Conversion efficiency of ultracold fermionic atoms to bosonic molecules via Feshbach resonance sweep experiments Academic Article uri icon


  • We explain why the experimental efficiency observed in the conversion of ultracold Fermi gases of K 40 and L i 6 atoms into diatomic Bose gases is limited to 0.5 when the Feshbach resonance sweep rate is sufficiently slow to pass adiabatically through the Landau-Zener transition but faster than “the collision rate” in the gas, and increases beyond 0.5 when it is slower. The 0.5 efficiency limit is due to the preparation of a statistical mixture of two spin states, required to enable s-wave scattering. By constructing the many-body state of the system we show that this preparation yields a mixture of even and odd parity pair states, where only even parity can produce molecules. The odd parity spin-symmetric states must decorrelate before the constituent atoms can further Feshbach scatter, thereby increasing the conversion efficiency;“the collision rate” is the pair decorrelation rate.

publication date

  • January 1, 2004