Ramsey Fringes in a Bose-Einstein Condensate between Atoms and Molecules

In a recent experiment, a Feshbach scattering resonance was exploited to observe Ramsey fringes in a ${}^{\mathrm{85}}\mathrm{R}\mathrm{b}$ Bose-Einstein condensate. The oscillation frequency corresponded to the binding energy of the molecular state. We show that the observations are remarkably consistent with predictions of a resonance field theory in which the fringes arise from oscillations between atoms and molecules.