Driving a Dark State Qubit in 3D Waveguide QED

The collective behavior of coupled qubits in a waveguide leads to sub-radiant and superradiant states. This effect was extensively studied theoretically and experimentally over the last decade. The appearing dark states can be used to generate an effective two level system that has longer coherence times than a single qubit in the same physical configuration. We engineered a system that creates subradiant and superradiant states by using a direct dipole-dipole, as well as a waveguide-mediated interaction. We show experimentally that this two-qubit dark-state can be used as a qubit state even though it is embedded in an open system. Furthermore, we use the bright state to read out the qubit encoded in the dark state.