We demonstrate experimentally the production of Rydberg positronium (Ps) atoms in a two-step process, comprising incoherent laser excitation, first to the $2{}^{3}P$ state and then to states with principal quantum numbers ranging from 10 to 25. We find that excitation of $2{}^{3}P$ atoms to Rydberg levels occurs very efficiently ($\sim 90\%$) and that the $\sim 25\%$ overall efficiency of the production of Rydberg atoms is determined almost entirely by the spectral overlap of the primary excitation laser and the Doppler broadened width of the $1{}^{3}S\mathrm{\text{−}}2{}^{3}P$ transition. The observed efficiency of Rydberg Ps production can be explained if stimulated emission back to the $2P$ states is suppressed, for example, by intermixing of the Rydberg state Stark sublevels. The efficient production of long-lived Rydberg Ps in a high magnetic field may make it possible to perform direct measurements of the gravitational free fall of Ps.

• Received 14 October 2011

DOI:https://doi.org/10.1103/PhysRevLett.108.043401