Quantum-State Controlled Penning Ionization Reactions between Ultracold Alkali and Metastable Helium Atoms

TL;DR

This study demonstrates that by controlling the spin states of ultracold alkali and helium atoms, reactive Penning ionization collisions can be significantly suppressed or enhanced, revealing quantum state-dependent collision dynamics.

Contribution

It provides experimental evidence of quantum-state control over Penning ionization in ultracold atom mixtures, confirming theoretical predictions and demonstrating near-universal loss in certain channels.

Findings

Long lifetimes for quartet spin states indicate suppression of Penning ionization.

Short lifetimes in other states depend linearly on doublet character.

Loss rates align with multichannel quantum-defect theory predictions.

Abstract

In an ultracold, optically trapped mixture of $^{87}$Rb and metastable triplet $^4$He atoms we have studied trap loss for different spin-state combinations, for which interspecies Penning ionization is the main two-body loss process. We observe long trapping lifetimes for the purely quartet spin-state combination, indicating strong suppression of Penning ionization loss by at least two orders of magnitude. For the other spin-mixtures we observe short lifetimes that depend linearly on the doublet character of the entrance channel. We compare the extracted loss rate coefficient with recent predictions of multichannel quantum-defect theory for reactive collisions involving a strong exothermic loss channel and find near-universal loss for doublet scattering. Our work demonstrates control of reactive collisions by internal atomic state preparation.