Waveguide-mediated interaction of artificial atoms in the strong coupling regime, part 2*

Photon-mediated interactions of quantum emitters in a one-dimensional radiation channel leads to collective emission and long-range exchange interaction. Observation of coherent cooperative dynamics via such interactions, however, has been obscured by radiative decay into the one-dimensional channel. Here, we employ transmon qubits and a microwave coplanar waveguide as artificial atoms coupled to a one-dimensional channel. We circumvent the radiative decay problem by utilizing the entangled dark state of a qubit array arising from collective waveguide emission. The entangled dark state, with a suppressed decay rate, effectively traps radiation as an atomic cavity while exhibiting a large exchange interaction rate with a designated probe qubit. We report the observation of coherent cooperative dynamics in the strong coupling regime and characterize the coherence properties of the collective states involved in the dynamics. In addition, we discuss potential applications of this platform and practical challenges in such systems. arXiv:1809.09752