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 emphgiant atom in a structured photonic environment. The non-local coupling produces interference with the CCA eigenmodes, selectively enhancing interaction with long-wavelength (low-effective k), symmetric modes about the array center, while suppressing coupling to antisymmetric and short-wavelength modes. For a subset of symmetric, low-effective k 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 inversion symmetry, the qubit seeds dressed eigenmodes confined to either the right or left of the qubit, which we exploit to implement and characterize a chiral photon-emission protocol. These results demonstrate precise control over multimode light–matter interaction in a structured photonic environment.
Enrico Di Benedetto
PhD Student
