Abstract
In the field of superconducting electronics, a π phase shifter based on a ferromagnetic Josephson junction is expected to provide various advantages to classical and quantum superconducting devices. Here we report niobium nitride (NbN)-based ferromagnetic π junctions on a silicon (Si) substrate with a titanium nitride (TiN) buffer layer, which have applications to flux-bias-free flux quantum bits (qubits) and classical digital logic elements. We fabricated and characterized NbN/aluminum nitride (AlN)/NbN Josephson junctions, NbN/copper nickel (CuNi)/NbN ferromagnetic Josephson junctions, and superconducting quantum interference devices (SQUIDs) consisting of these junctions on the Si substrate. The fabricated NbN/AlN/NbN junctions showed a high junction quality suitable for qubit applications. Furthermore, the magnetic field dependence of the SQUID’s critical current indicated that the NbN/CuNi/NbN junction worked as a π phase shifter on the Si substrate.
Highlights
Ferromagnetic Josephson junctions (superconductor/ferromagnet/superconductor junctions; SFS junctions) have been studied for many years from the perspective of fundamental physics of the interplay between superconductivity and magnetism[1,2,3,4]
Ferromagnetic Josephson junctions have been studied for many years from the perspective of fundamental physics of the interplay between superconductivity and magnetism[1,2,3,4]
The π junctions have been generally fabricated by using niobium (Nb) as superconducting electrodes[5,6,7,8,9], we have demonstrated a niobium nitride (NbN)-based π junction on a magnesium oxide (MgO) substrate to realize flux-bias-free q ubits[10]
Summary
Ferromagnetic Josephson junctions (superconductor/ferromagnet/superconductor junctions; SFS junctions) have been studied for many years from the perspective of fundamental physics of the interplay between superconductivity and magnetism[1,2,3,4]. An important step for realizing flux-bias-free flux qubits with the π phase shifter is the development of a NbN-based π junction and high-quality SIS junctions on the same Si substrate.
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