On the conversion efficiency of ultracold fermionic atoms to bosonic molecules via Feshbach resonances

Abstract

We explain why the experimental efficiency observed in the conversion of ultracold Fermi gases of ${}^{40}$K and ${}^6$Li 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.

4 pages, 3 figures, final version accepted to Phys. Rev. Lett

References in corpus (3)

• Creation of ultracold molecules from a Fermi gas of atoms
• Conversion of an Atomic Fermi Gas to a Long-Lived Molecular Bose Gas
• Production of Long-Lived Ultracold Li2 Molecules from a Fermi gas

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