Thermal noise in superconducting quantum point-contacts

TL;DR

This paper develops a theoretical model for frequency-dependent current noise in superconducting quantum point-contacts, revealing significant noise increases in quasi-ballistic regimes and discussing implications for experimental observations.

Contribution

It provides an analytical expression for current fluctuations in SQPCs across all barrier transparencies, extending understanding of noise behavior in these systems.

Findings

Noise levels can be significantly higher in quasi-ballistic SQPCs compared to normal contacts.

The theory applies to any barrier transparency, bridging tunnel and ballistic limits.

Implications for observing current-phase relations in experiments are discussed.

Abstract

We present a theory for the frequency-dependent current fluctuations in superconducting quantum point-contacts (SQPC) within the dc transport regime. This theory is valid for any barrier transparency between the tunnel and ballistic limits, yielding an analytical expression for the fluctuations spectrum in the subgap region. It is shown that the level of noise in a quasi-ballistic SQPC may have a huge increase in comparison with the case of a normal contact carrying the same average current. The effect of this high level of noise on the actual observability of the current-phase relation for a ballistic point-contact is discussed in connection with recent experimental measurements.