Enhanced Tantalum Superconducting Resonator Performance via All‐Surface Organic Monolayer Passivation

Tantalum is a promising platform for superconducting quantum circuits, yet coherence times remain limited by dielectric losses from interfacial two‐level systems (TLS), exacerbated by native oxide regrowth. Here, we implement molecular surface passivation using self‐assembled organic monolayers on freshly etched tantalum and silicon in coplanar waveguide resonators. Surface characterization by contact angle, XPS, FTIR, and TEM confirms the formation of ordered, nanometer‐thick films that suppress oxide formation. Microwave measurements in the ∼5–9 GHz range reveal internal quality factors up to 1.8 × 10 6 in the single‐photon regime at 100 mK, representing a ∼140% improvement over untreated devices with native oxide. Power‐ and temperature‐dependent measurements attribute this enhancement to reduced TLS‐induced losses. These results demonstrate that molecular passivation effectively engineers low‐loss interfaces and provides a scalable route toward high‐coherence superconducting quantum devices.