Shot noise and coherent multiple charge transfer in superconducting quantum point-contacts

TL;DR

This paper investigates shot noise in superconducting quantum point-contacts, revealing quantized effective charges related to multiple Andreev reflections at low transmission, and how this behavior diminishes with higher transmission.

Contribution

It provides a detailed analysis of shot noise and effective charge quantization in superconducting quantum point-contacts across different transmission regimes.

Findings

Effective charge exhibits step-like behavior at low transmission.

Quantized charges correspond to multiple Andreev reflections.

Interference effects reduce charge quantization at higher transmission.

Abstract

We analyze the shot noise in a voltage biased superconducting quantum point-contact. Results are presented for the single channel case with arbitrary transmission. In the limit of very low transmission it is found that the effective charge, defined from the noise-current ratio, exhibits a step-like behavior as a function of voltage with well defined plateaus at integer values of the electronic charge. This multiple charge corresponds to the transmitted charge in a Multiple Andreev Reflection (MAR) process. This effect gradually disappears for increasing transmission due to interference between different MAR processes.