Josephson radiation in a superconductor-quantum dot-superconductor junction

Baptiste Lamic,Julia S Meyer,Manuel Houzet

doi:10.1103/physrevresearch.2.033158

Abstract

We investigate the Josephson radiation emitted by a junction made of a quantum dot coupled to two conventional superconductors. Close to resonance, the particle-hole symmetric Andreev states that form in the junction are detached from the continuum above the superconducting gap in the leads, while a gap between them opens near the Fermi level. Under voltage bias, we formulate a stochastic model that accounts for non-adiabatic processes, which change the occupations of the Andreev states. This model allows calculating the current noise spectrum and determining the Fano factor. Analyzing the finite-frequency noise, we find that the model may exhibit either an integer or a fractional AC Josephson effect, depending on the bias voltage and the size of the gaps in the Andreev spectrum. Our results assess the limitations in using the fractional Josephson radiation as a probe of topology.

Highlights

The Josephson radiation is the electromagnetic signal emitted by a junction between two superconductors when it is voltage biased
This fractional Josephson radiation originates from the fact that the supercurrent flowing through such a topological Josephson junction is carried by single electrons, rather than Cooper pairs
The integer or fractional Josephson radiations result from the substitution φ = ωJ in the phase dependence of the current carried by an Andreev bound states (ABS) whose occupation is fixed

Summary

Introduction

The Josephson radiation is the electromagnetic signal emitted by a junction between two superconductors when it is voltage biased. Interest in the Josephson radiation was revived by the prediction of a fractional AC Josephson effect at frequency ω = ωJ /2 when the superconducting leads forming the junction are topological superconductors [3,4,5,6]. Random parity switchings generate current noise, and eventually bring another limitation to the coherence of the fractional Josephson radiation [7].

Results

Conclusion