The inherent interactions between the qubits and their environment lead to decoherence, limiting the performance of these devices. In this paper, we present a novel technique for improving T1 coherence times in transmon qubits by passivating the surface of niobium and preventing the formation of lossy surface oxide. Our comparative investigation across different qubit foundries demonstrates that surface-encapsulated niobium qubit devices exhibit T1 coherence times 2 to 5 times longer than baseline niobium qubit devices with native niobium oxides. Our surface-encapsulation strategy enables further reduction of dielectric losses while preserving scalability and compatibility with silicon processes.

This paper can be found here.