Coherence Measurements of Transmon Qubits with In-Situ Patches

In the fabrication of transmon qubits, an aggressive ion-mill step is required to remove the native oxide on the already present shunting capacitor and additively connect the deposited Al/AlOx/Al Josephson junction. To prevent ion milling underneath the junction, a potential source of loss for the qubit,¹ Osman et al. have demonstrated a novel three-angle deposition Manhattan style junction fabrication process, where the third angle deposition has the ion mill step and creates a “patch” between the junction and shunting capacitor. We discuss the fabrication and implementation of these in-situ patches with our Ta transmon qubits. We then compare the measured coherence times of the qubits, at a nominal temperature of 20 mK, with and without these in-situ patches.

References:

[1] A. Dunsworth, et al., Appl. Phys. Lett. 111, 022601 (2017).

[2] A. Osman, et al., Appl. Phys. Lett. 118, 064002 (2021).