Atomic Collisions in Ultracold Atomic Gases

It has recently become possible to form molecules in ultracold gases of trapped alkali metal atoms. Once formed, the molecules may undergo elastic, inelastic and reactive collisions. Inelastic and reactive collisions are particularly important because they release kinetic energy and eject atoms and molecules from the trap. The theory needed to handle such collisions is presented and recent quantum dynamics calculations on ultracold atom–diatom collisions of spin-polarized Li + Li2, Na + Na2 and K + K2 are described. All these systems have potential energy surfaces on which barrierless atom exchange reactions can occur, and both inelastic and reactive rates are very fast (typically k inel > 10-10 cm3 s−1 in the Wigner regime).It has recently become possible to form molecules in ultracold gases of trapped alkali metal atoms. Once formed, the molecules may undergo elastic, inelastic and reactive collisions. Inelastic and reactive collisions are particularly important because they release kinetic energy and eject atoms and molecules from the trap. The theory needed to handle such collisions is presented and recent quantum dynamics calculations on ultracold atom–diatom collisions of spin-polarized Li + Li2, Na + Na2 and K + K2 are described. All these systems have potential energy surfaces on which barrierless atom exchange reactions can occur, and both inelastic and reactive rates are very fast (typically k inel > 10-10 cm3 s−1 in the Wigner regime).

arXiv:physics/0610219International Reviews in Physical ChemistryJan 1, 200787 citations

Effect of glancing collisions in the cold-atom vacuum standard

Stephen Eckel, Daniel S. Barker, James A. Fedchak +3 more

We theoretically investigate the effect of ``glancing'' collisions on the ultra-high-vacuum pressure readings of the cold-atom vacuum standard (CAVS), based on either ultracold $^{7}\mathrm{Li}$ or $^{87}\mathrm{Rb}$ atoms. Here, glancing collisions are those collisions between ultracold atoms and room-temperature background atoms or molecules in the vacuum that do not impart enough kinetic energy to eject an ultracold atom from its trap. Our model is wholly probabilistic and shows that the number of the ultracold atoms remaining in the trap as a function of time is nonexponential. We update the recent results of a comparison between a traditional pressure standard---a combined flow meter and dynamic expansion system---and the CAVS [D. S. Barker et al., AVS Quantum Sci. 5, 035001 (2023)] to reflect the results of our model. We find that the effect of glancing collisions shifts the theoretical predictions of the total loss rate coefficients for $^{7}\mathrm{Li}$ colliding with noble gases or ${\mathrm{N}}_{2}$ by up to 0.6%. Likewise, we find that in the limit of zero trap depth, the experimentally extracted loss rate coefficients for $^{87}\mathrm{Rb}$ colliding with noble gases or ${\mathrm{N}}_{2}$ shift by as much as 2.2%.We theoretically investigate the effect of ``glancing'' collisions on the ultra-high-vacuum pressure readings of the cold-atom vacuum standard (CAVS), based on either ultracold $^{7}\mathrm{Li}$ or $^{87}\mathrm{Rb}$ atoms. Here, glancing collisions are those collisions between ultracold atoms and room-temperature background atoms or molecules in the vacuum that do not impart enough kinetic energy to eject an ultracold atom from its trap. Our model is wholly probabilistic and shows that the number of the ultracold atoms remaining in the trap as a function of time is nonexponential. We update the recent results of a comparison between a traditional pressure standard---a combined flow meter and dynamic expansion system---and the CAVS [D. S. Barker et al., AVS Quantum Sci. 5, 035001 (2023)] to reflect the results of our model. We find that the effect of glancing collisions shifts the theoretical predictions of the total loss rate coefficients for $^{7}\mathrm{Li}$ colliding with noble gases or ${\mathrm{N}}_{2}$ by up to 0.6%. Likewise, we find that in the limit of zero trap depth, the experimentally extracted loss rate coefficients for $^{87}\mathrm{Rb}$ colliding with noble gases or ${\mathrm{N}}_{2}$ shift by as much as 2.2%.

arXiv:2409.11226Physical Review AFeb 12, 20252 citations

We theoretically investigate the effect of ``glancing'' collisions on the ultra-high-vacuum pressure readings of the cold-atom vacuum standard (CAVS), based on either ultracold

^{7}\mathrm{Li}

^{87}\mathrm{Rb}

atoms. Here, glancing collisions are those collisions between ultracold atoms and room-temperature background atoms or molecules in the vacuum that do not impart enough kinetic energy to eject an ultracold atom from its trap. Our model is wholly probabilistic and shows that the number of the ultracold atoms remaining in the trap as a function of time is nonexponential. We update the recent results of a comparison between a traditional pressure standard---a combined flow meter and dynamic expansion system---and the CAVS [D. S. Barker et al., AVS Quantum Sci. 5, 035001 (2023)] to reflect the results of our model. We find that the effect of glancing collisions shifts the theoretical predictions of the total loss rate coefficients for

^{7}\mathrm{Li}

colliding with noble gases or

{\mathrm{N}}_{2}

by up to 0.6%. Likewise, we find that in the limit of zero trap depth, the experimentally extracted loss rate coefficients for

^{87}\mathrm{Rb}

colliding with noble gases or

{\mathrm{N}}_{2}

shift by as much as 2.2%.