Superconducting transmon qubits are one of the most promising platforms to realize fault-tolerant quantum computing and allow a rich parameter space of highly configurable qubit properties with various circuit elements. Ultra thin amorphous oxide tunnel barriers (such as Al/AlOx/Al) known as Josephson junctions (JJ) provide essential nonlinearity to the qubit energy landscape. Precise control over the morphology of these thin amorphous oxide tunnel barriers remains a significant challenge despite its critical role in determining structural and transport properties. Furthermore, materials defects known as two-level systems (TLS), found within thin amorphous oxide tunnel barriers, can strongly couple to qubits via an electric dipole interaction and can serve as a dominate loss channel. Recent post-fabrication techniques such annealing has shown high tunability over JJ parameters, possibly providing a pathway towards a reduction of TLS defects. In this project, we explore the annealing parameter space with the goal to correlate post-fabrication treatment techniques with the density of TLS defects. Specifically, we study merged-element transmon (MET) devices which utilize the self capacitance of the junction rather than relying on an external shunt capacitor. MET devices with lateral dimensions on the order of several microns and tunnel barriers only a few nanometers thick are substantially larger than the JJ’s used in conventional transmon qubits. As a result, they are thought to host a greater density of TLS defects within the barrier, making them an attractive platform for studying TLS defects.
Project is currently funded by: Federal