  We present a new model of BEC dynamics based on strong confinement near the
ground state. The model predicts oscillations in a two-component condensate,
based on interference of non-spreading wave packets moving within a pair of
tilted nearly square potentials. The oscillations are similar to those recently
reported for a magnetically trapped $^{87}$Rb condensate, and the model's
predictions give good quantitative agreement with the experiments.
