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Supercurrent noise in quantum point contacts

D. Averin·H. Imam
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Abstract

Spectral density of current fluctuations in a short ballistic superconducting quantum point contact is calculated for arbitrary bias voltages $V$. Contrary to a common opinion that the supercurrent flow in Josephson junctions is coherent process with no fluctuations, we find extremely large current noise that is {\em caused} by the supercurrent coherence. An unusual feature of the noise, besides its magnitude, is its voltage dependence: the noise decreases with increasing $V$, despite the fact that the dc current grows steadily with $V$. At finite voltages the noise can be qualitatively understood as the shot noise of the large charge quanta of magnitude $2Δ/V$ equal to the charge transferred during one period of Josephson oscillations.

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D. Averin, H. Imam. 1995-11-27. Supercurrent noise in quantum point contacts. https://doi.org/10.1103/physrevlett.76.3814

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