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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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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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