Enhanced coherence of all-nitride superconducting qubits epitaxially grown on silicon substrate

Improving the coherence of superconducting qubits is a fundamental step towards realization fault-tolerant quantum computation. However, times circuits made from conventional aluminium-based Josephson junctions are limited by presence microscopic two-level systems in amorphous aluminum oxide tunnel barriers. Here, we have developed based on NbN/AlN/NbN epitaxial silicon substrates which promise to overcome drawbacks Al/AlO$_{x}$/Al junctions. The all-nitride great advantages such as chemical stability against oxidation, resulting fewer fluctuators, feasibility for barriers that reduce energy relaxation and dephasing, larger gap $\sim$5.2 meV NbN, compared $\sim$0.3 aluminium, suppresses excitation quasiparticles. By replacing MgO substrate with TiN buffer layer growth nitride junctions, demonstrate qubit time $T$$_{1}$=16.3 $\mu$s spin-echo dephasing $T$$_{2}$=21.5 $\mu$s. These significant improvements explained reduced dielectric loss previously reported NbN-based ($T$$_{1}$$\approx$$T$$_{2}$$\approx$0.5 $\mu$s). results an important constructing new platform hardware.