DECOHERENCE OF A JOSEPHSON JUNCTION FLUX QUBIT

We have investigated decoherence mechanisms in a Josephson-junction flux qubit. Loss of the coherence due to energy relaxation and dephasing was studied by measurements of the time evolution of qubit states subjected to simple control pulse sequences. As a function of qubit bias parameters, the characteristic time scales of the decoherence as well as the decay envelope functions varied, from which information about the fluctuation spectrum of the environment were deduced.