Organic Self-assembled Monolayers at Superconducting CPW Resonator Interfaces

TLS defects within amorphous dielectrics at various circuit interfaces—including substrate-metal (SM) and air interfaces—are a critical source of decoherence in planar superconducting quantum circuits. We employed a molecular self-assembled monolayer (SAM) at different interfaces to mitigate TLS losses in superconducting coplanar waveguide (CPW) resonators. We observed an increase in the resonator quality factor (Q) when SAMs were applied to air interfaces [2], but a contrasting decrease when applied to SM interfaces [1]. This increase is attributed to the suppression of oxides at the air-interface by the SAM. Conversely, the decrease in Q is likely due to the cluster-like growth of the deposited niobium (Nb) on the SAM at the SM interface. This observed decrease is further attributed to an increased TLS defect density, as suggested by the topography of Nb deposited on the SAM. Our findings demonstrate that the roughness of deposited Nb at the SM interface, which is influenced by the SAM, significantly impacts the density of TLS defects at this critical interface. We recently performed simulations of these structures, and the results of that study will also be presented.