Spontaneous-stimulated annihilation of positronium atoms in the field of intrinsic and external annihilation photons

The Heisenberg equations of motion for the atomic and photonic operators are used, without recourse to perturbation theory, to calculate the lifetime, energy shift, phase relaxation time and oscillation frequency of a positronium atom under the conditions of two-photon annihilation decay in a field of 'seed' photons.