Reduction of Coherent Losses using Molecular Self-assembled Monolayers at Interfaces of Superconducting Quantum Circuits*

Defects at different interfaces in circuit quantum electrodynamics (cQED) systems - in particular, two-level-system (TLS) defects - contribute significantly to decoherence, ultimately limiting the performance of quantum computation and sensing. These defects cannot be ousted in conventional way, i.e. by depositing an inorganic passivating layer, because such additional layers can worst these interfaces. Chemisorption of self-assembled monolayers (SAMs) on metal and oxide is a promising option to engineer the desired properties of such interfaces. SAMs bonding strength and many more related properties are well established for more than a decade. In cQED etching can remove defects from air-interfaces however, their regrowth remains a problem. Here, we used SAMs to stop the regrowth of defects and observed sustained improvement in quality factor of the superconducting co-planer waveguide (CPW) resonators. We will present improvement in quality factor of CPW due to SAM and correlate the results to materials analysis, including TEM, SEM, AFM and XPS, which confirms that SAMs stop the regrowth of oxides and provide sustained improvement in the performance of superconducting quantum circuits.