Persistent current noise in narrow Josephson junctions

TL;DR

This paper investigates thermal current noise in narrow Josephson junctions, revealing how different phase states influence noise levels and identifying conditions that reduce or enhance noise, relevant for quantum and sensing applications.

Contribution

It introduces a detailed analysis of phase-dependent noise in long Josephson junctions using a tight-binding model, highlighting the impact of multiple stable states on noise characteristics.

Findings

Gradient phase branches show reduced noise compared to zero-length junctions.

Solitonic branch exhibits increased noise and suppressed current.

Transition frequencies between states produce peaks in the noise spectrum.

Abstract

Josephson junctions have broad applications in metrology, quantum information processing, and remote sensing. For these applications, the electronic noise is a limiting factor. In this work we study the thermal noise in narrow Josephson junctions using a tight-binding Hamiltonian. For a junction longer than the superconducting coherence length, several self-consistent gap profiles appear close to a phase difference $\pi$. They correspond to two stable solutions with an approximately constant phase gradient over the thin superconductor connected by a $2\pi$ phase slip, and a solitonic branch. The current noise power spectrum has pronounced peaks at the transition frequencies between the different states in each branch. We find that the noise is reduced in the gradient branches in comparison to the zero-length junction limit. In contrast, the solitonic branch exhibits an enhanced noise and a reduced current due to the pinning of the lowest excitation energy to close to zero energy.