C2QA

Recent decades have witnessed rapid development of quantum information science driven by the advances of superconducting quantum circuits (SQC). The core element in SQC is superconducting qubit, where the physics of light-matter interaction is realized. So far, a variety of superconducting qubit has been designed, among which transmon, composed of Josephson Junction shunted by a large capacitor, is one of the most promising platforms since its invention in 2007 because of greatly reduced sensitivity to charge noise. In recent a couple of years, it has been shown that tantalum is a good candidate material, in place of conventional aluminum and niobium, that can improve the coherence time of transmon qubit. However, the oxidation of tantalum surface is inevitable instantly upon exposure to the atmosphere. Consequently, various defects such as two-level system (TLS) would reside at the insulating surface oxide layer, which leads to dielectric loss and thus decreases qubit coherence time. This talk will focus on the novel methods of controlling surface oxide of superconducting tantalum film.