LONG-LIVED STATES OF POSITRONIUM IN CROSSED ELECTRIC AND MAGNETIC-FIELDS

We show that crossed electric and magnetic fields provide a unique way for stabilizing simple matter-antimatter systems. Theoretical calcula tions on positronium in crossed fields predict the existence of long-l ived states in which the average positron-electron separation is sever al thousand angstroms. These delocalized states are due to the existen ce of an outer well in the potential for certain values of the pseudom omentum and field strength. The near zero probability for positron-ele ctron overlap suppresses direct annihilation processes. Transition mom ents between the ground state in the outer well and the Coulomb states are also extremely small, resulting in lifetimes up to the order of o ne year.