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Creation of ultracold molecules from a Fermi gas of atoms


Following the realization of Bose–Einstein condensates in atomic gases, an experimental challenge is the production of molecular gases in the quantum regime. A promising approach is to create the molecular gas directly from an ultracold atomic gas; for example, bosonic atoms in a Bose-Einstein condensate have been coupled to electronic ground-state molecules through photoassociation1 or a magnetic field Feshbach resonance2. The availability of atomic Fermi gases offers the prospect of coupling fermionic atoms to bosonic molecules, thus altering the quantum statistics of the system. Such a coupling would be closely related to the pairing mechanism in a fermionic superfluid, predicted to occur near a Feshbach resonance3,4. Here we report the creation and quantitative characterization of ultracold 40K2 molecules. Starting with a quantum degenerate Fermi gas of atoms at a temperature of less than 150 nK, we scan the system over a Feshbach resonance to create adiabatically more than 250,000 trapped molecules; these can be converted back to atoms by reversing the scan. The small binding energy of the molecules is controlled by detuning the magnetic field away from the Feshbach resonance, and can be varied over a wide range. We directly detect these weakly bound molecules through their radio-frequency photodissociation spectra; these probe the molecular wavefunction, and yield binding energies that are consistent with theory.

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Figure 1: Atom loss following magnetic field ramps across a Feshbach resonance in 40K.
Figure 2: Dependence of atom loss on the magnetic field ramp rate through the Feshbach resonance.
Figure 3: Photodissociation spectrum of ultracold molecules, and resulting energy per atom.
Figure 4: Absorption images of the quantum gas using a Stern–Gerlach technique.
Figure 5: Binding energy of the molecules.

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  1. Wynar, R., Freeland, R. S., Han, D. J., Ryu, C. & Heinzen, D. J. Molecules in a Bose-Einstein condensate. Science 287, 1016–1019 (2002)

    Article  ADS  Google Scholar 

  2. Donley, E. A., Claussen, N. R., Thompson, S. T. & Wieman, C. E. Atom–molecule coherence in a Bose–Einstein condensate. Nature 417, 529–533 (2002)

    Article  ADS  CAS  Google Scholar 

  3. Holland, M., Kokkelmans, S. J. J. M. F., Chiofalo, M. L. & Walser, R. Resonance superfluidity in a quantum degenerate Fermi gas. Phys Rev. Lett. 87, 120406 (2001)

    Article  ADS  CAS  Google Scholar 

  4. Timmermans, E., Furuya, K., Milloni, P. W. & Kerman, A. K. Prospect of creating a composite Fermi-Bose superfluid. Phys. Lett. A 285, 228–233 (2001)

    Article  ADS  CAS  Google Scholar 

  5. Feshbach, H. A unified theory of nuclear reactions. II. Ann. Phys. (NY) 19, 287–313 (1962)

    Article  ADS  MathSciNet  CAS  Google Scholar 

  6. Stwalley, W. C. Stability of spin-aligned hydrogen at low temperatures and high magnetic fields: New field-dependent scattering resonances and predissociations. Phys. Rev. Lett. 37, 1628–1631 (1976)

    Article  ADS  CAS  Google Scholar 

  7. Tiesinga, E., Verhaar, B. J. & Stoof, H. T. C. Threshold and resonance phenomena in ultracold ground-state collisions. Phys. Rev. A 47, 4114–4122 (1993)

    Article  ADS  CAS  Google Scholar 

  8. Inouye, S. et al. Observation of Feshbach resonances in a Bose–Einstein condensate. Nature 392, 151–154 (1998)

    Article  ADS  CAS  Google Scholar 

  9. Cornish, S. L., Claussen, N. R., Roberts, J. L., Cornell, E. A. & Wieman, C. E. Stable 85Rb Bose-Einstein condensates with widely tunable interactions. Phys. Rev. Lett. 85, 1795–1798 (2000)

    Article  ADS  CAS  Google Scholar 

  10. Loftus, T., Regal, C. A., Ticknor, C., Bohn, J. L. & Jin, D. S. Resonance control of elastic collisions in an optically trapped Fermi gas of atoms. Phys. Rev. Lett. 88, 173201 (2002)

    Article  ADS  CAS  Google Scholar 

  11. Dieckmann, K. et al. Decay of an ultracold fermionic lithium gas near a Feshbach resonance. Phys. Rev. Lett. 89, 203201 (2002)

    Article  ADS  CAS  Google Scholar 

  12. O'Hara, K. M. et al. Measurement of the zero crossing in a Feshbach resonance of fermionic 6Li. Phys. Rev. A 66, 041401 (2002)

    Article  ADS  Google Scholar 

  13. Regal, C. A., Ticknor, C., Bohn, J. L. & Jin, D. S. Tuning p-wave interactions in an ultracold Fermi gas of atoms. Phys. Rev. Lett. 90, 053201 (2003)

    Article  ADS  CAS  Google Scholar 

  14. O'Hara, K. M., Hemmer, S. L., Gehm, M. E., Granade, S. R. & Thomas, J. E. Observation of a strongly interacting degenerate Fermi gas of atoms. Science 298, 2179–2182 (2002)

    Article  ADS  CAS  Google Scholar 

  15. Regal, C. A. & Jin, D. S. Measurement of positive and negative scattering lengths in a Fermi gas of atoms. Phys. Rev. Lett. (in the press)

  16. Bourdel, T. et al. Measurement of interactions energy near a Feshbach resonance in a 6Li Fermi gas. Preprint at 〈〉 (2003).

  17. Timmermans, E., Tommasini, P., Hussein, M. & Kerman, A. Feshbach resonances in atomic Bose-Einstein condensates. Phys. Rep. 315, 199–230 (1999)

    Article  ADS  CAS  Google Scholar 

  18. Abeelen, F. A. & Verhaar, B. J. Time-dependent Feshbach resonance scattering and anomalous decay of a Na Bose-Einstein condensate. Phys. Rev. Lett. 83, 1550–1553 (1999)

    Article  ADS  Google Scholar 

  19. Mies, F. H., Tiesinga, E. & Julienne, P. S. Manipulation of Feshbach resonance in ultracold atomic collisions using time-dependent magnetic fields. Phys. Rev. A 61, 022721 (2000)

    Article  ADS  Google Scholar 

  20. Stenger, J. et al. Strongly enhanced inelastic collisions in a Bose-Einstein condensate near Feshbach resonances. Phys. Rev. Lett. 82, 2422–2425 (1999)

    Article  ADS  CAS  Google Scholar 

  21. DeMarco, B. & Jin, D. S. Onset of Fermi degeneracy in a trapped atomic gas. Science 285, 1703–1706 (1999)

    Article  CAS  Google Scholar 

  22. Soldán, P., Cvitas, M. T., Hutson, J. M., Honvault, P. & Launay, J.-M. Quantum dynamics of ultracold Na + Na2 collisions. Phys. Rev. Lett. 89, 153201 (2002)

    Article  ADS  Google Scholar 

  23. Ratcliff, L. B., Fish, J. L. & Konowalow, D. D. Electronic transition dipole moment functions for transitions among the twenty-six lowest-lying states of Li2 . J. Mol. Spectrosc. 122, 293–312 (1987)

    Article  ADS  CAS  Google Scholar 

  24. Balakrishnan, N., Forrey, R. C. & Dalgarno, A. Quenching of H2 vibrations in ultracold 3He and 4He collisions. Phys. Rev. Lett. 80, 3224–3227 (1998)

    Article  ADS  CAS  Google Scholar 

  25. Forrey, R. C., Balakrisnan, N., Dalgarno, A., Haggerty, M. R. & Heller, E. J. Quasiresonant energy transfer in ultracold atom-diatom collisions. Phys. Rev. Lett. 82, 2657–2660 (1999)

    Article  ADS  CAS  Google Scholar 

  26. Petrosyan, K. G. Fermionic atom laser. JETP Lett. 70, 11–16 (1999)

    Article  ADS  CAS  Google Scholar 

  27. Torma, P. & Zoller, P. Laser probing of atomic Cooper pairs. Phys. Rev. Lett. 85, 487–490 (2000)

    Article  ADS  CAS  Google Scholar 

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We thank E. A. Cornell, C. E. Wieman, C. H. Greene and S. Inouye for discussions. This work was supported by the NSF and NIST; C.A.R. acknowledges support from the Hertz Foundation.

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Correspondence to Cindy A. Regal.

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Regal, C., Ticknor, C., Bohn, J. et al. Creation of ultracold molecules from a Fermi gas of atoms. Nature 424, 47–50 (2003).

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