Autoionization of spin-polarized metastable helium in tight anisotropic harmonic traps

TL;DR

This paper investigates how anisotropic harmonic traps affect the autoionization lifetimes of spin-polarized metastable helium atoms, revealing conditions that significantly suppress ionization.

Contribution

It extends previous spherically symmetric trap studies to anisotropic traps, analyzing the impact of trap aspect ratios on autoionization lifetimes of helium atoms.

Findings

Ionization suppression occurs at specific trap aspect ratios where states are degenerate.

Anisotropic traps can significantly increase the lifetimes of metastable helium states.

Results apply to 'cigar-like' and 'pancake-like' trap geometries.

Abstract

Spin-dipole mediated interactions between tightly confined metastable helium atoms couple the spin-polarized quintet ${}^{5}\Sigma^{+}_{g}$ state to the singlet ${}^{1}\Sigma^{+}_{g}$ state from which autoionization is highly probable, resulting in finite lifetimes for the trap eigenstates. We extend our earlier study on spherically symmetric harmonic traps to the interesting cases of axially symmetric anisotropic harmonic traps and report results for the lowest 10 states in "cigar-like" and "pancake-like" traps with average frequencies of 100 kHz and 1 MHz. We find that there is a significant suppression of ionization, and subsequent increase in lifetimes, at trap aspect ratios $A=p/q$, where $p$ and $q$ are integers, for those states that are degenerate in the absence of collisions or spin-dipole interactions.