Ultracold Fermi Gas

Atom/molecule conversion in ultracold gases. The blue lines show the energy of a pair of atoms that is magnetically tuned through a "resonance," corresponding to a bound vibrational level of the diatomic molecule. This is an example of a "Feshbach resonance" that can be used to vary the mean-field interaction energy of the atoms. The energy levels actually anti-cross, as shown by the yellow lines, owing to a hyperfine interaction. By preparing a gas of ultracold 6Li atoms at a field above the crossing, and then adiabatically ramping the field (changing the B field without any gain or loss of energy) through the crossing as indicated by the green arrow, the atoms are converted into diatomic molecules, Li2. Being composites of two fermions, these molecules are themselves bosons.

Reported by: Strecker et al., Physical Review Letters, 22 August 2003.

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