Passivating High-Quality Tantalum Resonators with Self Assembled Monolayers (SAMs)

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, tantalum-based transmon qubits have demonstrated coherence times exceeding 1 ms (Bland et al. 2025). However, they remain limited by losses associated with two-level systems (TLSs) in the tantalum native oxide (Crowley et al. 2023). Passivating the tantalum 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 niobium oxide with octadecyltrichlorosilane (OTS), leading to a significantly reduced native oxide thickness and improved low-power internal quality factors. Building on this approach, we investigated the ability of OTS to passivate tantalum. Surface characterization confirmed that OTS was able to effectively bind its native oxide and form a uniform and stable monolayer. These findings establish a basis for exploring SAM-based passivation as a means to mitigate oxide-related loss and enhance the performance of tantalum-based superconducting resonators.