Superstrong Dynamics and Directional Emission of a Giant Atom in a Structured Bath

• URL: http://arxiv.org/abs/2509.01579v2
• Date: Wed, 29 Oct 2025 09:47:50 GMT
• Title: Superstrong Dynamics and Directional Emission of a Giant Atom in a Structured Bath
• Authors: Vincent Jouanny, Léo Peyruchat, Marco Scigliuzzo, Alberto Mercurio, Enrico Di Benedetto, Daniele De Bernardis, Davide Sbroggiò, Simone Frasca, Vincenzo Savona, Francesco Ciccarello, Pasquale Scarlino,
• Abstract summary: Quantum emitters coupled to waveguides with nonlinear dispersion show rich quantum dynamics.<n>Recent advances in engineered photonic environments now allow the realization of discrete-site waveguides with tailored dispersion.<n>We study a transmon qubit non-locally coupled to a high-impedance coupled cavity array.
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• License: http://arxiv.org/licenses/nonexclusive-distrib/1.0/
• Abstract: Quantum emitters coupled to waveguides with nonlinear dispersion show rich quantum dynamics with the promise of implementing non-trivial non-Markovian quantum models. Recent advances in engineered photonic environments now allow the realization of discrete-site waveguides with tailored dispersion, yet most implementations of waveguide QED remain limited to a local qubit-waveguide coupling. Here, we study a transmon qubit non-locally coupled to a high-impedance coupled cavity array (CCA), thus implementing a \emph{giant atom} in a structured photonic environment. The non-local coupling produces interference with the CCA modes, selectively enhancing interaction with even and long-wavelength modes, while suppressing coupling to odd and short-wavelength modes. For a subset of symmetric, long-wavelength modes, we reach the superstrong coupling regime. In this regime, measurements of the atomic participation ratio reveal strongly hybridized eigenmodes on a par with a strongly reduced qubit participation at the frequency of maximum hybridization with the qubit, in agreement with theory. Time-domain measurements of the qubit dynamics show clear deviations from the single-mode Jaynes--Cummings model, marked by the emergence of mode--mode interactions. By breaking spatial inversion symmetry of the CCA, the qubit seeds dressed eigenmodes confined to either the right or 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 interaction in a structured photonic environment.

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