Engineering giant atoms with superconducting circuits

In the study of light-matter interactions, atoms, whether natural or artificial, are usually approximated as point-like dipoles due to their physical dimensions being much smaller than the wavelength of light. By coupling an artificial atom to a waveguide at multiple discrete points, separated on the wavelength scale, we can create a so-called giant atom. A giant atom can lead to phenomena such as self-interference and frequency-dependent coupling, as demonstrated in our previous work [1]. Despite achieving qualitative agreement, the measured frequency dependence of the coupling quantitatively deviated from theoretical prediction. Finite-element simulations suggested that the deviations were caused by spurious classical microwave effects. To address this, we have incorporated "air bridges" into our waveguide design to suppress parasitic modes in the devices. We have also developed tantalum-based devices, as a new material platform to enhance coherence. Beyond single giant atoms, we aim to realize two giant atoms in a nested configuration, exploring the feasibility of generating steady-state entanglement via incoherent decay processes. This experimental work highlights both the unique physics that can be offered by giant atoms and the fabrication advances needed to study their precisely engineered interactions.

[1] A. M. Vadiraj, A. Ask, T. G. McConkey, I. Nsanzineza, C. W. S. Chang, A. F. Kockum, and C. M. Wilson, “Engineering the level structure of a giant artificial atom in waveguide quantum electrodynamics,” Phys. Rev. A, vol. 103, p. 023710, Feb 2021.