Abstract
We present a rigorous quantum study of spin-exchange transitions in collisions of the alkali-metal atoms with $^{3}\text{H}\text{e}$ in the presence of an external magnetic field. Using accurate ab initio interaction potentials, we obtain refined estimates for the Fermi contact interaction constants for complexes of Na, K, and Rb atoms with $^{3}\text{H}\text{e}$. Ab initio calculations show that the Fermi contact interaction in $\text{Li-}^{3}\text{H}\text{e}$ varies more slowly with internuclear distance than predicted by the atomic model [R. M. Herman, Phys. Rev. 37, A1062 (1965)]. The calculated spin-exchange rate constants for Na, K, and Rb atoms in a gas of $^{3}\text{H}\text{e}$ are in good agreement with experimental data. Our calculations demonstrate that at a temperature of 0.5 K, collision-induced spin exchange of the alkali-metal atoms occurs at a very slow rate of $\ensuremath{\sim}{10}^{\ensuremath{-}22}\text{ }{\text{cm}}^{3}/\text{s}$, suggesting potential applications in cryogenic cooling, precision spectroscopy, and quantum optics.
Highlights
Collisions of atoms and molecules in the presence of external electromagnetic fields may lead to depolarization of their electronic and nuclear spins, causing decoherence of quantum superposition states1,2͔, reduction in the lifetime of trapped atoms3,4͔, and frequency shifts in atomic clocks and magnetometers1͔
The Fermi contact interaction constantsFCICsfor the complexes of Na, K, and Rb atoms with 3He are extracted from the measured frequency shift enhancement factors using the ab initio interaction potentials
We have presented a rigorous theoretical analysis of spinexchange transitions in collisions of the alkali-metal atoms with He based on state-of-the-art ab initio calculations of the interaction potentials, Fermi contact interaction constants, TABLE III
Summary
Collisions of atoms and molecules in the presence of external electromagnetic fields may lead to depolarization of their electronic and nuclear spins, causing decoherence of quantum superposition states1,2͔, reduction in the lifetime of trapped atoms3,4͔, and frequency shifts in atomic clocks and magnetometers1͔. In order to infer for the heavier alkali-metal atoms, we used recent experimental measurements of frequency shift enhancement factors to extract refined values of = 2.0 for Na-He and = 1.85 for K-He. Our calculated spin-exchange cross sections are consistent with the upper bounds derived from magnetic trapping experiments with spin-polarized 39K and 7Li atoms at subkelvin temperatures22͔. We present a rigorous analysis of spinexchange transitions in collisions of the alkali-metal atomsLi to Rbwith 3He. We use accurate ab initio calculations to evaluate the electron-spin density of Li-He and the interaction energy of Rb-He. The Fermi contact interaction constantsFCICsfor the complexes of Na, K, and Rb atoms with 3He are extracted from the measured frequency shift enhancement factors using the ab initio interaction potentials.
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