Atoms and photons interact in free space in one of nature's most fundamental processes. The dipolar interaction strength between the two systems is determined by fundamental constants, with one of its limiting factors being the mode volume of the propagating photons. A waveguide is an engineered medium that confines the electromagnetic field and in proximity to atoms allows light-matter interactions with stronger couplings compared to free space. In superconducting quantum circuits it
is possible to study quantum electrodynamics with a transmission line on a chip replacing the waveguide and a superconducting qubit playing the role of an artificial atom. By proper engineering of these circuits, a wide range of possibilities opens up: from atom-photon interactions in unexplored regimes to wide-band, on-demand single-photon generation. In this talk, I am going to present recent experimental progress coupling qubits to open transmission lines. In the first part I will show results from an on-demand single photon source engineered using a tunable boundary condition in a semi-infinite transmission line. In the second part I will discuss an experiment with a qubit ultrastrongly coupled to a transmission line realizing the driven, dissipative spin-boson model. I will also use the opportunity to introduce our new quantum computing group at BSC/ICN2, our current status and our goals.
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