π phase shifter based on NbN-based ferromagnetic Josephson junction on a silicon substrate

Area of Science:

• Superconducting electronics
• Quantum computing hardware
• Materials science

Background:

• Ferromagnetic Josephson junctions offer advantages for superconducting devices.
• π phase shifters are key components for flux-bias-free flux quantum bits (qubits) and classical digital logic.

Purpose of the Study:

• To fabricate and characterize niobium nitride (NbN)-based ferromagnetic π junctions on silicon (Si) substrates.
• To investigate the potential of these junctions for quantum and classical superconducting applications.

Main Methods:

• Fabrication of NbN/aluminum nitride (AlN)/NbN Josephson junctions and NbN/copper nickel (CuNi)/NbN ferromagnetic Josephson junctions on Si substrates.
• Characterization of fabricated Josephson junctions and superconducting quantum interference devices (SQUIDs).
• Analysis of magnetic field dependence of SQUID critical current.

Main Results:

• NbN/AlN/NbN Josephson junctions exhibited high quality, suitable for qubit applications.
• NbN/CuNi/NbN Josephson junctions were successfully fabricated on Si substrates with a TiN buffer layer.
• Characterization confirmed that the NbN/CuNi/NbN junction functions as a π phase shifter.

Conclusions:

• NbN-based ferromagnetic π junctions on Si substrates are viable for advanced superconducting applications.
• The developed π phase shifters are promising for flux-bias-free flux qubits and classical digital logic elements.
• This work contributes to the development of next-generation superconducting electronic devices.