Resonant shifts of positronium energy levels in MgO powder

Abstract

S transitions optically driven in positronium atoms while they are inside the open volumes of MgO smoke powder. The observed intervals are larger than the corresponding vacuum excitations, but, surprisingly, the transitions to Rydberg states are less strongly affected, and the energy shifts exhibit no dependence on the principal quantum number n of the final state. We attribute these shifts to resonant interactions between Ps atoms and MgO surfaces, mediated via spectrally overlapping MgO ultra violet (UV) photo-luminescent absorption bands. Since many insulating materials suitable for Ps confinement exhibit similar broadband UV absorption characteristics, the observed phenomena have implications for optical diagnostics and laser cooling schemes of relevance to studies of high-density Ps ensembles in insulating cavities, including the production of a Ps Bose-Einstein condensate.

Positronium density measurements using polaritonic effects

“…Another way to determine Ps densities would be to measure the density-dependant collisional frequency shift [32] of Ps atomic transitions. This technique has not been demonstrated for confined Ps and may be affected by the detailed interactions between the Ps gas and its environment [33].…”