All-nitride superconducting qubit made on a silicon substrate: New material platform for large-scale integration of superconducting qubits

Researchers have succeeded in developing an all-nitride superconducting qubit using epitaxial growth on a silicon substrate that does not use aluminum as the conductive material. This qubit uses niobium nitride (NbN) with a superconducting transition temperature of 16 K (-257 °C) as the electrode material, and aluminum nitride (AlN) for the insulating layer of the Josephson junction. It is a new type of qubit made of all-nitride materials grown epitaxially on a silicon substrate and free of any amorphous oxides, which are a major noise source. By realizing this new material qubit on a silicon substrate, long coherence times have been obtained: an energy relaxation time (T1) of 16 microseconds and a phase relaxation time (T2) of 22 microseconds as the mean values. This is about 32 times T1 and about 44 times T2 of nitride superconducting qubits grown on a conventional magnesium oxide substrate.