Observation of Cold Collisions between Trapped Ions and Trapped Atoms (0808.3620v2)

Abstract: We demonstrate a double-trap system well suited to study cold collisions between trapped ions and trapped atoms. Using Yb$^+$ ions confined in a Paul trap and Yb atoms in a magneto-optical trap, we investigate charge-exchange collisions of several isotopes for collision energies down to 400 neV (5 mK). The measured rate coefficient of $6 \times 10^{-10}$ cm$^{3}$s$^{-1}$, constant over four orders of magnitude in collision energy, is in good agreement with that derived from a semiclassical Langevin model for an atomic polarizability of 143 a.u.

Observation of Cold Collisions between Trapped Ions and Trapped Atoms

The paper "Observation of Cold Collisions between Trapped Ions and Trapped Atoms" presents a detailed investigation into the collision dynamics between trapped ions and neutral atoms in the semiclassical Langevin regime. The paper, authored by Andrew T. Grier, Marko Cetina, Fedja Orućević, and Vladan Vuletić, provides significant experimental insights into the behavior of cold collisions at low energies.

The authors utilize a highly controlled double-trap system, consisting of Yb$^+$ ions confined in a Paul trap and neutral Yb atoms in a magneto-optical trap (MOT), to explore charge-exchange collisions. This investigation covers a collision energy range spanning three orders of magnitude down to 3 $\mu$eV, allowing for the detailed exploration of the semiclassical collision regime. At this regime, classical interaction models based on long-range $r^{-4}$ potential adequately describe the system's behavior, while quantum phenomena become prominent only at the lower end of the energy range.

The experimental setup enables the authors to measure the charge-exchange rate coefficient over a wide energy range. The observed minimum rate coefficient of $6 \times 10^{-10}$ cm$^3$s$^{-1}$ closely matches the predictions of the Langevin model when an atomic polarizability of 143 a.u. is assumed, validating the model's applicability in this collision regime. The results show consistency with the theoretical expectations to within a factor of two over three decades of energy.

Key findings in the paper include a distinct transition observed in the collision dynamics from a high-energy classical regime to a semiclassical Langevin regime, characterized by a different dependency of the cross section on collision energy. At the lowest examined energies, the authors report that approximately 40 partial waves contribute to the cross section, highlighting the complexity of the interactions at play and the relevance of isotope shifts.

The authors propose intriguing implications for the observed behaviors. The feasibility of quantum gates, cooling mechanisms for atoms or molecules without closed optical transitions, and ion-atom interactions in quantum degenerate gases are noteworthy potential applications of this research. These findings illuminate unexplored avenues for quantum control and manipulation in hybrid systems of ions and atoms.

In summary, the work offers a methodologically robust and quantitatively significant exploration of ion-atom collision phenomena at low energies. It confirms theoretical models in this regime and provides a foundation for future research into advanced quantum systems involving ion-atom interactions. As such, further investigations might explore probing Feshbach and other resonances or explore sympathetic cooling with other atomic species, thus broadening the experimental and theoretical landscape. This work represents a pivotal step in bridging atomic physics with quantum information science through controlled ion-atom interactions.