Waveguide QED with a giant transmon

In a typical waveguide QED system, a quantum emitter, such as a superconducting transmon qubit, is coupled to a superconducting waveguide in order to study its interaction with the electromagnetic field. In these systems, the emitter is approximated as a point-like object when compared to the wavelength of light. However, recent experiments [1] demonstrated the ability to couple a transmon to surface acoustic waves (SAW) that have a wavelength much smaller than the transmon, thereby creating a “giant” artificial atom. Inspired by these results, there is a recent proposal [2] to couple a transmon at multiple points of a microwave waveguide, with wavelength-scale distances between each coupling point, also making a giant transmon. The proposal predicts the ability to custom design the relaxation rates of different transmon levels and proposes several interesting applications such as single-atom lasing and tunable coupling. We will present preliminary characterization of such a device.