Noise and adiabatic dynamics of superconducting quantum point contacts

Dynamics of superconducting quantum point contacts at small bias voltages is governed by a simple kinetic equation for occupation probabilities of the two current-carrying states localized in the contact region. Starting from this equation, I show that superconducting quantum point contacts should have unusual noise properties. In the stationary case, flow of the DC supercurrent at non-vanishing temperatures gives rise to a noise with very large spectral density at zero frequency. At finite voltages the contact exhibits giant shot noise. Surprisingly, the origin of the noise is the supercurrent coherence, because of which the charge is transferred through the contact in large quanta. In contact with small reflection the noise can be calculated in terms of Landau-Zener transitions between the current-carrying states.