Dynamical response of a Bose-Einstein condensate to a discontinuous change in internal state

A two-photon transition is used to convert an arbitrary fraction of the Rb-87 atoms in a \F = 1, m(f) = -1] condensate to the \F = 2, m(f) = 1] state. Transferring the entire population imposes a discontinuous change on the condensate's mean-field repulsion, which leaves a residual ringing in the condensate width. A calculation based on Gross-Pitaevskii theory agrees well with the observed behavior, and from the comparison we obtain the ratio of the intraspecies scattering lengths for the two states, a(\1,)-(1)]/a(\2,1)] = 1.062(12). [S0031-9007(98)06574-0].