Charge fluctuations in a quantum point contact attached to a superconducting lead

Andrew M. Martin; Thomas Gramespacher; Markus Büttiker

doi:10.1103/PhysRevB.60.R12581

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Charge fluctuations in a quantum point contact attached to a superconducting lead

Andrew M. Martin, Thomas Gramespacher, Markus Büttiker

DOI 10.1103/PhysRevB.60.R12581 · Physical Review B

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Abstract

We show how to calculate the charge noise spectrum in a normal mesoscopic conductor, which is capacitively coupled to a macroscopic gate, when this conductor is attached to L normal leads and M superconducting leads, the only restriction being that the superconducting leads must be at the same chemical potential. We then proceed to examine results for a quantum point contact (QPC) in a normal lead connecting to a superconductor. Of interest is the fluctuating current in a gate capacitively coupled to a QPC. The results are compared with the case when all leads are normal. We find a doubling of the equilibrium charge fluctuations and a large enhancement (>2) in the current noise spectrum to first order in |eV|, when a channel in the QPC is opening.