Photon-mediated interactions between artificial atoms with waveguide QED

Since the first observation, almost 15 years ago, of coherent oscillations in a superconducting qubit there have been significant developments in the field of superconducting quantum circuits. With improvements of coherence times by over 5 order of magnitude, it is now possible to implement simple quantum algorithms with these circuits. In parallel to these developments, much effort has been invested in using superconducting qubits as artificial atoms to explore quantum optics in unconventional parameter regimes. After a short introduction to superconducting quantum circuits, we will explore the situation where several superconducting qubits acting as artificial atoms are coupled to a one-dimensional superconducting transmission line. With microwave photons travelling without loss for a long distance along the line, real and virtual photons emitted by one atom can be reabsorbed or scattered by a second atom leading to collective behaviour. We will explain how these vacuum fluctuation-induced interactions lead to experimental signatures even when the qubits are separated by macroscopic distances.