Decay of the supercurrent in tunnel junctions

The current state in a Josephson junction is metastable. Thermal and quantum fluctuations destroy such a state and make its lifetime finite. By lowering the temperature the role of quantum fluctuations increases. If there is a gap in the excitation spectrum, then for quantum tunneling high-frequency processes (pair decay) are essential. Quantum tunneling is connected with a change of a large amount of electron states.