Autoionization of spin-polarized metastable helium in tight anisotropic harmonic traps
Spin-dipole mediated interactions between tightly confined metastable helium atoms couple the spin-polarized quintet ${}^{5}Σ^{+}_{g}$ state to the singlet ${}^{1}Σ^{+}_{g}$ 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.