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 calculations on positronium in crossed fields predict the existence of long-lived states in which the average positron-electron separation is several thousand angstroms. These delocalized states are due to the existence of an outer well in the potential for certain values of the pseudomomentum and field strength. The near zero probability for positron-electron overlap suppresses direct annihilation processes. Transition moments between the ground state in the outer well and the Coulomb states are also extremely small, resulting in lifetimes up to the order of one year.