Improved T2 in Josephson Phase Qubits

Phase qubit gate fidelities are limited by individual device dephasing times (T2). Reduction of dephasing is therefore an important immediate goal for phase qubit experiments. A simple way to reduce dephasing is to increase the device loop inductance in order to lower the noise currents driven by magnetic flux noise; T2 should scale linearly with loop inductance. Surface spin models for flux noise also predict that wider loop traces should reduce the noise. We present data on T2 for phase qubits with varied loop inductance and trace width. We present data from experiments in which we find that doubling the loop inductance increases T2 by 25\%.