Lifetime of weakly-bound dimers of ultracold metastable helium studied by photoassociation

TL;DR

This study investigates the lifetime of weakly-bound ultracold metastable helium dimers using two-photon photoassociation, revealing a lifetime of approximately 1.4 microseconds and analyzing the underlying decay processes.

Contribution

First experimental measurement of the lifetime of the least bound vibrational state of ultracold metastable helium dimers using photoassociation techniques.

Findings

Measured molecule lifetime as 1.4 microseconds

Identified decay processes limiting molecule stability

Analyzed effects of Penning ionization and inelastic collisions

Abstract

We describe two-photon photoassociation (PA) experiments operated in an ultracold gas of metastable $^4$He$^*$ atoms in the $2^3S_1$ state. Atom-molecule dark resonances as well as Raman signals provide information on the exotic molecule in the least bound vibrational J=2, $v=14$ state of the $^5\Sigma_g^+$ interaction potential of two spin-polarized metastable atoms. The physical origin of the various two-photon PA signals is first discussed. Their linewidths are interpreted in term of processes limiting the lifetime $\tau$ of the exotic molecule. A value of $\tau=1.4\pm0.3 \mu$s is found, which is discussed in view of two recent calculations of the Penning ionization rate induced by spin-dipole coupling and of the atom-molecule inelastic collisions.