Fig. 1: Transmon qubit design and performance.
From: Microscopic relaxation channels in materials for superconducting qubits
a False color optical image of a representative transmon qubit from our study. Niobium regions include the center-pin of the coplanar waveguide resonator (green), the transmon capacitor pads (purple), and the ground plane (gray). The aluminum Josephson junction is shown in white. Black areas indicate where the metal has been etched away, and the sapphire substrate is exposed. b Effective circuit diagram of a transmon qubit coupled to a resonator. Each circuit element is schematically colored as in (a). The resonator is comprised of a center-pin coupled to ground via a capacitor (Cr) and an inductor (Lr). EJ and C refer to the Josephson energy and the capacitance of the qubit respectively. The qubit is capacitively coupled to the center-pin of the resonator (Cc) and to ground (Cg). c Measured relaxation times (T1) for three rounds of devices fabricated with sputtered (purple circles), HiPIMS optimized (blue diamonds), and HiPIMS normal (green squares) niobium films, for a total of nine devices. Error bars indicate standard deviation across all T1 measurements taken on a particular device.
