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Atom–molecule coherence in a Bose–Einstein condensate

Nature volume 417, pages 529–533 (2002)Cite this article

Abstract

Recent advances in the precise control of ultracold atomic systems have led to the realisation of Bose–Einstein condensates (BECs) and degenerate Fermi gases. An important challenge is to extend this level of control to more complicated molecular systems. One route for producing ultracold molecules is to form them from the atoms in a BEC. For example, a two-photon stimulated Raman transition in a 87Rb BEC has been used to produce 87Rb2 molecules in a single rotational-vibrational state1, and ultracold molecules have also been formed2 through photoassociation of a sodium BEC. Although the coherence properties of such systems have not hitherto been probed, the prospect of creating a superposition of atomic and molecular condensates has initiated much theoretical work3,4,5,6,7. Here we make use of a time-varying magnetic field near a Feshbach resonance8,9,10,11,12 to produce coherent coupling between atoms and molecules in a 85Rb BEC. A mixture of atomic and molecular states is created and probed by sudden changes in the magnetic field, which lead to oscillations in the number of atoms that remain in the condensate. The oscillation frequency, measured over a large range of magnetic fields, is in excellent agreement with the theoretical molecular binding energy, indicating that we have created a quantum superposition of atoms and diatomic molecules—two chemically different species.

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Figure 1: Feshbach resonance bound-state energy and scattering length.
Figure 2: Magnetic field pulse shape.
Figure 3: An absorption image taken after the fast magnetic-field pulse sequence and the mean-field expansion.
Figure 4: Nremnant versus tevolve for n0 = 5.4 × 1013 cm-3.
Figure 5: Oscillation frequency versus magnetic field.
Figure 6: Number versus tevolve for n0 = 1.1 × 1013 cm-3.

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Acknowledgements

We acknowledge contributions from E. A. Cornell and the JILA quantum gas collaboration. We are grateful to C. H. Greene and S. J. J. M. F. Kokkelmans for providing the coupled-channels scattering calculations presented in Fig. 5 and to L. Pitaevskii for numerous discussions. S.T.T. acknowledges the support of an ARO-MURI Fellowship. This work was also supported by ONR and NSF.

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Authors and Affiliations

  1. JILA, University of Colorado and National Institute of Standards and Technology, Boulder, Colorado, 80309-0440, USA

    Elizabeth A. Donley, Neil R. Claussen, Sarah T. Thompson & Carl E. Wieman

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  1. Elizabeth A. Donley
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Correspondence to Neil R. Claussen.

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Donley, E., Claussen, N., Thompson, S. et al. Atom–molecule coherence in a Bose–Einstein condensate. Nature 417, 529–533 (2002). https://doi.org/10.1038/417529a

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