4211) is discussed.