Fast measurement and characterization of Novel Niobium Trilayer Superconducting Qubits

Major challenges with Aluminum based junctions are oxide barrier instability and structural and chemical inhomogeneities leading to noise, reduced coherence, and high device variability during scaling. Thermal instability during fabrication greatly complexes the oxide barrier chemistry, and two-level system (TLS) defects are a significant source of energy loss making qubits more prone to errors.

We present a novel junction fabrication process based on Niobium-based trilayer junctions process that leverages existing subtractive etch techniques with additional improvements to limit junction variation across a wide range of sizes. This offers superior control over the growth and stoichiometry of the enclosed Aluminum Oxide layer, which improves interlayer roughness, reducing TLS coupling and junctional oxide thickness variations. Using these Nb trilayers we have fabricated and observed tunable flux transmons at 9.1 GHz and resonators from 4-8.5 GHz with internal Quality factors exceeding . This work focusses on Nb based resonator spectroscopy, Nb trilayer based flux tunable transmon spectra and time domain measurements of qubits based on these improved Nb josephson junctions.

The qubits feature an improved and protected AlOx tunnel barrier, reducing variability across sizes and junction growth parameters enabling production of consistent qubits properties over multiple fabrication iterations.