**Abstract**
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) [1]. 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 [2].

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 [3]. Thus, many experiments could now be done with phonons instead of photons.

[1] 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)

[2] 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)

[3] 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