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Emergence of a molecular Bose–Einstein condensate from a Fermi gas


The realization of superfluidity in a dilute gas of fermionic atoms, analogous to superconductivity in metals, represents a long-standing goal of ultracold gas research. In such a fermionic superfluid, it should be possible to adjust the interaction strength and tune the system continuously between two limits: a Bardeen–Cooper–Schrieffer (BCS)-type superfluid (involving correlated atom pairs in momentum space) and a Bose–Einstein condensate (BEC), in which spatially local pairs of atoms are bound together. This crossover between BCS-type superfluidity and the BEC limit has long been of theoretical interest, motivated in part by the discovery of high-temperature superconductors1,2,3,4,5,6,7,8,9,10. In atomic Fermi gas experiments superfluidity has not yet been demonstrated; however, long-lived molecules consisting of locally paired fermions have been reversibly created11,12,13,14,13. Here we report the direct observation of a molecular Bose–Einstein condensate created solely by adjusting the interaction strength in an ultracold Fermi gas of atoms. This state of matter represents one extreme of the predicted BCS–BEC continuum.

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Figure 1: Time-of-flight images of the molecular cloud, taken with a probe beam along the axial direction after 20 ms of free expansion.
Figure 2: Molecular condensate fraction N0/N versus the scaled temperature T/Tc.
Figure 3: Dependence of condensate formation on magnetic-field sweep rate and measurement of condensate lifetime.
Figure 4: Total expansion energy per particle for the molecular condensate versus the interaction strength during expansion.
Figure 5: Dependence of the condensate fraction and the temperature of the atom–molecule mixture on the initial scaled temperature T/TF of the Fermi gas.

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  1. Leggett, A. J. Cooper pairing in spin-polarized Fermi systems. J. Phys. C (Paris) 41, 7–19 (1980)

    Google Scholar 

  2. Nozieres, P. & Schmitt-Rink, S. Bose condensation in an attractive fermion gas: From weak to strong coupling superconductivity. J. Low-Temp. Phys. 59, 195–211 (1985)

    Article  ADS  CAS  Google Scholar 

  3. Drechsler, M. & Zwerger, W. Crossover from BCS-superconductivity to Bose-condensation. Ann. Phys. 1, 15–23 (1992)

    Article  Google Scholar 

  4. Haussmann, R. Properties of a Fermi-liquid at the superfluid transition in the crossover region between BCS superconductivity and Bose-Einstein condensation. Phys. Rev. B 49, 12975–12983 (1994)

    Article  ADS  CAS  Google Scholar 

  5. Randeria, M. in Bose-Einstein Condensation (eds Griffin, A., Snoke, D. W. & Stringari, S.) 355–392 (Cambridge Univ. Press, Cambridge, UK, 1995)

    Book  Google Scholar 

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

    Article  ADS  CAS  Google Scholar 

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

    Article  CAS  Google Scholar 

  8. Ohashi, Y. & Griffin, A. BCS-BEC crossover in a gas of Fermi atoms with a Feshbach resonance. Phys. Rev. Lett. 89, 130402 (2002)

    Article  ADS  CAS  Google Scholar 

  9. Milstein, J. N., Kokkelmans, S. & Holland, M. J. Resonance theory of the crossover from Bardeen-Cooper-Schrieffer superfluidity to Bose-Einstein condensation in a dilute Fermi gas. Phys. Rev. A 66, 043604 (2002)

    Article  ADS  Google Scholar 

  10. Ohashi, Y. & Griffin, A. Superfluid transition temperature in a trapped gas of Fermi atoms with a Feshbach resonance. Phys. Rev. A 67, 033603 (2003)

    Article  ADS  Google Scholar 

  11. Regal, C. A., Ticknor, C., Bohn, J. L. & Jin, D. S. Creation of ultracold molecules from a Fermi gas of atoms. Nature 424, 47–50 (2003)

    Article  ADS  CAS  Google Scholar 

  12. Strecker, K. E., Partridge, G. B. & Hulet, R. G. Conversion of an atomic Fermi gas to a long-lived molecular Bose gas. Phys. Rev. Lett. 91 (2003)

  13. Cubizolles, J., Bourdel, T., Kokkelmans, S. J. J. M. F., Shlyapnikov, G. V., Salomon, C. Production of long-lived ultracold Li2 molecules from a Fermi gas. Preprint at 〈〉 (2003).

  14. Jochim, S. et al. Pure gas of optically trapped molecules created from fermionic atoms. Preprint at 〈〉 (2003).

  15. Regal, C. A., Greiner, M., & Jin, D. S. Lifetime of molecule-atom mixtures near a Feshbach resonance in 40K. Preprint at 〈〉 (2003).

  16. Carr, L. D., Shlyapnikov, G. V. & Castin, Y. Achieving a BCS transition in an atomic Fermi gas. Preprint at 〈〉 (2003).

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

    Article  CAS  Google Scholar 

  18. Regal, C. A. & Jin, D. S. Measurement of positive and negative scattering lengths in a Fermi gas of atoms. Phys. Rev. Lett. 90, 230404 (2003)

    Article  ADS  CAS  Google Scholar 

  19. 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 

  20. 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 

  21. Chin, C., Kerman, A. J., Vuletic, V. & Chu, S. Sensitive detection of cold cesium molecules formed on Feshbach resonances. Phys. Rev. Lett. 033201 (2003)

  22. Herbig, J. et al. Preparation of a pure molecular quantum gas. Science 301, 1510–1513 (2003)

    Article  ADS  CAS  Google Scholar 

  23. Durr, S., Volz, T., Marte, A. & Rempe, G. Observation of molecules produced from a Bose-Einstein condensate. Preprint at 〈〉 (2003).

  24. Xu, K. et al. Formation of quantum-degenerate sodium molecules. Preprint at 〈〉 (2003).

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

    Article  ADS  CAS  Google Scholar 

  26. 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 

  27. Petrov, D. S., Salomon, C. & Shlyapnikov, G. V. Weakly bound dimers of fermionic atoms. Preprint at 〈〉 (2003).

  28. Shvarchuck, I. et al. Bose-Einstein condensation into non-equilibrium states studied by condensate focusing. Phys. Rev. Lett. 89, 270–404 (2002)

    Article  Google Scholar 

  29. Anderson, M. H., Ensher, J. R., Matthews, M. R., Wieman, C. E. & Cornell, E. A. Observation of Bose-Einstein condensation in a dilute atomic vapor. Science 269, 198–201 (1995)

    Article  ADS  CAS  Google Scholar 

  30. Davis, K. B. et al. Bose-Einstein condensation in a gas of sodium atoms. Phys. Rev. Lett. 75, 3969–3973 (1995)

    Article  ADS  CAS  Google Scholar 

  31. Bradley, C. C., Sackett, C. A. & Hulet, R. G. Bose-Einstein condensation of lithium: observation of limited condensate number. Phys. Rev. Lett. 78, 985–989 (1997)

    Article  ADS  CAS  Google Scholar 

  32. Giorgini, S., Pitaevskii, L. P. & Stringari, S. Condensate fraction and critical temperature of a trapped interacting Bose gas. Phys. Rev. A 54, R4633–R4636 (1996)

    Article  ADS  CAS  Google Scholar 

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We thank L. D. Carr, E. A. Cornell, C. E. Wieman, W. Zwerger and I. Bloch for discussions, and J. Smith for experimental assistance. This work was supported by NSF and NIST. C.A.R. acknowledges support from the Hertz Foundation.

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Correspondence to Markus Greiner.

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Greiner, M., Regal, C. & Jin, D. Emergence of a molecular Bose–Einstein condensate from a Fermi gas. Nature 426, 537–540 (2003).

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