Can we measure the gravitational free fall of cold Rydberg state positronium?

In this paper we examine the possibilities for detecting the free fall of Rydberg positronium atoms. In our scheme, cold positronium atoms are emitted from a "point" source and excited to the n = 25 circular Rydberg state with L = n - 1. The positronium atoms are allowed to travel horizontally 10 m in a field free vacuum and focused onto a detector using an elliptical Van der Waals mirror. A free fall distance of order 50 mum and a few detected atoms per hour are anticipated. Various extraneous influences on the positronium, such as collisions with residual gas atoms, Stark mixing in stray electric and magnetic fields, photoionization due to thermal radiation, and accelerations due to patch potentials are estimated. (C) 2002 Elsevier Science B.V. All rights reserved.