Identifying Sources of Decoherence at Defects and Interfaces in Superconducting Qubit Systems*

Superconducting qubits have emerged as a platform technology for potentially addressing computational problems deemed intractable with classical computing. Despite recent advances enabling coherence lifetimes on the order of hundreds of μs, material quality and interfacial structures continue to curb performance. Two-level system defects in the superconductor and adjacent dielectric regions introduce stochastic noise and dissipate electromagnetic energy at cryogenic operating temperatures. Through a correlative approach combining secondary ion mass spectroscopy and advanced electron microscopy techniques, we systematically investigate interfaces associated with superconducting thin films to build a link between processing parameters, material structure, and resultant properties. We find that during film deposition, oxide and silicide layers form with varying stoichiometries at metal/substrate and metal/air interfaces. Additionally, we observe that lithography and etching procedures lead to the presence of impurity species such as hydrides, carbides, and fluorides, which can impact the superconducting properties, within the large-area contact pads and Josephson junctions.