“…As is well known, strong interaction in open space at the level of a single atom and a few photons can be created by coupling an artificial atom to photon modes. Superconducting artificial atoms are used extensively to reproduce typical quantum optics phenomena such as CPT [26], electromagnetically induced transparency (EIT) [27][28][29], Aulter-Townes splitting [30,31], multi-wave mixing (MWM) [32,33], the quantum Zeno effect [34,35], giant Kerr nonlinearities [36,37] and so on. Most recently, the resonance fluorescence spectrum (RFS) from a superconducting macroscopic two-level system was reported [38].…”