Experimental realization of a Giant Atom in a Structured Multimode Environment
Invited-In-person · Invited
Abstract
Superconducting microwave metamaterials provide a versatile platform for quantum optics and quantum information. Using high-kinetic inductance NbN thin films, we implement compact, high- impedance coupled cavity arrays (CCAs) with a strongly reduced footprint and controlled disorder, scalable to more than 100 resonators and supporting multiple photonic bandgaps [1].
By coupling a transmon qubit (the emitter) non-locally to several cavities at the center of such an array, we realize a giant atom [2] in a structured photonic environment. The non-local coupling reshapes the interaction with array eigenmodes, selectively enhancing coupling to symmetric, long-wavelength modes while suppressing others. This architecture enables access to the superstrong coupling regime (gi/Δωi > 1), where we observe strongly hybridized CCA eigenmodes mediated by the emitter, together with minimal qubit participation in the eigenmodes, in agreement with theory. Time-domain measurements of the qubit dynamics reveal clear deviations from the single-mode Jaynes–Cummings model, marked by the emergence of mode–mode interactions. By breaking inversion symmetry, the qubit seeds dressed eigenmodes confined to either the right or the left of the qubit, which we exploit to implement and characterize a directional photon-emission protocol.
These results demonstrate precise control over multimode light–matter interactions in a structured photonic environment and establish superconducting metamaterial CCAs as a powerful platform for waveguide QED and analog quantum simulation.
[1] Jouanny, V., et al. "High kinetic inductance cavity arrays for compact band engineering and topology-based disorder meters." Nature Communications 16, 3396 (2025).
[2] A. F. Kockum, G. Johansson, F. Nori. "Decoherence-Free Interaction between Giant Atoms in Waveguide Quantum Electrodynamics.", Physical Review Letters 120, 140404 (2018).
[3] Jouanny, V., et al. " Superstrong Dynamics and Chiral Emission of a Giant Atom in a Structured Bath.", arXiv:2509.01579v1
By coupling a transmon qubit (the emitter) non-locally to several cavities at the center of such an array, we realize a giant atom [2] in a structured photonic environment. The non-local coupling reshapes the interaction with array eigenmodes, selectively enhancing coupling to symmetric, long-wavelength modes while suppressing others. This architecture enables access to the superstrong coupling regime (gi/Δωi > 1), where we observe strongly hybridized CCA eigenmodes mediated by the emitter, together with minimal qubit participation in the eigenmodes, in agreement with theory. Time-domain measurements of the qubit dynamics reveal clear deviations from the single-mode Jaynes–Cummings model, marked by the emergence of mode–mode interactions. By breaking inversion symmetry, the qubit seeds dressed eigenmodes confined to either the right or the left of the qubit, which we exploit to implement and characterize a directional photon-emission protocol.
These results demonstrate precise control over multimode light–matter interactions in a structured photonic environment and establish superconducting metamaterial CCAs as a powerful platform for waveguide QED and analog quantum simulation.
[1] Jouanny, V., et al. "High kinetic inductance cavity arrays for compact band engineering and topology-based disorder meters." Nature Communications 16, 3396 (2025).
[2] A. F. Kockum, G. Johansson, F. Nori. "Decoherence-Free Interaction between Giant Atoms in Waveguide Quantum Electrodynamics.", Physical Review Letters 120, 140404 (2018).
[3] Jouanny, V., et al. " Superstrong Dynamics and Chiral Emission of a Giant Atom in a Structured Bath.", arXiv:2509.01579v1
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Presenters
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Vincent Jouanny
- Ecole Polytechnique Federale de Lausanne