Nonexponential decay of a giant artificial atom

The interaction between light and atoms has been conventionally studied using small atoms interacting with electromagnetic radiation of wavelengths that are several orders of magnitude larger than the atomic dimensions. In contrast, quantum acoustic experiments allow reaching the giant atom regime, where the coupled field wavelength is orders of magnitude smaller than the atomic dimensions. This is achieved by coupling a superconducting qubit to surface acoustic waves on a piezoelectric substrate at two points with separation on the order of 100 wavelengths. This approach is comparable to controlling the radiation of the atom by attaching an antenna. The slow velocity of sound leads to a significant internal time-delay for the field to propagate across the giant atom, and thus strongly non-Markovian dynamics. We demonstrate signatures of this non-Markovianity in the frequency spectrum as well as time domain relaxation of the giant atom.