Interference between magnetic field and cavity modes in an extended Josephson junction

TL;DR

This paper investigates how magnetic fields and cavity modes interact in an extended Josephson junction, enabling tunable coupling and control over the junction's quantum properties in the ultra-strong coupling regime.

Contribution

It demonstrates the interference effects between magnetic fields and cavity modes, allowing continuous tuning of the coupling strength in an extended Josephson junction.

Findings

Coupling strength can be tuned from 1 to -0.5.

Interference effects modify the critical current.

Static and dynamic control achieved in ultra-strong coupling regime.

Abstract

An extended Josephson junction consists of two superconducting electrodes that are separated by an insulator and it is therefore also a microwave cavity. The superconducting phase difference across the junction determines the supercurrent as well as its spatial distribution. Both, an external magnetic field and a resonant cavity intrafield produce a spatial modification of the superconducting phase along the junction. The interplay between these two effects leads to interference in the critical current of the junction and allows us to continuously tune the coupling strength between the first cavity mode and the Josephson phase from 1 to -0.5. This enables static and dynamic control over the junction in the ultra-strong coupling regime.