The decay of excited He from Stochastic Density-Functional Theory: a quantum measurement theory interpretation

Recently, time-dependent current-density functional theory has been extended to include the dynamical interaction of quantum systems with external environments [Phys. Rev. Lett. {\bf 98}, 226403 (2007)]. Here we show that such a theory allows us to study a fundamentally important class of phenomena previously inaccessible by standard density-functional methods: the decay of excited systems. As an example we study the decay of an ensemble of excited He atoms, and discuss these results in the context of quantum measurement theory.