Decoherence in Improved Transmon Qubits

The transmon is a simple superconducting qubit which has less dependence on the usual sources of 1/f noise, and has coherence which is mostly limited by a source of anomalous dissipation. The quality factors of transmon qubits on sapphire are observed to be $\sim$ 50,000, similar to that of transmission line resonators made with the same geometry. It is likely that both these devices may be limited by surface dielectric losses. We will report on the design and characterization of transmon qubits which are fabricated with reduced dielectric losses to possibly increase coherence times.