Theory of photon-assisted tunneling with radiation-activated barrier impurities

The addition of a new term in the conventional Hamiltonian is used to study photon-assisted tunneling for superconducting junctions containing active barrier impurities. For a sufficiently sharp molecular resonance, the impingent radiation can cause a large enhancement of the $n=1$ Dayem and Martin current step or a significant alteration of the dc Josephson current. The important mechanism is capture of a photon by a molecule followed by electron tunneling through the barrier.