In the last decade, experiments in quantum optics have increasingly been realised with various artificial atoms such as superconducting qubits, quantum dots or NV-centers, rather than with natural atoms. Also, hybrid systems with natural or artificial atoms, coupled to superconducting microwave resonators or to mechanical resonators, have attracted much interest.
In this talk, I will introduce a new hybrid system, where a superconducting transmon qubit is coupled to propagating phonons in the form of surface acoustic waves (SAWs) . The slow propagation speed of the phonons, and their correspondingly short wavelength, opens up possibilities to investigate new regimes of quantum optics. In particular, I will discuss the concept of a ”giant artificial atom”, an artificial atom which couples to its surroundings at several points that can be spaced wavelengths apart .
Quantum optics, or rather quantum acoustics, with SAWs is a new field with exciting prospects. It appears that not only superconducting qubits, but also quantum dots, trapped ions, and NV-centers can be strongly coupled to SAWs, and that high-quality SAW resonators and waveguides can be built . Thus, many experiments could now be done with phonons instead of photons.
 M. V. Gustafsson, T. Aref, A. F. Kockum, M. K. Ekström, G. Johansson, and P. Delsing, ”Propagating phonons coupled to an artificial atom”, Science 346, 207 (2014)
 A. F. Kockum, P. Delsing, and G. Johansson, ”Designing frequency-dependent relaxation rates and Lamb shifts for a giant artificial atom”, Physical Review A 90, 013837 (2014)
 M. J. A. Schuetz, E. M. Kessler, G. Giedke, L. M. K. Vandersypen, M. D. Lukin, and J. I. Cirac, ”Universal quantum transducers based on surface acoustic waves”, arXiv:1504.05127