Characterization of high quality-factor NbTiN resonators in a coaxial stripline geometry

Nitride superconductors have been recognized as a platform for realizing superconducting quantum circuits because of their high kinetic inductance (KI). KI can offer an intrinsic non-linearity allowing for the development of quantum devices without the need to fabricate junctions [1]. NbTiN, a material from the Nitride family which has the added benefit of a large superconducting gap allowing for potential operation at higher temperatures, has already been used to realize near-quantum limited parametric amplifiers [2]. To broaden its use, it is an interesting question to what extent the internal quality factor of the resonant modes and relative strength of the non-linearity are limited. It has been shown that internal quality factors of >1M are possible with NbTiN deposited on Si using deep substrate-etching techniques [3]. Studies of the quality factor of NbTiN thus far have mainly explored coplanar waveguide architectures. Here, we investigate devices in a coaxial stripline architecture [4], because it allows very high Q values and allows efficient characterization of different loss mechanisms [5]. Preliminary data shows that by patterning stripline resonators from NbTiN sputtered on Sapphire and measuring in a coaxial stripline architecture, we can obtain quality factors > 1M at the single photon level without need of advanced sample preparation techniques. This suggests that NbTiN on Sapphire is an inviting platform for realizing superconducting quantum circuits.