Passivating High-Quality Ta Resonators With Self-Assembled Monolayers (SAMs)

Abstract

One major bottleneck in the development of efficient, fault-tolerant quantum computers is the limited coherence times of modern qubits, which constrains meaningful applications. Most recently, Ta-based transmon qubits have demonstrated coherence times exceeding 1 ms [1]. However, they remain limited by losses associated with two-level systems (TLSs) in Ta's native oxide [2]. Passivating the Ta film with a self-assembled monolayer (SAM) offers a promising route to reduce TLS-related losses by limiting oxide growth to a minimum. When the SAM binds to the oxide, it prevents further growth from occurring. Alghadeer et al. demonstrated the successful passivation of Nb oxide with octadecyltrichlorosilane (OTS), leading to a significantly reduced native oxide thickness and improved low-power internal quality factors [3]. Building on this approach, we investigated the ability of OTS to passivate Ta. Surface characterization confirmed that OTS effectively bound to its native oxide and formed a uniform, stable monolayer. Furthermore, device measurements revealed no additional dielectric loss introduced by the monolayer. These findings establish a basis for exploring SAM-based passivation as a means to mitigate oxide-related loss and enhance the performance of Ta-based superconducting resonators.