Metastable Helium: Lifetime measurements using cold atoms as a test of QED

Abstract

Here we present the first complete measurement of the radiative decay rate to the ground state of the lowest four triplet states of helium i.e. the metastable 23S1 state and the 23P manifold. We employ laser cooling and trapping in an ultrahigh vacuum chamber to enable direct measurement of the trap loss rate for decay from the 23P 1 state to the ground state. We then use this rate to calibrate the XUV emission decay to the ground state for all the remaining transitions. The 23P1 and 23P2 transition rates are measured for the first time, an upper bound is placed on the 23P 0 decay rate, and the 23S1 metastable lifetime is determined for only the second time with a five-fold improvement in accuracy. These results are in excellent agreement with theoretical QED predictions, and anchor the helium-like isoelectronic sequences for these transitions at low Z