Radiation-suppressed superconducting quantum bit in a planar geometry
Martin Sandberg, Michael R. Vissers, Thomas A. Ohki, Jiansong Gao, José Aumentado, Martin P. Weides, David P. Pappas · Applied Physics Letters · 2013
We present a superconducting transmon qubit circuit design based on large, coplanar capacitor plates and a microstrip resonator. The microstrip geometry, with the ground plane on the back, enhances access to the circuit for state preparation and measurement relative to other designs. The device is fabricated on a silicon substrate using low loss, stoichiometric titanium nitride for the capacitor plates and a single small aluminium/aluminium-oxide/aluminium junction. We observe relaxation and coherence times of 11.7 ± 0.2 μs and 9.6 ± 0.5 μs, respectively, using spin echo. Calculations show that the close proximity of the superconducting back-plane has the added advantage of suppressing the otherwise high radiation loss of the qubit.