Suppressing charge noise decoherence in superconducting charge qubits

We present an experimental realization of the transmon qubit, which is an improved superconducting charge qubit derived from the Cooper pair box. We experimentally verify the predicted exponential suppression of sensitivity to $1∕f$ charge noise. This removes the leading source of dephasing in charge qubits which results in homogeneously broadened transitions with relaxation and dephasing times in the microsecond range. Our systematic characterization of the qubit spectrum, anharmonicity, and charge dispersion shows excellent agreement with theory.