Flux qubits in a planar circuit quantum electrodynamics architecture: quantum control and decoherence

We report experiments on superconducting flux qubits in a circuit quantum electrodynamics (cQED) setup. Two qubits, independently biased and controlled, are coupled to a coplanar waveguide resonator. Dispersive qubit state readout reaches a maximum contrast of $72\,\%$. We find intrinsic energy relaxation times at the symmetry point of $7\,μ\text{s}$ and $20\,μ\text{s}$ and levels of flux noise of $2.6\,μΦ_0/\sqrt{\text{Hz}}$ and $2.7\,μΦ_0/\sqrt{\text{Hz}}$ at 1 Hz for the two qubits. We discuss the origin of decoherence in the measured devices. These results demonstrate the potential of cQED as a platform for fundamental investigations of decoherence and quantum dynamics of flux qubits.