Decoherence Sources of a Superconducting Quantum Bit

The Quantronium, a superconducting circuit with Josephson Junctions, can be regarded as a solid state qubit prototype with a coupling to the environment over which some degree of control may be exercised. We have demonstrated experimentally that the quantum state of the circuit may be manipulated using pulse sequences derived from NMR and atomic physics and then readout. Measurements of the coherence time obtained in this way are analysed via a general theoretical framework to develop a simple model of the environmental noise sources. A complete picture of decoherence in this quantum electrical circuit can thus be provided.