Coherence Measurements of Tantalum Based Transmon Qubits

In recent years, the use of α-phase tantalum as the shunting capacitor material has resulted in improved coherence times for transmon qubits. In this talk, we discuss the design and fabrication of our Ta based transmon qubits, including the etch of the Ta thin film, the addition of the Al/AlOx/Al Josephson junction, and the cleaning methods used during the processing. We then present coherence time measurements at a temperature nominally 20 mK on a variety of devices including both planar and 3D transmon qubits.