Ultracold atom-ion collisions are an emerging field of research that can ultimately lead to their precise quantum control. In collisions in which the ion is prepared in an excited state, previous studies showed that the dominant reaction pathway was charge exchange. Here, we explored the outcome products and the energy released from a single ultracold collision between a single $^{88}\mathrm{Sr}^{+}$ ion and a single $^{87}\mathrm{Rb}$ atom prepared in excited metastable and ground electronic states, respectively, with control over their relative spins. We found that the ion's long-lived ${D}_{5/2}$ and ${D}_{3/2}$ states quench after roughly three collisions, acquiring immense kinetic energy in the process. By performing single-shot thermometry on the ion after the collision, we identified two dominant reaction pathways: electronic excitation exchange and spin-orbit change. In contrast to previous experiments, we observed no charge-exchange events. These processes are theoretically understood to occur through Landau-Zener avoided crossings leading to the observed reaction pathways. We also found that spin orientation has almost no effect on the reaction pathways, due to strong Coriolis-spin mixing. Our results provide a deeper understanding of ultracold atom-ion inelastic collisions and offer additional quantum control tools for the cold chemistry field.Ultracold atom-ion collisions are an emerging field of research that can ultimately lead to their precise quantum control. In collisions in which the ion is prepared in an excited state, previous studies showed that the dominant reaction pathway was charge exchange. Here, we explored the outcome products and the energy released from a single ultracold collision between a single $^{88}\mathrm{Sr}^{+}$ ion and a single $^{87}\mathrm{Rb}$ atom prepared in excited metastable and ground electronic states, respectively, with control over their relative spins. We found that the ion's long-lived ${D}_{5/2}$ and ${D}_{3/2}$ states quench after roughly three collisions, acquiring immense kinetic energy in the process. By performing single-shot thermometry on the ion after the collision, we identified two dominant reaction pathways: electronic excitation exchange and spin-orbit change. In contrast to previous experiments, we observed no charge-exchange events. These processes are theoretically understood to occur through Landau-Zener avoided crossings leading to the observed reaction pathways. We also found that spin orientation has almost no effect on the reaction pathways, due to strong Coriolis-spin mixing. Our results provide a deeper understanding of ultracold atom-ion inelastic collisions and offer additional quantum control tools for the cold chemistry field.

arXiv:1907.06736Physical Review ASep 16, 202011 citations

Molecular collisions in ultracold atomic gases

Jeremy M. Hutson, Pavel Soldán

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

Threshold phenomena in ultracold atom-molecule collisions

Robert C. Forrey

APSMay 1, 19980 citations

Charge-exchange collisions between ultracold fermionic lithium atoms and calcium ions

Shinsuke Haze, Ryoichi Saito, Munekazu Fujinaga +1 more

Charge-exchange collisions between ultracold fermionic $^{6}\mathrm{Li}$ atoms and $^{40}\mathrm{Ca}^{+}$ ions are observed in the millikelvin temperature range. The reaction product of the charge-exchange collision is identified via mass spectrometry during which the motion of the ions is excited parametrically. The cross sections of the charge-exchange collisions between $^{6}\mathrm{Li}$ atoms in the ground state and $^{40}\mathrm{Ca}^{+}$ ions in the ground and metastable excited states are determined. Investigation of the inelastic collision characteristics in the atom-ion mixture is an important step toward ultracold chemistry based on ultracold atoms and ions.Charge-exchange collisions between ultracold fermionic $^{6}\mathrm{Li}$ atoms and $^{40}\mathrm{Ca}^{+}$ ions are observed in the millikelvin temperature range. The reaction product of the charge-exchange collision is identified via mass spectrometry during which the motion of the ions is excited parametrically. The cross sections of the charge-exchange collisions between $^{6}\mathrm{Li}$ atoms in the ground state and $^{40}\mathrm{Ca}^{+}$ ions in the ground and metastable excited states are determined. Investigation of the inelastic collision characteristics in the atom-ion mixture is an important step toward ultracold chemistry based on ultracold atoms and ions.

arXiv:1403.5091Physical Review AMar 30, 201550 citations

Threshold phenomena in ultracold atom–molecule collisions

N. Balakrishnan, Robert C. Forrey, A. Dalgarno

Chemical Physics LettersNov 1, 199783 citations

^{88}\mathrm{Sr}^{+}

ion and a single

^{87}\mathrm{Rb}

atom prepared in excited metastable and ground electronic states, respectively, with control over their relative spins. We found that the ion's long-lived

{D}_{5/2}

and

{D}_{3/2}

states quench after roughly three collisions, acquiring immense kinetic energy in the process. By performing single-shot thermometry on the ion after the collision, we identified two dominant reaction pathways: electronic excitation exchange and spin-orbit change. In contrast to previous experiments, we observed no charge-exchange events. These processes are theoretically understood to occur through Landau-Zener avoided crossings leading to the observed reaction pathways. We also found that spin orientation has almost no effect on the reaction pathways, due to strong Coriolis-spin mixing. Our results provide a deeper understanding of ultracold atom-ion inelastic collisions and offer additional quantum control tools for the cold chemistry field.

Charge-exchange collisions between ultracold fermionic

^{6}\mathrm{Li}

atoms and

^{40}\mathrm{Ca}^{+}

ions are observed in the millikelvin temperature range. The reaction product of the charge-exchange collision is identified via mass spectrometry during which the motion of the ions is excited parametrically. The cross sections of the charge-exchange collisions between

^{6}\mathrm{Li}

atoms in the ground state and

^{40}\mathrm{Ca}^{+}

ions in the ground and metastable excited states are determined. Investigation of the inelastic collision characteristics in the atom-ion mixture is an important step toward ultracold chemistry based on ultracold atoms and ions.