Precise atomic radiative lifetime via photoassociative spectroscopy of ultracold lithium

Abstract

We have obtained spectra of the high-lying vibrational levels of the ${1}^{3}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}^{+}$ state of $^{6}\mathrm{Li}_{2}$ via photoassociation of ultracold $^{6}\mathrm{Li}$ atoms confined in a magneto-optical trap. The ${1}^{3}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}^{+}$ state of the diatomic molecule correlates to a 2${\mathit{S}}_{1/2}$ state atom plus a 2${\mathit{P}}_{1/2}$ state atom. The long-range part of the molecular interaction potential for this state depends on the 2P atomic radiative lifetime. By calculating the energy eigenvalues of a model potential for the ${1}^{3}$${\mathrm{\ensuremath{\Sigma}}}_{\mathit{g}}^{+}$ state and fitting them to the experimentally measured vibrational levels, we have extracted a value for the 2P lifetime of 26.99\ifmmode\pm\else\textpm\fi{}0.16 ns. The precision is currently limited by the accuracy of a region of the model potential provided by ab initio calculations.