Scattering spectroscopy of a superconducting artificial atom coupled to two half spaces

We propose a novel approach for spectroscopic characterization of quantum systems. A superconducting quantum system—an artificial atom—is coupled asymmetrically to two open-end transmission lines (1D half-spaces). The lines themselves are strongly decoupled from each other. This results in suppression of the direct microwave propagation from one side to another. The atom, excited from the weaker coupled side relaxes with photon emission preferably to the stronger coupled side. By measuring the emission spectrum, we reconstruct the energy levels of the artificial atom. Our method allows to reject the excitation tone and to detect only the elastically scattered emission corresponding to intra-atomic transitions. We also demonstrate visualization of the higher-level transitions by populating the excited levels. Such a system does not have an optical analog with natural atoms or quantum dots coupled to two half spaces.