Macroscopic quantum tunneling in spin filter ferromagnetic Josephson junctions

TL;DR

This paper demonstrates macroscopic quantum tunneling in spin filter ferromagnetic Josephson junctions with GdN barriers, revealing a transition from thermal to quantum regimes and highlighting their potential for quantum hybrid circuits.

Contribution

It provides the first evidence of quantum tunneling in active S-F-S Josephson junctions with ferromagnetic insulators, advancing their application in quantum technologies.

Findings

Transition from thermal to quantum regime at ~100 mK

Clear signature of unconventional superconductivity

Potential for use in quantum hybrid circuits

Abstract

The interfacial coupling of two materials with different ordered phases, such as a superconductor (S) and a ferromagnet (F) is driving new fundamental physics and innovative applications. For example, the creation of spin-filter Josephson junctions and the demonstration of triplet supercurrents have suggested the potential of a dissipationless version of spintronics based on unconventional superconductivity. Here we demonstrate evidence for active quantum applications of S-F-S junctions, through the observation of macroscopic quantum tunneling in Josephson junctions with GdN ferromagnetic insulator barriers. We prove a clear transition from thermal to quantum regime at a crossover temperature of about 100 mK at zero magnetic field in junctions which demonstrate a clear signature of unconventional superconductivity. Following previous demonstration of passive S-F-S phase shifters in a phase qubit, our result paves the way to the active use of spin filter Josephson systems in quantum hybrid circuits.